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Re: purpose of a variac?



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Steve,

Tesla list wrote:

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

You can adjust it right down to about 1 bps.

This is not a good way to control power though: the power factor is very poor at low break rates and the transformer draws a heavy current and gets very hot. I think I destroyed an NST by experimenting with this.

Yes, I agree. I've run low breakrates before with an rsg and caused a lot of havoc. I don't recommend itl. But, maybe a DC charging setup?

However if you're using a sync rotary with an AC charging system, adjusting the supply voltage could spoil the phasing. A higher voltage can jump a bigger gap, so it will fire earlier while the electrodes are still some distance apart.

I have noticed slight variation, but nothing of major consequence. The change in voltage/distance/phase point isn't all the great for typical voltages (10kV to 20kV). Part of the reason is the minimum gap distance. Phasing variation due to voltage decreases with increased gap distance. As John Freau explained, wider gaps cause erratic firing which may be both missed firings and possibly voltage firing variation. But, I wonder if setting up an srsg for 70% transformer voltage (as we do with static gaps where a running srsg is across only the transformer) would possibly be a decent method to ensure a decent gap width. The advantage may be quenching. But of course, I only consider these things after I've dismantled my srsg. Oh well.

Take care,
Bart