Powercraft 135 gas/nogas not striking

  1. Slimy New Member

    I've just been out welding, and suddenly my welder stopped working. It's still got the cooling fan running, and the wire is still being pushed out (and gas flows). 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 gun are connected back to the posts. I've opened it up and can't see anything obvious. The relay at the top of the machine still clicks when I pull the trigger. It doesn't strike on any power setting. I've even tried touching the wire to the earth post inside the welder to completely discount the earth clamp, still nothing.

    Is there anything I can look for? It's one of the Aldi welders, manufacturer date of 2009 apparently but it's been find up until now.
     
  2. mike 109444

    mike 109444 Member

    Messages:
    4,086
    uk Bristol
    There are two relays on the pcb. Is the bigger one operating ? (assuming you have same pcb ??)
    And welcome BTW:hug:
     
    • pcb 2 UNDERSIDE.jpeg
    • pcb 1 TOP SIDE.jpg
  3. mike 109444

    mike 109444 Member

    Messages:
    4,086
    uk Bristol
    Could be the thermal cut out has operated (were you running it harder than usual?). The thermal cut out is usually mounted on or burred in the main transformer and so when it operates (cuts out) it can take quite some time before it has cooled enough to reset as the transformer is a large chunk of steel and holds it;s heat. Usually when they operate the ONLY thing still working is the fan!! but that's not to say that all are wired like this.
     
  4. Slimy New Member

    It's a similar PCB, although no variable resistor. The big relay works fine, I register 230VAC on one side of the switch, then when the trigger is pressed the same appears on the other side. That voltage makes it's way all the way round the transformer, and the various screw fittings on the selector switch register varying voltages as I select positions. From memory it's about 12 volts on position one, up to about 120v at position 6 (or values in that sort of ballpark). So I'm happy it's getting all the way round to the switch (which also means the cut out is ok).

    Next step is the second transformer and the rectifier pack.

    The frustrating thing was that it was only applying a couple of tacks on hollow section steel, normally it's duty cycle is far longer than my ability to hold a torch steady!!
     
    cford14 likes this.
  5. mike 109444

    mike 109444 Member

    Messages:
    4,086
    uk Bristol
    The "second transformer" MAY be a choke not a transformer (one wire in one out ?) unless you mean the one on pcb ?
    If you check the output of the main transformer where it goes onto the diode pack (big nuts and bolts or ring connectors) then metering there for AC less than 35v ish would show there is input to the diode pack. The output of the diode pack should then be DC less than 25 ish volt
     
  6. Slimy New Member

    The second transformer is about half the size of the big one, it's not the one sat on the PCB. It's on the bottom of the welder. It could be a choke though.

    But checking the voltages on the rectifier seems to show a problem. Using the chassis as the ground reference, the two tags on the AC side register about 90 volts. But what I would expect to be the DC out (basically the connection to the gun) also registers 90 volts AC. If I switch to DC I get less than a volt. I'm assuming that's not right?

    I've found this pack on Ebay;

    http://www.ebay.co.uk/itm/111860923909

    It certainly looks like the right one.
     
  7. mike 109444

    mike 109444 Member

    Messages:
    4,086
    uk Bristol
    Well you should not be metering between the welder chassis and the AC out. You should meter across the INPUTS (two) to the diode pack. These INPUTS should be AC and will be a result of what ever the power selected from the power control switch(s). This should as you have worked out be rectified to DC at the output of diode pack. One connection of which will go to the "smaller transformer (choke)" input and the other one will go via the wire feed to the torch.
     
  8. Slimy New Member

    Ah, ok that makes more sense. I get between 20 and 30 volts AC from the inputs, as you say depending on the control switch. Each setting gives a different value.

    I'll have to test the DC output again as I removed the diode pack. I did test the diode pack out of the welder, all I managed to figure out is my multimeter can't test diodes...
     
  9. mike 109444

    mike 109444 Member

    Messages:
    4,086
    uk Bristol
    Just make sure you refit any insulating washers that are (maybe) present on the diode asy
     
  10. Slimy New Member

    It's all back together now, thanks for the pointer about insulating washers. Now I understand how to test across the pack rather than from ground, I can see 20 volts DC on the output side of the pack. The connectors do go to negative to the choke and positive to the torch.

    I have a sticker on the back of the box that suggests that at 30A, the voltage should be 15.5 volts. That sounds reasonable for the 20 volts out of the diode pack, but if I measure across the torch connector posts I only get 10 volts. It still increases as I turn the setting up, and it's the same voltage if I measure between the welding wire and the earth clamp. Does this mean it's actually the choke that has had it?
     
  11. mike 109444

    mike 109444 Member

    Messages:
    4,086
    uk Bristol
    Well as the choke is just a thick length of wire wound round an iron core then it would be a bit odd for it to play up apart form going open circuit. It could be that there is a connection issue between the diode pack and the input to the choke or the out put of choke to the chassis mount for the ground. You could try bypassing the choke with a car jump start cable clipped to the diode pack out put stud and onto the work piece. It wont weld as good due to lack of inductance but should prove the point that fault is in the Neg (-) side of out put. The thick wire on chokes (>4mm dia) is usually former into a loop and this is connected to where it has to go (stud or ground clamp post) but this loop can corrode and cause a poor connection. They sometimes have the star type washers to dig into the copper of theses loops to improve the connection. It is worth undoing and running a small file over the connections. Note they may meter as low resistance with a meter BUT under load of trying to pass >30 amps the connection is poor. A smear of vaseline gel on connections when re assembling should prevent corrosion.
     
  12. Slimy New Member

    The welder lives in a dry garage but hasn't been used for about six months, so you could be on to something. The two connections on the gun and the earth clamp were quite badly corroded so I gave them a scrub as the first thing. The thick copper loops from the transformer and choke on to the rectifier are actually a grey colour, I would guess some sort of conductive corrosion inhibitor? Cleaning them up sounds like an a good plan though. I'll give the rectifier itself a scrub on the bolt holes.

    Thanks for the ongoing help by the way, it's really appreciated.
     
  13. Mike O Donovan New Member

    Messages:
    15
    Location:
    ireland
    Hi Slimy, did you manage to repair your welder?, I have one of them as well and it's just developed the same problem
     
  14. the snooper

    the snooper getting older by the day

    Messages:
    20,066
    Location:
    Hull UK
    Put a multimeter accross the torch and earth clamp pull the trigger if you get a voltage look for bad connections on the earth lead especially crimps even if they look good they are often not
     
  15. Mike O Donovan New Member

    Messages:
    15
    Location:
    ireland
    Thanks snooper
     
  16. the snooper

    the snooper getting older by the day

    Messages:
    20,066
    Location:
    Hull UK
    let us know how you get on :D
     
  17. Mike O Donovan New Member

    Messages:
    15
    Location:
    ireland
    Will do I'll check it out in the morning
     
  18. Mike O Donovan New Member

    Messages:
    15
    Location:
    ireland
    Well I'm getting 36.5 volts on setting 1 and 64.5 on setting 6, but I'm also getting 5.5 at the torch with the trigger not pulled
     
  19. the snooper

    the snooper getting older by the day

    Messages:
    20,066
    Location:
    Hull UK
    Is that with the meter on DC
     
  20. Mike O Donovan New Member

    Messages:
    15
    Location:
    ireland
    The V with the wavy line after it, I can never remember which is which
     
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