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Re: NiMH Battery Question

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On 5/31/2018 1:43 AM, Dave Platt wrote:
>> Hello all,
>>
>> Quick question.  What would the expected voltage be
>> for a new VARTA 3.6vdc 70mAH NiMH rechargeable battery??
> 
> That depends on its level of charge.
> 
>> Or maybe the better question would be:
>> If the voltage is at 1.76vdc would the battery be good??
> 
> Possibly, if it's newly manufactured, and had been built and shipped
> in a discharged state.
> 
> NiMH cells have a nominal voltage of around 1.2 volts per cell, so a
> "3.6-volt" nominal battery consists of three cells in series.
> 
> They're often rather higher when freshly/fully charged... I see around
> 1.45 volts when they're being charged.
> 
> A NiMH or NiCd battery should not be discharged to below around 1 volt
> per cell.  Doing so risks fully discharging one cell before the
> others;  as the others continue to discharge the weaker cell will be
> "reverse charged" and this can permanently damage it.
> 
> So, 1.76 volts in a three-cell battery would probably indicate one of
> two things:
> 
> (1) Newly made, and the cells were never charged (or were test-charged
>      and then individually discharged, or were charged and then self-
>      discharged over time), or
> 
> (2) A battery which has been discharged to below the safety limit, and
>      might have been damaged.
> 
> Manufacturers often ship NiMH and NiCd cells and batteries in a
> discharged condition.  Safer that way - less risk of fire if something
> accidentally shorts one or more cells.  Older-style NiMH cells have a
> high self-discharge rate - they'll lose 10% or more of their charge
> every month even if not being used at all.
> 
> You'd need to actually test it to determine.  Charge it fully
> (according to the manufacturer's recommendations).  It should rise to
> at least 3.6 volts very quickly, then probably to 4 or 4.2 volts as it
> continues to charge.  If it doesn't behave like this, it may well be
> damaged or defective.
> 
> When fully charged, discharge it at a safe rate (5-10 mA in
> this case) until it drops to 3.0 volts, then disconnect.  Multiply the
> discharge time by the discharge current, to get the capacity.  If it's
> not in the 50-to-70 mAh range, it may be bad.
> 
> Expect that you may not get the full rated capacity until the battery
> has been charged and discharged several times - NiMH cells have a
> distinct "break-in" effect.
> 
> 

Dave & ehsjr,

Thanks for the quick response.  What I suspected was a bad battery.
The detail you provided was an extra bonus.  I purchased from
a local "Battery" store for a replacement backup battery that needs
to be soldered onto the motherboard.

The guy at the store said it just needs to be charged and shrugged his
shoulders.  The others that were checked in the bin all had the same 
voltage.  I ended up taking one of the others and only checked the
voltage when I returned to by office.  This one was for what ever reason
at 3.47vdc. Which makes more sense.

What frustrates me is that the "Battery Store Expert" doesn't know
batteries.

BTW as a side question.  Are the individual cell welded together in the
shrink tubing or are they just held together by the shrink tubing??

Thanks,

Les

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Thread

NiMH Battery Question ABLE1 <somewhere@nowhere.net> - 2018-05-30 21:08 -0400
  Re: NiMH Battery Question ehsjr <ehsjr@verizon.net> - 2018-05-31 01:45 -0400
    Re: NiMH Battery Question Brian Gregory <void-invalid-dead-dontuse@gmail.com> - 2018-07-19 00:45 +0100
    Re: NiMH Battery Question "Ian Field" <gangprobing.alien1@virginmedia.com> - 2018-11-17 20:33 +0000
  Re: NiMH Battery Question dplatt@coop.radagast.org (Dave Platt) - 2018-05-30 22:43 -0700
    Re: NiMH Battery Question ABLE1 <somewhere@nowhere.net> - 2018-05-31 08:04 -0400
      Re: NiMH Battery Question Jon Elson <elson@pico-systems.com> - 2018-06-04 17:36 -0500
        Re: NiMH Battery Question ABLE1 <somewhere@nowhere.net> - 2018-06-04 19:26 -0400
    Re: NiMH Battery Question "Ian Field" <gangprobing.alien1@virginmedia.com> - 2018-06-11 21:38 +0100

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