two drums

Post by john larkin
https://www.dropbox.com/scl/fo/qpfhkvbfig7elysx78lq3/ALGqgMaRq1tx8aIiN3p1TfM?rlkey=36bcqfdb9di22ko48j89vocut&dl=0
If I put two of these drum core inductors close together, and get the
phasing right, I get an extra 5 mH for free, without any more ESR. And
external mag fields drop too, I think.

It's got to be right two inductors. Put two unrelated inductors close
together, and you've got an embarrassing amount of cross-talk.

--
Bill Sloman, Sydney

Klaus Kragelund

2025-03-12 10:25:30 UTC

Looks like they are cheak unshielded types. But anyway, nice to get more
indtance for free.

When you put them in series, the SRF increases a little bit also.

I would suggest you measure with a Bode 100 or equivalent, that crappy
LCR does not give you much info.

john larkin

2025-03-12 14:30:05 UTC

On Wed, 12 Mar 2025 11:25:30 +0100, Klaus Kragelund

Post by Klaus Kragelund

Looks like they are cheak unshielded types. But anyway, nice to get more
indtance for free.

Ushielded drums are an unfortunate necessity here. Their specs greatly
exceed any shielded inductors that I can fit into the equivalent
volume. These Murata parts are tall and skinny, further optimizing my
use of PCB area.

There just aren't many inductors in the milliHenry range. All the cool
shielded surface mount things seem to stop at 1 mH. Audio transformers
are terrible as inductors.

Post by Klaus Kragelund
When you put them in series, the SRF increases a little bit also.

Not an issue in this application. I'm simulating r+l loads like motors
and solenoids, pretty slow stuff.

A jet engine FADEC might drive over 200 relays, soldenoids, and torque
motors, DC on-off and PWM from maybe 5 to 30 KHz.

Post by Klaus Kragelund
I would suggest you measure with a Bode 100 or equivalent, that crappy
LCR does not give you much info.

That's a classic, original AADE lc meter. I believe it in this range.
No L meter that reports a single number is really right, because
inductors are complex.

I cross-check L meters with a 50 ohm signal generator and a scope.
That finds L, ESR, SRF. Or I TDR the small stuff.

Inductors are by far the worse parts we use.

Buzz McCool

2025-03-12 19:09:55 UTC

Post by john larkin
Inductors are by far the worse parts we use.

Seems like a problem you're having is a problem
other inductor users are having and thus a market
opportunity for component manufacturers.

Have you talked to your Visahy rep about this? They
claim to be able to modify designs to help customers
like you.

https://www.vishay.com/en/capabilities/price-and-cost-are-not-the-same-thing-for-custom-magnetics/

legg

2025-03-13 11:42:28 UTC

Check ripple and transient load response (load one - measure the
other).

If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.

RL

john larkin

2025-03-13 14:41:04 UTC

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.

I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.

The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

Phil Hobbs

2025-03-13 15:08:47 UTC

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately. Coupled inductors in series
have a total inductance

Lseries = L1 + L2 +- 2M.

Since your inductance is going up, the current is going the same
direction in both cores, so the in the low frequency limit, the B field
contributions add everywhere.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

john larkin

2025-03-13 16:22:13 UTC

On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately. Coupled inductors in series
have a total inductance
Lseries = L1 + L2 +- 2M.
Since your inductance is going up, the current is going the same
direction in both cores, so the in the low frequency limit, the B field
contributions add everywhere.
Cheers
Phil Hobbs

If one core has a north pole up while the other is south, the flux
makes a tight local loop. That makes L go up. It's approaching an
all-ferrite gapless inductor.

I tested the theory with a probe coil. Along the centerline of the two
vertical inductors, induced field is zero. The two 5 mH inductors in
series add up to 16 mH in this configuration.

If the two series cores have current in the same direction, I get a
bunch of field radiated and only about 8 mH net. It's kinda like
winding all that wire onto one big drum core.

Phil Hobbs

2025-03-13 21:12:08 UTC

Post by john larkin
On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately. Coupled inductors in series
have a total inductance
Lseries = L1 + L2 +- 2M.
Since your inductance is going up, the current is going the same
direction in both cores, so the in the low frequency limit, the B field
contributions add everywhere.
Cheers
Phil Hobbs

If one core has a north pole up while the other is south, the flux
makes a tight local loop. That makes L go up. It's approaching an
all-ferrite gapless inductor.
I tested the theory with a probe coil. Along the centerline of the two
vertical inductors, induced field is zero. The two 5 mH inductors in
series add up to 16 mH in this configuration.
If the two series cores have current in the same direction, I get a
bunch of field radiated and only about 8 mH net. It's kinda like
winding all that wire onto one big drum core.

Ah, okay, I forgot that your inductors are actually vertical not
horizontal. My bad.

Cheers

Phil Hobbs

Joe Gwinn

2025-03-13 21:30:51 UTC

On Thu, 13 Mar 2025 17:12:08 -0400, Phil Hobbs

Post by john larkin
On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately. Coupled inductors in series
have a total inductance
Lseries = L1 + L2 +- 2M.
Since your inductance is going up, the current is going the same
direction in both cores, so the in the low frequency limit, the B field
contributions add everywhere.
Cheers
Phil Hobbs

If one core has a north pole up while the other is south, the flux
makes a tight local loop. That makes L go up. It's approaching an
all-ferrite gapless inductor.
I tested the theory with a probe coil. Along the centerline of the two
vertical inductors, induced field is zero. The two 5 mH inductors in
series add up to 16 mH in this configuration.
If the two series cores have current in the same direction, I get a
bunch of field radiated and only about 8 mH net. It's kinda like
winding all that wire onto one big drum core.

Ah, okay, I forgot that your inductors are actually vertical not
horizontal. My bad.

