Discussion:
DC Motor Control: H-Bridge +5A, 48v
(too old to reply)
Mike
2005-04-26 21:16:32 UTC
Permalink
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these capabilities
that uses SPI to communicate with a microprocessor.

Any ideas, anyone? Thanks.

Mike
Tim Wescott
2005-04-26 21:33:21 UTC
Permalink
Post by Mike
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these capabilities
that uses SPI to communicate with a microprocessor.
Any ideas, anyone? Thanks.
We looked into something like this a few years ago; at that time nobody
made monolithic parts that are rated for more than 40V or so, and I
doubt the situation has changed. Apex makes hybrids that will drive
that sort of voltage with a logic input, but they're $$$ -- sensible if
you're making a few and want to save on engineering, but not if you're
making a lot.

Hopefully someone has made or will make a controller for this where you
can add a couple of FETs and get a half-bridge. It certainly makes
sense given that the automotive market is going over to 42V rails.

As far as SPI to a microprocessor goes -- good luck! Your best bet will
probably be to put an itty bitty micro right next to a plain old amplifier.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Joerg
2005-04-26 22:58:03 UTC
Permalink
Hello Tim,
Post by Tim Wescott
Hopefully someone has made or will make a controller for this where you
can add a couple of FETs and get a half-bridge. It certainly makes
sense given that the automotive market is going over to 42V rails.
There has been many years of talk about a higher voltage bus for cars
but except on hybrid vehicles and some exotic prototypes I haven't seen
one materialize yet.
Post by Tim Wescott
As far as SPI to a microprocessor goes -- good luck! Your best bet will
probably be to put an itty bitty micro right next to a plain old amplifier.
What is your opinion with respect to the market shares of SPI and I2C?
There are two SM bus app notes for the MSP430 but the devices support both.

Regards, Joerg

http://www.analogconsultants.com
Tim Wescott
2005-04-26 23:51:24 UTC
Permalink
Post by Joerg
Hello Tim,
Post by Tim Wescott
Hopefully someone has made or will make a controller for this where
you can add a couple of FETs and get a half-bridge. It certainly
makes sense given that the automotive market is going over to 42V rails.
There has been many years of talk about a higher voltage bus for cars
but except on hybrid vehicles and some exotic prototypes I haven't seen
one materialize yet.
Post by Tim Wescott
As far as SPI to a microprocessor goes -- good luck! Your best bet
will probably be to put an itty bitty micro right next to a plain old
amplifier.
What is your opinion with respect to the market shares of SPI and I2C?
There are two SM bus app notes for the MSP430 but the devices support both.
Evenly divided, which isn't too surprising when you consider that the
I2C bus is sufficiently more complicated than the SPI to make it a pain
to work with if you don't need the features.

Where it's a _real_ pain is when you need to implement a bunch of ADCs
or DACs -- serial ADCs in particular always seem to be set up so they
can't be daisy-chained the way DACs can.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Mike
2005-04-27 15:09:26 UTC
Permalink
Tim,

Thanks for the lead on Apex. I found some really interesting
components there. I knew the SPI was going to be a long shot.

Mike
R Adsett
2005-04-26 21:39:20 UTC
Permalink
Post by Mike
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these capabilities
that uses SPI to communicate with a microprocessor.
Any ideas, anyone? Thanks.
I could build one for you easily enough, but I'd have to charge you :)

Agile Systems has (had?) modules like this. I think they are all larger
though. As I recall they dropped the low voltage stuff and concentrated
on higher voltage units. You'd probably get the 5A and you would have
lots of voltage headroom :)

Robert
Mike
2005-04-27 15:10:39 UTC
Permalink
I'll check out Agile, thanks Rob.
Michael Wieser
2005-04-27 16:44:55 UTC
Permalink
Post by Mike
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these capabilities
that uses SPI to communicate with a microprocessor.
Any ideas, anyone? Thanks.
Mike
Trinamic (www.trinamic.com) TMC249 can be controlled with SPI, needs
external drivers

Infineon TLE6209R, but only to 40V (45 VProtected)

Anyway, we decided to build such a H-bridge around the HIP4081 from
Intersil as this allows voltages up to 80V without gluelogic. An
Atmel AVR does the SPI-interface.
This 60V/5A-bridge requires around 23cm² including EMV/ESD-parts on a
4layer-board /one side components only

hth
--
Michael Wieser
Mike
2005-04-27 18:06:42 UTC
Permalink
What type of motors were you driving?
Michael Wieser
2005-04-27 18:37:56 UTC
Permalink
Post by Mike
What type of motors were you driving?
I don`t know brandnames- I saw mostly 24V/4A, sometimes 36V/3A.

Vcc in this application can go up to 60V for several seconds, usually
26 - 40V. The whole design allows a Vcc of up to 70V, main problem was
heat because of Rdson and TO252/100V-FETs.

motors are controlled via pwm (5-10kHz) from the uC when spinning up,
braking is done with pulling up both sides of the motor to Vcc

There is also an overcurrent-shutdown with feedback to the uC for
detection of mechanical blocked motors.

hth
--
Michael Wieser
Clifford Heath
2005-04-28 00:20:49 UTC
Permalink
Post by Michael Wieser
motors are controlled via pwm (5-10kHz) from the uC when spinning up,
braking is done with pulling up both sides of the motor to Vcc
Any reason why you chose high-side braking over low-side?

Presumably the motors have high enough DC resistance that this
is a sufficient loss mode for braking, so back EMF doesn't cause
over-current in the FETs. Did you consider using regeneration
instead? Just curious...

Clifford Heath.
Michael Wieser
2005-04-28 16:41:44 UTC
Permalink
On Thu, 28 Apr 2005 10:20:49 +1000, Clifford Heath
Post by Clifford Heath
Post by Michael Wieser
motors are controlled via pwm (5-10kHz) from the uC when spinning up,
braking is done with pulling up both sides of the motor to Vcc
Any reason why you chose high-side braking over low-side?
Brake-current goes up to 15A (measured with 20cm wire) for 300mS,
Current limit (on lowside, 2 SMD-resistors with 40% margin @5A
@Tamb=70°C) is set to ~5A So the current limiter would interrupt
braking, which doesn`t happen when braking with highside-fets.
Post by Clifford Heath
Presumably the motors have high enough DC resistance that this
is a sufficient loss mode for braking,
It`s an old mechanical design with some new electronis inside. To keep
the old sensoring my customer decided to brake the motor some 100ms
before the slider reaches the mechanical stoppers. So this "hard"
brake helps to reduce mechanical stress at the stoppers. The FETs
(IRFR3410) can handle these currents without problems and the sliders
don`t crash as hard as with the previous design...
Post by Clifford Heath
so back EMF doesn't cause over-current in the FETs.
Did you consider using regeneration instead?
Yes, but much to dangerous for this design as there is no load or
capacitor which can handle the back-EMF so voltage would rise to an
unknown level...

hth
--
Michael Wieser
Mike
2005-04-28 14:03:41 UTC
Permalink
I'm looking to do something within the same envelope. Did you try
their evaluation board?
Michael Wieser
2005-04-28 16:41:49 UTC
Permalink
Post by Mike
I'm looking to do something within the same envelope. Did you try
their evaluation board?
No. I jumped into a prototype without problems. Its a relative simple
and handsome chip as long as you read the realated ANs carefully.
--
Michael Wieser
R Adsett
2005-04-29 03:17:01 UTC
Permalink
Post by Mike
I'm looking to do something within the same envelope. Did you try
their evaluation board?
Whose evaluation board? I've lost track here.

Robert
Mike
2005-05-01 16:50:08 UTC
Permalink
Intersil HIP4081, I've contacted their resellers, there is a 17wk lead
time on obtaining the eval board for it.
Michael Wieser
2005-05-03 09:12:43 UTC
Permalink
Post by Mike
Intersil HIP4081, I've contacted their resellers, there is a 17wk lead
time on obtaining the eval board for it.
Here in Europa: Farnell
--
Michael Wieser
Mike
2005-05-03 15:16:37 UTC
Permalink
Can you post the link? So far I all of the different Farnell's I
checked don't stock it.

Thanks
Michael Wieser
2005-05-03 16:02:23 UTC
Permalink
Post by Mike
Can you post the link? So far I all of the different Farnell's I
checked don't stock it.
Thanks
http://de.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=640268&N=401

thats the german Farnell, I don`t know about "your" Farnell..

hth
--
Michael Wieser
Mike
2005-05-03 17:36:39 UTC
Permalink
I see the chip is available, how about the eval board to go with it? I
can't seem to find it anywhere.
R Adsett
2005-05-03 21:59:06 UTC
Permalink
Post by Mike
I see the chip is available, how about the eval board to go with it? I
can't seem to find it anywhere.
Are referring to any particular chip?

This thread is rather hard to follow, it seems as if nobody is providing
any context.

Robert
Mike
2005-05-03 22:18:59 UTC
Permalink
Yeah, tell me about it ......

The post was in reference to the: Intersil HIP4081 Evaluation Board

I am looking to obtain one, my nearest reseller (US) says there is a
17week lead time.

Weisser posted that Farnell in Germany may have it? I have not been
able to confirm that as of yet.

Any ideas?
Rich Grise
2005-05-04 01:59:07 UTC
Permalink
Post by Mike
Yeah, tell me about it ......
Tell you about what?

Some people don't even bother to respond to googlers that are too lazy
or stupid to learn to cut and paste - or maybe google has a setting
to quote some context, but then the google kiddies would have to bother
to find the setting.

