Why contactors weld, and how pre-charge circuits prevent it.
Inrush current and contactor damage
The inverter’s capacitors look like a short circuit for a few milliseconds — that is what pre-charge is for.
Sizing a pre-charge circuit
A resistor sized for the bus capacitance and a relay to bypass it afterwards.
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.
