Spot welder timer

[chevynut]

I have a Miller 220V spot welder and I have found it to be quite handy. However, it only has a switch under the handle to manually control the weld time and it can be very inconsistent, especially on thin metal when you need a short weld.

I plan to build a timer for it, based on some information I've found on the internet. I will be switching the power to the unit so current will be fairly low. I think I will need to push the switch on the welder, then hit the power switch that starts the timer to give a momentary pulse, with the pulse width controllable via a time delay relay. I would like to have it work by just pushing the switch on the spot welder, but I haven't seen any designs to do that so I may just have to somehow short the switch out. Seems like the switch on the welder would be redundant.

Have any of you guys done this yourselves? Any tips?

Here's one source: http://www.5bears.com/welder.htm

[MP&C]

The one on my Miller has an on-off switch and dial control for the timer. Once set, you still use the handle switch as before, and the timer interrupts the power per the setting..

[chevynut]

Robert, I wonder how they do that. I assume they're sensing the current to start the delay timer, then interrupting the current when timed out. Do you have a schematic for it?

[chevynut]

I just found the owner's manual on Miller's site. It looks like the models with the timer have an extra wire in the power cord to initiate the cycle. The cord is 3 wire with ground. The non-timer models are only 2-wire with ground.