Originally Posted by NC Cams  . Your particular R/C factor will determine the discharge rate of the cap + resistor combo you choose. |
Dear Bob,
I'm a bit rusty on this, so take it with several pinches of salt, and read other posters' input. Here goes.....
INMVVHO, if you want the power supply to come down from about 90 volts to effectively zero volts in two minutes from the time you turn off the PS, and you have a 39000uF capacitor........
1000 ohm bleed resistor rated at 8 watts continuous.
If I've done the calculations correctly, I would not put the bleed resistor directly across the cap. terminals. You will heat the cap. too much.
Incidentally, an 8 watt resistor is quite a heat generator, and quite big physically. You may well have to go for a much longer "shut-down" time.
My two cents..
Best wishes
Martin