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forums.rcpitstop.com  |  In The Pits  |  Battery talk  |  How a LiPoly charger works
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Author Topic: How a LiPoly charger works  (Read 740 times)

Offline rmfish

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How a LiPoly charger works
« on: June 13, 2012, 12:24:57 PM »
A LiPo battery at full charge is 4.2 volts, when removed from the charger the nominal full charge is 3.7volts per cell. When you are discharging them, they MUST NOT GO BELOW 3 Volts per cell. That is why a LiPo must be charged with a LiPo charger, preferably with Cell ballancing capabilities. A LiPo charger does not function like a NiCad or a NiMh charger. A LiPoly charger starts charging in what is called Constant current mode, so if you set the charge current to 5 amps, you will see the charge rate display start low and graduaoly increase until the display reads 5 amps. During the constant current stage you will see that the voltage of the LiPoly pack is gradualy increasing. When the voltage reaches 4.2 volts per cell, that would be 8.4 volts on a 2 cell pack, the charger switches to constant Voltage Mode. The display will now show that the voltage stays within a 100 milivolts or so of 4.2 volts per cell but now the charger is measuring the voltage and the charging amperage starts to fall. This is now at about 80% of the full charge. The last 20% of the charge cycle takes quite a long time, as the pack voltage increases slightly the current is reduced to bring the pack back down to 8.4 volts. The current will continue to fall until 10% of the set charge rate is reached, in our case the charge rate was 5 Amps, 10% of 5 Amps is 500 miliamps, within a few miliamps of this number, the charger will shut off.  There is no such thing as a peak voltage on a LiPoly. The discharge C rate is a multyplyer and it indicates that, if the battery was a 5000 miliamp one, and the discharge C rate was C20 you could place a continuouse load of 100 Amps on the battery. Batteries usualy have two discharge numbers, for example, C20 continuouse and C30 FOR THIRTY SECONDS ONLY. The C30 rating does not mean that you can load the battery at C30 and then wait until it reaches C20. C30 is for 30 seconds only, the big problem here is that the longer you overload the battery the shorter it's life will be, if you constantly charge at the highest amperage setting, the shorter the batteries life will be. Charge a 5 amp Battery at 2.5 amps and discharge a C30 battery at C20 and your packs will last as long as your Nicads used to.
I hope this helps,
Robert.

forums.rcpitstop.com  |  In The Pits  |  Battery talk  |  How a LiPoly charger works
 

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