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Re: Pig limiting...
Tesla List wrote:
>
> Original Poster: Travis Tabbal <bigboss-at-xmission-dot-com>
>
> When using a choke to limit current, does more L = more or less current?
> IIRC more L would increase the limiting action producing less current,
> but I would like to make sure I'm right. About half of the parts I need
> for a power controler are on the way, so it would be nice to know before
> I power the thing up. I'm thinking I want to use a choke and a small
> resistance like a heating element to control this. With the choke being
> the main limiter.
>
> Travis
Travis,
You're correct - in general (ignoring resonance effects with the tank
cap), the more the limiting inductance, the less the maximum current
will be. However, chokes with ferromagnetic cores (transformer steel,
ferrite, etc.) have an inductance that is also a function of the
current flowing through the winding. If this current climbs to the point
where the core begins to saturate, the effective inductance of the choke
will drop to a small fraction of the value before saturation. This
allows much more current to flow, driving it deeper into saturation, and
effectively eliminating most of it's capability to limit current flow. A
small air gap is inserted in the magnetic path of the core to prevent
this.
You can verify it your choke will if work properly by simply connecting
it in across your variac, and monitoring the current flow as you slowly
increase the voltage. If you're beginning to saturate, you'll see the
current begin to climb very rapidly, and the choke (and variac) may also
begin to hum or growl loudly as you increase the voltage. If your choke
does saturate before you reach maximum voltage, you'll need to add an
air gap in the magnetic path.
Safe coiling to you!
-- Bert --