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  • two drums

    From john larkin @21:1/5 to All on Tue Mar 11 19:35:38 2025
    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to john larkin on Wed Mar 12 14:22:49 2025
    On 12/03/2025 1:35 pm, john larkin 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.

    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Kragelund@21:1/5 to john larkin on Wed Mar 12 11:25:30 2025
    On 12-03-2025 03:35, john larkin 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.


    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin @21:1/5 to klauskvik@hotmail.com on Wed Mar 12 07:30:05 2025
    On Wed, 12 Mar 2025 11:25:30 +0100, Klaus Kragelund
    <klauskvik@hotmail.com> wrote:

    On 12-03-2025 03:35, john larkin 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.


    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.


    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.


    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Buzz McCool@21:1/5 to All on Wed Mar 12 12:09:55 2025

    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/

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From legg@21:1/5 to All on Thu Mar 13 07:42:28 2025
    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin @21:1/5 to legg on Thu Mar 13 07:41:04 2025
    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Thu Mar 13 11:08:47 2025
    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


    --
    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin @21:1/5 to pcdhSpamMeSenseless@electrooptical. on Thu Mar 13 09:22:13 2025
    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Thu Mar 13 17:12:08 2025
    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.

    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Thu Mar 13 17:30:51 2025
    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Thu Mar 13 14:56:03 2025
    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.

    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to john larkin on Fri Mar 14 16:46:18 2025
    On 14/03/2025 1:41 am, 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.

    It doesn't use the whole universe - just the bit in the immediate
    vicinity of the inductor. The bonus L comes from the field lines that go through the adjacent ferrite. A inductor wound onto a toroid can be
    completely shielded - but only if the winding is non-progressive.
    Something wound around a pot core is less perfectly shielded, so the semi-shielded inductor was invented a long time before people realised
    that toroidal cores were a good thing.

    --
    Bill Sloman, Sydney

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to john larkin on Sat Mar 15 01:49:56 2025
    On 14/03/2025 8:56 am, john larkin wrote:
    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.

    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.
    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

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  • From Phil Hobbs@21:1/5 to Joe Gwinn on Fri Mar 14 19:48:56 2025
    On 2025-03-13 17:30, Joe Gwinn wrote:> 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

    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

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