JRC JHP500 handheld transceiver

On Mon, 30 Jan 2006 10:40:05 -0600, David Dyer-Bennet wrote:

[snip]

All my NiMH chargers claim to be able to charge NiCD batteries too;
are they lying to me? Or are there big compromises? This is
completely intellectual curiosity, since haven't used any AA NiCD
batteries in years.

Well, you really didn't provide enough information to say one way or
another. But chances are, you're safe as along as it says it supports the
battery type. My own high-end DC charger must be told the type of battery
it is charging, when it is charging in peak mode. I suppose it's possible
that a charger can automatically detect both types of fall-off but it may
run a higher risk of a false positive. Keep in mind, that's a guess on
my part. Assuming it's peak charger, a false positive would mean the
battery did not get charged to capacity.

If it is a trickle charger, a false positive/negative means it's either
over or under charged. And frankly, trickle chargers are well known for
over charging batteries. Over charging a battery can result in everything
from simple cell damage (reduced capacity and lower supported discharge
loads) to an actual fire. Also, don't forget that damaged cells may cause
a fire during high load discharge cycles too. Which is to say, an
undamaged cell versus a damaged cell, is more prone is be a victim of
excessive heat build up, during high load cycles. Lastly, "high load" is
largely dependant on both the type of cell. Remember, not all rechargable
cells are equal.

As a rule of thumb, given your cells, if your cells are hot to the touch
during and immediately after use, the application is probaly high load for
them. Likewise, if during charging, your batteries are getting hot to the
touch, long before the charge cycle is complete, you might question if the
battery is being over charged...especially if it's a trickle charger.


Greg

On Mon, 30 Jan 2006, Greg Copeland wrote:

Be careful when switching to alternate battery technologies. NiCads are
designed to be charged at rates up to 3C while most NiMH are
typically designed to be charged no faster than 1 to 1.2C.

Can you back this up with some documentation? I'm not an expert, just a
relatively well informed user, but this runs counter to everything I've
read. The rule of thumb for most common battery chemistries is C/10 (1/10
the amp-hour rating) for 12 hours. As far as I'm aware there's no way to
safely (that is, without damaging the cells) speed that up significantly
without microprocessor controlled chargers and special waveforms. Even
with those things I doubt it's possible to charge NiCd's or NiMH's
anywhere near as fast as you suggest (20 min. to 1 hour) without severely
shortening their lifespan. Take care of your batteries, and you might
actually get the 1000 charges the manufacturers advertise; abuse them, and
you might get only a dozen or so charges.

In short, get an extra set or two of batteries, charge them slowly, don't
ever overcharge them, and they'll live a lot longer.

Long of the short, if you change battery technologies, make sure you
change chargers too! Otherwise, you may be in for a surprise including
very short battery life, batteries which never hold a full charge, and
maybe even fires.

To the contrary, all information I've ever come across indicates the
charge cycles are identical for NiCd and NiMH. In other words, they're
completely interchangeable, assuming of course that one accounts for the
different capacity when charging. NiCd's are lower capacity (usually
_much_ lower), so generally, NiMH's can be safely charged in chargers
designed for NiCd, but the reverse isn't necessarily true.

For some years I've been using NiMH's in cordless phones designed for
NiCd's, with absolutely no problems. Battery life between charges is much
longer with NiMH's, and lifespan is also much greater because of NiCd's
memory effect.

-Dan