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  1. #1
    Banned. Turboem1's Avatar
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    Help with battery charging.

    Hey guys I need some advice about battery charging as I am not to familiar with it. Here is what I have.

    Battery

    On the battery it says...

    "8.4V 4000mAh
    10C Ultra High Power
    Ni-MH Rechargeable Battery Pack
    Tamiya Connector"

    So it is an 8.4v 400mAh Ni-MH battery. That much I know. As far as "cells". If you count the number of things that look like a c size battery there are 7 of them. It says "10C Ultra High Power" but I don't think 10c means 10 cell as I can count 7.

    Now...

    Battery Charger

    Hitech Battery charger/discharger



    The charger has dials for number of cells going from 2 to 10 and then a switch you can go from 300mA to 600mA. On the back of the charger it says...

    "2 cell: 2.8Vd.c
    4 cells: 5.6Vd.c
    5 cells: 7.0Vd.c
    6 cells: 8.4Vd.c
    7 cells: 9.8Vd.c
    8 cells: 11.2Vd.c
    10 cells: 14Vd.c (battery pack)"

    Heres my confusion. I am guessing the battery is a 7 cell as thats what I count. But it is a 7 cell 8.4v which doesn't match what the back of the charger says.

    Should I put it on 6 or 7 cells or something different?
    Should it be on 300mA or 600mA?

    The battery charger has a discharge mode, recharge mode, trickle charge and says a bunch of other fancy words on the box.

    Is it necesary to everytime it needs to be rechrged to put it in the discharge mode and then charge it? Something about battery memory? I guess its bad to just charge a battery?

    Its brand new and I dont want to mess up the battery I have. Thanks

  2. #2
    Senior Member
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    First question:

    Did you get a manual with this charger and whatever device the battery powers? <curious Vega look>

  3. #3
    Senior Member russiankdi's Avatar
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    Quote Originally Posted by VegaVixen
    First question:

    Did you get a manual with this charger and whatever device the battery powers? <curious Vega look>
    +1

    Make sure that you set the charger at 8.4volts because that is what the batteries are. What type of battery is this? You can search it up online and figure out if it takes 300mA or 400mA.
    1978 Schwinn Varsity Single Speed

  4. #4
    Senior Member bitingduck's Avatar
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    Output voltages of NiMH (and NiCd) cells are nominally 1.2 V per cell (as compared to 1.5 V/cell of alkaline batteries). To charge them you have to have slightly higher voltage-- e.g. 1.4 V/cell, which is what your charger appears to provide (8.4/7=1.4). So the setting is fine.

    Either current setting should be ok for charging it-- 4000 mAh/300ma=13.3 h, or 4000 mAh/600ma=6.67h. Your charger should have some sort of circuitry to tell it when to stop charging. The cheapest use a timer, and are most likely to damage the battery from overcharging (though at lower currents it's less likely). Better chargers measure dV/dt (change in voltage with time, more common) or dT/dt (change in temperature with time) to know when to stop. Even better chargers measure both.

    The 10C probably refers to the discharge rate-- that it's capable of delivering 40 Amps (!!!),if only for a short time (0.1 hour, or 6 minutes), which seems optimistic.

    NiMH cells don't have any real memory effect (and whether NiCds do, except in specific conditions, is debatable) so it doesn't hurt to partially discharge them and then just plug them back in to charge. If your charger just has a timer though, you probably want to run them fairly low before you plug them in so they don't get over charged, which can hurt them. If your charger monitors voltage and/or temperature you don't need to worry much.

    (I just plugged in my 5 cell (6.0V) NiMH battery for my light to my fancy charger that automatically adjusts the charging voltage and it runs it up to about 7.1 V. It also has a temperature sensor held on with a magnet, and measures the change in voltage with time to figure out when to stop).
    Last edited by bitingduck; 04-01-07 at 01:43 AM.
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  5. #5
    Banned. Turboem1's Avatar
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    Thanks for the answer. The charger says "automatic battery voltage detection, delta v, safety timer and maximum voltage. Timer to avoid over charging, built in polyswitch to reverse polarity, short circuit and overload protection."


    Quote Originally Posted by bitingduck
    To charge them you have to have slightly higher voltage-- e.g. 1.4 V/cell, which is what your charger appears to provide (8.4/7=1.4). So the setting is fine.
    So I should leave it on 7 cell?

  6. #6
    Senior Member bitingduck's Avatar
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    Quote Originally Posted by Turboem1
    Thanks for the answer. The charger says "automatic battery voltage detection, delta v, safety timer and maximum voltage. Timer to avoid over charging, built in polyswitch to reverse polarity, short circuit and overload protection."



    So I should leave it on 7 cell?
    yep. And the delta V measurement should turn it off at the right time.
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