Scott Dorsey wrote:
Chuck Harris wrote:
But that is exactly backwards from the way chokes work. As the current
rises, and the core approaches saturation, the coil starts to lose the inductance
enhancement provided by the core, and it approaches the inductance of an
equivalent air core choke. That is, the inductance *drops*, and the inductive
reactance *drops* and the AC current shoots way up.

That makes perfect sense to me. So how _do_ current-limiting chokes work,
then? I always assumed they worked as I described but I may well be wrong.
--scott

On DC, they can't! No way, no how.

On AC, a choke can limit the current by being a reactive component...
kind of a lossless resistor for AC.

But! Swinging chokes always reduce their inductance when the current
rises. They typically have a 100:1 change in inductance over their
design current range.

-Chuck

Chuck Harris wrote:
Scott Dorsey wrote:
Chuck Harris wrote:
But that is exactly backwards from the way chokes work. As the current
rises, and the core approaches saturation, the coil starts to lose the inductance
enhancement provided by the core, and it approaches the inductance of an
equivalent air core choke. That is, the inductance *drops*, and the inductive
reactance *drops* and the AC current shoots way up.

That makes perfect sense to me. So how _do_ current-limiting chokes work,
then? I always assumed they worked as I described but I may well be wrong.

On DC, they can't! No way, no how.

Right, but I was thinking that in the position where that coil is in
the circuit, it's directly in series with the AC coming off the transformer.

On AC, a choke can limit the current by being a reactive component...
kind of a lossless resistor for AC.

But! Swinging chokes always reduce their inductance when the current
rises. They typically have a 100:1 change in inductance over their
design current range.

How does the reduced inductance translate to higher series impedance?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
Chuck Harris wrote:
Scott Dorsey wrote:
Chuck Harris wrote:
But that is exactly backwards from the way chokes work. As the current
rises, and the core approaches saturation, the coil starts to lose the inductance
enhancement provided by the core, and it approaches the inductance of an
equivalent air core choke. That is, the inductance *drops*, and the inductive
reactance *drops* and the AC current shoots way up.
That makes perfect sense to me. So how _do_ current-limiting chokes work,
then? I always assumed they worked as I described but I may well be wrong.
On DC, they can't! No way, no how.

Right, but I was thinking that in the position where that coil is in
the circuit, it's directly in series with the AC coming off the transformer.

On AC, a choke can limit the current by being a reactive component...
kind of a lossless resistor for AC.

But! Swinging chokes always reduce their inductance when the current
rises. They typically have a 100:1 change in inductance over their
design current range.

How does the reduced inductance translate to higher series impedance?

It doesn't.

Where did you get the idea that such an inductor exists?

A swinging choke aids in the *voltage* regulation of a choke input
power supply by having a high inductive reactance at low currents (where the
supply would tend to be too high in voltage), and having low inductive
reactance at high currents (where the supply would normally tend to droop.)

Is that what you are thinking of?

-Chuck

Chuck Harris wrote:

A swinging choke aids in the *voltage* regulation of a choke input
power supply by having a high inductive reactance at low currents (where the
supply would tend to be too high in voltage), and having low inductive
reactance at high currents (where the supply would normally tend to droop.)

Is that what you are thinking of?

Ahh! So the increased current causes the inductive reactance to drop,
causing the series impedance to drop. That makes sense, so long as the
source impedance is the same all the time, right?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
Chuck Harris wrote:
A swinging choke aids in the *voltage* regulation of a choke input
power supply by having a high inductive reactance at low currents (where the
supply would tend to be too high in voltage), and having low inductive
reactance at high currents (where the supply would normally tend to droop.)

Is that what you are thinking of?

Ahh! So the increased current causes the inductive reactance to drop,
causing the series impedance to drop. That makes sense, so long as the
source impedance is the same all the time, right?
--scott

If the source impedance changed, it could either help, or hurt the process.
It would all depend on how it changed. But I would expect that for the
usual diode, and transformer combination, the source impedance should be
pretty stable.

For a swinging choke to work, the power supply must be choke input. It
is necessary that the choke see the massive AC ripple that comes out of
the rectifier. No ripple, no regulating effect from the reactance.

-Chuck

Chuck Harris wrote:

For a swinging choke to work, the power supply must be choke input. It
is necessary that the choke see the massive AC ripple that comes out of
the rectifier. No ripple, no regulating effect from the reactance.

Okay, wait a second.

You're talking about a configuration where the choke is seeing both AC
and DC on it, and both are required for regulation. The impressed AC
is modulated by the DC, correct? As the DC voltage changes, the inductance
changes, so the reactive part of the impedance changes and the AC voltage
changes. Do I have that right?

I was thinking about a configuration where the choke sees entirely AC,
which would be a different thing altogether, like you see in arc lamp
power supplies. I thought they worked the same way but it's clear they
don't.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."