[Elecraft] External Battery for KX1

[W3FPR - Don Wilhelm]

Chuck,

It sounds like rather than regulating, you would only need to drop the
maximum available voltage to about 14 volts.  3 or 4 series diodes should do
the job nicely - and you could easily use a switch to short the diodes after
the battery voltage falls below 14 volts.  If you limit the maximum current
drawn to 1 amp (plenty for the KX1), 1N4007 diodes would do the job, but for
higher currents, use diodes rted for your highest expected current draw.

Certainly a regulator would do the job too, but the input-output
differential for a regulator must be at least 2 volts for loads in the 1 amp
vicinity (LM317 spec) - so while an LM317 could regulate to 14 volts OK with
a fully charged battery, the voltage available at the output of the
regulator would vary drastically with load as soon as the battery voltage
began to fall.

73,
Don W3FPR

> -----Original Message-----
>
>
> I have a pair of Radio Shack NiCad RC model car batteries 7.2 vdc
> 2000 mAh.
> I have but them in series and get 16vdc when fully charged.  In the past I
> have put a 12 volt fan on the batteries until the charged was reduced to
> 13.5 vdc and then used them as an external power supply for my
> KX1.  However
> there has to be a better way.  Can anyone offer a simple circuit that I
> might put together that would provide a regulated 14vdc?
>
>