JR North wrote:
Haven't seen your design, but my .02 anyway-if you are switching the
primary with a SS relay, be careful of letting it cook as you described.
The first indication the relay is overloading is when it pukes.

An SSR may be in its future, but now I was just closing a contactor.
About the cooking though - if I was well below the current rating of the
SSR, would it be OK? Say drawing 16A on a rated 25A SSR?

Also about the SSR: I've read that they should be derated 30-70% for
inductive loads. They were probably referring to motor loads, but the
spot welder is certainly inductive. As much as a motor, though? Did
you derate yours?

How
about posting some pics and a schematic in the dropbox?
Mine:
http://www.metalworking.com/dropbox/...retired_files/
See welder00.txt and the associated jpgs

I knew there was one in the DropBox! I'll be posting mine, as soon as I
use it some and work the kinks out. There are always kinks! Meanwhile,
here's a pic in it's prototype stage:
http://home.comcast.net/~bobengelhardt/welder.jpg

Bob