Thanks,
Rich
Post by Mike
The post was in reference to the: Intersil HIP4081 Evaluation Board
I am looking to obtain one, my nearest reseller (US) says there is a
17week lead time.
Weisser posted that Farnell in Germany may have it? I have not been
able to confirm that as of yet.
Any ideas?
Winfield Hill
2005-05-03 11:30:29 UTC
Permalink
Michael Wieser wrote...
Post by Michael Wieser
Post by Mike
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these capabilities
that uses SPI to communicate with a microprocessor.
Trinamic (www.trinamic.com) TMC249 can be controlled with SPI, needs
external drivers
That's an interesting company with interesting motor-control products.
Have you tried them?
--
Thanks,
- Win
Michael Wieser
2005-05-03 16:02:20 UTC
Permalink
On 3 May 2005 04:30:29 -0700, Winfield Hill
Post by Winfield Hill
Michael Wieser wrote...
Post by Michael Wieser
Post by Mike
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these capabilities
that uses SPI to communicate with a microprocessor.
Trinamic (www.trinamic.com) TMC249 can be controlled with SPI, needs
external drivers
That's an interesting company with interesting motor-control products.
Have you tried them?
No. TMC239 or 249 needs a lot of peripheral for voltages up to 65V so
that the HIP4081 seems to be the better choice, even that I need an
additional uC for SPI. The area saved beacause of fewer components
allowed more area for pcb-heatsink...
--
Michael Wieser
Winfield Hill
2005-05-04 00:48:10 UTC
Permalink
Michael Wieser wrote...
Post by Michael Wieser
Post by Winfield Hill
Michael Wieser wrote...
Post by Michael Wieser
Post by Mike
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these capabilities
that uses SPI to communicate with a microprocessor.
Trinamic (www.trinamic.com) TMC249 can be controlled with SPI, needs
external drivers
That's an interesting company with interesting motor-control products.
Have you tried them?
No. TMC239 or 249 needs a lot of peripheral for voltages up to 65V so
that the HIP4081 seems to be the better choice, even that I need an
additional uC for SPI. The area saved beacause of fewer components
allowed more area for pcb-heatsink...
I'm a big fan of the HIP4081 family, as you'll know if you've seen my
dozen or so posts here on s.e.d. suggesting them as the solution for
various problems. But in the TMC249 we have an IC that provides an
important functionality for motors, stuff that an HIP4081 can't do.

I have often used an HIP4081 with a fancy controller to drive MOSFETs,
because the controller was a wimp. For example, the UCC3895 is a fine
IC, a resonant phase-shift PWM controller that "implements control of a
full-bridge power stage by phase shifting the switching of one half-bridge
with respect to the other. This allows constant frequency pulse-width
modulation in conjunction with resonant zero-voltage switching to provide
high efficiency at high frequencies," as they say in the datasheet. But
it has rather wimpy 100mA gate-current output drive (despite its 1MHz PWM
frequency), and it expects one to use a transformer to solve the flying
high-side n-channel MOSFET drive. Whew! Two serious strikes against it.
But paired with an HIP4081A it became a truly elegant solution to a tough
problem (e.g., my 500W 10kV 600kHz resonant tank-circuit driver). So to
me the HIP4081 family is well used in conjunction with other powerful ICs.
Trinamic's TMC249 and other similar powerful chips may be a good examples.
--
Thanks,
- Win
Ethan
2005-05-04 02:15:50 UTC
Permalink
Post by Winfield Hill
Michael Wieser wrote...
Post by Michael Wieser
Post by Winfield Hill
Michael Wieser wrote...
Post by Michael Wieser
Post by Mike
I'm looking for a h-bridge that can handle in excess of 5A continuous,
48v. I would really like to find something with these
capabilities
Post by Winfield Hill
Post by Michael Wieser
Post by Winfield Hill
Post by Michael Wieser
Post by Mike
that uses SPI to communicate with a microprocessor.
Trinamic (www.trinamic.com) TMC249 can be controlled with SPI, needs
external drivers
That's an interesting company with interesting motor-control products.
Have you tried them?
No. TMC239 or 249 needs a lot of peripheral for voltages up to 65V so
that the HIP4081 seems to be the better choice, even that I need an
additional uC for SPI. The area saved beacause of fewer components
allowed more area for pcb-heatsink...
I'm a big fan of the HIP4081 family, as you'll know if you've seen my
dozen or so posts here on s.e.d. suggesting them as the solution for
various problems. But in the TMC249 we have an IC that provides an
important functionality for motors, stuff that an HIP4081 can't do.
I have often used an HIP4081 with a fancy controller to drive
MOSFETs,
Post by Winfield Hill
because the controller was a wimp. For example, the UCC3895 is a fine
IC, a resonant phase-shift PWM controller that "implements control of a
full-bridge power stage by phase shifting the switching of one half-bridge
with respect to the other. This allows constant frequency
pulse-width
Post by Winfield Hill
modulation in conjunction with resonant zero-voltage switching to provide
high efficiency at high frequencies," as they say in the datasheet.
But
Post by Winfield Hill
it has rather wimpy 100mA gate-current output drive (despite its 1MHz PWM
frequency), and it expects one to use a transformer to solve the flying
high-side n-channel MOSFET drive. Whew! Two serious strikes
against it.
Post by Winfield Hill
But paired with an HIP4081A it became a truly elegant solution to a tough
problem (e.g., my 500W 10kV 600kHz resonant tank-circuit driver).
So to
Post by Winfield Hill
me the HIP4081 family is well used in conjunction with other
powerful ICs.
Post by Winfield Hill
Trinamic's TMC249 and other similar powerful chips may be a good examples.
--
Thanks,
- Win
Several years ago I was using the HIP4082 in a couple motor controllers
and had a lot of trouble with EMC radiated susceptability. When the
controller was exposed to a big enough field it would start switching
incorrectly and turn on upper and lower MOSFETs at the same time,
resulting in a spectacular failure. This was several years ago so I
don't really remember the field strengths to get it to do this, it was
large but not too unreasonable, maybe 10V/m at around 100-300MHz,
maybe. Eventually with carefull board layout we were able to get it to
pass our internal testing requirements. It is not easy to improve EMC
performace on a high power device, the usual band aids such as ferrites
just saturate all the time, and don't really work, so you have to be
much more clever about how you filter noise. The product was never
particularly reliable, we had a lot of failures in the field, and the
HIP4082 was the scape goat. Eventually we replaced it with a couple
IR2110's and some extra dead time circuitry, which was not nearly as
clean of a design as the HIP4082, however the reliability was infinitly
better.

I always suspected part of the problem was the single ground pin on the
device for both the high power side and the logic inputs. Keeping the
input logic signals clean is always a chalange when they are referenced
to a high power ground plane.

Has anyone else experienced similar problems? Does anyone know if
Intersil has done anything to address EMC susceptability? If this
problem has been fixed in the IC, I would consider it again. It really
was a clean design.

Regards,

Ethan Petersen
Winfield Hill
2005-05-04 03:18:51 UTC
Permalink
Ethan wrote...
Post by Ethan
Several years ago I was using the HIP4082 in a couple motor controllers
and had a lot of trouble with EMC radiated susceptability. When the
controller was exposed to a big enough field it would start switching
incorrectly and turn on upper and lower MOSFETs at the same time,
resulting in a spectacular failure. This was several years ago so I
don't really remember the field strengths to get it to do this, it was
large but not too unreasonable, maybe 10V/m at around 100-300MHz,
maybe. Eventually with carefull board layout we were able to get it to
pass our internal testing requirements. It is not easy to improve EMC
performace on a high power device, the usual band aids such as ferrites
just saturate all the time, and don't really work, so you have to be
much more clever about how you filter noise. The product was never
particularly reliable, we had a lot of failures in the field, and the
HIP4082 was the scape goat. Eventually we replaced it with a couple
IR2110's and some extra dead time circuitry, which was not nearly as
clean of a design as the HIP4082, however the reliability was infinitly
better.
I always suspected part of the problem was the single ground pin on the
device for both the high power side and the logic inputs. Keeping the
input logic signals clean is always a chalange when they are referenced
to a high power ground plane.
Has anyone else experienced similar problems? Does anyone know if
Intersil has done anything to address EMC susceptability? If this
problem has been fixed in the IC, I would consider it again. It really
was a clean design.
This may be a possibility. But I have always used the HIP4081A
instead, which has separated logic-ground and MOSFET-source pins,
with an allowed +/-2V transient voltage difference. End of the
problem, or at least well on the way to solving it. But if I was
forced to live with an HIP4082 instead, I'd add to or increase the
gate series resistors to slow down the FET and thereby reduce the
FET's source-lead bounce, and isolate the driver at the same time.
--
Thanks,
- Win
Ethan
2005-05-04 04:13:40 UTC
Permalink
Post by Winfield Hill
Ethan wrote...
Post by Ethan
Several years ago I was using the HIP4082 in a couple motor
controllers
Post by Winfield Hill
Post by Ethan
and had a lot of trouble with EMC radiated susceptability. When the
controller was exposed to a big enough field it would start
switching
Post by Winfield Hill
Post by Ethan
incorrectly and turn on upper and lower MOSFETs at the same time,
resulting in a spectacular failure. This was several years ago so I
don't really remember the field strengths to get it to do this, it was
large but not too unreasonable, maybe 10V/m at around 100-300MHz,
maybe. Eventually with carefull board layout we were able to get it to
pass our internal testing requirements. It is not easy to improve EMC
performace on a high power device, the usual band aids such as ferrites
just saturate all the time, and don't really work, so you have to be
much more clever about how you filter noise. The product was never
particularly reliable, we had a lot of failures in the field, and the
HIP4082 was the scape goat. Eventually we replaced it with a couple
IR2110's and some extra dead time circuitry, which was not nearly as
clean of a design as the HIP4082, however the reliability was infinitly
better.
I always suspected part of the problem was the single ground pin on the
device for both the high power side and the logic inputs. Keeping the
input logic signals clean is always a chalange when they are
referenced
Post by Winfield Hill
Post by Ethan
to a high power ground plane.
Has anyone else experienced similar problems? Does anyone know if
Intersil has done anything to address EMC susceptability? If this
problem has been fixed in the IC, I would consider it again. It really
was a clean design.
This may be a possibility. But I have always used the HIP4081A
instead, which has separated logic-ground and MOSFET-source pins,
with an allowed +/-2V transient voltage difference. End of the
problem, or at least well on the way to solving it. But if I was
forced to live with an HIP4082 instead, I'd add to or increase the
gate series resistors to slow down the FET and thereby reduce the
FET's source-lead bounce, and isolate the driver at the same time.
--
Thanks,
- Win
My problem was more due to the EMC susceptability that the ground
bounce from switching transients. The HIP4082 has logic internal that
is supposed to make it impossible for the top and bottom FETs from
turning on at the same time. The example circuit in the data sheet
shows the input logic holding the high side FETs on all the time and
relying on the guts of the IC to take care of everything.
Unfortunately the internal logic would screw up when exposed to just
the right (wrong) RF signal, and the fireworks begin.

Keeping the input logic signals clean during the switching transients
is difficult with only one ground pin, but not insurmountable. Gate
resistors are always a good idea for driving power MOSFETs. I would
want a pretty good justification before not using one. You can get
some ugly oscillations on the gate without it. Not to mention radiated
emmisions from uncontrolled switching speeds.

