Repairing cheap chinese charger

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

  1. magudaman

    Thread Starter New Member

    Feb 27, 2012
    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


    Nov 30, 2010
    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
    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
    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
    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


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

    Thread Starter New Member

    Feb 27, 2012
    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
    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!