Butters AMT1800

  1. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    hi guys. Bit of advice from the electronically minded guys please.
    Bought this welder as a non runner. It trips breaker when pulling trigger. After looking through various posts I’m thinking maybe rectifier.
    This unit has 12 diodes on four heat sinks.
    One thing I noticed when having a quick nosey. When powering unit on the fan comes on fine and all seems good. I put my multimeter on the copper going into rectifier from transformer and it was reading 0.2v. Turning the power dial altered these readings marginally but not a lot.
    On the DC side of the rectifier the reading was 190mv which stayed constant varying the power setting.
    Is this the sort of output to expect when unit just turned on idle. I assumed but maybe wrong that there would be a higher voltage on the transformer wires.
    All the diodes look intact but I don’t have ability to check them. Any advice on this subject would be greatly appreciated. Thanks.
     
  2. pdg

    pdg Member

    Messages:
    10,697
    Location:
    Wiltshire
    First - what breaker is it tripping? RCD? MCB?

    Second - did you have the trigger pulled when you took voltage reading? I'd expect almost nothing if not.

    Third - you have a multimeter, chances are it has a diode test position, and that'll do rudimentary rectifier tests.
     
  3. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Hi. Thanks for reply.
    It’s the mcb not the rcd that’s tripping.
    No trigger not pulled. As soon as the trigger is very very slightly pressed it trips.
    Borrowing a meter with diode test. Will test them then.
    Do you think I’m in the right direction with it being a rectifier fault. Thanks.
     
    tinker jim likes this.
  4. pdg

    pdg Member

    Messages:
    10,697
    Location:
    Wiltshire
    I think it's unlikely to be the rectifier to be honest.

    The main transformer effectively isolates the rectifier (and everything else downstream) from the mains.

    Even if the rectifier had gone dead short the mcb wouldn't trip on the lower settings - because a dead short is what happens when you strike an arc.

    What rating is the mcb and what response curve is it? That will be written on the mcb (say, B32).

    If you have something like a B16 that could well be the issue.

    If not that, and it trips on every power setting when you pull the trigger, then that points to a fault on the transformer primary, or contactor.
     
  5. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Thanks again for your response.
    It’s mb32 breaker on a dedicated circuit.
    A lack of wiring diagrams for this unit don’t make life easy.
    Just taken the pcb off for a look to see if anything stands out. Nothing obvious though.
    It is in poor condition though. The welder although in very good condition externally seems to have been kept somewhere damp as the board and most components inside the unit have a degree off corrosion that doesn’t match the exterior.
    The contractor is the unit which resembles a transformer on the earth line?
    I’ve got a basic understanding of electronics but these days I forget more than I take in.
    I’m trying to figure the best way to disconnect components to try and isolate the fault. Thanks.
     
  6. pdg

    pdg Member

    Messages:
    10,697
    Location:
    Wiltshire
    Can you post a couple of photos of the insides?

    Then I may be able to point at stuff...
     
  7. pdg

    pdg Member

    Messages:
    10,697
    Location:
    Wiltshire
    If by earth you mean the lead with a clamp (it's 'return' rather than earth, earth is a safety connection) then something that looks like a transformer but with only two wires will be the choke/inductor.

    That's for smoothing the output.

    A contactor is a heavy duty relay.
     
  8. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Thanks will post pics in morning. Cheers.
     
  9. Robotstar5

    Robotstar5 Casanunda Staff Member

    Messages:
    16,471
    Location:
    Birmingham
    You could disconnect (and safely isolate) the rectifier then try pulling the trigger, if the mcb holds, it's time to test the rectifier.
     
  10. eddie49 Member

    I agree with Robotstar5, the problem of the breaker tripping when pressing the trigger could be a shorted diode in the rectifier ( or a shorted smoothing capacitor, if this machine has them - large cylinders with two screw terminals connecting to heavy wires or metal strips ). You will probably have to disconnect the rectifier to check each diode, and with multiple diodes in parallel, test each one individually. Make a note of where all the connections go first.
    A diode is like a one-way valve, it will only conduct in one direction, open circuit the other way. A meter on "diode test" should show no conduction, infinity Ohms, or "OL" one way, and, by reversing the probes on the diode, the forward voltage drop across the diode ( about 0.6 to 0.7 V, or 600 to 700 millivolts ) the other way. If you have to dismantle the rectifier, make sure the insulating washers between the heatsinks go back correctly.
     
  11. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Thanks Eddie and robotstar for that.
    I get very annoyed with myself these days. An illness has left me with problems remembering things and skills I’ve got. Little snippets I get off here just help to keep me sane with things like this and help jog my mind into the right track with things.
    Pdg who has also been very patient and helpful in his replies asked for some pics. I’m posting them soon.
    A sincere thanks to all on here.
     
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  12. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    D0677CE8-36F9-4C0A-A18F-0C115095616F.jpeg EA99EA2C-4362-40DC-B3B9-76FC69BB572C.jpeg 16E7C3EA-0DDB-41BD-8F64-3C8E9917FD31.jpeg
     
  13. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Circuit board was removed for closer inspection. It’s not in the best of condition. It’s suffering exposed tracks underneath which I will clean and lacquer. None of components appear damage just a degree of damage due to oxidising.
     
  14. pdg

    pdg Member

    Messages:
    10,697
    Location:
    Wiltshire
    As long as nothing is touching them any exposed tracks won't cause any immediate problems. It's a good idea to go over them at some point though.

    The first test I'd do is to unbolt the two leads that go to the rectifier from the transformer (left hand side of rectifier in the pictures) and bend them slightly out of the way so they're not touching anything.

    Then plug it in, turn it on and pull the trigger, starting at the lowest power setting.

    If it still trips then the rectifier isn't at fault (doesn't necessarily mean it's not faulty at all, just that it's not the cause of this particular fault).
     
  15. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Yes done that. Still trips but see next photo post. As I’ve taken torch handle apart. Thanks.
     
  16. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    382F84C7-EF97-45C4-B6E5-872945B4EFAE.jpeg
     
  17. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Taken torch apart at connector end. Found this blue wire loose inside. Not sure if it’s been touching the crimp on the cable or anything else metallic. Before I go any further can you suggest what it is for does it need reconnecting anywhere or just a spare that needs properly terminating. Thanks.
     
  18. pdg

    pdg Member

    Messages:
    10,697
    Location:
    Wiltshire
    That's the torch plug that goes into the machine, yes?

    You need two wires that go from the pins in that plug up to the switch in the torch - anything else is superfluous.

    You can test if the problem is in the torch (I don't think it is)...

    Unplug the torch from the machine and do the "first test" I detailed above, but instead of pulling the trigger put a bit of wire into the two little terminals in the torch socket to connect them (that's all the torch trigger does).
     
  19. bigfellayork

    bigfellayork Member

    Messages:
    207
    Location:
    York UK
    Thanks.
    Will try the torch test you mentioned then it’s out of the loop.
    As mentioned still tripped with rectifier disconnected at transformer side.
    Power and feed are all set at minimum when trying these things.
    ive Had a good look at the board and can see no shorts due to debris or corrosion.
     
  20. pdg

    pdg Member

    Messages:
    10,697
    Location:
    Wiltshire
    I really think the problem is the transformer primary or the rotary switch - or maybe the 'contactor'.

    I can't see a proper contactor in the machine - a lot of hobby level welders use a small relay on the pcb but I can't see one of those either.

    Yours might use a transistor to switch (in that heatsink on the pcb) which could also be the problem...

    Whatever you do, don't take any wires off the rotary switch without tagging them and making copious notes first ;)
     
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