NiCd Battery Charger Schematic

I need a schematic for a 2N3055 variable current power supply using a full wave rectifier and a 24V (filament transformer from Radio Shack), the cuircut lets the voltage float and regulates the current. A pot is used to vary the current output. I use an ammeter to set the current. Current runs about 200 milliampers to maybe 1.5 Amps. I use it to charge NiCd batteries. It also has a LED in the circuit and a diode. I intend to substitue and TIP3055 vice the 2N3055. I have seen tons of schematics using voltage regulators to control the battery charging rate. I am not so sure about using that as it allows unregulated full current to flow until battery voltage is obtained. The current regulating circuit is better as I charge at lower rates for longer times. And since the voltage floats, I can charge up to ten or more cells at one time.

I have lost the original schematic and have had a problem. I suspect the 2N3055 has been blown.

Advise please.

 

Bob, no intention to continously charge the battery, but trickle charges are a lot better than fast chargers. Charging 10 - 14 hours at the C-1 rate (10% of the rated capacity in milliampere hours of the battery) is the ideal rate. All R/C wall wart chargers do just that. They are cheap and work but with many different capacities ehich means many different current rates and wall warts are limited to 4.8 V and 9.6 V batteries. I used typically 5 cell receiver batteries (6 V). Thus the wall wart does not work for me with its fixed low voltage output. I have 6 V batteries rated from 600 milliampere hours to 2500 milliampere hours. It would take a wall wart even if I could get more than 6 V out of it, a couple days to charge the battery to its full capacity. That is why I am looking for an adjustable current charger.

 

Actually, Bob. I have used my home built charger for several years quite successfully. Unfortunately, I believe I suffered a power peak and blew out the transistor or diode rectifier in the circuit. Regardless, the old charger no longer works. Other than going piece by piece through it, I was looking for something a little more modern. But all the circuits seem to be voltage based, which is okay, except they either charge at very high rates or similar conditions. I rather charge at low rates and prolong the life of the battery. It is my peculiarity.

I grew up in the vacuum tube days and have very limited transitor experience. I realize there are many chips out there that make life easier. In fact, I worked for TI for several years in the defense business as a system safety engineer. I am retired now and fly RC for fun. And use home brew circuits to charge batteries.

Not particularly interested in charging LI-po and the like as I do not fly electri powered airplanes. But I do fly airplanes that require receiver batteries to run the receiver as well as the servos. And both my transmitter and receivers have rechargeable batteries. I rather use NiCd batteries in the airplanes as they can deliver very high current demands for short periods of time. NiMh do not do that well. And the NiCd has a graceful discharge characteristic while NiMh have a definite knee in their discharge curve and have cost me one airplane already.

So I charge batteries from one cell to as many as 8 cells.

Chip