Welder playing up

  1. Julian_P Member

    Messages:
    139
    Warrington
    Good evening chaps, I wonder if anyone has some advice?

    It concerns my Wolf Weld 200amp DC inverter welder that I purchased as a reader offer from The Daily telegraph about 10 years or so ago.

    It's been a great bit of kit, I hardly use it these days but it it brilliant with 4mm rods running at full chat for welding end plates onto RSJs.

    Anyway, it's started playing silly buggers, you can switch it on and you always hear the cooling fan spinning up but sometimes the output is zero. Switching it on and off repeatedly eventually seems to coax it into life, so then I leave it on until the job is done.

    Before I remove the casing, can anyone say what component I should be looking at as the culprit? I hope I can fix it as it is very good. TIA Julian.
     
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  2. eddie49 Member

    It sounds like you have definitely had your money's worth out of that welder. Ten years at 200A from a cheap-ish inverter is good going!
    Due to the complexity, lack of data, and hard-to-source components, DIY repair of an inverter welder is not really possible. I would suggest that you leave it switched off for an hour or two, to allow charged capacitors to drain, then open it up and look for loose connections. Check for poorly-seated plugs on cables between the PCBs, loose or burnt push-on tags ( especially at the power switch and the four tags on the nearby bridge rectifier ), and loose bolts or screws on the high-current connections. These would be thick cables, heavy tracks on the PCB, copper or aluminium bus-bars, and cables bolted to heatsinks and the back of the front-panel Dinse sockets.
     
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  3. Julian_P Member

    Messages:
    139
    Warrington
    Thanks Eddie, I shall do just that. Fingers crossed that it's something simple. I've got to like the thing over the years and for what I do with it it would be hard to justify buying a replacement, but my little MIG welder isn't up to doing heavy stuff.
     
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  4. eddie49 Member

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  5. Julian_P Member

    Messages:
    139
    Warrington
    Hell's teeth they're cheap. Oh well, I'll just buy a new one if nothing is obvious inside mine. It's cold in the workshop now, I'll look tomorrow.
     
  6. hunter27

    hunter27 Pete

    Messages:
    485
    Location:
    Lancashire UK
    I have seen a few reviews on these welders and it looks like on full output they only give out just over half the amps they claim to.
    This Old Tony reviewing one and using it as a tig machine
     
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  7. the snooper

    the snooper getting older by the day

    Messages:
    20,128
    Location:
    Hull UK
    Look for a dry solder joint aswell
     
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  8. Memmeddu

    Memmeddu Member

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    Don't forget to check capacitors they could be gone
    They use to wear down by the time and by the heat charge and discharge process.
     
  9. zzr1200

    zzr1200 Working at 650 ft on open steel work

    Messages:
    3,591
    Location:
    Brimington, Chesterfield, Derbyshire
    If you can just switch it off and then on, first thing you need to do is replace the on/off switch assembly (just to know it's a good switch) , its probably only a couple of quid from RS Components..or a good electrical supplier.
     
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  10. Wildefalcon Member

    Messages:
    182
    Location:
    Gloucestershire, England
    Another option is to send it away for repair.

    There are a couple of listings on eBay for repair services.

    Example ( no idea as to quality - random selection):
    Screenshot_2020-01-02-12-44-24-145_com.ebay.mobile.jpg
     
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  11. Memmeddu

    Memmeddu Member

    Messages:
    1,492
    Location:
    Italia Sardegna
    I would like to know if I can contact them from Italy in case I need...
    Should be great
     
  12. the snooper

    the snooper getting older by the day

    Messages:
    20,128
    Location:
    Hull UK
    He says when he switches on the cooling fans work but zero output so can't be the switch
     
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  13. Memmeddu

    Memmeddu Member

    Messages:
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    Location:
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    I think it can maybe it's enough good to charge capacitors and keep going the power supply board but not enough to manage the current required to make the welder work
     
  14. zzr1200

    zzr1200 Working at 650 ft on open steel work

    Messages:
    3,591
    Location:
    Brimington, Chesterfield, Derbyshire
    After 10 years of off/on the contacts will be burnt on the contacts surface inside the switch if he's going to pull the case off to check for loose connections investing in a 5 quid switch is worth it. I'd rather spend a fiver than send it of for repair, at least try to repair it yourself...
     
