DIYbanter - View Single Post

wrote in
ups.com:

You were right. The charger for my dying 12 volt Robi was marked 17v.
Plus I always left the battery in the charge between uses. Hopefully,
I'll get better life from the new one with careful charging
proceedures.
Dan K wrote:
wrote in message
oups.com...
How to recharge new NiCad battery
I bought a new 18 volt cordless drill-driver
that has 1200 mAh recharceable NiCad battery.
What is the best way to get longest battery
life out of it?
Alzerimers setting in? Can't remember if you
completely discharge first or fully charge to
get longest life.

Your getting a bunch of different answers, so here's mine: Its been
my experience that store bought chargers have one object in mind, to
charge the battery fast. They really don't care if your battery dies
a year from now. I've had store bought chargers that actually get a
battery hot when its charging. I've thrown out my store bought
chargers or modified them to charge at a reduced rate. Always start
with a discharged battery (don't charge a battery that doesn't need
charging) and put it on a timer so you know how long its been
charged. I too have just gotten a couple new 18v drills with 1200
mah battery's. These are the first cordless drills I've owned. The
charger said to charge for 5 hours and I measured a charge rate
around 350 ma. Do the math: 5 hrs at 350 ma = 1750 mah into a 1200
mah battery. Not too bad, but I modified mine with a 13 ohm resistor
to get the charge rate down to around 200 ma and will charge them for
8 hours (beacuse I just happen to have a nice 8 hour timer). I'll
keep one of the chargers un-modified and use it to quick charge if
necessary for an hour or two, but the 8 hour one will be what I use
most of the time.

You *have to* charge the cells at a higher than rated voltage,you don't
charge a 12V pack with a 12V supply.
Typical charge V for NiCds is 1.55V per cell.
Measure some good packs that are fully charged,you will find that they read
higher than 12V.(my Makita 9.6 packs charge to ~10.4V)

That's why you want a smart charger or a fast charger that actually
monitors the pack,not the slow chargers that are just a simple current
source with no feedback control.

You NEED a timer shut-off if you use a slow charger,to prevent
overcharging,and then the charger may discharge the cell if left
connected,it depends on the charger circuitry.

--
Jim Yanik
jyanik
at
kua.net