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Telephone Circuits, Battery Chargers
Do It Yourself Portable Cell
Phone Charger June 4, 2000
It seems that as cell phones become more sophisticated, their operating times
become shorter and shorter. If you are on the go all the time and have
difficultly finding AC or DC outlets to charge your phone, you might consider this
to see what voltage your cell phone requires. The AC power adapter should list
its voltage and current output. Most phones have their own internal lithium ion
battery charger circuit, which accepts an external 5 volts, from either an AC wall
adapter or a special 12v DC cigarette lighter plug. A pack of 4 NiMH
rechargeable cells delivers very close to this voltage and should charge nearly any
cell phone battery. With quality cells rated at 2.5 Amp-hours, the pack stores
about 12 watt-hours of energy. This is about 4 times what many cell phone
batteries store. This allows the pack to recharge a nearly dead cell phone
battery some 3 or 4 times, extending talk time by that same factor.
|The scheme is
pretty low tech. First, buy a covered 4 AA cell battery pack like shown below.
Radio Shack and other places sell such battery holders. Buy a pack of four
cells. I have had very good luck with the Energizer brand. Wire a
coaxial power plug to the two wire leads coming from battery pack. The red wire
should be soldered to the center plug terminal. Next, tap into the red and black
wires of your AC or DC charge adapter for your phone with two insulated wires.
Your adapter might look something like the one shown below. Solder the
other end of the two wires from the phone plug to a DC power jack, matching the plug
from the battery pack. That is it. When you plug the phone adapter into
the phone and the battery pack to the power connectors, your phone should indicate a
charging mode. Disconnect the pack when the phone is fully charged.
|After two to
four charge cycles, the AA cells should be removed from the holder and recharged in a
charger as shown below. Both AC and DC charge stations are
on Drawing Below to view PDF version of Schematic