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More  Cell Phones, 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 simple scheme.
First, check 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 AA 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 2500ma-hour NiMH 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 standard NiMH charger as shown below.  Both AC and DC charge stations are available.

Click on Drawing Below to view PDF version of Schematic

telephone Charger June 4, 2000

More  Cell Phones, Telephone Circuits, Battery Chargers

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