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Thread: Same MIG new problem
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15th Mar 2020, 09:09 PM #1Most Valued Member
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Same MIG new problem
My trusty old MIG has a new issue.
Was welding the other day when the wirefeed lost speed and the current went way down, followed shortly after by tripping a 20A breaker.
A couple of necessarily short videos.
With the voltage on 1 you can see the power light dim, hear the gas and will have to trust me the wirefeed is slow.
https://www.youtube.com/watch?v=7EByM2TTXLg
With voltage on 4 the power light dims much more, there doesn't seem to be even enough V to open the gas solenoid and the wirefeed is much slower(on the same setting).
https://www.youtube.com/watch?v=qpMy53i61Jg
There was no smoke or smell.
What am I asking? I guess I want someone to tell me its the diodes, the caps or possibly even the inductor(?) and not the transformer lol
I will find out one of these days I guess. Have extra brownie points from fixing SWMBO's Akso washing machine so at least I have that going for me.
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15th Mar 2020, 09:29 PM #2Most Valued Member
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Is this an intermittent fault or a one off? Is the unit set up with a remote wire feeder, asking as you've added a pic of what appears a remote feeder wiring diagram.
Have you checked the wiring, as it sounds as if you've a voltage supply problem.
KrynTo grow old is mandatory, growing up is optional.
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15th Mar 2020, 09:53 PM #3Most Valued Member
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Well it's intermittent in the sense that the breaker trips after about 5 seconds
No. The first one is the PCB, the second is "the rest"
I would get that if it wasn't tripping the breaker though it is on the end of a pretty long lead.......... Still, its cheap enough to check, even if it does mean some grunt work getting the welder out of the shed. unlikely to have a chance to do that for a couple of days though
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15th Mar 2020, 10:46 PM #4Most Valued Member
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What size cable are you using, a proper 15 amp rated and what length is it?
How many times has it tripped approx? Asking, as often a circuit breaker will weaken from constant tripping and required to be replaced. Other than that I'm out of ideas, and should probably be checked out by a qualified sparky.
KrynTo grow old is mandatory, growing up is optional.
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16th Mar 2020, 01:17 AM #5
Hi Stuart, Guys,
Is the cooling fan running properly ? If so then do you have the expected 24 volts coming out of the small transformer ?
If the fan is running properly then the mains feed is OK. So you need to check the small transformer output voltage, since this feeds the wire feed motor, indicator lamp etc.
It also provides the power to pull in K1 which feeds power to the main transformer.Best Regards:
Baron J.
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16th Mar 2020, 08:33 AM #6Most Valued Member
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Morning Guys,
Its a 10amp machine. Though it is on 15amp cable, so they say but I haven't checked wire size. Length is "plenty long" but I've been using it happily for a couple of years.
Three (none of this approx rubbish lol. New breakers less than 3 years ago)
While it is not shown, the fan is switched with temp. BTW its not a bad set up, when the fan comes on its a warning "hey you are pushing me" if you keep pushing to much longer a thermal overload trips, which takes out everything, fan included. So it takes a fair while to cool down with no fan, which is encouragement not to trip the thermal overload*.
Well the light is on so I assume it is at least close(Well its on until the trigger it pulled)
This is where things get tricky... so I'm told. The transformer only does its thing until the trigger is pulled, then the welding V takes over. I believe this explains the strange "control side of things" issues. If it was simply a control side of things issue I wouldn't have thought it would trip the breaker given (at least part of) the controls are on a 400mA fuse. Of course I could be wrong, maybe there is a very dead lizard inside somewhere.
*Now I think the fan thremo is on the heatsink and the second overload is in the tranny and maybe that explains some of the "slow to reset". But the fan story seems good.
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16th Mar 2020, 09:14 AM #7
Hi Stuart, Guys,
OK, there are two large diodes on the output of the main transformer that should be checked, however there is a large capacitor and a fairly low resistance switched by K1 across the output.
MAKE SURE THAT THE MAINS IS DISCONNECTED !
Use a lollipop stick or similar to hold K1 in the operated position. Carefully disconnect the diodes from the transformer and measure the transformer resistance, it will read quite low almost a short circuit. Then check the diodes for resistance both forwards and backwards. They should read open circuit one way and maybe 20 ohms or so the other way and both diodes should read within a few ohms the same as each other.
Now whilst you have the diodes disconnected check that you have zero resistance between the ground terminal and the transformer. That will check the ground out. Now there are other components connected to the plus side including the large capacitor, 80.000 uf is a big capacitor and needs to be checked, but the only way to test it is by disconnecting one of its terminals. Using your ohmmeter putting the probes across the capacitor terminals should show a low resistance that starts to climb in value. When it stops climbing, you will be able to set your meter to the voltage range and measure the meter output voltage across the capacitor terminals, probably about 10 volts. The voltage will depend upon the meter battery voltage on the ohms range.
