NiCad charger

[ulot]

hello
how do i modify any of this circuits to supply about 500mA for fast charging? both suppy a maximum of 45 and 50mA respectively which is about 15hrs of charging but my NiCad battery indicates that it can be charged for just 5hrs at 500mA

 

[audioguru]

You will have an explosion if you don't learn about Ni-Cad battery chargers!

The battery's temperature and pressure increase dramatically when the battery reaches full charge at such a high current:
1) Your circuit doesn't detect the amount of charge when it starts.
2) It doesn't detect and shut off when the battery is fully charged.
3) It doesn't measure the battery's temperature.
4) It doesn't detect the battery's pressure.

Energizer don't make Ni-Cads anymore and replaced them with much better Ni-MH cells. Here's an old applications manual about their Ni-Cads:

 

[DigiTan]

Would one of those single-chip chargers like the kind that's popular for Lead Acid cells be any better? Unitrode makes some with built-in temperature comphensation.

 

[audioguru]

A lead-acid battery needs a charger that is completely different than one for Ni-Cads.
Maxim and other chip makers have ICs for fast-charging Ni-Cads and an option for Ni-MH. They detect current, actual voltage, rate of rise of voltage, the slight drop of voltage just before full charge, temperature and have a timer.

 

[ulot]

Sorry i got the value of the current wrong it's surposed to be 210mA not 500mA. thanks for the tips but NiMHbatteries are not common here and even the NICds are very expensive too. It was written on the batter that you need 15hrs to charge at 70mA but 5Hrs for speed charge at 210mA
so will this ciruit work without blowing the battery and how do i add overcharge protection?

 

[audioguru]

You are charging old Ni-Cads that I used about 15 years ago. New Ni-MH cells have nearly 4 times their capacity. When you compare their cost to the cost of throw-away batteries then they pay for themselves.

Of course this project will blow them up when its current is set too high, it is designed for slow overnight charging with a mechanical timer.
The project is in two parts: the left is the battery charger and the right powers a digital camera. Therefore the transformer is big enough for both functions.
https://www.electronics-lab.com/projects/power/035/index.html

The text tells you all about it:
"This circuit was created for digital cameras. It's known the digital cameras have considerable power consumption. For example my camera Minolta E223 requires approximately 800 mA. In practice a mains power supply or high capacity NiMH accumulators (batteries) can satisfy this demand.

This circuit consists of two parts, charger and adapter. The transformer, rectifier bridge and buffer condensator are common. Adapter is quite simply its main part is an adjustable voltage regulator LM 317 according to usual setting. Output is a suitable for camera jack plug. Voltage can be adjusted in range 2-9 V.
In the charger circuit a 7805 fixed voltage regulator works as current generator assured constant current during charging. This charging current can be adjusted with the 100 /1W potentiometer in range about 50-300 mA indicated by a small current measuring instrument. From one to four batteries can be charged simultaneously. The switch must be set according to number of batteries, and charging current of batteries given by manufacturer must be adjusted. This circuit doesn't measure charging time and charging condition of batteries. Manufacturers give charging time, usually 14-16 h. I solved this problem with a simply, cheap mechanical mains timer. I think its accuracy is sufficient."

 

[ulot]

okay so what exactly will that mechanical timer be?
and can neglect the adapter part of it?

 

[audioguru]

okay so what exactly will that mechanical timer be?

Hardware stores sell the mechanical main timer for turning on and off lights at set times.

can neglect the adapter part of it?

You can leave off the right side of the schematic and use a transformer rated for less current.