Page last updated: 10/12/2009
Having recently bought a SIP MIGMATE 100, and after several hours of trying to MIG weld (well it certainly felt like hours) came to the conclusion I aught to stick to radio and electronics, and give up the welding altogether. It was looking as though it would be much simpler to ask my father to weld the odd bits I needed to get done.
That might have been the end to my MIG welding, but that shortly after my failed attempts I was over at fathers house. Watching him MIG weld, green with envy, whilst recanting the story of my failed attempts at MIG welding. Then I find his MIG torch thrust into my hand, " Come on then, have a go with mine. MIG welding is quite similar to gas welding, without some of the distortion problems". Damn me, I can MIG weld after all...
Now we come back to the MIGMATE, or should I say my MIGMATE and the problems I found:
Wire feed rate somewhat erratic.
Wire feed motor tending to stall at low feed rates.
Shield gas supply erratic particularly at low welding currents.
After a bit of research on the net, and a copy of the original manual kindly sent to me by SIP, I found the original design to be a little bit lacking. Although I suspect it may well have worked quite satisfactorily when originally manufactured, the ravages of 20 years of abuse, that and being stored in the back of someone's damp and dusty garage whilst not in use, have taken there toll.
The following points need to be taken into account:
The wire feed motor supply is derived from the main welding transformer, as such the erratic nature of the wire feed rate seems to be effected primarily by voltage drop on the main transformer upon striking of the arc.
The wire feed motor speed control circuit is somewhat primitive in nature, being that of a simple current limiting arrangement. A commonly found side effect of this method of motor speed control, is a loss or torque at low speed.
The shield gas control valve is driven directly from the main welding transformer, at low welding currents the main welding transformer output voltage is below the 48v operating voltage of the shield gas control valve. Add to that any additional voltage drop upon striking of the arc, making the issue still worse.
And now onto the fix. I have made considerable alterations to the original with regards to both control and wire feed electronics. The modifications I have implemented on my MIGMATE are summarized below:
Provision of a dedicated auxiliary control power supply with its own power transformer.
Provision of a PWM wire feed motor speed controller, drawing its power from the new auxiliary control power supply.
Power for the shield gas control valve to be derived from the new auxiliary control power supply.
New control relays, again driven by the new auxiliary control power supply.
AUX PSU and PWM Generator.htm
Control Relays & Auxiliary Supply Transformer.htm