Electrical Engineering - NiMH Battery Re-Charging

Author

NiMH Battery Re-Charging

Robert11

2008-01-03, 9:25 am

Hello,

Just got a new handheld radio scanner, and am using rechargeable NiMH
batteries in it (four AA).

The manual, and the Forums for the radio, really don't provide a decent
explanation for the re-charging
techniques in the radio. I can of course use an external re-charger, but
would like to use the radio's built in one, for now.

Questions:

The radio apparently just recharges for a specific number of hours, which is
adjustable.
The default is 16 hours. It says that it charges at a current rate of 150
mA.

But everytime you turn the radio on and off and then back on again, the
timer resets to 16 hours.

So, it seems very easy to overcharge the batteries.

Any potential problems if the batteries already have a full, or nearly full
charge, and the radio resets and wants to keep charging them (again) for
another 16 hours ?

Sure seems like a poor way of doing it; I would have thought that they would
monitor the voltage of the battery directly, and not use this kind of
scheme. Probably a bit cheaper, though in circuitry.

Any potential over charging problem ? Caveats ?

Thoughts on ?

Thanks,
Bob

ehsjr

2008-01-03, 1:25 pm

Robert11 wrote:
> Hello,
>
> Just got a new handheld radio scanner, and am using rechargeable NiMH
> batteries in it (four AA).
>
> The manual, and the Forums for the radio, really don't provide a decent
> explanation for the re-charging
> techniques in the radio. I can of course use an external re-charger, but
> would like to use the radio's built in one, for now.
>
> Questions:
>
> The radio apparently just recharges for a specific number of hours, which is
> adjustable.
> The default is 16 hours. It says that it charges at a current rate of 150
> mA.
>
> But everytime you turn the radio on and off and then back on again, the
> timer resets to 16 hours.
>
> So, it seems very easy to overcharge the batteries.
>
> Any potential problems if the batteries already have a full, or nearly full
> charge, and the radio resets and wants to keep charging them (again) for
> another 16 hours ?
>
> Sure seems like a poor way of doing it; I would have thought that they would
> monitor the voltage of the battery directly, and not use this kind of
> scheme. Probably a bit cheaper, though in circuitry.
>
> Any potential over charging problem ? Caveats ?
>
> Thoughts on ?
>
> Thanks,
> Bob
>
>

You'll get less than optimum life from the batteries, but
so what?

It is probably a "non-issue". 16 hour charging is not the best
approach, but it is not horrible, either. It's actually a pretty
good compromise. Eventually, your batteries will fail due to age,
overcharging, undercharging, whatever. You can put time, energy
and money into getting the absolute maximum life from them, or
accept the fact that less than optimum charging and use will give
you less than optimum life. In most cases, the delta between
optimum life and a somewhat shortened life is not worth the cost
and effort needed to get the optimum.

We don't know the specifics of the radio's charger, but as long as
you charge using it you are "stuck" with whatever it does. You can
manage the situation to some extent, if you wish. If you are
concerned about "10 minute per day" (or whatever) operation, you
can use the radio that way, and estimate how many days to wait
between charges. Or you can pull the batteries out of the radio and
charge them with an external charger that has the features you want.

Ed

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