Transformer testing

  1. a111r Member

    Messages:
    889
    Location:
    London
    I did a few tests on an end of life Mightymig, before I broke it up.
    The test failed was OCVs on the two power settings: 75 V and 90 Vdc!
    So I assumed a failed transformer.
    When remove, I wired it 'direct' and the output was 30 Vac, about right. Thoughts folks?

    DSCN3472.JPG

    If I was making welders, I would try to weld them together better....

    Now I have another handy spare / or a door stop. Shane to scrap it for a fivers worth of copper?
     
  2. WorkshopChris

    WorkshopChris Forum Supporter

    Messages:
    5,046
    Location:
    South East Essex
    Is it aluminium primary and secondary?
    Was your 30v ac or rectified dc?
     
  3. a111r Member

    Messages:
    889
    Location:
    London
    The secondary is Aluminium or partly, I think.
    30 Vac, as the rectifier was removed (all 8 diodes were working)
     
  4. eddie49 Member

    I think that it's really hard to weld transformer laminations together. Those joints or welded air-gaps seldom look perfect.

    The very high secondary output - 75 and 90 volts instead of 30v - implies that the transformer turns ratio has dropped. The secondary voltage is now a bigger fraction of the primary voltage. The effective number of turns on the primary has decreased.
    I think that the fault you saw when the welder was fully assembled could have been due to short-circuit(s) in the MIN/MAX and 1/2 switches, effectively putting the primary windings in parallel instead of series. Now that the mains is wired straight in, the faulty switches have been discarded. So the transformer is actually OK, you could reassemble the welder and it may well work !
     
    a111r likes this.
  5. a111r Member

    Messages:
    889
    Location:
    London
    Thanks Eddie. Yes that would make perfect sense, it can only have been the max / min switch, removed from the equation.

    I've already sold some of it's good parts to a forum member. (I bought it for spares anyway, for £5)
    1985 Mightmig 100 with permanent live torch (= no relay on the pcb), badly damaged torch, and a 'fish nor fowl' 35 A / 80A range.

    I might PM you shortly with another 'electronics question', be warned...:laughing:
     
  6. Wedg1e

    Wedg1e They call me Mr. Bodge-angles

    Messages:
    6,611
    Location:
    Teesside, England
    That is one hideous transformer :vsad:
     
    Hopefuldave and a111r like this.
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