COLIN LAMB wrote:
The Radio Shack regulators are very inefficient. If you need 5 volts and
run 13 volts input, the 8 volt drop represents total loss. Total power loss
is determined by multiplying the 8 volt drop by the current draw. When
battery power is precious, it is better to use a converter chip to actually
convert the 13 volts to 5 volts - at over 80% efficiency.

The few extra dollars paid to purchase a converter rather than a voltage
dropping regulator is paid back over the life of the equipment.

Colin N12US


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To elaborate on what Colin said: to provide 700 milliamp charging
current to the Ipaq, your 12 volt battery must supply:

* Radio Shack voltage regulator at 12 volts: 700 milliamps
at 14 volts: 700 milliamps

* 80% efficient switching regulator at 12 volts: 360 milliamps
at 14 volts: 310 milliamps

My 3835 Ipaq can draw over 900 milliamps while charging and running a
program; my 2215 can draw abut 700 milliamps. It does drop off by about
50% when fully charged.

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Eric Greenwell
Washington State
USA