Isn't this the difference between a dipole field and a quadrupole
field, regardless of vertical or horizontal?

Joe

Phil Hobbs

2025-03-14 23:48:56 UTC

On 2025-03-13 17:30, Joe Gwinn wrote:> On Thu, 13 Mar 2025 17:12:08
-0400, Phil Hobbs

Post by Joe Gwinn

Post by john larkin
On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs

https://www.dropbox.com/scl/fo/qpfhkvbfig7elysx78lq3/ALGqgMaRq1tx8aIiN3p1TfM?rlkey=36bcqfdb9di22ko48j89vocut&dl=0

Post by Joe Gwinn

Post by john larkin
If I put two of these drum core inductors close together, and get the
phasing right, I get an extra 5 mH for free, without any more ESR. And
external mag fields drop too, I think.

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately. Coupled inductors in series
have a total inductance
Lseries = L1 + L2 +- 2M.
Since your inductance is going up, the current is going the same
direction in both cores, so the in the low frequency limit, the B field
contributions add everywhere.
Cheers
Phil Hobbs

If one core has a north pole up while the other is south, the flux
makes a tight local loop. That makes L go up. It's approaching an
all-ferrite gapless inductor.
I tested the theory with a probe coil. Along the centerline of the two
vertical inductors, induced field is zero. The two 5 mH inductors in
series add up to 16 mH in this configuration.
If the two series cores have current in the same direction, I get a
bunch of field radiated and only about 8 mH net. It's kinda like
winding all that wire onto one big drum core.

Ah, okay, I forgot that your inductors are actually vertical not
horizontal. My bad.

Isn't this the difference between a dipole field and a quadrupole
field, regardless of vertical or horizontal?
Joe

A quadrupole is basically a current distribution whose total dipole
moment is near zero, e.g. two closely-spaced antiparallel dipoles like
John's.

Cheers

Phil Hobbs

john larkin

2025-03-13 21:56:03 UTC

On Thu, 13 Mar 2025 17:12:08 -0400, Phil Hobbs

Post by john larkin
On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately. Coupled inductors in series
have a total inductance
Lseries = L1 + L2 +- 2M.
Since your inductance is going up, the current is going the same
direction in both cores, so the in the low frequency limit, the B field
contributions add everywhere.
Cheers
Phil Hobbs

If one core has a north pole up while the other is south, the flux
makes a tight local loop. That makes L go up. It's approaching an
all-ferrite gapless inductor.
I tested the theory with a probe coil. Along the centerline of the two
vertical inductors, induced field is zero. The two 5 mH inductors in
series add up to 16 mH in this configuration.
If the two series cores have current in the same direction, I get a
bunch of field radiated and only about 8 mH net. It's kinda like
winding all that wire onto one big drum core.

Ah, okay, I forgot that your inductors are actually vertical not
horizontal. My bad.
Cheers
Phil Hobbs

My electromagnetics physics skills are greatly enhanced by
experiment.

My Fields teacher at Tulane was Japanese and nobody could understand
anything he said, but he graded on the curve. Class average scores on
quizzes ran in the low 20's.

Bill Sloman

2025-03-14 14:49:56 UTC

Post by Joe Gwinn
On Thu, 13 Mar 2025 17:12:08 -0400, Phil Hobbs

Post by john larkin
On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs

Check ripple and transient load response (load one - measure the
other).
If chanels not synchronized at the switching frequency, odd results
might be seen at mixing frequency.
RL

The two inductors will be in the two legs of, basically, a floating
power supply, to decouple it from whatever customer impedance. So I'll
be running the exact same current through both inductors. If I get the
polarities right, I get the bonus inductance and the far-field
magnetic cancellation.
I don't want signal coupling to other channels on the same board, so
the field cancellation benefit is squared. That overcomes some
peoples' objections to unshielded drum cores.
The physics is kinda weird. The 5 mH per inductor uses the universe
for its energy storage, but the bonus L is energy stored in ferrite, I
guess. I just invented the semi-shielded inductor.

The far field won't cancel, unfortunately. Coupled inductors in series
have a total inductance
Lseries = L1 + L2 +- 2M.
Since your inductance is going up, the current is going the same
direction in both cores, so the in the low frequency limit, the B field
contributions add everywhere.
Cheers
Phil Hobbs

If one core has a north pole up while the other is south, the flux
makes a tight local loop. That makes L go up. It's approaching an
all-ferrite gapless inductor.
I tested the theory with a probe coil. Along the centerline of the two
vertical inductors, induced field is zero. The two 5 mH inductors in
series add up to 16 mH in this configuration.
If the two series cores have current in the same direction, I get a
bunch of field radiated and only about 8 mH net. It's kinda like
winding all that wire onto one big drum core.

Ah, okay, I forgot that your inductors are actually vertical not
horizontal. My bad.
Cheers
Phil Hobbs

My electromagnetics physics skills are greatly enhanced by
experiment.

Which is to say that your grasp of the theory is poor. I didn't get
remotely comfortable with it until I got exposed to the transformer
equations in the Siemens ferrite data book, and years of hands-on
understanding gelled with that. I wasn't able to persuade Win Hill to
put them into the 3rd edition of "The Art of Electronics", so the years
of hands-on work may be a crucial precursor.

Post by Joe Gwinn
My Fields teacher at Tulane was Japanese and nobody could understand
anything he said, but he graded on the curve. Class average scores on
quizzes ran in the low 20's.

Tulane isn't famous for the quality of its instruction, but I do get the
impression that transformer and inductor theory is pretty badly taught
everywhere.

Thermodynamics is another famously difficult subject to teach, but a
least it is recognised to be swine to get across to the students

--
Bill Sloman, Sydney

Bill Sloman

2025-03-14 05:46:18 UTC