I just charged one of these. The charger supplied with mine is only
300mA, so I used my bench supply to charge it at 450mA till it got to
6.9V. It took about 15 hours from a dead flat battery to full charge.
The 12V supply is a problem, since if you leave it on, it'll cause the battery to die due to overcharging. How hard could it be to design a simple CCCV supply, and build it into the thing, so you could just leave it on the charger? Oh, I guess they are are also selling batteries, aren't they? ;)
--
Regards,
Bob Monsen
If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
Thomas Henry Huxley, 1877
I pulled the battery out of the flashlight before I charged it, but there may be a resistor in mine as well. Sadly, that doesn't help much with the overvoltage thing, because the current drops, making the resistor useless to drop voltage.
Your battery is 4AH. Thus, at 250mA, minimum time is at least 16 hours. However, you generally get less than 100% charging efficiency, so it'll be longer than that. This presumes a completely flat battery, which isn't usually the case unless you've let it set for a while, or drained it.
A constant current constant voltage source can be built using a 3 NPN transistors, a few resistors, and a TL431 shunt regulator. If you are interested, I'll post it. I use it to charge li-ion batteries, which are picky about final voltage. CCCV is the same strategy suggested by the manufacturers for sealed lead acid batteries, except that the actual voltages aren't so critical, and they suggest a final 'float' voltage that is lower than the constant charging voltage.
--
Regards,
Bob Monsen
If a little knowledge is dangerous, where is the man who has
so much as to be out of danger?
Thomas Henry Huxley, 1877
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