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  15. Julian_P Member

    Messages:
    139
    Warrington
    Well I took the cover off. Of course it's working fine now I did that. You switch it on an the cooling fan starts up, and 5 seconds later you hear the click of (I assume) a relay and then you get output (about 80 volts open circuit) The only thing I discovered was that the earth wire from the power cable was lose where it was screwed to the chassis. I tried to tighten it with a screwdriver and it just turned so the thread is stripped (must have come from the factory like that as I have never touched it) so tommorw I will fix it properly with a nut and bolt. But I can't think a dodgy earth on the chassis will cause an issue - just make it less safe for the user?

    It is a really good bit of kit compared to that little thing if you go to the top of the thread. It has banks of diodes on the most enormous heat sinks and electrolytic capacitors, about 6 I think) the size of small yogurt pots. For a DIY thing it looks hellish solid and fit for many more years.

    I could easily illiminate the switch by just by-passing it temporarily but somehow I don't think that's the issue but you never know. Also there's a couple of small ceramic resistors that have been getting quite warm as they have gone a bit brown, but ceramic resistors are designed to do this and my multimeter suggests that they are still resisting OK. So I'm out of ideas, but the darn thing is working again so I'll play around again tomorrow, stick it back together if all's well and forget this ever happened. ;-)
     
  16. eddie49 Member

    The relay closing after 5 seconds implies that the welder has a soft-start circuit. During the delay, the DC capacitor bank is being pre-charged via a resistor, to avoid the large initial current surge that happens with empty electrolytic capacitors. This feature is often neglected in low-end units nowadays, so it was a well-designed machine.
    Even if it is a bit loose, it is also a luxury to actually have an earth wire at all ! Many small inverters just have a 2-wire mains lead, which, as you say, makes them rather unsafe.
    It's good that the machine works. Probably still worth checking inside for poor connections.
     
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  17. Julian_P Member

    Messages:
    139
    Warrington
    Indeed. I shall look again tomorrow. The capacitor bank has it's own PCB and is at the bottom. You can't get to see the solder side of the board or even try and check the capacitors without unscrewing it. That doesn't look too arduous so I will give it a go tomorrow. Thanks for all the replies so far.
     
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  18. Yamhon

    Yamhon Member

    Messages:
    893
    Location:
    Yorkshire, UK
    I know nothing about repairing welders, but as you've had it for that long, you could try using an air can or take the outer cover off to remove any dust and debris that may have built up over the years. Having looked in old computers you'd be surprised how chocked up machines can get... might do it some good.
     
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  19. Parm

    Parm I have fun doing stuff

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    Location:
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    A good blow out may solve the problem. It’s the IT equivalent of turning it off and on again
     
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  20. Julian_P Member

    Messages:
    139
    Warrington
    Well Eddie, I'm sure you're on the right track here as I found some stuff online from a Polish guy that tells the exact same story as you. Anyway, this is dragging on a bit now and it's playing up worse than ever now and switching it on and off sometimes gets the relay to click and an output but sometimes not.

    This machine has banks of Mosfets and diodes or whatever the hell they are and no fewer than 6 large smoothing capacitors, all of which show no signs of distress and when you compare the innards of mine to the cheap stuff on ebay I've come to the coclusion that it's worth repairing as it will be probably something of nothing.

    But it's beyond me I'm afraid and so I'm going to contact those chaps in Nottingham above and see if they will look at it, it's deffo worth spending a few quid on I think. Luckily I often work at East Midlands so I can take it in person.
     
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