Repairing cheap chinese charger

Discussion in 'General Electronics Chat' started by magudaman, Oct 13, 2013.

  1. magudaman

    Thread Starter New Member

    Feb 27, 2012
    27
    2
    So I have a pure sinewave inverter that came in with a built in charger. While the specs claimed 0-5 amp 48v charger when I set it at 3 amps (via internal pot) it ran for about 10 seconds and then popped its internal 15 amp AC fuse. I used a meter current mode as a bypass for the fuse and popped the meter's fuse.

    So I am assuming the primary switching fet blew. But it sounds like if that is the case this charger circuit is dead as it could have taken control components with it.

    I can get the same FET that is currently installed from digikey and but is pretty much a given that it is a waste of time or is there hope it could work?
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    All I have for you is a frowny face.:(

    It's up to you whether to bet $10 you can fix it, but I would just try to get a refund.
     
  3. tindel

    Active Member

    Sep 16, 2012
    568
    193
    Was the FET properly heat sinked? 5A through a cheap FET (read: high on resistance) = a lot of heat.

    FET's failure mode is short (at least I've never seen one fail open). Can you verify it's short by using your meter (with a new fuse) in the ohm setting mode and see if the source-to-drain resistance is low with the unit powered off?
     
  4. magudaman

    Thread Starter New Member

    Feb 27, 2012
    27
    2
    Thanks for the replies and sorry for mine being so belated.

    So I removed the charger board from the unit. I pulled the suspected fet out and found its drain and source are shorted. I also found that two of the four rectification diodes also seems to be dead. So I think I will order the fet and the diodes and replace them all. I would suspect that several other components could have died in the failure too but here hoping not.
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    In about 30 years of doing power supplies, I can't remember a single blown unit where the only part damaged was one switch FET.
     
  6. eyesee

    Member

    Oct 19, 2013
    33
    3
    You may want to uprate the FET while you're changing components.
     
  7. magudaman

    Thread Starter New Member

    Feb 27, 2012
    27
    2
    Well I'm $10 dollars in and then I'm done. I lost the diodes too. If doesn't work I'm hoping I can just cut the charge circuit out completely, shorten the case and just have the sine wave inverter.
     
  8. magudaman

    Thread Starter New Member

    Feb 27, 2012
    27
    2
    So I cut the circuit out. I started to get worried that if the unit failed in the wrong way it would take the sine wave inverter out too. So I have some diodes and a nice 20a 600v fet coming that I will just have to add to my stockpile. Thanks for all the help guys!
     
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