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Anyone try to make a new auto battery charger "old school" ?

Discussion in 'Power Electronics' started by The_cat, Sep 18, 2015.

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  1. The_cat


    Sep 17, 2015
    I got these new 12 volt automotive battery chargers but the auto feature prevents them from being used as a 12 volt DC power supply.

    Also they won't turn on when connected to a fully dead battery cause they cant tell they are connected.

    This must be increasing battery sales and service calls for cars.

    Has anyone taken one apart yet and fixed this ?
  2. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    All you do it take the electronics out and only leave the bridge.
    Then you add 2 x 2200u across the output.
    The_cat likes this.
  3. AnalogKid


    Jun 10, 2015
    Note that a 12 V batter charger does *not* mean that its output is 12 V. It means that the output is whatever the designer decided was necessary to charge a 12 V battery that actually is a 14 V battery. Peak voltage after the bridge could be 20V or more.

    "This must be increasing battery sales and service calls for cars." - No, it isn't; not everything you don't like is a conspiracy. An automotive battery charger is designed specifically to do one thing in one environment, and has some protections built in to protect itself *and the user* from improper use. Resurrecting a completely dead lead-acid battery is not what it was designed for because that is a much more complex and dangerous task than merely topping off an otherwise moderately healthy one.

    davenn likes this.
  4. Kiwi


    Jan 28, 2013
    The auto feature is built into battery chargers to protect the charger from reverse battery connection etc. Even the best of us sometimes have a spot of brain fade and get it wrong. Also protects against turning the charger on with the terminals touching.
    Getting the charger to start on fully discharged batteries can be a problem. The ones at work have a "Flat Start" momentary button that you have to press until the battery voltage increases enough to keep the charger working. The alternative is to parallel another battery to the discharged one.

    As suggested you can rip the guts out, but it would be a waste of a good battery charger.
    Probably be better to build a power supply from scratch using a transformer that has the output you want.
    If you check the Project Logs you can see how I built my power supply from an old computer power supply.
  5. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    I have added a manual override button to an oem battery charger (golf cart).
    When I get a battery that is nearly completely dead, I hold down my override button for about 30 seconds or so, to bring up the battery voltage to an acceptable level so the charging board will initiate a charge. Works quite well.

    Another words, the charger will not charge a battery with less than 10v, But the override button will boost the battery voltage from 8v up to 10v.
  6. rickselectricalprojects


    Feb 1, 2015
    when i first started out i went to bunnings and purchased a 12v projecta old school battery charger and it was great. i also purchased one of these ebay death traps: and i just put a big cap on the end and it worked fine but i think if you drew to much current the voltage would go back to 0 or what ever the voltage was so i would add some big caps.
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