parnass@ihuxz.ATT.COM (Bob Parnass, AJ9S) (08/28/87)
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. -- ===-===-===-===-===-===-===-===-===-===-===-===-===-===-===-===-===-===-===-=== Bob Parnass, Bell Telephone Laboratories - ihnp4!ihuxz!parnass - (312)979-5414