Battery overcharged?-
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  1. #1

    Join Date
    May 2008

    Battery overcharged?

    I just charged up my 14.4 Ni-mh, 5000 mah battery with the charger that came with it from Battery Space, I then hooked it up to my light and after running for 20 seconds or so the light shut off, I tried my other light (both are Halo with lightbrain controllers) and it did the same. I checked the voltage of the battery at 16.39 volts. Is this a common voltage for these batteries? Is my charger "overcharging" all of a sudden? I havent checked the voltage of the battery before but my lights have never shut off like this until now.
    Thanks! Aaron

  2. #2
    mtbr member
    Join Date
    Apr 2008
    16.39 for a 12 cell pack fresh off the charger would be about what you would expect. A single cell in a fast charger can come off at up to 1.4V, it will not stay there for long under load though. I am not aware what the max your Halo will take is so no idea why they are shutting down.


  3. #3

    Join Date
    May 2008
    Thanks, I ran the light on low for 30 minutes then checked the battery again, its down to 16 volts, the light will stay on and run on high now but I am still confused because the lights are supposed to have a 20 volt limit.

  4. #4
    Reputation:'s Avatar
    Join Date
    Mar 2007
    In my experience (this combo) the "smart" charger that comes with the battery/charger combos from batteryspace isn't all that smart. It should be monitored from time to time. The charger typically charges batteries at too low a current to reliably detect when the battery is fully charged (the battery voltage peaks and then declines a little bit, you need to charge at a 1C or higher rate to see this).

    I've put a lightly discharged 9.6V NiMh on one of their chargers and come back 12 hours later to find the red LED on (still charging) and the battery pack very very hot. On the other hand, the times I've plugged a pretty drained battery into the charger, it has done the right thing, charged the battery, and the LED has switched to green.

    I suspect the charger has troubles distinguishing between a mostly discharged 12 V pack and a near fully charged 9.6 V pack. Assuming a 1.4 volts per cell fully charged pack, a 9.6 V pack can deliver over 11.2 volts. That's close enuff to 12 V to cause confusion.

    I think the trick is too keep track of how long you've been using your battery, and never charge it for longer than ((run_time * current_draw) / charger_current) * fudge_factor. A good value for fudge_factor is probably 1.2. So if your charger can deliver .6 amps and you rode for 3 hours at 2 amps, you should charge for ((3 * 2)/0.6) * 1.2 = 12 hours.

    In the above example you are probably OK plugging in your battery pack before bed and checking to see what's happening in the morning.


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