I am building an isolated 240V test rig for single phase welding and cutting machines. I have used two transformers with 30V secondary back to back.

I have wired a 240V toroidal transformer in series with the output (switchable) to limit the output to around 60W.

I am looking for suggestions to use the output of this transformer, it swings from 0V to about 10V on a short circuit output.

I hope this makes sense.

 

Welding and cutting are usually two completely different methods.
Draw out exactly what you are trying to do. !

 

Electric arc welding i.e. MIG, TIG, MMA, Plasma and Plasma cutting are closely related.

I am building this supply from parts I have laying around hence the unusual design.

 

Electric arc welding i.e. MIG, TIG, MMA, Plasma and Plasma cutting are closely related.

MIG to Plasma cutting? They have many differences and technologies used.
Much higher voltages required for Plasma.

 

Thing is, This is my line of work. Since everything went over to inverter technology, they are very similar inside. MIG works on constant voltage, TIG and MMA constant current. Yes, Plasma uses higher voltage but the main difference is the deign of the torch head.

 

Here's a small set TIG welder which will plasma cut up to 10mm.
However I was looking for ideas for my power supply.

 

Interesting project. My first suggestion is to not use that toroid in the output , or is it to check for short circuits?? Use a current shunt in the line 30 volt line between the two isolation transformers. By using a shunt you can have an isolated current measurement, and a way to switch off at a preset current limit.
And is the plan to test welders? As in production testing? Or to develop new products? or develop processes for clients? Or is this a service/repair organization that repairs failed welders and cutters??

For the power supply, do you need a variable voltage? And what sort of current will it need to deliver? I am thinking that the supply will need to be fairly clean, so as to simulate mains power. That could be 30 amps max or maybe 50 amps max, at 120 or 240. One option would be tap-changing to see how a welder works at 10% lower supply voltage.
So certainly it is all possible, not horribly complex nor awfully expensive. BUT that is without arc-flash protection circuits.

 

All the MIG I have worked on used LV DC,
For TIG, depends on the material, DC used for Mild Steel & Stainless and AC for Aluminum.
And of course, Plasma is very HV DC.

 

Interesting project. My first suggestion is to not use that toroid in the output , or is it to check for short circuits?? Use a current shunt in the line 30 volt line between the two isolation transformers. By using a shunt you can have an isolated current measurement, and a way to switch off at a preset current limit.
And is the plan to test welders? As in production testing? Or to develop new products? or develop processes for clients? Or is this a service/repair organization that repairs failed welders and cutters??

For the power supply, do you need a variable voltage? And what sort of current will it need to deliver? I am thinking that the supply will need to be fairly clean, so as to simulate mains power. That could be 30 amps max or maybe 50 amps max, at 120 or 240. One option would be tap-changing to see how a welder works at 10% lower supply voltage.
So certainly it is all possible, not horribly complex nor awfully expensive. BUT that is without arc-flash protection circuits.

It is for the service / repair sector Mr Bill. The series transformer is for short circuit protection. I had one case where a fault which I missed blew the newly replaced IGBT out of the machine.

I have seen a 40W incandescent light bulb do the same job, but where’s the fun in that?

The rig is for circuit testing so no large welding currents. Here is a better drawing of what I have so far.

 

OK, the drawing makes sense, but it will need a bit of interlocking to prevent two slightly out of synch power feeds to the DUT. (Device Under Test)
And a serious consideration is that when the bypass is active that the device will not be "oscilloscope safe"at all. So I would suggest separate connections to the DUT to avoid nasty results if the connections were change accidentally.

 

OK, the drawing makes sense, but it will need a bit of interlocking to prevent two slightly out of synch power feeds to the DUT. (Device Under Test)
And a serious consideration is that when the bypass is active that the device will not be "oscilloscope safe"at all. So I would suggest separate connections to the DUT to avoid nasty results if the connections were change accidentally.

I agree, after test / repair I put the welding output onto a load bank that will simulate a weld up to several hundred amps. I could just use a separate socket. If I need to use a scope under weld conditions I just have to be careful.