Vicki Powys wrote:
>
> Syd, Walt, Suzanne and all,
>
> It's a bit of a trap to think that all batteries should be fully discharg=
ed
> before recharging. My Sony TCD D10 DAT takes a rechargeable 6V 1800 ah
> NP-22H. Nowhere in the documentation can I find the words "Ni-cad" but I
> suppose it is? Sony told me that for best battery life I should run the
> batteries in the machine until the tape stopped running (inconvenient for
> field use though).
> So I made a discharging gadget with torch globes that discharged the batt=
ery
> at about the same rate that the DAT did. My mistake was in running the
> battery down DEAD FLAT before recharging. My batteries soon died and cou=
ld
> not be revived. Syd will know of Dave Stewart who also uses a Sony DAT.
> Dave was HORRIFIED when I told him I ran my batteries right flat. He sai=
d
> you should never do that, and additionally you should measure the voltage=
in
> the batteries with a voltage meter, before recharging.
>
> So I measured what the battery voltage was "when the tape stopped running=
" -
> it was 5.5V. Now when I'm discharging a part-used battery, I am careful =
to
> take it down ONLY to 5.5V, before recharging. I've had no battery proble=
ms
> since then.
Theories as to how to handle Nicads have changed over the years. I can
remember when we would put heavy wire clips on all of them after use to
fully discharge them until the next use when we would charge them with a
slow charge. A slow charge is still considered better, but not the
shorting wires.
Rechargable batteries should not be discharged below 1 volt per cell. At
least that's the turnover point of the automatic system in my chargers
and what I've seen elsewhere. Using a resistor, shorting terminals, or a
lamp (just a resistor that puts out light) will have no control on the
final voltage and if not monitored will run the battery right down to
nil. This damages the chemistry of the cell, which reduces it's life.
BTW, current theory seems to say discharge them at a rate that will get
them to 1 volt in about 5 hours. For custom pacs you can also measure
their normal load in amps and apply that load. Probably best if your
batteries have a charger that contains a discharger built for them to
use that.
If it's a nicad pac, fully charge it, let it set a hour or so and
measure it's voltage. Divide that by 1.35 volts/cell and it should give
you a good idea how many cells are in it. For NIMH the magic number is
1.39 volts/cell. (at least these are the voltages I've managed to find)
Note that's the unloaded voltage to expect out of the battery cells in
good condition if fully charged. As soon as loaded it drops. A NIMH
battery cell will drop to the 1.2volt mark when about 80% used up, for
Nicad that figure is about 40-50% used up. This is the reason a
Portadisc will sit there saying 99% for the remaining battery nearly til
the end when running on NIMH.
BTW, in looking something up on batteries tonight I was reminded of
another important thing about fast chargers. Many of the older designs
don't actually fast charge the battery all the way to full capacity and
to get to there may take a hour or two on the trickle charge that
follows fast charge. And note that starting a 2nd fast charge cycle on
them can damage batteries by overcharging. Some of the newer chargers
like the ones I use have a microprocessor control to handle all the
details. And for NIMH it's fairly important to have a good charger, they
don't tolerate overcharging very well at all. Pretty much don't try
charging them on a charger designed only for nicads.
Sitting beside me right now are two of the Maha C204F chargers
containing 8 1800 mah NIMH AA's undergoing new battery break-in . The
batteries were started on the reconditioning discharge cycle which
drains them at a rate of 240 ma 8 hours ago and are still going. That
calculates out to running the Portadisc at it's rating of 4.5 watts
while recording for over 3 1/2 hours. So they definitely look like it's
a significant increase to go to them.
> I can also recharge the batteries from a car cig-lighter and adapter, no
> problems, engine not running, but like Walt I make sure I've got a good
> heavy duty car battery before I go off on a long recording trip.
Some equipment actually will have more problems when the car is started
and the voltage dips way down. I've had my chargers on at this point
without damaging them. Ditto for the GPS and Cell Phone.
Walt
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