Ancient 140 mono s schematics

  1. Teemuzz

    Teemuzz New Member

    Messages:
    6
    Location:
    Finland keski-pohjanmaa
    Anyone here who could point me out a couple of things?
    I'm repairing this thing for garage use and already sourced New caps.. Problem is, i lost the pictures with my old phone as it didnt have Google images and the images werent on the sd card.

    I also were lead to believe it's hevily related to the 180 mono, so that could help me out too...


    I need to figure two things:
    Capacitor wiring (there's also a resistor, how is that wired?)
    What diodes there are in the rectifier (as i believe after reading here that the rectifier screws up the caps)

    A total of four caps were toast out of 8

    Can this also be modified for flux wire?
     
  2. eddie49 Member

    Hello, and welcome to the Forum !
    Could you please expand on the name of the welder? Other than "140 Mono S" or "180 Mono", what is the name of the manufacturer ?
    Is it a Migatronic ? Some photos, of the inside and outside, may help.
    The wiring should be fairly straightforward. The rectifier will be wired to the secondary of the main welding transformer, with 2 x AC wires in and then plus and minus DC out. That goes first to the capacitor bank. All capacitors will be in parallel, ensure polarity is correct. The negative will go via the inductor to the work return cable and clamp ( the "Earth" ). The positive, out of the capacitor bank, will go to the Eurotorch socket.
    For flux wire, you need to reverse this polarity, at the output, so that the "Earth" is positive and the Eurotorch is negative.
    The resistor is probably a low-resistance, high-wattage wirewound resistor ( such as 50 Ohm, 20 Watts ). It is used to discharge the capacitors between on/off welding operations. It may be wired permanently across the capacitor, or via a normally-closed pair of contacts on the Contactor.
    The diodes will be rated for the capacity of the welder, such as 140 Amps, and maybe 200 Volts, or higher. Single large stud-mounted diodes of this size may be used, or an array of smaller diodes may be wired in parallel to share the current ( e.g. 4 x 40A diodes in parallel ).
    Yes, faulty diodes can destroy the capacitors. A shorted diode will pass AC, which will cause the electrolytic capacitors to bulge, heat up, and explode. However, capacitors can age and fail on their own, without diode failure.
     
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  3. Teemuzz

    Teemuzz New Member

    Messages:
    6
    Location:
    Finland keski-pohjanmaa
    Thanks! Yes it's a migatronic and the only symptom on the capacitor was leakage/burning marks

    This was a really informative comment and i'll show pictures after i get the machine under repair
     
  4. eddie49 Member

    You could test the diodes in the rectifier using the "Diode Test" function on a digital meter.
    Maybe you could confirm that everything is OK by starting with just the transformer connected. The AC output from the transformer secondary should go from about 15v to maybe 30v as you turn up the power selector. Adding the rectifier will change that to about the same DC voltage. Then add the capacitor bank, which will increase the DC voltages slightly. The discharge resistor should have the effect of dropping the voltage across the capacitors to zero within a second or two when you release the torch trigger.
     
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  5. R Kraft Member

    Messages:
    976
    Wyoming,USA
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  6. Teemuzz

    Teemuzz New Member

    Messages:
    6
    Location:
    Finland keski-pohjanmaa
    Hey guys just wanted to come and report back since it's not always that new users do. I ended up wiring the load resistor straight to the bank, and measuring the rectifier with the diode test on a multimeter. After everything was done regarding electronics we ended up diagnosing the biggest problem on it with a friend that was affecting welding to be a faulty wire liner that was sticking. After getting that in order the machine worked like a charm. Converting it to flux wire would be a pita since the motor runs from a distributor metal that is behind the torch so it would mean rewiring. Also the heat up protection works, that's nice if you ask me.


    Thanks to everyone who helped me out! As a note to others make sure you use at least 4mm² wire for a 140amp machine capacitor bank, the cables can get hot if you use 2.5mm².. Didn't melt tho, internet didn't really provide any good information on capacitor bank wire sizing.
     
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  7. eddie49 Member

    Thank you for the update, and I am pleased that you have got the machine working properly !
    I agree about the capacitor bank cable size. There seems to be general agreement that you need high-quality ( "computer grade" ) capacitors, with screw-terminals. Multiple small( ish ) ones are better than a single large one - i.e. 5 x 10,000uF rather than 1 x 47,000uF. Paralleling the caps is often done with aluminium plates or bars - on mine, they are 4mm thick and 20mm wide.
     
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