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Mystical Welding Powersupply

Discussion in 'Troubleshooting and Repair' started by Spanero, Jun 18, 2014.

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  1. Spanero

    Spanero

    3
    0
    Jun 18, 2014
    Hello
    I have a power supply in a small welding machine rated at 110v input 100A output at around 20vdc.

    I have drawn out the supply and see an obvious short when the thyristor is pulled in.
    The breaker trips out when the machine is triggered (thyristor triggered) i have checked the gate to the thyristor and the pulses are 1.2usec and duty cycle of around 5% for the start current.

    if i remove the fuse (which is causing the trip to trip out) then the trip will stay in but no output, i am taking it that the inductor and 20A fuse creates some sort of limited circuit but just cant see how this would work.

    Anyone with power supply knowledge willing to help.
    PS This machine could be connected wrong in the past (it is an option !!)
    Nb the coil is inside the heatsing which is the transformer and the inductor at the side of the fan is the L=391

    Come on you inverter experts !!!!

    Thankyou

    Mark.
     

    Attached Files:

  2. Spanero

    Spanero

    3
    0
    Jun 18, 2014
    sorry i should have posted the pictures the correct way up !!!!!!!!
     

    Attached Files:

  3. shrtrnd

    shrtrnd

    3,827
    524
    Jan 15, 2010
    Not much to go on, but he's my input:
    The oil-filled can capacitors last a very long time. The big blue electrolytics, not so long, especially in high heat applications (like an inverter).
    I'd check the bridge, just to be sure. Almost all of my inverter failures are because of blown Thyristors. The hockey-puck type typically don't test out of circuit, because they require the pressure of the heat sink compression to operate correctly.
    Are your thyristors the hockey-puck pressure type, or just bolted onto the heat sink?
    From what little I know, I'd guess you've got a thyristor failure. I'd consider the electrolytic caps and bridge for troubleshooting.
    I don't see any obviously burned wiring or components to make this easy, do you?
     
  4. Spanero

    Spanero

    3
    0
    Jun 18, 2014
    Hello

    Thankyou for taking time to reply.

    I usually work on IGBT driven inverters so this should be quite easy but it is doing my head in. lol


    As can be seen from the drawing the rectifier is live all the time and supplying 160v DC to the thyristor, in rest the circuit is fine, it looks like the path through the inductor and fuse is causing a large load to be drawn and trips out the mains switch only when the thyristor is triggered. No shorts are reported in the circuit.

    I am after someone who could check the circuit diagram as this could have been wired incorrectly maybe at some time, and i cant get hold of the diagram for this unit.

    Thankyou
    .
     
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