12 volt battery charger problem

Discussion in 'General Electronics Chat' started by songster24, Mar 18, 2012.

  1. songster24

    Thread Starter New Member

    Mar 18, 2012
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    0
    I'm trying to charge a riding lawn mower battery with a 12 volt, 10 amp/ 2 amp charger. I'm told I should have it on the 2 amp setting for this. Before charging, the battery tested at less than 1 volt. After charging 14 hours, it shows 3.5 v. Checking output of the charger, I get 4.5 volts. The test/charging indicator needle does not move. What's up? Is it operating properly or not, and why? Thanks! I do some household electrical repairs, but I'm not familiar with DC or electronics at all.
     
  2. BillO

    Well-Known Member

    Nov 24, 2008
    985
    136
    I'm sorry to say that that battery is useless. It sounds like you have one good cell left, but by putting that charger on it, you will end up killing it too.

    So, here is how you fix things. Find out where you can safely re-cycle or dispose of the battery, then take it there. Then go and buy a new one, charge it with your charger according to the battery manufacturers recommendations and you'll be in business.

    If a 12V lead acid battery falls below about 7.2V for any appreciable length of time (days or weeks at the most), it will likely be unrecoverable. If it falls to less than 1 volt I would bet my last dollar that it is just hazardous waste. Time to buy an new one.

    Sorry :(.
     
  3. songster24

    Thread Starter New Member

    Mar 18, 2012
    4
    0
    I really appreciate the reply, even though it's "bad" news about the battery. But what about the charger only putting out 4.5 Volts? Is it bad too? Thanks again.
     
  4. BillO

    Well-Known Member

    Nov 24, 2008
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    136
    Is that without any load on it?
     
  5. songster24

    Thread Starter New Member

    Mar 18, 2012
    4
    0
    Yes, just attaching test leads from a dmm to the charger's spring clamps.
     
  6. BillO

    Well-Known Member

    Nov 24, 2008
    985
    136
    It may still be okay. Many low priced chargers use what is called half wave rectification. A lot of meters will measure such a signal as somewhat less than V(peak)/pi. If this is the case, then you are alright.

    Do you have an electrolytic capacitor at your disposal? Something with a 25V operating voltage and about 100uF or more would be ideal. Just attach to the leads of the charger (observe polarity, this is important!!!) and make the measurement again using your DMM.

    An alternative would be to put the charger on a good battery. Measure the voltage of the battery before you put the charger on it and a few minutes after. The voltage should increase.
     
  7. songster24

    Thread Starter New Member

    Mar 18, 2012
    4
    0
    OK--thanks again very much! I'll check the charger on the new battery when I get it. I don't have a capacitor, and I'll have to go further in the e-book tutorial to begin to understand the rest of your answer more fully! I look forward to that.
     
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