MIG welder fault

[Stustoys]

Ok so I'll start with the fact that I know it isn't technically a MIG welder.

So my 33 year old Hobart MIG has had a bit of an issue lately and I'd like a sanity check before I go looking.

The transformer is staying on longer than it should. At first I thought something in the burn back timer* was going out of spec as after a few welds it would start working properly again. Last time I used it I noticed the transformer was staying on longer than the post flow gas, which if I am reading the diagrams correctly cant happen unless the problem is the contactor. So if the gas if off and the transformer is on, its the contactor right?




*non adjustable externally on this welder. I had always thought it was adjustable internally but can't see it in the diagram.

[Commander_Keen]

So, explain the actual symptom.
Your gas stops while the arc is still active? What's the wire drive doing?

[sossity]

I wrote a load of useless info but have deleted it. I think you are right and the gas valve should operate at the same time as the contactor. I think the motor can switch off before both the gas and contactor for that post flow timing.
Sorry about the silly post before.

[Stustoys]

Thank you guys


So, explain the actual symptom.
"The transformer is staying on longer than it should. "


Your gas stops while the arc is still active? ?
Well no, sorta. But the arc is only "out" because the wirefeed is working correctly. The transformer is still on after post flow time so there "could" still be an arch, but there isn't. You could say "the gas stops while the transformer is still active" making the question "is that possible on this welder unless the contactor is the issue?".


I think you are right and the gas valve should operate at the same time as the contactor. I think the motor can switch off before both the gas and contactor for that post flow timing.

Yes the motor does turn off before that gas/contactor. I'm pretty sure some welders and burn back and post flow as separate adjustments, But we seem to agree that on my welder there is only the one timer for both. Maybe 30 years of dust is slowing it down, just like me.

[KBs PensNmore]

It pays to blow out the electronics and the liners from time to time. For home use every other roll is what I've been told.
When I had my business I did it on a monthly basis, surprising how much dust and crap gets in there.
Kryn

[Grahame Collins]

The transformer is staying on longer than it should.

What is the indication that the transformer is still operating. Is it the clack of the coil electromagnet releasing or a just the hum of the transformer?

Given that your mig is old and like all migs operated in a metallic dust environment what's the chances of the contact points being arced and pitted.

It would follow that point damage would slow down the shut down/close off sequence, I would have thought.

I do recall mention of a contactor replacement talked about on one of the UK mig welding forums. The brand name part was not available but a suitable substitution was available.

Just some food for thought. A thirty three year run is not too bad compared to the longevity or lack of it, in some of today's products.


Grahame

[Stustoys]

It has been blown out a few times over the years, but I wouldn't say "often" by any means.


What is the indication that the transformer is still operating. Is it the clack of the coil electromagnet releasing or a just the hum of the transformer?
Its the burnback going long. Transformer humming, then contactor clicks and humming stops.


Given that your mig is old and like all migs operated in a metallic dust environment what's the chances of the contact points being arced and pitted.

It would follow that point damage would slow down the shut down/close off sequence, I would have thought.

As it "clears" itself my guess is its just the movement of the contactor, I'd guess if it was pits it wouldn't "clear".... but thats just a guess. An airline with some extra attention to the contactor sometime in the next week should sort something out, and I'll get some part numbers while I'm in there in case it comes back.


Just some food for thought. A thirty three year run is not too bad compared to the longevity or lack of it, in some of today's products.
Given that for the price of this unit* I could have bought a $300 welder and replaced it every 3 years I should hope it would!!


*I got the welder cheap due to a phone call by a friendly TAF teacher to one of their suppliers. Though granted hobby MIGs were not a thing then. And thats excluding interest that could have been earned.

[Vernonv]

It does sound like the contactor is sticking. One way to be sure is to measure the contactor coil voltage. If it goes to 0V and the contactor is still on then the contactor is sticking, otherwise it's an issue with the control electronics.

Note there are dangerous (lethal) voltages inside welders so be especially careful, or get an experienced person to look at it for you..

[Stustoys]

Seems there is more going on here than I thought.
Fingers crossed on the contactor.
Will likely be a few days before I can start looking and as is "comes good" if I don't catch the fault in the first X tries before it comes good I've no idea how long I have to wait to try again. I have a few things to try. Longest shot, I'll manually operate the contactor and see if hangs..... couldn't be that lucky could I?

[racingtadpole]

Yes, if the gas is off and the transformer is still on your problem is the contactor. Control for both comes from the triac on the control board, if one is working as expected the controller is working normally.

[Stustoys]

The tax man will have to wait a little longer until I get my return done. Went to the shed this morning with a collection of paper work and meters.

Well the longest shot came in, though I could have found a better screwdriver.
https://www.youtube.com/watch?v=7y_zofmgJMc

Din mount and opens up very easily. Quick blow out and everything is working as it should for now. I guess I'll find out in a couple of weeks if the problem will return. At least I know what replace if it does. Checked a few other things while I was in there but they all appear fine.

Thank you all

[BaronJ]

Hi Stuart,

Some of those contactors, not all, can be easily disassembled and the coil and armature separated and the anvil cleaned. A layer of dust or dirt under the armature will cause the problem that you illustrated in the video. You shouldn't have to remove the wiring either, the contact block usually just lifts off bringing the coil and armature with it.

A lot cheaper than a replacement.

[simonl]

Glad you got it sorted Stu.

Simon

Sent from my SM-G970F using Tapatalk

[Stustoys]

Some of those contactors, not all, can be easily disassembled and the coil and armature separated and the anvil cleaned.
This one was. Pretty much the same squeeze used to get it off the Din rail is used to open it.
Good for another 33 years. :2tsup:
Still I learnt a bit about just whats going on on that board.