Homemade Battery Recharger w/ Regulator -- HELP!

[swimfan24k]

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

 

[(*steve*)]

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.

 

[swimfan24k]

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?

 

[(*steve*)]

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.

 

[BobK]

But 3 x NIMH batteries is 3.6 V!

There are battery management ICs that do what you want and actually use the correct algorithm for charging the batteries. A "simple" charger will reduce the life of NI-MH batteries significantly.

Try Linear Technologies, for example:

http://www.linear.com/products/battery_charger_ic?gclid=CKSDqent260CFUPd4AodfRdYlw


Bob