Hobart Problem

Arkhermit · Aug 15, 2013

I have a Hobart Handler 120. When you trigger the gun the contact won't stay closed and the wire feed motor won't run. However if you hook the motor wires to a battery it works. I am thinking the contactor is bad. I cleaned the points in it, nothing. Am I on the right track ?

yomax4 · Aug 15, 2013

I would say the contactor is bad but usually you can hear it trying to close. Not sure what the old handlers used but im sure it's a tiny little thing. The good news is you can buy contactors cheap on the internet. Just get the numbers off of it and save some cash. Good Luck..

Arkhermit · Aug 20, 2013

Well, it wasn't the contactor. When you trigger the gun the contactor chatters, by that I mean it opens and closes very rapidly and seems to put a large draw on the electricity, the fan slows considerably and the wire feed don't turn. Any one got ideas or know a website that might ? I removed the wires to the feed motor thinking it might be the problem, but it didn't change anything. Thanks for any help

deereman75 · Aug 20, 2013

That sounds like the contactor....... It shouldnt act like that. It should close and stay closed until you release the trigger.
Either the contactor its self is bad, or the drive motor is shorting, drawing way too much power, and making the contactor do that.
The fan bogging sounds to me like there is a short somewhere. You need to figure out if the short is in the contactor or the motor.
I would try disconnecting the drive motor, and hooking a dummy load to the contactor, something like a lightbulb. If the contactor stays closed, your motor is gone. If it still does it, replace the contactor.

deereman75 · Aug 20, 2013

I just noticed that you removed the motor from the contactor. You have already done the test....
That sounds exactly like the contactor is bad to me..... Not sure why you think that shows its fine?

CNC Dan · Aug 20, 2013

There is a short somewhere. I suspect the transformer. See what kind of voltage you get accross the output when you pull the trigger.
If you don't get what you should, try disconecting the diodes, and see what you get then.

Arkhermit · Aug 21, 2013

I replaced the contactor with a new one, no change. There is a square plate above what I assume is the transformer, it has two round things bolted too it that the wires are soldered to and has square blue (I think may be diode) soldered with the wires and the other end screwed to the plate, the plate appears to be insulated from the machine on rubber mounts. Now, would I check each wire to grd as I trigger the gun ? What voltage should there be. this would be DC or AC ?

CNC Dan · Aug 21, 2013

Arkhermit said:
I replaced the contactor with a new one, no change. There is a square plate above what I assume is the transformer, it has two round things bolted too it that the wires are soldered to and has square blue (I think may be diode) soldered with the wires and the other end screwed to the plate, the plate appears to be insulated from the machine on rubber mounts. Now, would I check each wire to grd as I trigger the gun ? What voltage should there be. this would be DC or AC ?

The transformer will be the largest and heaviest item in the welder.
You should be able to see the core, made of thin sheets of metal stacked together. The core has wire coiled in and arround it. One coil is the primary, fed 120 volt power from the contactor. The other is the secondary, connected to the diodes, and then out to the output leads.

If you can disconnect the secondary coil from the transformer and check to see if:
1) still sounds like it's under load.
and
2) what voltage (ac) you have.

Also get a manual online so you can look at a wiring diagram. There can be different ways to make them so you may need to figure out what is what in your welder.

Arkhermit · Aug 23, 2013

Update, I unhooked the transformer wires from the heat sink plate and the other side had three wires bolted together, removed them, the contactor will stay closed and the feed motor runs and it doesn't sound like it is under load. I unhooked the two diodes and checked them with multimeter and both are open, no reading at all either way. Is it possible that could be the problem ? or maybe something else is wrong and burned them out ?

CNC Dan · Aug 23, 2013

some meters don't do so well with big power diodes. If you can remove the diodes(or un-hook one side) you could try running a small load (tail light?) from a battery (power tool?). First through one way, then the other.

How do the diodes look? Any darker areas that looks like it was hot?