DVM monitoring electric bike battery voltage

Monitoring Battery Voltage

DVM monitoring electric bike battery voltage
A voltmeter is clipped to the charging port to monitor the battery voltage under various conditions.

A battery charger generally needs to know the voltage on the battery being charged, among other things. In order for my design to work right, I’ll need to know when the battery is full, when it needs current-limited charging, and when it needs a boost because the motor is running. So I strapped a $5 digital voltmeter to the headset to monitor the battery voltage under various conditions. ┬áHere is what I found.

Condition Voltage
Fully charged, with charger connected 31.8
Fully charged, charger just disconnected 26.8
Fully charged, after motor run just a little 25.8
Upon motor startup (high torque acceleration) 21.9
After 10-20 sec, motor running at terminal speed 23.5

Those readings were taken with the old, weak batteries. I should redo the experiment now that fresh batteries have been installed. But this data gives me encouragement that my power transfer circuit can work by monitoring battery voltage alone.

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