🚀 go-pugleaf

x
ray@cs.rochester.edu  (Ray  Frank) asked:


 > Finally, does any one know of a reliable way to determine how much charge is
 > left in a nicad?
 > .....  I have measured my fully charged
 > nicad pack at 5.2 volts (4 AA) and after about 2 hours they are down to around
 > 4.8 volts.  But they will still read over 5 volts even after 90 minutes of
 > flying so they begin dying all at once and this can be dangerous when 500 feet
 > in the air.  I bring the plane in every 45 minutes or so to check the voltage.

Paradoxically, an advantage of Nickel Cadmium  batteries  is
also  a  drawback.   The  voltage of a NiCd battery is rela-
tively constant from a few minutes after a full  charge,  to
just before it dies.

This discharge characteristic assures  constant  performance
of  the  powered  device,  like  a  radio  or  a motor.  The
drawback is that voltage measurement made during most of the
discharge cycle will tell you nothing.

A recent QST article by Canadian hams  presented  a  rechar-
geable  battery with a negative slope discharge curve.  Sim-
ply put, by measuring the voltage of the battery, one  could
tell  how  close it was to death.  As the authors point out,
their  batteries  should  only  be  used  to  power  devices
tolerant of a voltage that decreases over time.

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Bob Parnass,  Bell Telephone Laboratories - ihnp4!ihuxz!parnass - (312)979-5414