Re: two drums

On Thu, 13 Mar 2025 17:12:08 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2025-03-13 12:22, john larkin wrote:

On Thu, 13 Mar 2025 11:08:47 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

On 2025-03-13 10:41, john larkin wrote:

On Thu, 13 Mar 2025 07:42:28 -0400, legg <legg@nospam.magma.ca> wrote:
>

On Tue, 11 Mar 2025 19:35:38 -0700, john larkin <jlArbor.com> wrote:
>

>
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.

>
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