Electronics Forums > Re: DC Current in Parallel Inductors?

# Re: DC Current in Parallel Inductors?

Greg Ewing
Guest
Posts: n/a

 07-04-2009, 11:07 AM
Miss_Koksuka wrote:

> So strange, but none of my
> (many) school books seems to cover any of this, they only say that an
> ideal inductor is a "short" to DC.

Ideal inductors don't exist in real life -- they're
just a convenience used in simplified mathematical
models of circuits. When building such a model, you
wouldn't bother putting two ideal inductors in
parallel, you'd just lump them together into a single
inductance. And having done that, you can indeed treat
it as a short to DC.

If you have a real circuit in which it's important to
know the DC current distribution between parallel
inductors, then you can't model them as ideal inductors.
You *have* to take their resistance into account,
because that's what ultimately determines the current
distribution.

--
Greg

greg
Guest
Posts: n/a

 07-05-2009, 05:03 AM
John Larkin wrote:

>>If you have a real circuit in which it's important to
>>know the DC current distribution between parallel
>>inductors, then you can't model them as ideal inductors.
>>You *have* to take their resistance into account

>
> Tedious, but wrong. Consider superconducting magnets.

What I mean is, if they have any resistance at all,
however small, you can't ignore it if you want to know

If the inductors are superconducting, they never reach
steady state in the sense of a current distribution
that's independent of the voltage history they've been
subjected to. In that case, you have to take the
history into account.

Since most people never have occasion to have to deal
with superconducting magnets, introductory electronics
books can be forgiven for not going into that level
of detail.

Now, if someone comes up with a room-temperature
superconductor and superconducting components become
commomplace, that might change...

BTW, I'm not sure that you can call a superconductor
an "ideal inductance" in the mathematical sense, since
they have limitations such as a maximum magnetic field
before they stop superconducting. But I'll grant they're
certainly a much better approximation of one than any
ordinary inductor.

--
Greg

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