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The charger has the following specs and characteristic:
1. Simple and minimal parts thus good for beginners and hobbyist.
2. Can be used to charge Ni-Cd of different voltages (2.4V, 3.6V, 7.2V, and other battery voltage)
3. Automatic with battery over-voltage protection . Current limited and voltage controlled.
4. Visual led indicator . Charging (red) and full-charge (yellow) indicator.

Part List:
R1 - 1.2 kilo ohms 1/4W
R2 - see R2 vs Charging current below
R3 - 2 kilo ohms 1/4W
Q1 - TIP41C or any NPN transistor min 1A current and 3W power
Q2 - 2N2222, CS9013, or similar NPN transistor
LED1 - Red or any LED with forward voltage around 2V (see LED)
LED2 - yellow or any LED color except Red
D1 - 1N4001 or similar diode
D2 - see D2 vs Battery voltage below
DC supply - 12V to 15V DC supply or battery

project originally from http://www.simple-electronics.com/2011/10/simple-ni-cd-charger-automatic.html
<p>I managed to build the circuit and it seems to work except for the red led, it won't turn on when the circuit is charging the battery, any suggestions?</p>
<p>If you need to charge an 18 volt battery, I would recommend a 20 volt zener diode. An 18 volt NiCd Battery should be fully charged at about 21 volts. I am going to try a 20 volt zener and I'll comment with the results. For the resistor I would chose the one rated for the current of your wall wart or power supply. (I would recommend a 24 volt supply)</p>
<p>Does this work if USB is used as DC supply (5V/&lt;500mA)?</p><p>Of course only those under 5V batteries 2.4V-4.8V. </p><p>Any modification needed?</p>
<p>I like it. Quick, simple to make and simple to use. great Instructable, thanks.</p>
My yellow led light up when connected to input, but switch off as soon as it is connected to the battery. Does it again switch on when battery fully charge. please help me
Thanks! Works well!
As far as electronics I'm a beginner myself. I'd like to know the correct values so I could build this to charge 18v nicad batteries for my power tools. <br>
Hello,<br/><br/>Pretty cool circuit. As some other people I would like to charge a NIMH-Battery 7,2 at 5000ma. Thus I would set your circuit to charge at 500ma. You said this circuit is not recommended for NIMH batteries. What does it take to make it compatible? I just couldn't find a better circuit so I'm very interested in this one. Could you help?
hello and good day to you ! <br> <br>this is an awesome instructable, just what ive been searching for ! <br> <br>only a beginner in electronics so im a little stuck for finding the R2 and D2 values for charging a 1.2v battery, would you be able to shed some light on this for me please please ? <br> <br>i had also posted this kind request on the original page you linked to but i dont think the original author is responding to questions anymore lol ! <br> <br>many thanks in advance for the help !

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