Another good trick for controlling switching speeds is to use a gate
resistor and add a cap from gate to drain to increase the Miller
capacitance. This makes the FET look like an integrator and you get a
very clean slope on the drain voltage.

This works for each leg of a bridge if the current is always flowing
through the load the same direction. Then it is always one FET
controlling the switching and the other is just there for synchronous
rectification. If current starts to flow in the other direction the
wrong FET will start to control the switching, and the miller cap will
cause some ugly transients on the gate of the FET that is suppose to be
off.


Ethan Petersen
Carl D. Smith
2005-05-05 04:59:39 UTC
Permalink
Post by Ethan
My problem was more due to the EMC susceptability that the ground
bounce from switching transients. The HIP4082 has logic internal that
is supposed to make it impossible for the top and bottom FETs from
turning on at the same time. The example circuit in the data sheet
shows the input logic holding the high side FETs on all the time and
relying on the guts of the IC to take care of everything.
Unfortunately the internal logic would screw up when exposed to just
the right (wrong) RF signal, and the fireworks begin.
In a previous life I worked for a electric forklift manufacturer.
We designed our own motor controllers. It could PWM about 700A
at 36V into each of the lift and traction motors. Fun stuff,
where interesting things happen when things fail. The first
version used the HIP4081, but it was later redesigned to use the
HIP4082 to save some money.

Now it's been a while so you might want to check the datasheets
to make sure I know what I'm talking about (I am on a slow dialup
connection at the moment or I'd check myself), but I seem to
remember one huge difference between the two chips.

The 4081 has built in oscillator for the charge pump circuit.
That means you can turn on the upper FETs and just leave them on.
The 4082 doesn't have the oscillator. It just uses a cap and
diode to power the upper FETs. So that means that it needs
constant PWM of the upper FETs to keep the cap charged. We just
changed the software to put a maximum PWM of 0xFE out of 0xFF,
and it worked fine.

With the 4082, if you just leave the upper FETs on at 100%, the
cap will quickly discharge and the gate voltage will start to
drop and bad things will happen. :-)

Carl Smith
Mike
2005-05-05 22:58:14 UTC
Permalink
Post by Carl D. Smith
In a previous life I worked for a electric forklift manufacturer.
We designed our own motor controllers. It could PWM about 700A
at 36V into each of the lift and traction motors. Fun stuff,
where interesting things happen when things fail. The first
version used the HIP4081, but it was later redesigned to use the
HIP4082 to save some money.
What kind of FETs were you using? PWM Frequency?
Carl D. Smith
2005-05-06 04:16:36 UTC
Permalink
Post by Mike
Post by Carl D. Smith
In a previous life I worked for a electric forklift manufacturer.
We designed our own motor controllers. It could PWM about 700A
at 36V into each of the lift and traction motors. Fun stuff,
where interesting things happen when things fail. The first
version used the HIP4081, but it was later redesigned to use the
HIP4082 to save some money.
What kind of FETs were you using? PWM Frequency?
Now that I think about it, the HIP4082 had the easy job. :-)
The traction motors were separately excited motors.
The field was reversible with an H bridge that the 4081, and
later the 4082, controlled, and it took only 50A or so tops, and
usually more like 30A. The FETs were Harris RFG70N06's in TO-247
packages. This thing was designed in 1994 or so. There are much
better FETs available now.

The interesting part was the armature drive. Since the field was
reversible, the armature didn't have to be reversible to be able
to change the motor direction. The armature drive was a bank of
six IXYS IXFN200N07 in the SOT-227 "minibloc" package (a block
with 4 screws on top). The gate drive for the bank of FETs was a
4424 (both drivers in the package paralleled for higher current)
connected to the gates through 10 ohm resistors. This controlled
up to 700 amps maximum, and 350 or so in average usage.

PWM frequencies weren't very high. The system couldn't handle
the switching losses at really high frequencies. I think the
field was PWMed at around 700 hertz, and the armature less than
that. Maybe like 400 Hz or so. The motors did whine with these
PWM frequencies. At one point we implemented a varying PWM
frequency that started higher as you began to move and lowered as
the speed went up. That gave more torque from the motors when
it was needed to get the forklift rolling, and cut down on
heating from switching losses by lowering the frequency when the
torque wasn't needed as much.

One of the things I always wanted to do just as a joke, but never
did, due to having real work to do, was re-program that frequency
changing routine to change the PWM frequency such that the motor
whine would play the theme to Jeopardy. :-)

Maybe later when I have more time I'll post some stories of the
interesting failures that can happen in such a system, if anyone
is interested.

Carl Smith
R Adsett
2005-05-06 14:58:59 UTC
Permalink
Post by Mike
Post by Carl D. Smith
In a previous life I worked for a electric forklift manufacturer.
We designed our own motor controllers. It could PWM about 700A
at 36V into each of the lift and traction motors. Fun stuff,
where interesting things happen when things fail. The first
version used the HIP4081, but it was later redesigned to use the
HIP4082 to save some money.
What kind of FETs were you using? PWM Frequency?
I've worked on the same sort of drive (IR MGDs though) 1000A peak,
nominal battery voltage of 24-48V, switching frequencies of 10kHz
dropping to 5kHz when 'plugging'. Originally used IRFZ44s

You can get some interesting pyrotechnics when these fail under load.

Robert
Carl D. Smith
2005-05-09 01:28:21 UTC
Permalink
On Fri, 6 May 2005 10:58:59 -0400, R Adsett
Post by R Adsett
Post by Mike
Post by Carl D. Smith
In a previous life I worked for a electric forklift manufacturer.
We designed our own motor controllers. It could PWM about 700A
at 36V into each of the lift and traction motors. Fun stuff,
where interesting things happen when things fail. The first
version used the HIP4081, but it was later redesigned to use the
HIP4082 to save some money.
What kind of FETs were you using? PWM Frequency?
I've worked on the same sort of drive (IR MGDs though) 1000A peak,
nominal battery voltage of 24-48V, switching frequencies of 10kHz
dropping to 5kHz when 'plugging'. Originally used IRFZ44s
You can get some interesting pyrotechnics when these fail under load.
I remember an incident where I leaned down to take a close look
at a board under test, right when all the armature mosfets
decided to blow like popcorn. I jerked back just quick enough
that the foot long flames flying out the side just missed burning
off my eyebrows. :-)

Another memorable one wasn't a failure, but more of a software
bug. The controller stored the configuration in the flash
memory. Early in the prototype development the software guys
were more worried about getting something working than saving
write cycles on the flash memory where the configuration data was
stored, so they erased one of the flash banks and wrote the
configuration to the beginning of that bank on each power down.
The process was to open the main power contactor, then erase the
flash bank, save the configuration, then power off the
controller. Later when they had the time they implemented a wear
leveling procedure that wrote the configurations consecutively
through that flash bank, and the software used the last one on
power up. This made it so that you only had to do the erase on
one out of several hundred power off cycles, since the size of
that flash bank was much larger than the size of the
configuration data.

The problem was that this eliminated the 1 second delay, caused
by the wait for the flash to erase, that had been there on every
power down. This is where I should point out that due to the
inductance and mechanical design of the main power contactor, it
stays closed for about 0.1 seconds after power is removed from
it's coil. The result was that the controller de-energized the
main power contactor, wrote the configuration to flash, and
powered off the controller. When an erase was not needed, the
controller powered off before the contactor had actually opened.
This resulted in all the mosfets on both traction controllers and
the lift controller turning on, and full power being applied to
all the motors momentarily. It caused a huge arc as the main
power contactor tried to open under load, and more impressive to
engineer types like me, the battery cables that dangled down the
side of the forklift to the battery would jump apart by about SIX
INCHES momentarily. Addition of a short delay to the power down
routine fixed the problem. :-)

Carl Smith
Winfield Hill
2005-05-09 09:30:42 UTC
Permalink
Carl D. Smith wrote...
[ snip fascinating story ] When an erase was not needed, the
controller powered off before the contactor had actually opened.
This resulted in all the mosfets on both traction controllers and
the lift controller turning on, and full power being applied to
all the motors momentarily. It caused a huge arc as the main
power contactor tried to open under load, and more impressive to
engineer types like me, the battery cables that dangled down the
side of the forklift to the battery would jump apart by about SIX
INCHES momentarily. Addition of a short delay to the power down
routine fixed the problem. :-)
The hardware design defaulted to all the MOSFETs turned on?
--
Thanks,
- Win
Carl D. Smith
2005-05-10 04:02:24 UTC
Permalink
On 9 May 2005 02:30:42 -0700, Winfield Hill
Post by Winfield Hill
Carl D. Smith wrote...
[ snip fascinating story ] When an erase was not needed, the
controller powered off before the contactor had actually opened.
This resulted in all the mosfets on both traction controllers and
the lift controller turning on, and full power being applied to
all the motors momentarily. It caused a huge arc as the main
power contactor tried to open under load, and more impressive to
engineer types like me, the battery cables that dangled down the
side of the forklift to the battery would jump apart by about SIX
INCHES momentarily. Addition of a short delay to the power down
routine fixed the problem. :-)
The hardware design defaulted to all the MOSFETs turned on?
Yes. Yes, it did.

That one is kind of a sore spot with me. I suggested many times
over several years, to the engineer that was in charge of that
design, that he add a resistor from the armature FET gates to
ground to keep them from floating on when the power to the gate
drive circuitry went away. Something like a 10k resistor to
ground would have cured the problem and presented no significant
extra load to the driver chip. He never wanted to rev the board
to add one resistor, because he didn't think it was a problem.


