[Prev][Next][Index][Thread]
Re: new power transformer (variac as ballast)
In a message dated 98-08-31 20:46:57 EDT, you write:
<< Ed,
> > Did you have to cut a slot in the core to prevent saturation? I've always
> > heard this was necessary. Does the TC draw basically the same amount
> > of current with the variac as with the welder?
> > John Freau
>>
> John,
> I haven't cut a slot in it - I didn't want to ruin it for possible future
use.
> Maybe I should as I think it does saturate sometimes. I am guessing by the
> occasional bumps and humming that it does. If it is rated at 40 amps, then
it
> should not saturate with less than that through it, correct? Of course I am
> running all the current through only about one half of it. I am running 35
to
> 40 amps through the pole transformer primary - about the same as with the
> welder. Only now my safety gap across the caps does not fire. Possibly I
> eliminated a 60 hz resonance problem by replacing the welder.
> Ed Sonderman
>>
Ed,
I think the key is that you're using half the variac, so the volts per turn is
kept reasonably low. In a test I did, I drew only (less than) 3 amps through
a 20A variac, but it saturated, but I was using only about 10 turns or so of
the variac, so maybe the volts per turn went too high. But then another
possibility is that the current peaks were a lot higher than 20 amps.
In any case, the
system drew twice the total power with the variac ballast than when
using the original straight cored ballast, to obtain the same spark length.
I don't blame you for not wanting to ruin that variac by cutting it.
Thanks,
John Freau