# Thread: Automatic Ni-Cd/Ni-MH battery Charger

1. ## Automatic Ni-Cd/Ni-MH battery Charger

Hi guys, i am working on a small project and have to make a simple automatic battery charger circuit for charging Two AAA Ni-Cd/Ni-MH batteries, 1.5V each.

I looked over the net and I am not interested in using any Micro-controller.
I would be glad if anyone could help me with the circuit, keeping the parts to minimum. Also i am using Laptops USB port 5 volts as source for charging. Please Help me out.

Thank You.

2. Hi ,
Its hard making a batter charger with USB without a micro. USB can give about 100mA current unless more current is demanded ,during enumeratuion process of a USB device(one requires a controller/ASIC for that) and why do you want to use a USB as power source. Get the basics and then only go ahead for the build USB is not good power source. Make a simple timer based (NE555) circuit with a liner constant current source using LM317 , the crude and easiest curcuit without a micro. Charge the battries with constant current for fixed amount of time (say at 1C for 50mins or so). this will charge battery to 75-80% of its rated capacity but will work. For more info check the data sheet of the two ICs

Asimov

3. USB charger is a useless thing for AAA ,will be a joke ..why to keep 20W PC (standby) running for 100ma current that too for 8-9hours
... USB chargers of ipods etc can be useful for places like office.

many chargers use simple LEd and resistor as charging circuit
AAA Nicd are real cheap and lasts 2yr+ with this charger ..
(chargers are cheap too
I bought a chamellion at 150/- )

whatz the point of using linear chips etc .. just because u want to show u have done a project??

4. Hi,
Just calculate the charging current as current
= 5V-(1.35 x n)V/Rs
for single cell n=1 and for two cell in series, n=2
Can calculate a diverter resistance for 20mA for LED Drive as indicator.

You may can do a simple SMPS like circuit like Black Regulator as below
http://www.romanblack.com/smps/smps.htm

Moreover you can charge from Live 220V, 50Hz AC. The charging current can be controlled by series resistance and diode bridge.
for the current of 100mA, use 1uF Capacitor. Use Polar DC Filter capacitor and surge resistance to reduce high Dv/dt. Please use capacitor to live circuit and make off before touching any circuit.

Thanks

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