adding a switched chassis outlet to my welder

Thread Starter


Joined Apr 26, 2007
.. my first post.

I just purchased a TIG welder. I am building a dedicated torch cooler for it utilizing an automotive heater core, a dual shaft fractional hp 115/230 motor - with pump on one end and fan on the other and a one gallon reservoir.

The TIG welder is 230vac with a three pronged plug. Unfortunately it does not have any auxilliary outlets. It is vital that my cooling unit power up when the welder is turned on. If it is forgotten even once, the torch can be destroyed.

This is a pretty sophisticated inverter-type welding machine. There is a beefy two-gang main switch on the back panel for turning it on and the internal leads to this switch are very readily accessible with the removal of a small panel.

Normally I wouldn't hesitate to simply piggyback this switch, since the motor I intend to use is only a couple of amps draw. But I want to be 100 percent certain that I won't be disrupting any of the functions of this machine by doing so. I also wonder if I have the option of running either a 115v or 230v motor off of these taps, or if using only one of them would imbalance anything?

The first .pdf is linked to the owners manual and the following attachment is a file condensing the relevant pages from it. ArcMaster 185 ACDC-OpMan.pdf

Thanks very much for any advice!



Joined May 16, 2005
As far as the welder is concerned, it makes no difference if you parallel off the switch contacts, off the wall outlet, or off the breaker box.

Does your cooler motor draw "a coule Amps" at 230Vac or at 115Vac?

If the current drawn by both welder and motor do not exceed what the switch is rated for, you will be okay. If there is too much current through the switch, then the switch will burn up (if is really just a switch) or trip (if it is really a breaker disguised as a switch.)


Joined Nov 1, 2006
I looked at the ThermalArc welder schematic on page A1 & also the specs; the max. 230V AC input current is 34A. S1 appears to be just a switch; see if there's a current rating on it. Now add the circulating pump motor full load amps [at 230V] to the max. welder amps [34A]. If the sum of these two currents is less than 80% of the switch rating you're home free.

If it were me, I'd connect the motor for 230V & connect it to the load side of S1 which is connected to R3 & S4 on the Diode ass'y., D1. One more thing I strongly recommend is connecting a 260-270V varistor [also called an MOV] across these terminals to protect D1 from high voltage spikes from the motor when S1 is turned off. A typical part no. for an MOV like this V260LA20 or V270LA20.