Re: PFC Question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>


> I'm having a hard time understanding how there can't be any series 
> inductance when, say, the setting as at the midway point.

It all depends on a lot of things.

When the variac is wired as a variac, it does introduce some 
inductance. I noticed this when testing rectifiers that draw sharp 
spikes of current from the supply and are very sensitive to 
inductance. It seems to go from about a couple of millihenries when 
the dial is set to 50%, down to practically zero when it's set to 
100%, then back up again as you go above 100% on an overwound variac.

This is of course leakage inductance: the result of whatever flux 
lines can squeeze their way around the core. The iron core doesn't 
play any part because it links all the windings.

When the variac is wired as a ballast, the core contributes to the 
inductance which can then be several henries, and probably varies as 
the square of the dial setting. But it may only take an amp or two 
before saturating, unless you modify it by adding an airgap.

Steve Conner
http://www.scopeboy.com/