Timer Advice Needed for MOT Spot Welder

Thread Starter


Joined Jan 22, 2012
I have completed a MOT spot-weld unit, but I am further refining it. I am primarily spot-welding sub c ni-cad battery tabs, and am implementing a timer to control weld duration. The welder is 120V and works well.
I intend to use an Allen-Bradley 700-HX digital unit (octal socket) along with an Omron G3NA-240B 120V solid state relay. I am not sure if these are the optimum parts, but they are what I have. I will also be using a generic style momentary contact switch or micro switch for a trigger. Approx .3 seconds spot time will be needed, which is within the timer capability. I would like to utilize "one-shot" logic.
I am looking for wiring schematic information for the timer in conjunction with the relay.
I have reviewed the 5bears.com site, but the timer differences are confusing. The user manual for the timer is also a bit overwhelming for me.
Thanks for the advice!


Joined Jul 17, 2011
A relay with a high coil resistance activated thru a capacitor charge, could work. The
relay could have an extra contact to discharge the capacitor thru a resistor, between cycles.


Joined Dec 19, 2007
The Omron SSR is designed for switching resistive "heater" loads. The spot welder is an inductive load. Look for relays that can safely switch motor-type loads.

I think Crydom had an app note on de-rating their SSR's for inductive loads.