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Re: PFC Question



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Steve,

Yes, this fits my belief structure and I believe the performance curves for the powerstat. This leakage inductance also explains why SRSG's need to be rephased as the variac output is brought up. Dmitry did, however, bring up a good point about the mutual coupling between windings that I wasn't thinking about.

Gerry R.


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/