Battery float charger question

Discussion in 'General Electronics Chat' started by Gdrumm, Mar 30, 2014.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Should a battery float charger put out more than 12 volts, when it is not under a load?

    I'm getting 19+ volts AC from the wall wart, but downstream I'm only 10+ volts at the Pos. Neg alligator clips.

    It's a Harbor Freight item, and I probably got it on sale for cheap.
    Perhaps it would work on a low battery, but not raise above the 10 volts when hooked up to my multimeter.

    Does that make sense?

    Thanks,
    Gary
     
    Last edited: Mar 30, 2014
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I am not an expert, but my understanding is 13.7V is nominal. You can sense the state of change on a SLA battery by the voltage on it, which is what a float charger uses to determine how much current to feed in.

    The Battery University
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,009
    3,233
    The output voltage with no load may be undefined. Try a resistive load of about 100 ohms or so.
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    I will try the resistive load, but now there is another problem.

    I found a swolen capacitor, and replaced it.
    As soon as I plugged it all back in, I smelled smoke.
    I thought I had left my soldering iron on a shop towel.

    It took a couple of seconds to realize the replacement cap was smoking..

    Are there any general things to look for, when that happens?

    All of the resistors look good.

    Thanks,
    Gary
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Most likely you installed the capacitor backwards.

    What was the capacitance and voltage of the original capacitor?
     
  6. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I thought of that after I posted.
    It is / was a 25v 100mf.

    Here is a drawing of two capacitor symbols
    The top one is the one I'm used to seeing.
    The bottom one is what is on this board.

    I thought I was paying attention when I took the old one out, but perhaps not.

    Have you seen this bottom symbol for a cap before, and do I have it labeled correctly?

    There are no + - on the board.

    Thanks
     
  7. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    I found it,
    On the board, Pos is the white side, Neg is the black side.
     
    Last edited: Mar 30, 2014
  8. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Got it, now reading 13+ volts.

    Thanks everyone.

    Gary
     
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