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Thread: Charing my NiMh

  1. #1
    RC Racer
    Join Date
    Jan 2011
    Posts
    142

    Charing my NiMh

    Just grabbed a Traxxas Summit 1:10 from ebay, it came with 4 batteris Traxxes 8.4V 3000mah.

    I normally fly Planes with LiPos, my LiPo Charger has a NiMh Programm as well. I know from lipo: a cell is 3.7v regular and 4.2v full - therefore a 2s Lipo 7.4v full shows 8.4v

    But I am a bit confused:
    My 8.4v NiMh battery has 7 cells each 1.2v, summing up 3000mAh
    On my multimeter I read 9.16v on one battery and 8.5v on another battery.

    I took the 9.16v battery, hooked it up to the charger, chose the NiMh Programm, being conservative I chose only 1.5A charging and push GO. The charger starts pumping a bit and after 10 Minutes, it stops and the battery says 8.5v.

    In theory:
    An empty NiMh cell is 1.2v equals 8.4v on my 7 cell setup.
    A full NiMh cell is about 1.4v so it's 9.8v

    For charging a 3000 mAh battery I should be allowed to chose 3.0A for charging and it should take about 1h t ofully charge.

    Where am I wrong?

  2. #2
    RC Turnbuckle Jr.
    Join Date
    Jul 2010
    Location
    England
    Posts
    5,791
    Charging nimhs is more of an art than a science- the fully charged voltage can and will vary a fair bit depending on how well they take a charge at different currents, and how sensitive the charger is with regards detecting the peak voltage. If your charger has an adjustable mV setting or something to that effect try setting it around 3.5 and see if the packs reach a higher voltage when freshly charged. Thats another thing too- the freshly charged/ peak voltage of nimhs will drop fairly quickly, so a batt charged a day before hand will read closer to it's nominal rating than the theoretical charged voltage.

    That, and traxxas nimhs arent great either- would be worth investing in some decent side by side assembled ~4200-5000mah 6 or 7 cell packs..
    Keeping the Mods busy is my specialty...

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