Here's another story. Maybe it should be titled "Ground is
relative." Working at this forklift manufacturer was my first
real engineering job just out of college. At that point I don't
think I had designed anything that handled more than about 10
amps of current, and I end up at a place that designs motor
controllers that control 700A. I learned a lot quickly. Like
when ground isn't. :-) The forklift had a capacitor bank
connected across the battery, and the negative bus bar was used
as a central ground point for all the high current stuff. Each
of the three motor controllers were connected to this point by a
cable about 18 inches long. I could put a scope probe ground on
one end of the cable and the tip on the other end of the cable.
This cable is about half an inch in diameter. But there would
still be a spike of voltage as much as 7 volts across this length
of cable at each PWM pulse turn on, when the controller was
running at full current. That always amazed me, that there could
be 7V of drop on an 18 inch cable half an inch in diameter. I
learned a lot quickly about how to handle such problems...
R Adsett
2005-05-10 17:13:10 UTC
Permalink
Post by Carl D. Smith
On 9 May 2005 02:30:42 -0700, Winfield Hill
Post by Winfield Hill
Carl D. Smith wrote...
[ snip fascinating story ] When an erase was not needed, the
controller powered off before the contactor had actually opened.
This resulted in all the mosfets on both traction controllers and
the lift controller turning on, and full power being applied to
all the motors momentarily. It caused a huge arc as the main
power contactor tried to open under load, and more impressive to
engineer types like me, the battery cables that dangled down the
side of the forklift to the battery would jump apart by about SIX
INCHES momentarily. Addition of a short delay to the power down
routine fixed the problem. :-)
The hardware design defaulted to all the MOSFETs turned on?
Yes. Yes, it did.
That one is kind of a sore spot with me. I suggested many times
over several years, to the engineer that was in charge of that
design, that he add a resistor from the armature FET gates to
ground to keep them from floating on when the power to the gate
drive circuitry went away. Something like a 10k resistor to
ground would have cured the problem and presented no significant
extra load to the driver chip. He never wanted to rev the board
to add one resistor, because he didn't think it was a problem.
Of course not ;)
Post by Carl D. Smith
Here's another story. Maybe it should be titled "Ground is
relative." Working at this forklift manufacturer was my first
real engineering job just out of college. At that point I don't
think I had designed anything that handled more than about 10
amps of current, and I end up at a place that designs motor
controllers that control 700A. I learned a lot quickly. Like
when ground isn't. :-) The forklift had a capacitor bank
connected across the battery, and the negative bus bar was used
as a central ground point for all the high current stuff. Each
of the three motor controllers were connected to this point by a
cable about 18 inches long. I could put a scope probe ground on
one end of the cable and the tip on the other end of the cable.
This cable is about half an inch in diameter. But there would
still be a spike of voltage as much as 7 volts across this length
of cable at each PWM pulse turn on, when the controller was
running at full current. That always amazed me, that there could
be 7V of drop on an 18 inch cable half an inch in diameter. I
learned a lot quickly about how to handle such problems...
Why were the capacitor banks so far from the FETs? That's an order of
magnitude further (or more) apart than I've seen on any non-SCR based
design.

It would seem to me that you end up nullifying a lot of the benefit of
the caps by placing them so far away and using such a low switching
frequency.


Robert
Carl D. Smith
2005-05-10 22:35:29 UTC
Permalink
On Tue, 10 May 2005 13:13:10 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
That one is kind of a sore spot with me. I suggested many times
over several years, to the engineer that was in charge of that
design, that he add a resistor from the armature FET gates to
ground to keep them from floating on when the power to the gate
drive circuitry went away. Something like a 10k resistor to
ground would have cured the problem and presented no significant
extra load to the driver chip. He never wanted to rev the board
to add one resistor, because he didn't think it was a problem.
Of course not ;)
Well, his excuse was that the only way to remove power from the
controller was to open the main power contactor, which also
removed power from the motors. So the only time there was a
problem was that 0.1 seconds between when the contactor was
de-energized and it finally opened, and that never actually
happened in normal operation because the contactor was opened
with the PWM off.

Never mind what might happen if the main power contactor welded
shut...
Post by R Adsett
Post by Carl D. Smith
That always amazed me, that there could
be 7V of drop on an 18 inch cable half an inch in diameter. I
learned a lot quickly about how to handle such problems...
Why were the capacitor banks so far from the FETs? That's an order of
magnitude further (or more) apart than I've seen on any non-SCR based
design.
It would seem to me that you end up nullifying a lot of the benefit of
the caps by placing them so far away and using such a low switching
frequency.
Yeah, you're right. Some design tradeoffs were made. One was
that things were crammed in really tight into this forklift, and
there wasn't room to put the cap bank closer to the motor
controllers.

In later years we were working on a new controller that had a row
of capacitors right across the bus bars in the controller, and it
wouldn't have needed that external cap bank.

In 1994 when the original system was designed they couldn't find
caps small enough to fit in the space under the top cover that
could still handle the ripple current, so an external bank was
used.
R Adsett
2005-05-13 18:44:37 UTC
Permalink
Post by Carl D. Smith
On Tue, 10 May 2005 13:13:10 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
That one is kind of a sore spot with me. I suggested many times
over several years, to the engineer that was in charge of that
design, that he add a resistor from the armature FET gates to
ground to keep them from floating on when the power to the gate
drive circuitry went away. Something like a 10k resistor to
ground would have cured the problem and presented no significant
extra load to the driver chip. He never wanted to rev the board
to add one resistor, because he didn't think it was a problem.
Of course not ;)
Well, his excuse was that the only way to remove power from the
controller was to open the main power contactor, which also
removed power from the motors. So the only time there was a
problem was that 0.1 seconds between when the contactor was
de-energized and it finally opened, and that never actually
happened in normal operation because the contactor was opened
with the PWM off.
Never mind what might happen if the main power contactor welded
shut...
Post by R Adsett
Post by Carl D. Smith
That always amazed me, that there could
be 7V of drop on an 18 inch cable half an inch in diameter. I
learned a lot quickly about how to handle such problems...
Why were the capacitor banks so far from the FETs? That's an order of
magnitude further (or more) apart than I've seen on any non-SCR based
design.
It would seem to me that you end up nullifying a lot of the benefit of
the caps by placing them so far away and using such a low switching
frequency.
Yeah, you're right. Some design tradeoffs were made. One was
that things were crammed in really tight into this forklift, and
there wasn't room to put the cap bank closer to the motor
controllers.
In later years we were working on a new controller that had a row
of capacitors right across the bus bars in the controller, and it
wouldn't have needed that external cap bank.
In 1994 when the original system was designed they couldn't find
caps small enough to fit in the space under the top cover that
could still handle the ripple current, so an external bank was
used.
Hmm, we are talking the same time frame. That must have been a rather
small compartment. We managed the riple current with seven 35mmx35mm
snap-ins. The end product was rather smaller than the SCR systems it
replaced.

Of course one of the adavantages is that the duty cycle is such that you
don't spend much time at the worst case ripple and can treat those as
surge cases. If you had to rate for full current and 50% PWM
continuously you would need a lot more caps.

Robert
R Adsett
2005-05-13 19:05:13 UTC
Permalink
Post by Carl D. Smith
On Tue, 10 May 2005 13:13:10 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
That one is kind of a sore spot with me. I suggested many times
over several years, to the engineer that was in charge of that
design, that he add a resistor from the armature FET gates to
ground to keep them from floating on when the power to the gate
drive circuitry went away. Something like a 10k resistor to
ground would have cured the problem and presented no significant
extra load to the driver chip. He never wanted to rev the board
to add one resistor, because he didn't think it was a problem.
Of course not ;)
Well, his excuse was that the only way to remove power from the
controller was to open the main power contactor, which also
removed power from the motors. So the only time there was a
problem was that 0.1 seconds between when the contactor was
de-energized and it finally opened, and that never actually
happened in normal operation because the contactor was opened
with the PWM off.
Line contactor, what's a line contactor? :)

Most of the systems we went into didn't have a line contactor, only a
manual emergency disconnect. They relied on that and the direction
contactors for interlocks. Needless to say, we couldn't relay on timing
there.

One of the first application note I did was for adding a line contactor.
It could be wired in for two purposes, 1) to prevent the spark from
plugging a battery into a bank of 21+mF work of caps and/or 2) keep a
battery of reverse polarity from being plugged in.

Reversing a 600AH 48V battery across the controller doesn't do it a whole
lot of good.

Robert
R Adsett
2005-05-10 17:08:49 UTC
Permalink
Post by Carl D. Smith
On Fri, 6 May 2005 10:58:59 -0400, R Adsett
Post by R Adsett
Post by Mike
Post by Carl D. Smith
In a previous life I worked for a electric forklift manufacturer.
We designed our own motor controllers. It could PWM about 700A
at 36V into each of the lift and traction motors. Fun stuff,
where interesting things happen when things fail. The first
version used the HIP4081, but it was later redesigned to use the
HIP4082 to save some money.
What kind of FETs were you using? PWM Frequency?
I've worked on the same sort of drive (IR MGDs though) 1000A peak,
nominal battery voltage of 24-48V, switching frequencies of 10kHz
dropping to 5kHz when 'plugging'. Originally used IRFZ44s
You can get some interesting pyrotechnics when these fail under load.
I remember an incident where I leaned down to take a close look
at a board under test, right when all the armature mosfets
decided to blow like popcorn. I jerked back just quick enough
that the foot long flames flying out the side just missed burning
off my eyebrows. :-)
I managed to avoid being that close. :) Although I have fried a trace or
two.

<snip>
Post by Carl D. Smith
powered off the controller. When an erase was not needed, the
controller powered off before the contactor had actually opened.
This resulted in all the mosfets on both traction controllers and
the lift controller turning on, and full power being applied to
all the motors momentarily. It caused a huge arc as the main
power contactor tried to open under load, and more impressive to
engineer types like me, the battery cables that dangled down the
side of the forklift to the battery would jump apart by about SIX
INCHES momentarily. Addition of a short delay to the power down
routine fixed the problem. :-)
I once did the SW for a variant that used a pair of controllers to
control a series wound traction motor in an H-bridge configuration. We
had the current oscillating at about +-700A IIRC with the motor reversing
direction every few seconds. I could swear I could feel the magnetic
field off of that sucker. Twitching 00 cable does make for an intriguing
sight.
Post by Carl D. Smith
Carl Smith
Robert
Carl D. Smith
2005-05-10 22:35:30 UTC
Permalink
On Tue, 10 May 2005 13:08:49 -0400, R Adsett
Post by R Adsett
I once did the SW for a variant that used a pair of controllers to
control a series wound traction motor in an H-bridge configuration. We
had the current oscillating at about +-700A IIRC with the motor reversing
direction every few seconds. I could swear I could feel the magnetic
field off of that sucker. Twitching 00 cable does make for an intriguing
sight.
That reminds me of another thing. Way back when I started at the
forklift company in 1994, the engineering department was a bit
lacking in equipment. So for a while, we had to use an old WYSE
terminal for debugging. The forklift had a serial port on the
controller board and you could plug in a terminal or computer
with terminal program, and look at things like all the sensor
readings, examine memory contents, etc.

