those coupled drum core inductors

[john larkin]

Loading Image...

Loading Image...

I was surprised to get K=0.6 by just putting them along side.

[Bill Sloman]

Post by john larkin
https://www.dropbox.com/scl/fi/cd8gxmlrar3kvv3iz36xe/Mu_twin.jpg?rlkey=dvl8e7fbtjnzz3l9q9urkyyfn&raw=1
https://www.dropbox.com/scl/fi/nm1ksdn7eufm90ol0b0ec/Murata_Coupled_1.jpg?rlkey=e7yvk464xupz4axy7lt6zj3zk&raw=1
I was surprised to get K=0.6 by just putting them along side.

Why? And your second url doesn't exactly make the point in a way that is
easy to follow.

The ferrite in the drums has permeability that is about a thousand times
higher than that of free space, so the adjacent drum is going to suck in
a whole lot of flux lines.

The transformer equations are

V1=L1.dI1/dt+M.dI2/dt

V2=M.dI1/dt+L2.dI2/dt

where M=K.sqrt(L1.L2)

[Jeroen Belleman]

Post by john larkin
https://www.dropbox.com/scl/fi/cd8gxmlrar3kvv3iz36xe/Mu_twin.jpg?rlkey=dvl8e7fbtjnzz3l9q9urkyyfn&raw=1
https://www.dropbox.com/scl/fi/nm1ksdn7eufm90ol0b0ec/Murata_Coupled_1.jpg?rlkey=e7yvk464xupz4axy7lt6zj3zk&raw=1
I was surprised to get K=0.6 by just putting them along side.

That's somewhat surprising, indeed. Are the cores dumbbell-shaped?
Does the coupling vary steeply with the spacing?

Jeroen Belleman

[Liz Tuddenham]

Post by john larkin
Loading Image...
vl8e7fbtjnzz3l9q9urkyyfn&raw=1
https://www.dropbox.com/scl/fi/nm1ksdn7eufm90ol0b0ec/Murata_Coupled_1.jp
g?rlkey=e7yvk464xupz4axy7lt6zj3zk&raw=1
I was surprised to get K=0.6 by just putting them along side.

That's somewhat surprising, indeed. Are the cores dumbbell-shaped? Does
the coupling vary steeply with the spacing?

Stick a sig-gen across one and a 'scope across t'other, that will tell
you how much coupling there is at any given spacing.

[john larkin]

Post by Liz Tuddenham

Post by john larkin
https://www.dropbox.com/scl/fi/cd8gxmlrar3kvv3iz36xe/Mu_twin.jpg?rlkey=d
vl8e7fbtjnzz3l9q9urkyyfn&raw=1
https://www.dropbox.com/scl/fi/nm1ksdn7eufm90ol0b0ec/Murata_Coupled_1.jp
g?rlkey=e7yvk464xupz4axy7lt6zj3zk&raw=1
I was surprised to get K=0.6 by just putting them along side.

That's somewhat surprising, indeed. Are the cores dumbbell-shaped? Does
the coupling vary steeply with the spacing?

The inductors are covered by shrink tubing but seem to be tall skinny
drum cores, dumbbells.

Post by Liz Tuddenham
Stick a sig-gen across one and a 'scope across t'other, that will tell
you how much coupling there is at any given spacing.

I've done that but didn't quantify coupling vs distance. I measured
coupling and series inductance assuming two parts mounted as close to
one another as makes sense, not quite mechanically interfering.

I used a third one as a mag field probe, to verify that the series
pair has a magnetic null plane between the parts, and doesn't couple
far-field very much.

The extra 6 mH helps my circuit a bit, without adding ESR. Cute trick.

I guess there could be other uses for this coupling.

[piglet]

Post by john larkin
I guess there could be other uses for this coupling.

I have made cheap high isolation voltage data coupling transformers that
way.