I'm considering using a Vishay FVT series resistor for precharging some capacitors.
- Capacitance: 3300uF
- Voltage: 730V
- Resistance: 500 ohms
- Resistor continuous wattage: 25W
This series, like many wirewound resistors I've seen, have a spec'd overload rating of 10x for five seconds. So my 25W resistor can handle 250W for five seconds, or 1250 joules.
In my precharge configuration, the peak power dissipation in the resistor will be 1080 watts, 43x the continuous rating. Obviously the resistor can't survive that indefinitely, but the power dissipation will decay exponentially. My reasoning is that if the total energy dissipated in the resistor is under 1250 joules, it should be safe.
The total energy dissipated in the resistor is the same as the total energy stored in the caps, giving me ~880 joules, less than my 1250-joule limit. Is my analysis valid? Should my resistor be safe? Or will the high instantaneous peak power break something even though I'm within my computed joule limit?