On 05/06/2013 08:39 AM, Tim Flood wrote:
Looking for a variable transformer for my new find, a 14,400/120V potential transformer. I have have checked eBay. Does anyone have a variac for sale, at least 30 amps?
Hi Tim, one thing to keep in mind about variacs is that most domestic versions are rated for continuous duty. This means that a 30A variac is rated to control 30A 24/7.
If you want to run them at a higher current than they are rated for, you can do this, provided that you limit the duty cycle of the variac (the limiting factor is the amount of heat that builds up). The manufacturers actually plan for this, and provide a duty cycle chart for the units.
As an example, here is the duty cycle chart for GE Volt-Pac variacs (other manufacturer use a similar curve):
http://i.imgur.com/2fOYa7N.jpgAs you can see, you can run a variac at double the rated current, provided that you limit the duration to less than ten minutes. In Tesla coiling, this usually isn't a problem, because we generally limit the run time to less than a minute or two (I personally use a 25A, 240V variac at 60A with no problems whatsoever, and actually built the power supply with this in mind).
Jon _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla