How many amp for a direct drive P7-
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  1. #1

    Join Date
    Sep 2008

    How many amp for a direct drive P7

    I have tried connecting up a p7 direct to 3 x AA fully charged 2900 MAH NIMH batteries and the LED only shows it is using 1.4 amps with a fluke rms multimeter in series.
    Is this the maximum nimh aa batteries can discharge at or am I doing something wrong.
    I was expecting around 2.4 amps at full charge.

  2. #2
    mtbr member
    Join Date
    Feb 2009
    I'm not surprised at the current with 3 AA NiMh cells. The issue may have more to do with forward voltage of the LED. Are you using I or J voltage bins?

    Most high capacity AA cells have pretty high internal resistance. Under load the voltage drops. At 2 amps the voltage may only be 1.15 volts. Three of those only gives 3.45 volts and that may be the forward voltage of your LED.

    Don't try four cells. You will fry the LED almost instantly.

    Go with four or more cells and a driver board.

  3. #3
    I like bloody ankles
    Reputation: dsjc's Avatar
    Join Date
    May 2007
    Sorry if I'm stating the obvious, but a single 18650 may be a better match. At 4.2v on full charge you have plenty of room for Vf. I have a light with a P7C drawing 3.05a on direct drive with a single 18650. Of course the driver may be a good idea for other reasons.....

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