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Topic: Is there a minimum current to charge a battery? (Read 1 time) previous topic - next topic

Tom Carpenter

#5
Aug 23, 2012, 01:35 am Last Edit: Aug 23, 2012, 01:45 am by Tom Carpenter Reason: 1
If it is a Li-Ion or Li-Po battery, you will need to make or get a special charger for it. You can't just hook up a solar cell and hope for the best.
Generally for these two types of battery you want a charge current of 0.1C, in other words one tenth (0.1) of the capacity (C). For a 100mAh battery, this is approx 10mA.
You use a CC mode (constant current) until the cell voltage has reached 4.2V, then you switch to a CV mode (constant voltage) until the current flow has tailed off to near 0. At which point it is fully charged.

For CV mode, a constant voltage of 4.2V from your cell and appropriate circuitry is required.
For CC mode, a constant current of around 0.1C or 10mA for your case is required.

It should be possible to charge it at a slower rate (say 1mA without a problem). However, consider this: If you charge at 0.01C, it will take a VERY LONG TIME - say over a hundred hours at least.
~Tom~

retrolefty


If it is a Li-Ion or Li-Po battery, you will need to make or get a special charger for it. You can't just hook up a solar cell and hope for the best.
Generally for these two types of battery you want a charge current of 0.1C, in other words one tenth (0.1) of the capacity (C). For a 100mAh battery, this is approx 10mA.


I question your 0.1C charge rate, most are rated at 1C charge rate. Most cell phone these days use Li cells and they certainly don't take 10 hours to fully charge.

Lefty

Tom Carpenter

#7
Aug 23, 2012, 01:44 am Last Edit: Aug 23, 2012, 01:48 am by Tom Carpenter Reason: 1
You can charge it much faster yes, but 0.1C is a good rate for prolonged life of the battery. I have seen 0.3C given as a good charge rate as well. Perhaps modern batteries are more resiliant - the last time I played around with Li-Po batteries was about 3 years ago so lots may have changed since then (Model helicopters used to be one of my hobbies).
~Tom~

mauried

You need a blocking diode between the Solar Cell and the battery to prevent the battery discharging back through
the Solar Cell when its dark.
So without knowing the power rating of the Solar Cell, and if its a small cell, its quite likley that the charge current is
very small, maybe only a few milliamps,which means a charging time of weeks.


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