I'd bet that a trickle charge current for a car battery is probably way
too much to trickle charge some C or sub-C cells! Look on the internet
for charge rates for cells of the same type and size as yours, and
compare that to the trickle charge current rating on your car battery
On Mon, 27 Oct 2003 02:24:09 -0500 (EST), email@example.com (John)
With a car battery charger you will never know when the cordless
drill battery is fully charged and will risk overcharging it and
destroying it. The $60 charger has a built in circuit to stop
charging when the battery voltage rises to the correct voltage for a
full charge. This is very different from that for a lead-acid car
MAHA sells a unit that will charge Nickel Cadmium, and Nickel Metal Hydride,
batteries. It has charging pins that will adapt to almost any pack. I find
it very useful as it will charge almost any pack, in any configuration, from
I believe three to twelve volts. It has a corded temp sensor that will
disconnect the charger if the pack gets too hot.
It also includes an adapter that will allow operation from a cigarette
The feature I really like is the ability to discharge then charge the pack.
I find that this will bring back many NiCad packs.
It's not as convenient as the OEM charger, but it makes up for it by
adapting to many packs.
I believe this same model is also sold at Radio Shack for $29 to $39.
Remove the two fish in address to respond
The auto type charger is not good for this. You can build
a simple charger for less than $10.00. The trick is to
figure a way to conveniently connect the charger to the
The simple charger consists of a DC supply providing at
least 2 volts more than the battery voltage, an LM317 chip
configured as a current regulator, and a 22 ohm resistor
to set the current to ~56 mA for trickle charging. The DC
supply can be a wall wart rated to provide ~200 mA or more.
Generally speaking, if you set the charge rate for between
50 and 60 mA you'll be ok for recharging drill batteries at
a trickle rate. If you want to be more exact, you'll need
to determine the capacity, C of your batteries in order to
determine charging rate. It will take about 30 hours of
charge at this rate (~56 mA) to fully recharge a completely
discharged drill battery. If you go to a C/10 rate (about
100 mA), you can recharge in about 14 - 16 hours. The
downside of that is a greater probability that you will harm
the battery by overcharge - say by leaving it on the charger
too long, or perhaps by having the circuit operate at
something lower than C/10. The ~C/20 rate (56 mA) gives you
a much better margin for error.
A more sophisticated charger can be built or bought, but
if you want to keep it cheap and simple, it's hard to
beat three components.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.