On Sat, 8 Dec 2001, Frank Gruendel wrote:
> likely.
> Using rechargeables that are not part of a pack is another cup of tea of
> course. It can easily happen here that cells with a different charge
> state are used.
>
> > (Incidentally, you'll notice on any pack of you buy Alkalines, you are
> > told never to replace just one cell in a device, you should replace all
> > the cells at the same time. The cell reversal issue is again why you are
> > told to do this).
>
> Assuming that you mean non-rechargeable alkalines this wouldn't be much
> of a problem, you'd just throw the
> bad cell away and replace it with another. The problem here is that the
> internal resistance increases with discharge and you won't get as much
> current through the empty batt as you would maybe like to.
It can also cause the bad cell to heat up and do other "unwatned" things.
It's sound advice to not just replace one cell but the pack. Again,
recycle your dead batteries!
>
> > A 1kiliohm resistor across the pack/cell is typically a sufficient
> > load(don't violate the power rating on the resistor either! Use a 1/4 or
> > 1/2 Watt to be safe).
>
> For real-life measurement the current should probably be in
> the range of 20...100 milliAmperes, this would mean 250...50 Ohms.
> When using 50 Ohms 1/2 watt would be a good idea, unless you are
> interested in first-hand experience of how fast a fully charged pack
> can burn a resistor.
You're right, I was off by an order of magnitude, I was thinking of a
value from a voltage divider ;). But I have gotten decent results with
loads of 1k and so on, I don't have my data in front of me so I can't
comment with 100% certainty though.
>
> > If a charger says it can charge NiMH but doesn't say NiCd, then it is
> > however OK to charge both NiCds & NiMHs.
>
> Well, I politely disagree. The charge requirements for NiCd and NiMH
> are different. Your best be is to charge NiMH with NiMH chargers and
> NiCd with NiCd chargers. Or both with a charger that is intelligent
> enough to find out automatically which type it is charging.
If a charger is peak detecting(using a point of inflexion or delta
0V/-deltaV technique) and it works on a NiMH it will work on an NiCd too.
The possibility exists for the NiCd to be slightly undercharged, but IMO
is better than being overcharged.
A charger cannot actually detect between NiCd and NiMH unless it is told
or there is some intelligence (even a thermistor like in the Newton). But
the charging algorithms are closely matched that what works on NiMH works
well on NiCds.
0-deltaV / point-of-inflexion is what is suggested for NiMH, while most
chargers use -delta-V for NiCd. -Delta-V actually slightly overcharges the
NiCds but the 0-deltaV/POI method doesn't, so I actually use it on my
NiCds.
> This is why the Newtons have a switched voltage regulator. Its job is to
> ensure that the voltage the Newton electronics sees stays at 5 volts as long
> as the battery voltage is higher than about 3.7 volts (measured on a
> 120 and on a 130).
Just curious, do you know which switching regulator is in the 2000? I
think the 2000 runs most of the logic of 3.3V though 5V is needed for
PCMCIA, etc. I haven't yet checked mine, so I can't comment.
>
> > The pack should be discharged to .7 volts.
I am not sure who said this, but I don't think it was me, perhaps the
other gentlemen who suggested the diode bit.
Thanks,
Speedy2.
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