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  1. #1
    RC poster
    Join Date
    Dec 2019
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    10

    NiMH cell Battery Voltage

    Hi everyone,

    I'm a bit confused and help would be appreciated.

    I have two NiMH batteries: https://traxxas.com/products/parts/b...t-2/3a-1200mAh

    Yesterday, I was running them in parallel and the car, after a good ride, started to slow down. No problem there, I thought the batteries had run out.

    Out of my curiosity, I plugged them into a multimeter and they BOTH measured a surprising 7.7V! but... they are the traditional 6cell batteries... so they should measure 7.2V... right? I don't think I could be messing up the measure in the Multimeter...

    Also, if they are showing these values, should't the car be running just fine? Or, if they are in parallel, can one be affecting the other?

    I'm a bit lost in here...

    Thanks in advance!

  2. #2
    RC Enthusiast
    Join Date
    Nov 2019
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    25
    Batteries can sag under high load, and then the voltage can creep back up when the load is removed. What vehicle was this in? How long did they sit before you measured them?

    Sent from my SM-G950U1 using Tapatalk

  3. #3
    RC Qualifier
    Join Date
    Dec 2014
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    Adirondacks
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    650
    Quote Originally Posted by tmbcma View Post
    ...I was running them in parallel and the car, after a good ride, started to slow down. No problem there, I thought the batteries had run out.

    Out of my curiosity, I plugged them into a multimeter and they BOTH measured a surprising 7.7V! but... they are the traditional 6cell batteries... so they should measure 7.2V... right? I don't think I could be messing up the measure in the Multimeter...
    As soon as you start putting them under a load they start losing voltage quickly. Here is a discharge chart of a NiMh cell. Also 7.2v is called nominal voltage of the pack, not what voltage it should be. A 7.2v battery pack has (6ea) 1.2v cells.

    (1.5 volts - fully charged, 1.25 volts - 50% charged, 1.0 volts - almost fully discharged)

    nimh graph

  4. #4
    RC poster
    Join Date
    Dec 2019
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    10
    @omen this was on my e-revo 1:16 VXL.

    @grizzly03 thank you for the pic, now it is clear!

    The batteries sat quiet for a while indeed. Today, without charging them, i plugged them back into the merv and went for a spin until the car came to a full stop.

    Then, I immediately measured them and they had around 6.8v (so a little bit more than 1v per cell).

    So I guess this all makes sense.

    Thanks guys!

    Enviado do meu SM-A505FN através do Tapatalk

  5. #5
    RC Enthusiast
    Join Date
    Nov 2019
    Posts
    25
    Since you have the vxl model, I highly suggest getting lipo batteries. There is significantly less voltage sag under load, and they have higher energy density too.

    Sent from my SM-G950U1 using Tapatalk

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