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julieyantachk julieyantachk
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11 years ago
Ok so I want to charge this little li-mh 1.2v 100mah battery with a little tiny solar panel and the panel puts out about 40mah and I'm wondering how much voltage and miliamps I should use to charge a battery. The battery came out of a little tiny zip zap rc car.
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wrote...
11 years ago
you need about 1.5 volts. 40 mA will charge it in 2.5 hours, but that is a bit fast to charge a battery without any control on charge or any shutoff when fully charged.

Get a multimeter so you know the voltage and current. If need be, put in a series resistor to limit the charge rate to something safe like 10 ma.

.
wrote...
11 years ago
Normally you don't charge a battery over 10% of its MAH capacity. So charge it at 10 milliamps. You will need to use ohm's law to calculate the dropping resistor needed. (V solar panel - 1.2 Volts)/0.01 = dropping resistor in ohms. The panel must put out more than 1.2 volts to charge the battery.
wrote...
11 years ago
Your battery doesn't sound quite right. Li would be Lithium. However, I don't recognize the -mh suffix although it could be Hydride. The two don't go together. Lithium has a voltage of between 3 and 3.7v so if it is Lithium, the cell voltage is not correct.

This voltage is quite important as you are asking about recharging from a solar cell. The voltage to recharge the cell must be higher than the voltage from the battery. A solar cell charger for a Ni-Mh cell is different to a solar cell charger for a Li-ion cell. The Lithium charger would have more cells.

Taken on face value, you need to recharge for a longer time than the ampere/hour capacity of the cell shows. About 130%. So your 40mA/h charger would need to charge for about three and a quarter hours (from fully discharged). Any other discharge level would have to be estimated based on this time.
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