When we would run the lift motor at about half PWM, which
resulted in maybe 250 amps or so, the image on the CRT of that
old WYSE terminal would shake up and down about 1/4 inch, even
though it was on a table a couple feet away.
Winfield Hill
2005-05-11 09:49:48 UTC
Permalink
Carl D. Smith wrote...
Post by Carl D. Smith
That reminds me of another thing. Way back when I started at the
forklift company in 1994, the engineering department was a bit
lacking in equipment. So for a while, we had to use an old WYSE
terminal for debugging. The forklift had a serial port on the
controller board and you could plug in a terminal or computer
with terminal program, and look at things like all the sensor
readings, examine memory contents, etc.
When we would run the lift motor at about half PWM, which
resulted in maybe 250 amps or so, the image on the CRT of that
old WYSE terminal would shake up and down about 1/4 inch, even
though it was on a table a couple feet away.
Great stories.

Magnetic-field generation and wiring-loop inductance go hand in
hand. I'm surprised more attention wasn't paid to the current
path, wires beside each other, twisted, etc. If twisting is not
practical, often the case with fat cables, one can drop the loop
inductance (and magnetic field) dramatically by using a bundle
of four wires instead of two, with each paralleled pair arranged
on opposite corners of the bundle. Reducing the wiring and load
inductance is usually beneficial to the controller in some way.
--
Thanks,
- Win
Carl D. Smith
2005-05-12 01:53:38 UTC
Permalink
On 11 May 2005 02:49:48 -0700, Winfield Hill
Post by Winfield Hill
Magnetic-field generation and wiring-loop inductance go hand in
hand. I'm surprised more attention wasn't paid to the current
path, wires beside each other, twisted, etc.
These wires were all thick enough that twisting wouldn't be
practical. You might get one twist per foot or so.
Post by Winfield Hill
If twisting is not
practical, often the case with fat cables, one can drop the loop
inductance (and magnetic field) dramatically by using a bundle
of four wires instead of two, with each paralleled pair arranged
on opposite corners of the bundle.
Interesting. That sounds perfectly logical, but I never would
have thought of it.

Had that been suggested, I suspect the management would have
immediately shot it down due to the extra wire cost. That's the
way things went there.


Here's another story. Not high current related, but it is from
the same engineering lab. One of the engineers there had the
idea that he knew everything, and then wondered why nobody liked
him. He was trying to debug a controller board one day, claiming
that the microprocessor clock was running at something like 700
Hz. The micro being a static design would happily run at that
speed, but should take forever to do anything since it normally
ran at 20 MHz. Anyway, since he "knew everything" nobody was
volunteering to help him out with the problem.

He was looking at the clock signal with a digital oscilloscope.
It was a Tektronix TDS420. Digital scopes are great as long as
you understand the differences in how they behave compared to an
analog scope. The scope was showing a nice sine wave on the
screen, and he even had a measurement set on screen that also
verified the frequency to be about 700 Hz.

After an hour or so with him tinkering around at the work bench,
he lifted the board up while it was running. Mounted on the back
side of the controller was the display board, which was a dot
matrix LED display. The display was multiplexed and scanned in
software run in the timer interrupt on that very same
microcontroller that supposedly was running with a 700 Hz clock.
But I saw that the display was scanning normally.

At that point, I realized that the clock circuit was just fine.
He just had the digital scope timebase set way to slow, and it
was aliasing. I walked up to the bench, said "Here's your
problem" and pressed the "Autoset" button on the scope. It
automatically reset the timebase and showed him the 20MHz clock.
As I walked away I heard him muttering something about "damn
digital scopes."

Carl Smith
Winfield Hill
2005-05-12 03:26:49 UTC
Permalink
Carl D. Smith wrote...
Post by Carl D. Smith
As I walked away I heard him muttering something about "damn
digital scopes."
In a way, he had a legitimate grip. The digital scopes advertise
that they run at high sampling rates and digitally filter the data
thereby avoiding aliasing. But actually as you turn the timebase
knob, at high ratios of input frequency-to-scan-rate, the antialias
filter fails and all mayhem breaks loose. This is as true for the
$20k Agilent Infinium as it is for the digital Tektronix.
--
Thanks,
- Win
Jonathan Kirwan
2005-05-12 10:06:57 UTC
Permalink
On 11 May 2005 20:26:49 -0700, Winfield Hill
Post by Winfield Hill
Infinium
Infiniium?

;)

Jon
R Adsett
2005-05-13 18:44:37 UTC
Permalink
Post by Carl D. Smith
On Tue, 10 May 2005 13:08:49 -0400, R Adsett
Post by R Adsett
I once did the SW for a variant that used a pair of controllers to
control a series wound traction motor in an H-bridge configuration. We
had the current oscillating at about +-700A IIRC with the motor reversing
direction every few seconds. I could swear I could feel the magnetic
field off of that sucker. Twitching 00 cable does make for an intriguing
sight.
That reminds me of another thing. Way back when I started at the
forklift company in 1994, the engineering department was a bit
lacking in equipment. So for a while, we had to use an old WYSE
terminal for debugging. The forklift had a serial port on the
controller board and you could plug in a terminal or computer
with terminal program, and look at things like all the sensor
readings, examine memory contents, etc.
When we would run the lift motor at about half PWM, which
resulted in maybe 250 amps or so, the image on the CRT of that
old WYSE terminal would shake up and down about 1/4 inch, even
though it was on a table a couple feet away.
Seen that too. It sounds like we had similar experiences at roughly the
same time. Any chance your lift truck was a reach? :)

Speaking of current limits. The controller was designed, over my
objections, to use the NMI to signal an over-current. The hardware would
cut out the PWM for one cycle and leave it up to the SW to correct the
problem more permanently. Under the right circumstances, which of course
were not too hard to produce, you would get a cascade of NMIs as the SW
tried to react to one NMI and failed to do so before the next occurred.
The end result was either a small hesitation which was not really
noticable unless you were looking for it, or overloading the processor so
much that it either blew the stack or triggered the watchdog resetting
the controller in the process or worst of all loading the processor down
such that it was effectively stuck for a short period of time. I managed
to eliminate the last in SW. The board was eventually redesigned to put a
one-shot on the NMI. Ugly, but workable.

Robert
Carl D. Smith
2005-05-14 00:05:04 UTC
Permalink
On Fri, 13 May 2005 14:44:37 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
When we would run the lift motor at about half PWM, which
resulted in maybe 250 amps or so, the image on the CRT of that
old WYSE terminal would shake up and down about 1/4 inch, even
though it was on a table a couple feet away.
Seen that too. It sounds like we had similar experiences at roughly the
same time. Any chance your lift truck was a reach? :)
Nope. Just a stand up counterbalance.
Post by R Adsett
Speaking of current limits. The controller was designed, over my
objections, to use the NMI to signal an over-current.
Already sounds bad...
Post by R Adsett
The board was eventually redesigned to put a
one-shot on the NMI. Ugly, but workable.
Our boards all had the overcurrent implemented totally in
hardware so such things couldn't happen. But there was a logic
signal back to the controller so that it could tell when the
overcurrent was tripping.

The overcurrent was controlled by a one-shot. So if you
continually pushed the forklift into an overcurrent condition, it
would make a ratchet like sound as the overcurrent re-tripped on
the next PWM cycle after the one-shot. The problem is that while
that is happening the average power was far less than what the
controller could do right at the edge of current limit, so the
only way out of it would be to back off on the control handle and
ease into it again.

Later we were designing a new controller that did cycle by cycle
current limiting. That worked so much better there was no
comparison. It would just take the controller to maximum power
and sit there. You could even slam the PWM on to 100% and just
watch each cycle current limit a little later as the motor sped
up. But that design never made it to production, as it was in
progress at the time of the Great Downsizing that left the
company with 1 employee.
Winfield Hill
2005-05-14 02:13:30 UTC
Permalink
Carl D. Smith wrote...
Post by Carl D. Smith
But that design never made it to production, as it was in
progress at the time of the Great Downsizing that left the
company with 1 employee.
What was the name of the company, and what happened to it?
--
Thanks,
- Win
Carl D. Smith
2005-05-15 04:15:14 UTC
Permalink
On 13 May 2005 19:13:30 -0700, Winfield Hill
Post by Winfield Hill
Carl D. Smith wrote...
Post by Carl D. Smith
But that design never made it to production, as it was in
progress at the time of the Great Downsizing that left the
company with 1 employee.
What was the name of the company, and what happened to it?
Schaeff Incorporated. They eventually somewhat came back and are
still around.

What happened was a combination of a company that was always on
the edge of financial trouble, and the bad economy around 2001
and 2002, and a merger with another company.

Normally most companies have blown their capital equipment
budgets before December rolls around, so they always had low
sales in December. Traditionally they would have a temporary
shutdown for a couple weeks in December, to let some orders build
back up. But normally us engineers weren't included in that
unpaid shutdown because we always had plenty of work to do.

But in December 2004 I think their financial troubles were worse
than usual, because their shutdown was supposed to be for a month
and included us engineers.

Now the Schaeff Inc. forklift company in Sioux City, IA, was a
division of Schaeff Inc. in Germany. And in December 2001,
Schaeff Inc in Germany was bought out by Terex.

This part is conjecture on my part, but I think Terex just wanted
the construction and mining equipment that Schaeff made in
Germany, and didn't care about the relatively tiny forklift
manufacturing business in Iowa. So they just let them try to
continue on their own without any further financial help, and
they didn't have the money to bring us all back, so the temporary
layoff turned permanent about 6 weeks later. Actually at that
point they still had more than 1 employee. But they had gone
from something like 120 people down to maybe 10.

Then Terex moved the whole operation to someplace near Chicago.
Only one employee from the Sioux City plant went to Chicago.
Terex later sold the whole operation to someone else.

Their web site is at www.schaeffinc.com. The products I worked
on were the W-Series and Schaeff ECHO forklifts.

Carl Smith
R Adsett
2005-05-15 17:02:35 UTC
Permalink
Post by Carl D. Smith
On 13 May 2005 19:13:30 -0700, Winfield Hill
Post by Winfield Hill
Carl D. Smith wrote...
Post by Carl D. Smith
But that design never made it to production, as it was in
progress at the time of the Great Downsizing that left the
company with 1 employee.
What was the name of the company, and what happened to it?
Schaeff Incorporated. They eventually somewhat came back and are
still around.
Now they weren't on my list of suspects. I wasn't aware they were
developing their own controller.

Your tale sounds very familiar.

