Ron, the over current device, more than likely is both thermal and over current.
The thermal part is to shut off the charge current if the batteries start to
get too warm during the charge cycle. There could be a thermistor as well to
provide feed back on temperature to the charger. Make sure the over current
device carries an agency listing, such as TUV or VDE. We have tested some that
do not have agency listings and they were not any good for the application. We
have watched some turn cherry red instead of opening.
If you test for short circuit currents, expect them to be greater than 60 amps.
How good your connectors are, wire lengths will play a part in what the max.
current will be. It would be a good idea to test all of the connectors, if there
is more than one connector, for short circuits. Test fully charged and mostly
discharged batteries for what happens with short circuits.
Jim
Jim Bacher, Senior Engineer
Paxar - Monarch
e-mail:jim_bac...@monarch.com
voice:1-937-865-2020
fax:1-937-865-2048
____________________Reply Separator____________________
Subject: N-MH Batteries
Author: ron_du...@agilent.com
List-Post: emc-pstc@listserv.ieee.org
Date: 9/19/00 11:25 AM
Hi,
I am in the process of qualifying a product the uses a nickel metal hydride
(N-MH) battery. It is shrink wrapped and appears to be four AA cells in
series. the rating is 4.8 volts, 1100 mAh.
My standard requires a fault analyses of the charging circuit. As I have had
no experience with N-MH batteries I can only guess what the expected outcome
will be when overcharged. The faulted charging circuit could be either 6.5
volts at 2 amps, or 9 volts at 1 amp.
I have only one sample to test so I can't afford to make a mistake.
What will I expect to see?
Does the N-MH battery come with a built in vent?
If so, does the vent release toxic, flammable, or any other hazard?
Is there a chance of explosion?
There appears to be a fuse under the shrink wrap. Is it to prevent high
current in the event of a short? Our could it be a thermal device to prevent
overcharging?
Any other hints or advice?
Ron Duffy
Agilent Technologies
Colorado Springs Division.
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