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Simple way to salvage a car charger?

Discussion in 'General Electronics Discussion' started by haryo, Apr 12, 2013.

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  1. haryo


    Apr 12, 2013
    Howdy all,

    I have a 10 amp Napa car battery charger, the circuit board of which has died. The transformer still puts out a healthy DC current at maybe 16 volts. My thinking is to simply put in (only) a hefty 12v IC regulator and use it to bring a battery up the the point (12v) where it will presumably start the car. I don't have a problem if it doesn't charge the battery to a desired higher voltage. The question is will I have to closely monitor the charging, or will the battery stop charging when it reaches 12 volts? Or..what am I missing here. I just don't want to thrown the thing out but would like to get something useful out of it without getting too elaborate with the circuitry. Thanks.
  2. GreenGiant


    Feb 9, 2012
    what makes you say the board has died?

    most portable car chargers range from 14-18V thats perfectly normal, lead acid batteries are perfectly happy going up to 14..16...18...sometimes 20V even when rated at 12V, the reason your charger is reading 16V is because there was no load, if you were to load it down it would probably drop to 13/14 or so, again perfectly normal.
  3. duke37


    Jan 9, 2011
    Most car alternators are set for 13.8 to 14.4V. The battery should be fully charged at 14.4V.
  4. haryo


    Apr 12, 2013
    Thanks for the answers.

    I tested the board directly in-circuit, and while voltage is inputted to it, it's 0 volts out.I've removed and inspected it for loose parts, etc, but it all looks fine. It's got a fair amount if chips and transistors and without a circuit diagram or more knowledge that I have I'm writing it off. I realize my plan would leave a battery undercharged, but once I started the car I'm assuming it would be finished off properly. When I momentarily connected the unregulated output of the transformer directly to the already charged battery it was 14-15 volts or so. I don't know what a safe maximum (surface?) voltage is under charge, hence my thinking of playing it safe by using a possibly unmonitored 12 volts the get the battery in a usable range and finishing the charge by the then-running car.
    Last edited: Apr 13, 2013
  5. BobK


    Jan 5, 2010
  6. haryo


    Apr 12, 2013
    Thanks, Bob. That answers my core question. On examining the board I did find a solder connection that was loose, so I re-soldered it. There was still no output on the leads, however, a similar charger was acting likewise, so I began to wonder if the charger needed to see a load for any voltage to be seen at the 'clips'. Sure enough, when I put a load on it it appears to be working. Whether I fixed it or just wrongly assumed it to be broken by the person who borrowed it and reported it as broken I don't know. Anyway, I'm glad to have found the forum and appreciate all the responses.
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