I build a circuit that charges a 400V 4.7µF capacitor to 307V. I have been discharging this capacitor by shorting the terminals using a large piece of metal. The capacitor makes a small spark and then my multimeter reads 0-5V from the capacitor.
I have heard in various places that this is bad for the capacitor because it causes a large current spike that can permanently reduce the capacitance and might blow up the capacitor. People also recommend using a resistor to discharge the capacitor.
I found a listing for a resistor on Amazon that has a resistance of 1K ohms and can dissipate 100W of heat.
I don't know if it is necessary to use a resistor like this or if a regular 1/4W resistor would suffice.
I calculated that at 1000ohms and 300V there should be a current of 0.3A and a wattage of 90W. This made me think that I need this big resistor.