Selective equalizer for NiMH batteries

[Bob Tregilus]

Hi all -

I was plinking around the 'net for info on Saft NiMHs and
found the following document that I thought some of you may
find of interest:

A selective equalizer for NiMH batteries

Abstract
A unique method has been developed to equalize nickel metal
hydride (NiMH) battery packs using a new selective
equalizer. This equalizer detects batteries either at a very
low state of charge (SOC) or at an extremely high SOC. In
this system a set of electromechanical relays is connected
in a matrix to route boost current to the weaker batteries.
The relay switching is controlled by a 32 bit
microcontroller, and the boost current is supplied by a
boost charger. Once a weak battery is detected, it is
scheduled for a specific boost time by a special “Round
Robin” (RR) algorithm. The equalizer was tested on a pack of
12 series connected 12 V 93 ampere hour (Ah) NiMH batteries.
Test results show that the equalizer was able to re-balance
an artificially unbalanced pack, and the capacity was
increased by 27% within six charge–discharge cycles. Results
indicate the number of cycles required to re-balance the
pack was significantly reduced by using this technique.

The full paper (which includes schematics) is posted here:
http://ElectricNevada.org/download/nimheq.pdf

Bob
in Reno

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[Nick Drouin]

It's a pity they don't cite Lee Hart as a reference:

http://www.geocities.com/sorefeets/balancerland/intro.htm

Looks like his predates this paper by a solid 4 years.

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[EVDL Administrator]

On 3 Jul 2008 at 20:25, Bob Tregilus wrote:

> The equalizer was tested on a pack of 12 series connected 12 V 93
> ampere hour (Ah) NiMH batteries.

Great!  Now if we could just buy some 12 volt, 93 ah NiMH batteries ...

David Roden - Akron, Ohio, USA
EVDL Administrator

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