Precharge Circuit
Definition
A circuit that limits inrush current when initially energizing high-voltage bus capacitors by using a current-limiting resistor in series with a bypass contactor.
Why It Matters
- Prevents contactor welding from high inrush current
- Protects bus capacitors from current stress
- Required for systems with significant capacitance on HV bus
- Failure to precharge can damage contactors and capacitors
Common Pitfalls
- Undersizing precharge resistor power rating (typical: 50W-100W)
- Not monitoring precharge completion before closing main contactor
- Ignoring resistor cooling time between precharge cycles
- Using precharge resistor that limits charge time excessively