On Mon, 17 Dec 2007 18:42:23 +0100, "Steve Lusardi"
wrote:

Grant,
I use a lot of these devices. They are wonderful! However an AC version will
turn on once, but never turn off on DC, until the power source is removed.


SNIPPED a TON

It has been noted often in this thread that SCR's and such will turn
on and then not turn off until the power is removed. That occurs by
both literally "removing" power, and by zero crossing in AC. They will
also "turn off" if commutated, which is effectively what the welder
would do if the relay was strapped across the welding lead outputs.

I still have not figured out what the OP wants to do.

Brian Lawson.