2 Sep
2000
2 Sep
'00
3:25 a.m.
Your weird device is probably a thermal switch. A lot of battery packs
have high rate chargers so that they can quickly recharge the bvattery and
then they use the switch to disconnect the charger in order to keep from
over-heating/over-charging the battery. I had trouble folowing your
explaination but you'll probably find that the pack has at least three
contacts and the "device" if in series with one of them. That will be the
charging contact. One other contacts will supply power to the phone (so
that it isn't disconnected when the switch opens) and the other will be a
common battery return. The return is usually the negative side of the
battey but not always.
I can't make any suggestions about replacing the Ni-MH batteries with
Ni-Cads. A lot of people have asked me about doing the opposite and I've
always recommended against it. I've read the manufacturer's literature and
they point out that the Ni-MH batteries use a different charging technique
than Ni-Cads and they need a different charger. Now having said that, I
will tell you that several people have told me that they have substituted
Ni-MH batteries for Ni-Cads and that everything worked fine. But I still
wonder how well it will work in the long term. I have a number of Ni-Cads
that have lasted over ten years (one set is nearly 30 years old!) and I
wonder if the mis-used Ni-MH batteries will last anywhere close to that long.
My 2 cents worth,
Joe
At 01:11 AM 9/2/00 +0100, you wrote:
I was wondering whether anyone here could help me on this one:
I have a battery pack of a mobile phone I'd like to replace for a set
of AA Ni-Cad batteries (reason: cheaper!). The mobile phone even has
the necessary mechanical/electrical pieces necessary for the mobile to
work with 4 AA batteries. The question is a couple of extra small
terminals the pack provides. I dismantled the pack and I found out
that one of them was connected to the pack (-) terminal, and the other
one was connected to a weird component, which is connected to the (-)
terminal. My question is: *what* weird component is that?
Some clues: It looks like a common 1N4148 diode: glass
capsule, two small copper-color cylinders, and something really small
in between. However, it is not a (common) diode! However, I suspected
it were a zenner pair (in series, symmetric polarity), and therefore I
tryed to measure the zenner voltage by connecting the component in
series with a 1K resistor, to a variable voltage power supply. In
fact, varying the voltage does not affect the voltage drop across the
component, remaining at 9.1V. At this time I was pretty sure it was a
zenner pair, maybe for protection or something like that.
However, the mobile does not charge the batteries (and does
not recognize their presence) if this component is removed! The mobile
charger has about 7V (open circuit), so I was expecting the supposedly
zenner pair to be "open". What I did was to measure the extra pin
voltage: without the component it measures about 2.5V, *with* the
component it drops to about 1.2V. So the component cannot be a zenner
pair. And this was the time I had the idea to post this message...
Thanks for any help/clues/(flames?) given!
Cheers,
--
*** Rodrigo Martins de Matos Ventura <yoda(a)isr.ist.utl.pt>
*** Web page: http://www.isr.ist.utl.pt/~yoda
*** Teaching Assistant and PhD Student at ISR:
*** Instituto de Sistemas e Robotica, Polo de Lisboa
*** Instituto Superior Tecnico, Lisboa, PORTUGAL
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