On 2/15/2015 1:53 AM, whit3rd wrote:
On Sunday, February 15, 2015 at 1:02:31 AM UTC-8, mike wrote:

As long as you stay out of saturation, the main component of the
primary current is due to the shorted secondary.
I think I'll give my SCR the benefit of switching on when there's zero
voltage.

Not really the best idea; it is then possible that the previous turn-off
happened after a half-cycle (+), and if this ON state starts with a half-cycle (+)
as well, that's two half-cycles of the same polarity. The likelihood
of saturation is very high. Turn-on at peak V is a strategy that
minimizes saturation risk.

Well, I'll repeat what I wrote earlier in the thread:

I set the weld time by an integral number of cycles of 60 Hz.

The key word there is "integral" as in complete as in full as in
you don't get two half cycles of the same polarity.

Designing your welder to avoid saturation is a
strategy that minimizes saturation risk.