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How to charge a low amperage battery?

  1. Feb 11, 2015 #1
    I have a motorcycle battery which is 6Ah, with a maximum charging current of 0.6A/h. Is there a method of charging it whilst using a 2.7Adc (4A RMS) charger?

    I was thinking using resistors in parallel or series between the charger and the battery, but I am not sure exactly how.
  2. jcsd
  3. Feb 11, 2015 #2


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    Staff: Mentor

    2.7Adc is not 4A RMS...
  4. Feb 13, 2015 #3


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    More info needed about the charger.

    If the charger really delivers 2.7A DC to the battery on charge then putting a resistor in parallel with the battery might work but it's not without problems... Lets say the battery is 12V (on charge) and needs 0.6A. Then the resistor would need to shunt 2.7 - 0.6 = 2.1A. The required value would be about 12/2.1 = 5.7 ohms. However the power dissipated in the resistor would be 12 * 2.1 = 25W so it would need to be big resistor and it would get hot. Probably need a heat sink and a fan to cool it.

    One option might be to experiment with a 25W or 30W motorbike light bulb in parallel with the battery while on charge. However since light bulbs aren't exactly high precision devices you would need to measure the battery current and experiment with different bulbs until the battery current was within limits. Problem then is if the bulb fails too much current will flow through the battery.

    Is it just easier to buy the right charger?
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