Robert
Carl D. Smith
2005-05-16 04:47:15 UTC
Permalink
On Sun, 15 May 2005 13:02:35 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
On 13 May 2005 19:13:30 -0700, Winfield Hill
Post by Winfield Hill
Carl D. Smith wrote...
Post by Carl D. Smith
But that design never made it to production, as it was in
progress at the time of the Great Downsizing that left the
company with 1 employee.
What was the name of the company, and what happened to it?
Schaeff Incorporated. They eventually somewhat came back and are
still around.
Now they weren't on my list of suspects. I wasn't aware they were
developing their own controller.
But you were aware of the existence of Schaeff Inc?

Actually they developed all the electronics for their products
before the Great Downsizing. Which consisted of all the
different models of the W-Series and ECHO forklift product lines.
The other products they have on their web page now were acquired
from other companies. They also wrote all the control software
for the forklifts, which I occasionally had a part in, between my
hardware design projects.

During my years there I put much work into improving the design
of the system controller and operator display PCBs in the
W-Series, and I designed the system controller, operator display
PCB, and power supply / hydraulic coil driver PCB for the ECHO
model, among other things.
Post by R Adsett
Your tale sounds very familiar.
How so?
R Adsett
2005-05-16 21:54:46 UTC
Permalink
Post by Carl D. Smith
On Sun, 15 May 2005 13:02:35 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
On 13 May 2005 19:13:30 -0700, Winfield Hill
Post by Winfield Hill
Carl D. Smith wrote...
Post by Carl D. Smith
But that design never made it to production, as it was in
progress at the time of the Great Downsizing that left the
company with 1 employee.
What was the name of the company, and what happened to it?
Schaeff Incorporated. They eventually somewhat came back and are
still around.
Now they weren't on my list of suspects. I wasn't aware they were
developing their own controller.
But you were aware of the existence of Schaeff Inc?
I was. The only separtely excited development work I was aware of at the
time was at Raymond though.
Post by Carl D. Smith
Actually they developed all the electronics for their products
before the Great Downsizing. Which consisted of all the
different models of the W-Series and ECHO forklift product lines.
The other products they have on their web page now were acquired
from other companies. They also wrote all the control software
for the forklifts, which I occasionally had a part in, between my
hardware design projects.
My emphasis started off in the other direction. I did the control SW and
as resources grew tighter (fewer people) I started picking up the
electronics. A physics background seems to produce a bit of a JOAT.
Post by Carl D. Smith
During my years there I put much work into improving the design
of the system controller and operator display PCBs in the
W-Series, and I designed the system controller, operator display
PCB, and power supply / hydraulic coil driver PCB for the ECHO
model, among other things.
Post by R Adsett
Your tale sounds very familiar.
How so?
I worked for SRE Controls. At one point we were down to 3 people. One
person in production, one management etc and me. I was R&D, customer
support, and 1/2 dozen other things for a while. They've since gone
through receivership and re-emerged.

Resources were almost always quite constrained.

One of my experiences with customer service early on involved, for lack
of a better term, a Samson test. I had gone down with another employee
to replace a controller at a customer site. We replaced it, got some
feedback on the behaviour of the diagnostics and sent the truck back into
service. The driver took the forklift, placed it against a load bearing
pillar and pressed the accelerator to the floor! The wheels slipped an
1/8 of a turn or so and the truck stalled. He held it there for a
moment, sort of nodded said "it seems to work" and headed off. At which
point I sort of picked my jaw up off the factory floor and we left.

Robert
Carl D. Smith
2005-05-17 16:41:53 UTC
Permalink
On Mon, 16 May 2005 17:54:46 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
But you were aware of the existence of Schaeff Inc?
I was. The only separtely excited development work I was aware of at the
time was at Raymond though.
When I started at Schaeff in 1994, several people there were
ex-Raymond employees, including the General Manager and the guy I
mentioned previously that spent an hour trying to figure out why
the clock on a controller board was running at 700 Hz.
Post by R Adsett
One of my experiences with customer service early on involved, for lack
of a better term, a Samson test. I had gone down with another employee
to replace a controller at a customer site. We replaced it, got some
feedback on the behaviour of the diagnostics and sent the truck back into
service. The driver took the forklift, placed it against a load bearing
pillar and pressed the accelerator to the floor! The wheels slipped an
1/8 of a turn or so and the truck stalled. He held it there for a
moment, sort of nodded said "it seems to work" and headed off. At which
point I sort of picked my jaw up off the factory floor and we left.
Schaeff's forklifts have "stall protection". We just programmed
them to use the encoders on the traction motors to detect when
there was no movement for a couple seconds even though
significant power was being dumped into the motors. It would
just stop and display an error message. If you returned the
control handle to center it would automatically reset and let you
drive again.


I learned real fast to never underestimate the ability of a
customer to abuse a forklift.

Normally service issues were handled by the dealers and Schaeff's
service department. But occasionally when they were stumped one
of us engineers would go out to the customer site with Schaeff's
service people.

One of the sites I went to was a customer that managed to scrape
all the paint off the sides of the forklift by bumping the sides
into things, and then dragging the forklift against whatever it
was, such that all the paint was gone on the sides. And the
steel was always polished nice and shiny where the paint was
missing, meaning that they were doing it constantly, since
otherwise the bare steel would get some sort of thin layer of
rust rather quickly. Oh, and the quarter inch steel plate that
the side of the forklift was made of would be bent inward a bit.
That sort of made me wonder about the structural integrity of the
building they were working in.


One of the common things that customers would do is to plug the
battery charger into the forklift instead of the battery. If
you've worked on forklifts you probably know this, but for
others, someone way back when decided to design the standard
forklift battery connector in a symmetrical shell shape, so that
there is no male or female style connector. Two identical
connectors can be plugged into each other by turning one 180
degrees. This allows the customer to plug the charger cord into
the forklift battery connector instead of plugging the charger
into the battery connector.

The problem with this is that a lot of older chargers are just a
giant transformer and full wave diode bridge. No filtering on
the output even. And a charger for a 36V forklift can go as high
as 70V at the peaks of the full wave rectified sine waves.
Schaeff's controllers didn't appreciate that, and it tended to
let the magic smoke out.

So I had an idea. We put a textbook over voltage crowbar circuit
into the controller. The idea was that if someone plugged the
charger into the forklift and turned on the key, the crowbar
would short out b+ and b- and blow the 5 amp fuse for the
electronics. The electronics would be saved and it would also
send up a red flag to the user that they did something wrong and
they should figure out what they did, and then replace the fuse.

Implementation was a bit harder, since one of these chargers can
put out 350 amps. It turned out that in the few milliseconds
that it takes a 5A fuse to disappear in a blinding flash you
would still get a current pulse of about 1000 amps through the
crowbar circuit. I ended up finding an SCR from Motorola that
was rated for something around 800A for one half cycle of 60Hz.
And in a TO-220 package at that. A little underrated for the
task, but it was the highest current part I could find that could
be mounted on the PCB, and it worked.

The problem that goes back to not underestimating the ability of
the customer to abuse the forklift was that instead of replacing
the fuse properly, they would wrap the blown fuse with some of
the foil paper from their pack of cigarettes, or replace it with
a 30A fuse. At that point, the crowbar would try to do it's
job, but in the process the trace on the PCB between the power
connector and crowbar circuit would disappear.

I ended up redesigning it with a different circuit that used a
100V p-channel MOSFET to just open power to all the electronics
when the voltage went over about 50V.

Carl Smith
R Adsett
2005-05-17 22:03:39 UTC
Permalink
Post by Carl D. Smith
On Mon, 16 May 2005 17:54:46 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
But you were aware of the existence of Schaeff Inc?
I was. The only separtely excited development work I was aware of at the
time was at Raymond though.
When I started at Schaeff in 1994, several people there were
ex-Raymond employees, including the General Manager and the guy I
mentioned previously that spent an hour trying to figure out why
the clock on a controller board was running at 700 Hz.
Post by R Adsett
One of my experiences with customer service early on involved, for lack
of a better term, a Samson test. I had gone down with another employee
to replace a controller at a customer site. We replaced it, got some
feedback on the behaviour of the diagnostics and sent the truck back into
service. The driver took the forklift, placed it against a load bearing
pillar and pressed the accelerator to the floor! The wheels slipped an
1/8 of a turn or so and the truck stalled. He held it there for a
moment, sort of nodded said "it seems to work" and headed off. At which
point I sort of picked my jaw up off the factory floor and we left.
Schaeff's forklifts have "stall protection". We just programmed
them to use the encoders on the traction motors to detect when
there was no movement for a couple seconds even though
significant power was being dumped into the motors. It would
just stop and display an error message. If you returned the
control handle to center it would automatically reset and let you
drive again.
That wouldn't have worked for us for several reasons. First there was no
separate speed feedback and there is no good way of determining speed of
a series wound motor w/o one. Probably more important was hill-hold, you
had to be able to hold the tractor at stop on an upward incline. That's
really a superset of starting on an incline.

We did have three levels of current limit. A HW limit that protected the
controller againstunreasonable demands. It would normally only activate
under degenerate conditions. A short term limit with a 10-100mS response
meant to offer some controller protection and to protect the mechanicals
from over-torque. And a third long term limit operating over minutes to
hours that was meant to protect the motor from overheating. Those last
two would have some of the same effect as your stall protection.

