I need to charge my car battery (12V)

Discussion in 'General Electronics Chat' started by ranatungawk, Dec 6, 2010.

  1. ranatungawk

    Thread Starter Senior Member

    Oct 30, 2008
    I need to charge my car battery (12V) from my home when it’s very low. I found this circuit from the internet. Please tell me..

    • is this a good circuit for my requirement
    • 1N4007 (1A) diodes are used for rectifying. But I think it need to use 5A rectifiers instead of 1As. If so tell me a what is good for this ?
    • can I use this to charge my car battery when it is in the car, ( with out disconnecting battery wires which are connected with the battery)

    about the circuit:

    [​IMG]This very simple circuit uses a transformer ,two diodes , a capacitor and an ammeter.
    To charge a battery just connect the + and - terminals of the circuit to the corresponding terminals of the battery.
    When the battery is not charged, the ammeter reading shows 1-3 amps.
    When the battery is fully charged the ammeter reads Zero or nearly zero, after which the battery should be removed from the
    The circuit is a full wave rectifier using 2 diodes for rectification. The capacitor is used for smoothing.
    I think the circuit works fine without the capacitor since the battery itself acts a BIG capacitor. But when you are using the
    circuit to supply 12V (as a battery eliminator) the capacitor needs to be present.
    Care should be taken NOT to reverse the + and - terminals while connecting it to the battery.s while connecting it to the battery.
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    5A is a little weak for charging a dead battery. The schematic is more of a trickle charger/maintenance charger.

    For a charger to boost a dead battery, you typically want 15A for charging, and over 75Amps for boost.

    The DIY method usually costs more than buying a charger due to the cost of a transformer capable of handling the required currents.

    Otherwise, 5Amps would be OK for boosting overnight, but transformer may get warm/hot on a very low battery.

    Three are a LOT of things to consider when charging a battery of any type. There are typically 3 or more "phases" of charging. You may want to get more info, most places that sell chargers cover the reasons for the different values and what charging type to use when.

    Having said that, your charger will work just like any other charger connected to the battery. The battery will hold down the voltage (the transformer will give about 16V after the rectification). That extra voltage is needed to charge. At the same time, it has NO protection circuits, or charge state feedback.

    How experienced are you with electronics and schematics? You may want to build a constant current / contstant voltage mode charger with overload and overcharge protection.
  3. SgtWookie


    Jul 17, 2007
    Have a look at this thread in the Completed Projects forum:

    Beenthere's battery charger has both an unregulated and a regulated mode. It's more complex, but when properly adjusted and used in the regulated mode, you can leave it connected without worrying about overcharging the battery.

    Note that his design includes a 15A circuit breaker.

    Allowing your battery to become discharged is VERY hard on it; automotive batteries will quickly fail after being deeply discharged.

    They will also fail quickly if they are left in a partially charged state. This happens very frequently if you only take short trips. Plate sulfation begins when the battery voltage is around 12.5v @ 25°C/77°F, once the battery is heavily sulfated, it will no longer accept a charge nor provide power.