# Homemade Battery Recharger w/ Regulator -- HELP!

Discussion in 'Power Electronics' started by swimfan24k, Jan 19, 2012.

1. ### swimfan24k

3
0
Jan 19, 2012
Hey, I was hoping I could get some help with a project that I hope to finish in the next couple of months... I have searched the depths of the internet, and have not been able to find any help on this at all!

Simply, I am looking to build a recharging circuit for 3x1.2V NiMh batteries (3.6V total) which are fueled by a single 5V solar cell (700mA output max).

The one function on this recharger that I want, and am not sure if this is even possible, is to install a regulator which would begin charging the batteries once they got to a certain low voltage (i.e. 2V), and then would stop charging the batteries once they got to a certain high voltage (i.e. 4V). Is there a name for this type of IC? or could anyone give me some guidance as to how this could be done?

Would be greatly appreciated!!

S

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
I would take a 5W 5V zener diode and place it across the solar panel (This limits the voltage to 5V). The I would connect the -ve side to the -ve terminal of the battery, and the positive side via a diode (say a 1N4001) to the +ve terminal of the battery.

When the battery voltage falls below 4.3 volts, the solar panel will begin to charge the battery -- assuming the solar panel is producing >= 5V.

3. ### swimfan24k

3
0
Jan 19, 2012
hmm, well that's quite interesting actually.

How did you get the value 4.3V, before the batteries start accepting charge again? what calculations did you do to get to that number?

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,214
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Jan 21, 2010
5 volts less the voltage drop across a silicon diode (0.7V).

You would get 3.6V from a 4.3V zener and a diode.

Last edited: Jan 19, 2012

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Jan 5, 2010