I was just surprised at the forklift operators confidence that the tall
skinny pole he was pushing wouldn't give way under the sidways push he
was giving it. Stall tests were part of the production tests for the
controller itself.
Post by Carl D. Smith
I learned real fast to never underestimate the ability of a
customer to abuse a forklift.
Isn't that the truth. I ran into another one today. I got a call from
one of my clients to deal with a service call. Apparently a customer had
used the EV's 36V battery to boost the battery on an ICE powered
Forklift!
Post by Carl D. Smith
One of the sites I went to was a customer that managed to scrape
all the paint off the sides of the forklift by bumping the sides
into things, and then dragging the forklift against whatever it
was, such that all the paint was gone on the sides. And the
steel was always polished nice and shiny where the paint was
missing, meaning that they were doing it constantly, since
otherwise the bare steel would get some sort of thin layer of
rust rather quickly. Oh, and the quarter inch steel plate that
the side of the forklift was made of would be bent inward a bit.
That sort of made me wonder about the structural integrity of the
building they were working in.
We had a client that essentially ended up building there own forklift.
Sideloaders in their case. First the mast wasn't strong enough so they
milled their own out of a block of metal. Then the bumpers were being
bent when they hit the end of the, narrow, end of aisles so they beefed
those up, finally the end of aisle bumpers were being bent so they
replaced those :)
Post by Carl D. Smith
One of the common things that customers would do is to plug the
battery charger into the forklift instead of the battery. If
you've worked on forklifts you probably know this, but for
others, someone way back when decided to design the standard
forklift battery connector in a symmetrical shell shape, so that
there is no male or female style connector. Two identical
connectors can be plugged into each other by turning one 180
degrees. This allows the customer to plug the charger cord into
the forklift battery connector instead of plugging the charger
into the battery connector.
The problem with this is that a lot of older chargers are just a
giant transformer and full wave diode bridge. No filtering on
the output even. And a charger for a 36V forklift can go as high
as 70V at the peaks of the full wave rectified sine waves.
Schaeff's controllers didn't appreciate that, and it tended to
let the magic smoke out.
They can be keyed to prevent that, but I think I've only seen one
facility that actually did that.
Post by Carl D. Smith
So I had an idea. We put a textbook over voltage crowbar circuit
into the controller. The idea was that if someone plugged the
charger into the forklift and turned on the key, the crowbar
would short out b+ and b- and blow the 5 amp fuse for the
electronics. The electronics would be saved and it would also
send up a red flag to the user that they did something wrong and
they should figure out what they did, and then replace the fuse.
Implementation was a bit harder, since one of these chargers can
put out 350 amps. It turned out that in the few milliseconds
that it takes a 5A fuse to disappear in a blinding flash you
would still get a current pulse of about 1000 amps through the
crowbar circuit. I ended up finding an SCR from Motorola that
was rated for something around 800A for one half cycle of 60Hz.
And in a TO-220 package at that. A little underrated for the
task, but it was the highest current part I could find that could
be mounted on the PCB, and it worked.
The problem that goes back to not underestimating the ability of
the customer to abuse the forklift was that instead of replacing
the fuse properly, they would wrap the blown fuse with some of
the foil paper from their pack of cigarettes, or replace it with
a 30A fuse. At that point, the crowbar would try to do it's
job, but in the process the trace on the PCB between the power
connector and crowbar circuit would disappear.
I ended up redesigning it with a different circuit that used a
100V p-channel MOSFET to just open power to all the electronics
when the voltage went over about 50V.
For control circuitry, I think I'd use a polyswitch in and a zener for
that.

One of the app notes I did for a line contactor dealt with the power
section for that case. Although I think that the original complaint was
that they didn't like the spark they got from charging up the caps. In
any case if the key was left on and the battery unplugged the contactor
would drop out and plugging it back in would not cause it to pick up, you
had to move the key to the start position to do that and it had a spring
return away from that position.

Oddly enough we didn't run into much problem with that. For a couple of
reasons I suspect. One was that the power section could withstand that
kind of voltage as long as it wasn't switching with the possible
exception of the coil drivers. The control was probably protected with a
polyswitch. The other reason though would be if you did plug the charger
in with the key on you would hear that startup diagnostics and that might
be enough to startle you into disconnecting again. If the key was off
the only item to be affected would be the power section. We did get a
few that might be traced down to that though.

A bigger but related issue we had was with hot batteries. A battery just
off charge can sometimes have a quite high voltage on it. We ended up
adding an overvoltage shutdown where the controller refused to start if
the voltage was more than 55V.

Robert
Carl D. Smith
2005-05-18 03:24:05 UTC
Permalink
On Tue, 17 May 2005 18:03:39 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
Schaeff's forklifts have "stall protection". We just programmed
them to use the encoders on the traction motors to detect when
there was no movement for a couple seconds even though
significant power was being dumped into the motors. It would
just stop and display an error message. If you returned the
control handle to center it would automatically reset and let you
drive again.
That wouldn't have worked for us for several reasons. First there was no
separate speed feedback and there is no good way of determining speed of
a series wound motor w/o one. Probably more important was hill-hold, you
had to be able to hold the tractor at stop on an upward incline. That's
really a superset of starting on an incline.
Now that you mention hill-hold, I realize my explanation above
wasn't right. The stall protection cutout required the control
handle to be pushed forward significantly with no movement from
the forklift for a few seconds, precisely so that it wouldn't cut
out when sitting on a ramp or going up a ramp extremely slowly.

Schaeff's W-Series has a closed loop control system. If you have
a 7 mph top speed, and you push the handle half way forward, it
will go 3.5 mph, no matter what the load was, or even if you were
going down a ramp. Yes, you had to push the handle forward to go
down a ramp. I thought it felt weird at first, but later when I
got used to it I decided that it was the coolest feature for a
forklift.

I was always impressed when I stepped on the brake on a ramp and
you could hear the traction motors kick on and hold position.
Post by R Adsett
We did have three levels of current limit. A HW limit that protected the
controller againstunreasonable demands. It would normally only activate
under degenerate conditions. A short term limit with a 10-100mS response
meant to offer some controller protection and to protect the mechanicals
from over-torque. And a third long term limit operating over minutes to
hours that was meant to protect the motor from overheating. Those last
two would have some of the same effect as your stall protection.
Schaeff's current limits were all in hardware. But we also had a
fancy software routine that monitored the current going into the
motor and did an estimation of motor temperature. I was
skeptical when they first started developing that code, but in
the end it proved to be surprisingly accurate and more than
sufficient to protect the motors from overheating.
Post by R Adsett
The other reason though would be if you did plug the charger
in with the key on you would hear that startup diagnostics and that might
be enough to startle you into disconnecting again. If the key was off
the only item to be affected would be the power section. We did get a
few that might be traced down to that though.
Schaeff's forklifts had a key it was kind of like a car ignition.
It had an off, on, and start position. The start position was
spring loaded to return to on. So if they unplugged the battery
and then plugged in the charger, it wouldn't go into run mode
anyway, so you wouldn't hear any of the startup diagnostics that
tested the contactor and motors and stuff.
Post by R Adsett
A bigger but related issue we had was with hot batteries. A battery just
off charge can sometimes have a quite high voltage on it. We ended up
adding an overvoltage shutdown where the controller refused to start if
the voltage was more than 55V.
Schaeff's forklifts were mostly 36V but they occasionally sold
48V ones as well. We used the same controllers on each, but they
had to be software configured for the right battery voltage for
the control systems to work right. So even though the
electronics could take a hot 36V or 48V battery, we still had a
software check that the user had connected the proper voltage
battery. It was a bit picky to get that working and not have a
hot 36V battery be detected as a 48V, or a low 48V battery
detected as a 36V battery, and cause a wrong battery type error.

--
Carl Smith
R Adsett
2005-05-18 04:33:28 UTC
Permalink
Post by Carl D. Smith
Schaeff's W-Series has a closed loop control system. If you have
a 7 mph top speed, and you push the handle half way forward, it
will go 3.5 mph, no matter what the load was, or even if you were
going down a ramp. Yes, you had to push the handle forward to go
down a ramp. I thought it felt weird at first, but later when I
got used to it I decided that it was the coolest feature for a
forklift.
One of the last projects I did was a separately excited controller for
series wound motors. It did this, although we did dispense with the
feedback sensors. You can't get to quite the degree of control but it
physically more robust and it's not an autonomous vehicle after all. It
did hold pretty well though.
Post by Carl D. Smith
Schaeff's forklifts had a key it was kind of like a car ignition.
It had an off, on, and start position. The start position was
spring loaded to return to on. So if they unplugged the battery
and then plugged in the charger, it wouldn't go into run mode
anyway, so you wouldn't hear any of the startup diagnostics that
tested the contactor and motors and stuff.
As near as I can tell pretty much the same keyswitch type is used for
them all. In fact the aftermarket ones I've seen use the same 'key' for
all trucks. Most controllers seem to ignore the strt position though.
That's where the line contactor app note came in. Even though all it
involved was an extra diode I'm not sure more than one outfit ever used
it.
Post by Carl D. Smith
Schaeff's forklifts were mostly 36V but they occasionally sold
48V ones as well. We used the same controllers on each, but they
had to be software configured for the right battery voltage for
the control systems to work right. So even though the
electronics could take a hot 36V or 48V battery, we still had a
software check that the user had connected the proper voltage
battery. It was a bit picky to get that working and not have a
hot 36V battery be detected as a 48V, or a low 48V battery
detected as a 36V battery, and cause a wrong battery type error.
Ours worked over a nominal 24-48 and had to be setup as well. I was
asked occasionally to auto-recognize the battery voltage but always
resisted to avoid confusing a higher voltage battery with a bad cell and
a hot low voltage battery. Doing that on every startup seemed a bit
risky to me. Also that was only one of the items that had to be setup so
we ended up doing an assisted setup where we would ask the installer to
confirm the nominal voltage was what we thought it was.

It gets even worse when you move to higher voltages (as we did). I don't
think there is much hope of certainty when the nominal voltages you are
trying to distinguish are 60V, 72V and 80V, all of which are reasonably
common once you move above 48V.


Robert
Carl D. Smith
2005-05-18 16:17:34 UTC
Permalink
On Wed, 18 May 2005 00:33:28 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
Schaeff's W-Series has a closed loop control system. If you have
a 7 mph top speed, and you push the handle half way forward, it
will go 3.5 mph, no matter what the load was, or even if you were
going down a ramp. Yes, you had to push the handle forward to go
down a ramp. I thought it felt weird at first, but later when I
got used to it I decided that it was the coolest feature for a
forklift.
One of the last projects I did was a separately excited controller for
series wound motors. It did this, although we did dispense with the
feedback sensors. You can't get to quite the degree of control but it
physically more robust and it's not an autonomous vehicle after all. It
did hold pretty well though.
We tried to come up with a way to calculate motor speed in
software and dispense with the encoders on the traction motors,
but we could never get the ramp hold to work as well as we
wanted.

The encoders were kind of overkill. They were 256 count
encoders, but the ASIC that Schaeff designed for motor control
stuff counted all 4 edges, so you got 1024 counts per motor
revolution. There was a 20:1 gear reduction to the wheel, so you
got 20480 counts per wheel revolution. I don't remember exactly,
but the wheel diameter was in the ballpark of a foot, so that
means we could measure something like 1/6500 of an inch of
movement. Way overkill, but once we found an encoder that was
capable of surviving the environment, the high resolution sort of
came along with the package.