At this point you will have checked the major components except for the main transformer output voltage, which will need to be done under mains power. I've deliberately not explained how to do this unless you are confident that you can do this safely. Hopefully you will discover the cause of the problem before this. Which I suspect is one of the diodes or the capacitor.Best Regards:
Baron J.
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16th Mar 2020, 10:21 AM #8Most Valued Member
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Hi Baron
Thanks for that(though it will be a couple of days before I can get to it)
I checked discharge resistor was working last time I was in there(though of course I'll short them out just in case).
Why hold K1 in?
One thing just crossed my mind reading your post about checking transformer to ground. It's an RCD breaker......so it may not be over current tripping it, which I've been assuming until now! that changes things!
While I would be happy enough to check the transformer output, assuming down stream of the diodes/caps would be ok, its just V between tip and earth clamp. If it comes to that I'm screwed lol not like I'm going to be able to buy a new one.
I could put a megger tester on it.
I should add, its not that I doubt what I was told. I was just trying to saying I wasn't smart enough to work it out for myself, it really had me scratching my head.
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16th Mar 2020, 06:48 PM #9
Hi Stuart,
Because according to the diagram you posted, a pair of contacts connects a low value resistor across the capacitor when the trigger is released. This resistor will give false readings when checking.
One thing just crossed my mind reading your post about checking transformer to ground. It's an RCD breaker......so it may not be over current tripping it, which I've been assuming until now! that changes things!
While I would be happy enough to check the transformer output, assuming down stream of the diodes/caps would be OK, its just V between tip and earth clamp. If it comes to that I'm screwed lol not like I'm going to be able to buy a new one.
I could put a megger tester on it.
I should add, its not that I doubt what I was told. I was just trying to saying I wasn't smart enough to work it out for myself, it really had me scratching my head.Best Regards:
Baron J.
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16th Mar 2020, 10:07 PM #10Most Valued Member
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The fault is common to any position on the switch, and it’s bogging the little control supply transformer, so it’s on the incoming mains side.
Check your contactor, you’ve probably cooked it again.
The transformer is probably ok, there wasn’t any smoke, if a transformer lets go there’s normally an apocalyptic amount of smoke and sometimes flames.
Rule no 1 of fault finding.. nothing runs without power
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17th Mar 2020, 05:56 PM #11Most Valued Member
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Similar
Well maybe, but as I said once welding starts the welding V takes over from the control transformer, so maybe not...
I'll have a look.
That's what I'm hoping!
I should hit the shed now but its been a long day so perhaps not the best idea. Likely will get onto tomorrow.
Thanks
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17th Mar 2020, 08:52 PM #12
Hi Stuart,
Interestingly I've just noticed that on the control circuit diagram, C13 is shown wrong way round !Best Regards:
Baron J.
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17th Mar 2020, 09:00 PM #13Most Valued Member
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The fault is the same just manifested in a similar fashion because the transformer is multi tap primary. The 24Vac transformer is fed from line side of the contactor and powers the control board all the time, there is no means in that circuit to power it otherwise nor would you want that as the welding voltage is poorly regulated and variable upon switch setting. The 24 transformer is operating correctly until you pull current through the primary of the transformer then the unit bogs because of lack of incoming line voltage. Only things in that circuit are the primary, the switch and the transformer. As it’s not unique to switch position that rules out the switch, and likely the primary too, leaving the contactor. I would check the contactor if it pits/burns the contacts you’ll never know, if the transformer is burnt see previous comments, and it will stink inside. For funsies, check the transformer on both primary and secondary to see if you have coil resistance as there is a chance it has a spot short not a meltdown short, although based on your videos I don’t believe that is the case.
Hope that helps
Rule #2 of fault finding... the simplest solution is usually THE solution
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17th Mar 2020, 09:43 PM #14Most Valued Member
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I tend to agree, but I certainly don't know it. lol
ummm I'm not so sure thats 100% true. I'm not seeing how the (small)transformer feeds the top half of the circuit. But then I'd hate to say it doesn't. My WAG is that it uses the welding V to control arch length by varying the wire feed speed. Of course I really have no idea.
Having said that I see what you are saying about checking the simple things first and certainly will.
Maybe someone manage to not put the contactor back together properly
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18th Mar 2020, 01:38 AM #15
Hi Stuart, Racingtadpole,
I agree with racingtadpole that the contactor should be checked out first. However I’m not 100% convinced that it would cause RCD tripping. The favourite for that would be rectifiers or the big capacitor.Best Regards:
Baron J.
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