Sizing a Charger

How to pick the current, and why faster is not always better.

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How to pick the current, and why faster is not always better.

Charger current and pack size

Charge time is capacity divided by charger current; size the charger to the time you will actually accept.

Heat, BMS limits and derating

The cell rating and BMS set the ceiling; heat decides how long it can be held.

Charging & BMS questions

Short answers to the ones that come up most.

What charger does a lithium battery need?

One with a lithium profile matching the pack voltage and BMS protocol.

What does a BMS protect against?

Over- and under-voltage, over-current, short circuit and temperature, plus cell balancing.

What voltage should I charge to?

3.45–3.65V per cell — about 14.2V for 12V packs, 56.8V for 48V packs.

Can I charge below freezing?

Not without a heater — charging below 0°C damages the cells.

How do I know the charger matches?

Voltage, current limit and protocol. If it cannot read the BMS, it will eventually mis-charge the pack.

Back to Charging & BMS · All Redway guides

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