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MIG welder not striking
Slimy38 - 2/1/16 at 01:56 PM

I've just been out welding, and suddenly the welder stops working. It's still got the fan running, and the wire is still being pushed out. But it's not striking, almost like the earth is no good.

I've tested from the connecting posts inside the welder for continuity, both the earth clamp and the wire are connected back to the posts. I've opened it up and can't see anything obvious.

Is there anything else I can look for? I should mention it's a Powercraft/Wolf cheapie one, but all the information online suggests they're just really difficult to work with rather than suffering from premature failure.

rusty nuts - 2/1/16 at 02:02 PM

You might be better off asking on the mig welding forum?

big_wasa - 2/1/16 at 02:08 PM

Have you exceeded the duty cycle ? Ie let it cool down and try again.

Open the gun up and check the power cable hasn't come away. Same at the machine.

Slimy38 - 2/1/16 at 02:09 PM

quote:
Originally posted by rusty nuts
You might be better off asking on the mig welding forum?


Just getting my password reset...

Slimy38 - 2/1/16 at 02:18 PM

quote:
Originally posted by big_wasa
Have you exceeded the duty cycle ? Ie let it cool down and try again.

Open the gun up and check the power cable hasn't come away. Same at the machine.


It's stone cold, but I wasn't welding long enough to hit the duty cycle. I've just tried again (about fifteen minutes later) and no change.

There is connectivity from the wire back to the connector post. I had to redo the gun connection when I first got it, it had been put together rather hastily so I opened it up and made sure everything was secure.

jacko - 2/1/16 at 02:43 PM

try a lower or higher setting it may be a transformer has burnt out
we had this on one at work
cheaper to get a new welder

gav2612 - 2/1/16 at 02:49 PM

You have definately got a good earth connection? Wire hasn't worked loose at the clamp

[Edited on 2/1/16 by gav2612]

Slimy38 - 2/1/16 at 02:51 PM

quote:
Originally posted by jacko
try a lower or higher setting it may be a transformer has burnt out
we had this on one at work
cheaper to get a new welder


I've tried all the settings, no joy. I've also tested the transformer side of the contactor relay, it gets mains voltage when the trigger is pressed.

Unless I've misunderstood welder construction, the only thing between the constructor relay and the gun is the transformer and the selector switch? If the selector switch doesn't work on any position, that does suggest the transformer...

Slimy38 - 2/1/16 at 02:52 PM

quote:
Originally posted by gav2612
You have definately got a good earth connection? Wire hasn't worked loose at the clamp

[Edited on 2/1/16 by gav2612]


I've tried to weld directly to the negative post in the welder, completely bypassing the clamp. No luck. And I've buzzed out the earth clamp, it's ok.

ReMan - 2/1/16 at 06:04 PM

don't they have a rectifier/diode pack?
And possibly fail safe electronics protecting the gubbins from over cycle?
Any more info

Slimy38 - 2/1/16 at 07:12 PM

quote:
Originally posted by ReMan
don't they have a rectifier/diode pack?
And possibly fail safe electronics protecting the gubbins from over cycle?
Any more info


There is something that looks like a rectifier, I can check the voltages on there. The fail safes 'should' kill the wire feed as well (according to the mig forum).

The various connections on the selector switch get varying AC voltages as I change settings (something like 12 volts at lowest setting, up to about ten time that at the highest), so I'm happy that transformer and the switch are also ok. That leaves the second transformer and the diode pack.

Slimy38 - 2/1/16 at 07:35 PM

OK, I think I'm almost there, but I'd appreciate a sanity check. The input side of the rectifier pack registers 90 volts AC. The output side of the rectifier pack also registers 90 volts AC, and that goes straight to the gun. Switching to DC on the multimeter shows less than a volt on both sides.

That's a fecked rectifier isn't it?

ReMan - 2/1/16 at 08:07 PM

If we're guessing it's a rectifier" how many pins/markings?
Check the resistances of it unconnected with the leads both ways round +_ and _+
Is there a model to get the diagram off the net?

ReMan - 2/1/16 at 08:17 PM

Sorry I'm no mig expert but I do think they're Dec
But it will be rough DC so measure the output on the DC setting of your meter

Slimy38 - 2/1/16 at 08:26 PM

quote:
Originally posted by ReMan
Sorry I'm no mig expert but I do think they're Dec
But it will be rough DC so measure the output on the DC setting of your meter


Yep, that's the point, it's only registering as AC on both sides of the pack. Even without smoothing I believe there should be a DC component.

It's an odd looking device though. Here's a similar one on Ebay;

Welder Rectifier

From what I remember from college, there should be two connections on the AC side (which is two of the tags), then two more on the DC side (which is one tag and the bolt to earth). Using the earth as reference, all three tags register the same 90 volts AC. Switching to DC gives me zip, nada, nothing.

Slimy38 - 2/1/16 at 08:47 PM

Better one;

REPLACEMENT 130 AMP SINGLE PHASE MIG WELDER BRIDGE RECTIFIER

The two central tags are AC input, the central bolt and the one plate are the DC output.

ReMan - 2/1/16 at 08:58 PM

Yep that looks like a rectifier of old !
So try resistance across them. The no DC volts suggests that they are dead short I've no longer diodes!