Monday, 22 June 2015

unimig wire feeder failure

A friend of mine has been looking for a mig for a while now. Like the rest of us, he's on a tight budget.
All the bargains were getting snapped up before he could get a look in.
Then one day they re clearing out some storage that's been sitting a while and on a pallet sits a unimig 175 solid state mig/ stick welder.
Wire feed no longer regulating. One fixed low speed all the time.
Some sweet talking later and the mig is his.

Initial hopes were that the pot for the wire feed is failed but it tested fine.
The wire feed is regulated by this card.

 Priced a replacement at $220.

Plan B.

I got a PWM dc motor speed card for something a while back and decided to set up an alternative power supply and regulator for the wire feed. Bypassing the wire feed circuit while retaining the other functions of the card.
A 4A 24Vdc (I would have preferred 36Vdc) was sourced and its mounting location determined. there isn't a lot of space so i had to mount it in the wire feed side.

The PM was also squeezed into a tight location. The plate it mounts to was originally inverted and covers other pots and switches.

The torch trigger now activates a relay supplied by the 24Vdc. The relay triggers the original torch input on one set of contacts while the other are supplied from the output of the PWM card. This allows the wire feed to operate independent to the original fault but also keeps the gas and welding current control as original.