MIG welder feed motor always running

[sanddrag]

I recently picked up an older Hobart Handler 120 MIG welder. For the most part it seems to be in working condition, except that the feed motor is always running (whether the trigger switch is plugged in or not) from the moment the welder is turned on. The speed control on it works just fine but the motor does not shut off. When I have the trigger switch plugged in and I press it, I hear what I believe is the gas solenoid opening. I've been told the contactor could be sticking. I'm not sure what this part is. Does anyone have a picture of one?

I found one part that I believe is a relay. The part number on it was T91P5A52-24. It had two small wires and three slightly larger wires going to it. I carefully took it apart and observed it. Inside, it has a little lever arm which can touch one of two contacts and a little white cylinder (electromagnet?). When the welder is powered on, I can see this little lever arm jump over to the other contact. If I hold it at the side it defualts to when powered off, the feed motor does not run.

I do not know the history of this welder. It looks like it may have had some poorly executed wiring repairs done.

Anyway, does anyone here know anything that might help me resolve the motor always on problem? Does it sound like something is just hooked up backwards? Is something stuck? I plan to call the service center on Tuesday, but before then, I know we have some smart people here who might be able to help.

[John Gutmann]

try just rewiring to the switch on the gun, it shouldn't be always on and power/ground shouldn't be constantly coneected to the relay it should have been ran through the switch. I had this problem once. No biggie, easy fix.

[Starke]

I work at Mahany Welding Supply. It sounds like you have a bad trigger switch on the gun itself. Like you said, the contacts on the switch are probably bad. Although I can not give you the part numbers and prices for things right now (my work is closed today), I will get back to you by Thursday. My work is able to UPS parts to you if needed. It is ironic that you mention the Hobart Handler 120. I believe we have one on the showroom floor right now that has a clearance tag on it. Ill get back to you on that as well.

I suggest taking the machine to a Welding Supply near you. Many places will look at machines and fix them for a cheap cost to the consumer. I hope this helps.

[KenWittlief]

the feed motor is always running (whether the trigger switch is plugged in or not)

this makes it sound like its not the trigger switch, if its not plugged in there is no way the wire feed should be powered

but its possible they used some weird wiring trigger circuit. You should be able to check the trigger with an ohm meter - unplug it from the welder and ohm across the trigger switch. If the meter reads ~0, and then infinity when you press and release the trigger, then the tigger switch is ok, and the problem is inside the welder.

[Starke]

Ken, you are correct. Ill have to ask my co-workers tomorrow and see what they say. I also get back to you on the other information as well.

[KenWittlief]

I just got a Lincoln Quick Weld (110 VAC, flux wire only) welder for my son's '70 VW bug project. It doenst have provisions for gas, but I can hear that same kinda relay click when you pull the trigger. Im assuming relay control of the motor on/off function is standard on this type of equipment.

(which leads me to think you have a shorted/ stuck relay contact- if the contacts are stuck you might still see the level move, and it would still click, but the contacts might never open)

BTW, be cautious working on a wire welder - when the trigger is pulled the whole spool of wire is electrically live to ground!

[Jay H 237]

There may not be anything actually wrong with any of the components. You mention that it looks like someone had been playing around with the wiring in there. It's possible that it's now wired wrong and causing this. If you have, or can find, a wiring diagram you can check this.

Hobarts are made by Miller (same factory) so if you're unable to find a Hobart wiring diagram the Miller may be identical. I'll have to see if I can find the paperwork and if there's a wiring diagram for my Millermatic 135.

[sanddrag]

I found the hobart manual with wiring diagram http://www.hobartwelders.com/om/6digit/o210088d_hob.pdf but mine is older than that one and it doesn't quite match.

[Dick Linn]

You can always ask the folks at http://www.hobartwelders.com/mboard/

Great source of welding info. On that forum, I'm "USMCPOP".

Check the voltage across the coil of the relay that runs the motor if you can. If it's always on, something is amiss. If it's always off, then maybe the contacts of the relay are welded.

