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12 Battery charger transformer issue/identification

Discussion in 'Power Electronics' started by Fred012, Aug 4, 2021.

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  1. Fred012

    Fred012

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    Aug 4, 2021
    I have a 12v battery charger that had a capacitor and ac fuse blow. I replaced both on the board put it back together and still no power to the 12vdc board cooling fan, any of the led's or the output to battery leads. The charger does nothing when plugged in to AC power. I was able to track down what i believe to be the issue. After the capacitor that failed it goes to a Transformer where i have 170vdc on the primary side. But 0vdc out of the secondary side. (There is resistance between all secondary windings so there is no open winding). Even with the secondary side isolated from the rest of the circuitry still 0v. I tried to google the id numbers on the transformer to get a ratio but got no where. Maybe someone on here may know how to interprete the numbers on it or advise on what to look at next.
    I found the name Doye stamped on the frame of it, also these numbers.

    30713047
    PQ3230 1749
    Please see image attached.

    Any help is greatly appreciated.
    Thanks
     

    Attached Files:

  2. Bluejets

    Bluejets

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    Oct 5, 2014
    More likely to be a switchmode type by the looks of the opto feedback chip centre right.
    Cannot say for sure with the limited photo range.
    I don't see where you tested the primary offhand.
    These transformers rarely fail, so I'd be looking elsewhere in the circuit.
    Not an easy task for inexperienced.
     
  3. Fred012

    Fred012

    3
    0
    Aug 4, 2021

    If you turn the board over you can test the voltage on the primary side via solder joints... But i ended up removing it from the board and jumpering to each tap on the primary side (measured 170Vdc). Secondary side was completely disconnected and measured 0vdc.
     
  4. Bluejets

    Bluejets

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    Oct 5, 2014
    Transformers don't transform DC.
    The switchmode transform a high frequency switched dc from the input rectifiers.
    If your input is solid dc from the input rectifier and filter then there is a problem in the switcher section.
    The unit needs to be assembled for the switcher to work.
     
  5. Fred012

    Fred012

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    Aug 4, 2021
    Gotcha ill look at the opto
     
  6. Bluejets

    Bluejets

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    1,045
    Oct 5, 2014
    Seriously doubt the opto will be faulty....look around the switcher ic circuit
     
  7. Martaine2005

    Martaine2005

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    May 12, 2015
    What components are under the heatsink after the X2 capacitor?
    Have you checked the fuse again to see if a short has caused it to fail again?

    Martin
     
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