Hobart Problem

[Arkhermit]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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?

 

[Arkhermit]

I looked the diodes over, can't see any dark spots. I hooked up a 12V battery and a taillight bulb and did not get anything either way on either diode. ( the battery and bulb is good). So I hope I have located the problem. I am curious as to what caused them to quit ? I suppose it just happens. I am retired heavy equip mechanic and there are lots of things go wrong there is no explaination for. So I shall replace the diodes and try again.

 

[CNC Dan]

looks like the diodes are cooked. How many are there? could be two to four. You may have two different kinds of diodes also. Some will conduct stud to lead, others lead to stud. Look for a diode symbol printed on the side, or for two different part numbers.
Diodes usualy fail from overheating, or severe over current. They can fail from overvoltage, but that uaualy happens in the early design phase.

 

[Arkhermit]

Mine aparrently has two bolted to the plate then transformer wire and capaciter soldered to the top. Locally they are $26.00 online I found some hobart brand for $21.00 is this about right or is there some place better, Like one of the sponsers of this forum ?

 

[CNC Dan]

Mine aparrently has two bolted to the plate then transformer wire and capaciter soldered to the top. Locally they are $26.00 online I found some hobart brand for $21.00 is this about right or is there some place better, Like one of the sponsers of this forum ?

Price wise that seems about right.
If you order parts from hobart, they will be the right kind and polarity.
You could look arround and find diodes that have a higher current and voltage rating, but you will need to be sure to get the right stud size, polarity, etc.

I guess that you have a center tapped secondary winding transformer, if you have two diodes.
And if they are both bolted to the same heatsink, then they are one of each polarity. Usesome heatsink compound between the diodes and the heatsink to help keep the diodes cool.

 

[CNC Dan]

I just looked at a manual for a 220 volt handler, and the diodes are shown in a single package.

If that is the case with your model, just get the part from hobart.

 

[CNC Dan]

also:
http://www.hobartwelders.com/weldtalk/showthread.php?14505-Handler-120-diodes