[Al Skierkiewicz]

Sanddrag,
It sounds like you have isolated the problem. When you intentionally hold the relay in the normally open position the motor does not run. That would indicate either a shorted switch in the handle or an intentional rewire of the control circuit to keep the wire feeding. I am going to bet the switch in the handle is at fault. It could be a simple microswitch.

[KenWittlief]

I missed the part that Al caught, if you hold the relay contacts open the motor stops (like it should)

but since it runs with the handle unplugged there must be a short or mis-wire somewhere inside the welder, not in the handle itself.

start at the handle connector inside the welder, if you have an ohm meter that will make it easier. With the unit unplugged from the wall ohm across the handle tigger connector in the welder. It must be shorted (near zero ohms) if the motor is running.

if not, the input (coil) of the relay has been wired to something other than the trigger connector. Its possible the wire feed motor relay is chained off a gas solonide relay, and that one is stuck on?

so, either you have to find where that trigger connector is shorted inside the welder,

or you have to figure out where the relay is miswired and correct it.

hold on.... (its fun debugging a machine over the internet).....
you said the trigger does control the gas solonoid - its very unlikely they have two switches in the handle, one for the gas and one for the feeder.... so the trigger circuit is probabally ok

and the wire feed motor must be chained off the gas solonoid circuit - so its not the wires to the handle connector inside the welder, its the circuit that drives the feed motor relay that is always on.

There is a bright side to all this. Someone tried to fix this welder and screwed it up, that is why it was for sale, and Ill bet you got a better deal on it than if you bought it new.

so..... when you get it working you got an awesome deal ! :^)

[Starke]

We had a discussion about the topic at work today. Similar to what was previously mentioned, we decided that it is most likely the relay. The relay is what lets the current go in and out. WE also decided that it is not the board.

To purchase this relay, you can go to Radio Shack, or and good "Mom and Pop" Electronics store should carry it. It should run anywhere around the range of $20 and $50 dollars.

[Al Skierkiewicz]

sanddrag,
The schematic shows a pretty simple wiring job for the feed motor. Both the relays (sometimes called contactors) K1, K2 are fed from a winding on the fan motor. Not sure if the motor is acting as a generator or just has a 24 volt winding. The completed circuit through the handle switch turns on both the feed motor relay (the one you opened) and the main relay which starts the arc and opens the valve for the gas. Please note that if someone has not rewired the control, then the arc circuit is also possibly turned on. Since you say you can hear something clicking when you depress the handle switch, the circuit for the maincontactor, K1 and the solenoid valve appears to be working. There is likely a short near (or in the the connector) marked J1 (handle) on the diagram. The two white wires labeled 5WT and 6WT should go back to the contactor K1 coil contacts. (K1 is the part marked "9" in the block diagram) I suspect that you will find that one of them is connected to S3, the thermal cutout switch, which is part of the transformer. It is likely a simple matter to remove this wire from the transformer and return it to the empty tab on the contactor, K1. Be careful to get it on the right contact.

An interesting side note. If you look at the schematic, the normally closed (NC) contacts of K2 short the output of the feed motor when the handle switch is released. This will cause the motor to stop quickly. The fan circuit is also a safety, if the fan fails and does not provide the 24 volts, then you cannot weld or feed wire.
A picture of the inside of your device might help.

[sanddrag]

Well, I had someone I know who is good with these sort of things look at it today. Turned out the contactor (big relay I guess) was indeed stuck. We opened it up, unstuck it, and now it welds absolutely beautifully!

[Dick Linn]

Sanddrag, Please do me a favor. Post the result of the fix over at the Hobart welding forum so it's there in case someone else encounters the same problem.

As I mentioned, there are some good folks over there. One guy won a bid for an Abene vertical/horizontal mill (Swedish) for $103.50, and he is willing to sell it to me for what he paid, just because he knew I was interested in that make. Of course It'll cast plenty to have it shipped here