Pre-charge and Main Contactor

by VladM

16 parts

Closing a 48V battery onto an empty DC-link capacitor would draw a destructive inrush. A pre-charge resistor limits it; once the bus reaches 90% of the battery voltage, the main contactor shorts the resistor out. Press Run, then close "connect". About 10 seconds later on screen (127ms of the circuit's own time) the bus passes 90% and K1 closes. Real systems: a 48V pack pre-charges its DC link in tens to hundreds of milliseconds through tens to a hundred ohms; here 100Ω and 127ms.