NIMH charge control [RE-wrenches]

[jberdner at sma-america.com]

Dave:

NIMH, (and NICad, and Lithium ion) batteries typically use specialized
charge controllers that look for a rising battery voltage followed by a
decrease.  Another technique is to use a rising temperature as a shut off.
Unfortunately using a Lead Acid type constant voltage charger probably won't
work.
You may be able to charge the batteries with a CV charger but they probably
wont last very long.

Benchmark circuits makes some cool chips to do this but they require
additional circuitry so it is not an "off the shelf" solution.
The resistance of NIMH rises as the battery reaches a full state of charge.
Unfortunately the batteries can overheat if you continue to charge them too
long at a constant voltage.

Some of the manufacturers of NIMH packs, e.g. Makita, make special 12 Volt
chargers for use in cars.
This may work well with PV but I would double check the maximum allowable
input voltage.

Best Regards,

John Berdner






-----Original Message-----
From: David Palumbo, Independent Power & Light [mailto:ipl at sover.net]
Sent: Monday, April 02, 2001 9:56 AM
To: Wrenches
Subject: NIMH charge control [RE-wrenches]


The following is a question posed to my web site that I do not have an
answer. Anyone on the list who can help?

"I have a siemens st-5 (5w, 12vdc) panel, and a 12vdc, 3.4 Ah NIMH battery
pack. Do I need to be concerned with a charge controller of any type? as I
keep adding panels, and batteries, when would a charge controller be needed,
and what type is optimal for NIMH cells?"

Dave Palumbo

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