NiCad Discharger for Tx & Rx Packs
by John Nooyen
Resistors: 10K(7), SOT 16K4 & 6.9K, 470 Ohm(2), 4K7(2), 1K(3), 47 ohm/5W, 47ohm(2 parallel).
Capacitors: 10uF (electrolytic), 0.1uF (ceramic).
Transistors: BD681(2), BC548(1)
Led's: Red, 5mm(2)
IC: LM3900, 14pin, plus 14-pin socket
Switches: Momentary, push-on(2)
The Care and Feeding of NiCad Batteries:
The reason I designed this discharger are many, however I will list a typical example. A modeler charges his
batteies for 14 hrs, then goes to the field for a fly. He then rests for a week, then charges his batteries
again for 14 hrs and flies again. The third time, he repeats the procedure, then wonders why his aircraft has a
major argument with the runway. The problem with this method is that he is rechargeing a battey pack which after
the first week, is in an unknown state of charge. The second and subsquent chargings are grossly overcharging the
batteries. When they are full, ni-cad batteries begin gassing off the electrolyte, and being a sealed battery, the
electrolyte (unlike a car battery), can never be topped up. Over-charging the batteries seriously degrades them,
and reduces their capacity drastically.
For all your questions, tips, and suggestions, contact the author of this circuit,
John Nooyen in Australia.
Back to Gadgets Menu