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Do It Yourself Portable Cell
Phone Charger August 24, 2009
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. |
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Master Schematic
Category List -
David A. Johnson, P.E.
Cell
Phones, Telephone Circuits,
Battery Chargers |
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