Electrical – How to detect completion of Lithium-Ion charging

batteriesbattery-charginglithium ionlithium-poly

Is there a simple way to detect when a lithium-ion battery charging process is complete?

I have a basic system as shown here:

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The load represents my application (including its own voltage regulation), and the voltage regulator symbol represents a cheap off-the-shelf Lithium-ion battery management system that handles tapering off the voltage and current as the battery becomes charged. Unfortunately, the BMS doesn't have pinouts to detect charging status.

What would be the simplest way to alter this circuit so I could get a high signal when the battery is fully charged? My application includes a microprocessor with some ADC pins. Could I measure voltage before or after the BMS to tell when charging is complete? I know that Lipo recharging includes separate constant voltage and constant current stages, so this might not be 100% accurate, but I just need a rough estimate.

Best Answer

Charging is usually terminated based on a charging profile and some termination current. So if the charging voltage is say 4.35V, the cell will charge at a current based on the state of discharge. When the current drops below a threshold, charging is terminated. Termination current and charge voltage are often programmable in a given charging system.

Here's an example from the TI bq25895 single cell charger:

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