--
Carl Smith

Rich Grise
2005-05-17 23:08:37 UTC
Permalink
I learned real fast to never underestimate the ability of a customer to
abuse a forklift.
Like this?
Loading Image...
;-)

I've seen some forklift pix that induce horripilation, but don't remember
where. I'm sure some kind sould will assist us here. :-)
--
Cheers!
Rich
Carl D. Smith
2005-05-18 02:52:48 UTC
Permalink
On Tue, 17 May 2005 23:08:37 GMT, Rich Grise
Post by Rich Grise
I learned real fast to never underestimate the ability of a customer to
abuse a forklift.
Like this?
http://images.foundrymusic.com/JPEG/forklift_bomb.jpg
;-)
When that photo first hit the net, everyone I knew that knew I
worked at a forklift manufacturer had to send me a copy. :-)

--
Carl Smith
R Adsett
2005-05-14 03:40:12 UTC
Permalink
Post by Carl D. Smith
On Fri, 13 May 2005 14:44:37 -0400, R Adsett
Post by R Adsett
Post by Carl D. Smith
When we would run the lift motor at about half PWM, which
resulted in maybe 250 amps or so, the image on the CRT of that
old WYSE terminal would shake up and down about 1/4 inch, even
though it was on a table a couple feet away.
Seen that too. It sounds like we had similar experiences at roughly the
same time. Any chance your lift truck was a reach? :)
Nope. Just a stand up counterbalance.
Post by R Adsett
Speaking of current limits. The controller was designed, over my
objections, to use the NMI to signal an over-current.
Already sounds bad...
Once I managed to get the NMI down to something like three instructions
it worked rather well. It all depends on latency, how close you are to
the end of the pwm cycle when you hit current limit and the motor
inductance. It worked for all but the most degenerate cases.
Nonetheless capping the maximum repeat rate was a definite improvement.

<snip>
Post by Carl D. Smith
Later we were designing a new controller that did cycle by cycle
current limiting. That worked so much better there was no
comparison. It would just take the controller to maximum power
and sit there. You could even slam the PWM on to 100% and just
watch each cycle current limit a little later as the motor sped
Saw a controller (I did the production test benches for it) that used
that for an inner current loop. Quite effective.

I did software current control on multiple bridges in a single micro to
do similar control. Once it's tuned it's very effective. You do have to
be careful while tuning though.

We did run into an issue with plugging. It turns out that under certain
circumstances once you start plugging it will self sustain and the only
way to get it to stop braking is to open the direction contactors. The
motors we first tested on actually braked very nicely in that mode.
Post by Carl D. Smith
up. But that design never made it to production, as it was in
progress at the time of the Great Downsizing that left the
company with 1 employee.
Ouch.


Robert
Carl D. Smith
2005-05-15 04:39:29 UTC
Permalink
On Fri, 13 May 2005 23:40:12 -0400, R Adsett
Post by R Adsett
We did run into an issue with plugging. It turns out that under certain
circumstances once you start plugging it will self sustain and the only
way to get it to stop braking is to open the direction contactors. The
motors we first tested on actually braked very nicely in that mode.
That reminds me of another one. We sort of accidently discovered
an interesting thing about our forklifts. If you got them up to
full speed, and while continuing to hold the control handle
forward, reached across with your left hand and hit the battery
disconnect, the momentum of the forklift turning the traction
motors while coasting to a stop would generate enough power to
continue to power all the electronics of the forklift. The power
would feed backwards right through the armature mosfets and feed
back into the B+ bus. It provided enough current to sustain the
field winding current and keep the generator effect going, and
even power the electric steering pump motor.

If you let go of the control handle, the armature mosfets would
turn off and cut the current flow to the B+ and everything would
shut down pretty much instantly. And on one model that had
electric brakes, the electric brakes would close and the forklift
would screech to a halt. :-)

So, of course, the next "unofficial" experiment was to push one
forklift with another, then have the one being pushed disconnect
the battery. This worked well enough that the one being pushed
could run all the functions including lifting and lowering the
mast. As long as you held the control handle forward so the
controller would keep the armature mosfets on, it would continue
to work as a generator.

Carl Smith
R Adsett
2005-05-15 17:02:36 UTC
Permalink
Post by Carl D. Smith
On Fri, 13 May 2005 23:40:12 -0400, R Adsett
Post by R Adsett
We did run into an issue with plugging. It turns out that under certain
circumstances once you start plugging it will self sustain and the only
way to get it to stop braking is to open the direction contactors. The
motors we first tested on actually braked very nicely in that mode.
<snip>
Post by Carl D. Smith
So, of course, the next "unofficial" experiment was to push one
forklift with another, then have the one being pushed disconnect
the battery. This worked well enough that the one being pushed
could run all the functions including lifting and lowering the
mast. As long as you held the control handle forward so the
controller would keep the armature mosfets on, it would continue
to work as a generator.
I like :), there is certainly a lot of energy in forklift weightd down
with 400-600AH batteries even a low speeds :)

Robert
Carl D. Smith
2005-05-16 05:03:15 UTC
Permalink
On Sun, 15 May 2005 13:02:36 -0400, R Adsett
Post by R Adsett
I like :), there is certainly a lot of energy in forklift weightd down
with 400-600AH batteries even a low speeds :)
Robert
The batteries in the Schaeff trucks that I worked on were bigger
than that. 900 to 1300 AH.

The forklifts weigh from about 6000 to 16000 pounds without the
battery (most of that is counterweight).

That reminds me of another story, but it's late and time for me
to sleep. I'll try to remember to post it tomorrow.

Carl Smith
Daniel Haude
2005-05-11 14:34:39 UTC
Permalink
Magnetic fields are fun.

What's better -- I've once visited an aluminium foundry. In the hall with
all the electrolysis cells you could stack half a dozen (iron) coins on
top of each other standing straight up on their edges. When you moved in
the hall this "stack" would lean over on one or the other side, depending
on which direction the field was...

--D.
Carl D. Smith
2005-05-12 02:00:15 UTC
Permalink
On 11 May 2005 14:34:39 GMT, Daniel Haude
Post by Daniel Haude
Magnetic fields are fun.
What's better -- I've once visited an aluminium foundry. In the hall with
all the electrolysis cells you could stack half a dozen (iron) coins on
top of each other standing straight up on their edges. When you moved in
the hall this "stack" would lean over on one or the other side, depending
on which direction the field was...
Mentioning coins in a thread where I've been talking about
forklifts reminded me of this one.

While working at the forklift company I learned how to pick
quarters up with a forklift. :-)

You place the quarter on the floor a bit in front of one of the
forks. Tilt the mast forward as far as it will go and lift it up
so that the tip of the fork is just off the floor. Drive the
forklift forward so that the tip of the fork is over the quarter,
then slowly lower the mast a bit until some of the weight of the
fork is resting on the quarter. Then slowly back up the
forklift. When the fork tip slides off the top of the quarter,
the quarter will flip up and land on the tip of the fork.

It's a good one to win a few bets...

Carl Smith
Winfield Hill
2005-05-13 02:21:14 UTC
Permalink
Carl D. Smith wrote...
Post by Carl D. Smith
You place the quarter on the floor a bit in front of one of the
forks. Tilt the mast forward as far as it will go ...
Great stories Carl, don't stop now just when you're up to speed.
--
Thanks,
- Win
Carl D. Smith
2005-05-13 21:14:51 UTC
Permalink
On 12 May 2005 19:21:14 -0700, Winfield Hill
Post by Winfield Hill
Carl D. Smith wrote...
Post by Carl D. Smith
You place the quarter on the floor a bit in front of one of the
forks. Tilt the mast forward as far as it will go ...
Great stories Carl, don't stop now just when you're up to speed.
I am going to run out of stories eventually. And being a lot
younger than most of the regulars on this group, I haven't had as
much time to accumulate stories.

One day I was sitting in our lab area when the power went off.
It wasn't a clean quick power loss like when a breaker trips.
This time the lights went dim and kind of flickered for a few
seconds before going out. It was clearly a "something really bad
just happened in the factory" kind of power loss.

It turns out they had a problem with one of the forklifts they
were building where the bearings in the mast rails were binding
up so that the forks wouldn't lower all the way. The width of
the channel in the mast rail probably wasn't to spec, but even so
it's easier to just get out the grinder and grind off a little in
the offending area than to tear it all apart. So that's what
they tried to do. The problem was that this mast was an optional
mast that was unusually tall. They couldn't extend it up enough
inside the building to get access to the area on the rail that
needed adjustment. So they drove it outside to do the job, and
neglected to notice the power lines coming into the factory right
above the area they decided to work in.

So the power loss was when they lifted the mast right into the
power lines. I don't remember the exact voltage of those lines,
but I believe the safety guy later told me they were several
thousand volts.

Fortunately neither of the guys working on the forklift were
hurt. One was standing in the forklift (these were stand up
models) and was lifting the mast at the time of contact with the
power lines. But the controls of the forklift were all plastic,
and apparently well enough insulated that he didn't even get a
shock. He had enough sense to let go of the controls and hop out
of the back of the forklift in one jump. I don't know if the
other guy, with the grinder, was touching anything on the
forklift or not. Probably not, since they were still lifting the
mast at the time.

When we moved the forklift the conductive rubber static strap
that used to be underneath was gone and there was a sooty blast
mark where it used to be. And there was a 1 inch hole in the
concrete below that point where all that power burned through the
concrete looking for a path to ground.

The power lines had big notches melted out of them at the point
of contact. The electric company's fix for that was to cut the
line right at that point, clean up the ends, and push them into
some sort of splice connector that locked the wires in because of
their own tension. Sort of like an 18 inch long steel chinese
finger cuff for power lines.

I was somewhat proud of the fact that the electronics that our
group designed survived the incident intact. They replace the
mast bearings just in case of any pitting caused by the current,
and replaced all the electronics just in case the reliability had
been affected.

So we took all the motor controllers and system controller box
and put them on a shop forklift just to see if they would work
reliably. That forklift drove around the shop, used by the
production workers, for years with no problems.

Carl Smith
Daniel Haude
2005-05-03 16:27:20 UTC
Permalink
On 3 May 2005 04:30:29 -0700,
Post by Winfield Hill
That's an interesting company with interesting motor-control products.
Have you tried them?
I've used some of their older stepper-motor control modules (not chips).
They work fine. The new stuff (the TMC3xx modules) looks even neater.
About a year ago I pestered them about servo motor stuff and they said
they'd been working on it for a long time, but it kept been pushed away by
more pressing issues -- they seem to be a VERY normal company ;-)

--Daniel
BobG
2005-05-03 23:19:02 UTC
Permalink
Mike... how about the h bridge board from Procyon Engineering Pascal
Stang? 50V 5A as I recall...
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