Automatic Capacitor Discharging Recommendation

[acvegas]

What resistor value and wattage value should I use to act as a “Bleeding Resistor” on a 26 MFD AC POWER CAPACITOR within a 120 AC Line Circuit?

AN ADDITIONAL NOTE: I would like to install a "permanent" resistor within the circuit to take care of this automatically. Would a 100K/5 Watt work? (I need actual values)? Thanks

 

[Sceadwian]

The 100k resistor should work fine. It'll discharge the cap to bellow 2 volts in 10 seconds, it will however constantly draw 1ma of power (about .15watts) So you could get away with using a 1 watt resistor with a 10X saftey factor, 5watts is 30X over required that's a bit overkill and I'm generally a conservative fellow but if that's what you got, use it.

If a longer discharge time is okay you could use a 1meg resistor. It will take about 60 seconds for the cap to discharge to 10 volts. The power used would be only .01 watts, you could safely use a 1meg 1/4 watt resistor for that. I'd lean towards the 100k resistor, but if that tenth of a watt of waste power bothers you 1meg would be better, as long as it's within your acceptable discharge time.

 

[Mr RB]

A 5Watt resistor is normally wire-wound. Good luck finding a 100k version!

Also you should be careful about the voltage rating of the resistor, mains voltages can have high spikes and you need resistors capable of withstanding high voltages.

If you can't get a specialised high voltage resistor I would use two 220K 1W resistors in series. That gives you a 2W resistor with approx double the voltage rating.

 

[Sceadwian]

Digikey's parametric search pulls up several canidates. To avoid shock voltages a simple transient absorber could be used rather than a higher rated resistor,