Difference of charging Ni-MH/Ni-CD and Li-ion batteries on a smart charger

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XTAR Light

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Apr 26, 2010
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China
The Ni-MH/Ni-CD and Li-ion batteries have different charging needs based on their different chemistry. A smart charger supporting both of the Ni-MH/Ni-CD and Li-ion batteries are designed with separate charging procedures, to adopt the pulse current charge for Ni-MH/Ni-CD batteries and constant current constant voltage (CCCV) for Li-ion batteries.

Ni-MH/Ni-CD batteries charge with constant current and the voltage is allowed to fluctuate. The temperature rise is normal with Ni-MH/Ni-CD batteries, especially when reaching the 70% charge level. The reason for this is a decrease in charge efficiency and the charge current should be lowered to limit stress. As the Ni-MH/Ni-CD battery will quickly heat up when it's nearly fully charged, some people use the thermal detection. But it's not so accurate. The battery will often feel warm when it is being overcharged. The favoured method of full charge detection for a Ni-MH/Ni-CD cell is the 0ΔV and -ΔV method. It means observing a slight voltage drop after a steady rise, when the battery gets fully charged.

As for the Li-ion battery, it has accurate cut-off voltage 4.2V (+-0.05V). Based on its characteristics, the better charging way for a charger is to adopt 3-stage charging methods: TC wake-up, CC fast-charge and CV fully charge. When the battery is almost fully charged, the charger starts CV charging to make sure the battery is fully charged and less damaged. And it won't make over-charge with the 3-stage charging, more safely.
 
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