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  1. #1
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    Default 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.
    Attached Images Attached Images

  2. #2
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    Default

    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.
    Kryn
    To grow old is mandatory, growing up is optional.

  3. #3
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    Default

    Quote Originally Posted by KBs PensNmore View Post
    Is this an intermittent fault or a one off?
    Well it's intermittent in the sense that the breaker trips after about 5 seconds
    Quote Originally Posted by KBs PensNmore View Post
    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.
    No. The first one is the PCB, the second is "the rest"

    Quote Originally Posted by KBs PensNmore View Post
    Have you checked the wiring, as it sounds as if you've a voltage supply problem.
    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

  4. #4
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    Default

    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.
    Kryn
    To grow old is mandatory, growing up is optional.

  5. #5
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    Default

    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.

  6. #6
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    Default

    Morning Guys,

    Quote Originally Posted by KBs PensNmore View Post
    What size cable are you using, a proper 15 amp rated and what length is it?
    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.

    Quote Originally Posted by KBs PensNmore View Post
    How many times has it tripped approx?
    Three (none of this approx rubbish lol. New breakers less than 3 years ago)

    Quote Originally Posted by BaronJ View Post
    Is the cooling fan running properly ?
    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*.

    Quote Originally Posted by BaronJ View Post
    If so then do you have the expected 24 volts coming out of the small transformer ?
    Well the light is on so I assume it is at least close(Well its on until the trigger it pulled)

    Quote Originally Posted by BaronJ View Post
    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.
    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.

  7. #7
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    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.

  8. #8
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    Default

    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.

    Quote Originally Posted by Stustoys View Post
    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 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.

  9. #9
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    Hi Stuart,

    Quote Originally Posted by Stustoys View Post
    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?
    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.
    A megger test to check for any leakage to earth would be good, but make sure that all transformer conections are removed first, you don't want to do any damage to other components with the 500 volts from the megger.

    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.
    I wouldn't worry about it that is why we ask questions...
    Best Regards:
    Baron J.

  10. #10
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    Default

    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

  11. #11
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    Quote Originally Posted by racingtadpole View Post
    The fault is common to any position on the switch,
    Similar
    Quote Originally Posted by racingtadpole View Post
    and it’s bogging the little control supply transformer, so it’s on the incoming mains side.
    Well maybe, but as I said once welding starts the welding V takes over from the control transformer, so maybe not...

    Quote Originally Posted by racingtadpole View Post
    Check your contactor, you’ve probably cooked it again.
    I'll have a look.

    Quote Originally Posted by racingtadpole View Post
    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.
    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

  12. #12
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    Hi Stuart,

    Interestingly I've just noticed that on the control circuit diagram, C13 is shown wrong way round !
    Best Regards:
    Baron J.

  13. #13
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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

  14. #14
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    Quote Originally Posted by BaronJ View Post
    Hi Stuart,

    Interestingly I've just noticed that on the control circuit diagram, C13 is shown wrong way round !
    I tend to agree, but I certainly don't know it. lol

    Quote Originally Posted by racingtadpole View Post
    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.
    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

  15. #15
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    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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