Charger said:
Opened it up, (the yellow Tesco version) there is an in-line 10R 5W
resistor.
Rather than try to calculate, I unsoldered a lead, put charger in
circuit, measured 250 ma.
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.
So I presume charge time is around 8 hours, plus a bit extra.
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
