How you charge NiMH (nickel metal hydride) batteries in parallel, and
not in series as they are done traditionally?

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Request for Question Clarification by aht-ga on 16 Feb 2004 17:42 PST

Can you clarify what the application is for the NiMH batteries, and
what sort of charger you are referring to? There are parallel chargers
available for NiMH batteries that fall into the typical consumer sizes
(AAA through D), for example.

Regards,

aht-ga
Google Answers Researcher

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Clarification of Question by wuzonge-ga on 16 Feb 2004 18:44 PST

Hi, thanks for replying. No application, just a basic AA or AAA NiMH
charger, which charges them in parallel, and not in series.
Specifically, I am trying to find out what is necessary to peak charge
them, as I understand simple parallel charging cannot charge the
batteries to full capacity.

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Request for Question Clarification by aht-ga on 26 Feb 2004 22:35 PST

Hi wuzonge-ga:

My apologies for the delay in getting back to you; for some reason, I
did not receive a notification that you had replied to my
clarification request.

The reason why NiMH battery manufacturers such as Panasonic (see:
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_NIMH_Precautions.pdf
) caution against parallel charging, is because of the sensitive peak
voltage aspect of NiMH batteries during charging. Overcharging of NiMH
batteries can cause them to overheat and possibly explode.

The majority of NiMH batteries only contain a single monitoring chip,
meaning that they can only monitor one battery during charging. By
charging the batteries in series, it is possible for a fast or
constant current charger to bring all of the batteries close to their
peak charge without exceeding the peak voltage for any one cell, then
finish off the job with trickle charging.

The most expensive chargers are able to dedicate one monitoring
circuit per battery, allowing them to charge each battery
individually, effectively in parallel. This is the only way to safely
charge NiMH batteries together from the same power source. Examples of
such chargers include:

http://www.ansmann.de/en/index.htm?view=list&pr2id=11

What additional information can I provide you to help you with this question?

Regards,

aht-ga
Google Answers Researcher

My only suggestion is to use more chargers. ie. parallel chargers
charging in series, this serves the same function.
You can also adapt a charger and put more charging racks into it
however you would also have to make sure you changed the current
circut as well to match the extra amps it would draw...Don't burn your
house down, all electric products are UL or CSA approved so they are
not dangerous and adapting them and using them could nullifie your
fire insurance