Why
should you trust anything said by a company that tries to sell you a vibrating
razor? Thus I present to you
Afroman's guide to
recharging alkaline batteries
Parts list
Resistors - Free from junk
Diodes: 1N400x - Free from junk, especially old power supplies
Q1 2N3904 or equivalent NPN - $0.12
or Free
Circuit Description
This is a simple current source that you
will find in any textbook. The two diodes are forced on, resulting in a
constant 1.3V at the transistor's base. This gives a constant 0.65V at the
emitter. R2 sets the charge current, which will be (0.65/R2). In this case,
0.65/10 gives 65mA out of the emitter. So regardless of what battery you attach
to the collector, ~65mA will be pulled through it to charge it. 65mA is a
pretty small charging current, and was chosen for safety. R1 can be anything
over 500 ohms and is just there to stop the diodes from exploding.
Trying
it on a 9v battery
I completely drained a 9v battery, then used the circuit to recharge it at
a measured 63mA overnight. When I woke up the battery was charged to over
10V, and wasn't even warm! It was able to function as a brand new battery
just as if nothing had happened and Laura Prepon was still hot.
I used some big power resistors and a big blue led/smurf dildo to discharge
the battery as fast as I could, and used a stopwatch to time how long it took.
When the led became as dim as Doom 3, a pretty redhead told me that it was
time to stop the watch. I measured the 'dead' voltage to be 7.5V. I did two
discharge runs, with current drains ranging from 530mA to 150mA. That's a
lot btw- 5 to 10 times more than a remote control or an mp3 player would drain.
The average capacity of the battery worked out to be 148mAh. Proper 9v NiMH
rechargeable batteries are typically rated at 160mAh. When you take into account
my high discharge current and their BS marketing, I think its safe to
say the capacity of a recharged alkaline 9v is on par with a real rechargeable
battery.
Trying it on AA batteries
I used the same 63mA current source to charge a pair of dead alkaline AA batteries
in series. Since AAs have higher capacity than a 9v, it took all day to fully
recharge them.
I discharged them at a current of 330mA for hours, and they still hadn't gone
flat. I said screw calculating capacity and decided to call it a fully charged
success.
Destructive testing: After two full days of charging the AAs eventually popped
open making a fizz noise, and leaked 3 drops of weak acid that was easily
cleaned up with my bare hands. The experience was about as life threatening
as a squirrel urinating on my lawn. The final measured voltage that killed
it was 2.0V, which doesn't surprise me. Charging a 1.5V battery past 1.8V
is kinda dumb.
Summary
You can fully recharge a depleted 9v alkaline battery at 63mA overnight
without problems. You can fully recharge a depleted alkaline AA battery all
day without problems. I recharged both types of batteries twice, and I would
expect them to easily take many more charges. If you care about safety more
than I do, attach a multimeter to the batteries and monitor them so they never
reach more than 110% of their rated voltage.
Punishermark 2099
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Myths dispelled: 1
Companies bankrupted: 2
Total cost of ownership for sex toys: down 86%
Giant Douche '04!