Re: Bleed Resistor for Capacitor Question

gtslabs wrote: 
I am looking for bleed resistors for my 5hp 240v single phase
compressor motor start capacitors. It draws about 24 amps.
There are 2 capacitors in parallel giving close to 500 uF.
Since P=VI I figured P=240*25 = 6,000 w or 6kW
And V=IR or R = V/I or 240/25 = 10 ohms.

But Grainger only supplies Capacitor Resistors at 2 watts and 15 k ohms
Can I use this resistor?
http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?xi=xi&ItemId=1611755421&ccitem=

Thanks
Steve


You are WAY off base. The cap is wired centrifugal switch -> start cap -> start winding. From the way you wrote your email, I believe you are thinking the resistor goes in series with the cap i.e. centrifugal switch -> resistor -> start cap -> start winding. This is WRONG. The bleeder resistor is wired in parallel with the start cap. When you put 240 volts across the start cap it will draw 24 amps, but when you put 240 volts across a 15k resistor, it only draws 240/15000 = .016 amps, or 16 mA.

Figuring power at VI, get 3.84 watts.

So a 5 watt 15k resistor would work fine.

I used to scrounge big motor run caps from Seattle City Light (came out of old street lights) and those had multiple tab-type terminals. They often had a 10k resistor wired across the capacitor.

Note that run caps don't need bleeder resistors since they're wired across the windings of the motor. When you shut down a phase converter, any voltage that would have been stored on a run cap bleeds down through the motor windings.

GWE

.

Relevant Pages

  • Re: 12V to 7.2V DC converter circuit?
    ... I see your point about the cap giving it the start up power. ... surface, in my hand I have a small battery back and in my real vehicle, ... complicated to get the stall ampsto start the electrical motor. ... Put a 3 ohm, 50 watt resistor ...
    (sci.electronics.basics)
  • Re: The KISS AMP: a progress report
    ... supply topologies and in particular how a choke input works or why it ... you appear to think that a resistor will give off ... the conventions guiding SE amp design towards the desired result. ... 'cause if that cap should fail, ...
    (rec.audio.tubes)
  • Re: draining filter caps
    ... Expert (sorry, still no fuck. ... that one cap doesn't *see* more voltage than the other, ... parallel with each cap. ... You can either piggyback each resistor to the cap leads, ...
    (alt.guitar.amps)
  • Re: Cap. Discharge Res.
    ... I am referring to the capacitor across the ... I am assuming that either the appliance has a faulty resistor connected ... Any cap that is placed across the mains in a piece of equipment, ... should not in theory require any resistor to discharge it, ...
    (sci.electronics.repair)
  • Re: Homebrew ^V^ amp, which preamp triode for nil microphonics?
    ... the preamp heaters off well filtered dc. ... Grid cap wire is currently shielded and grounded at chassis on opposite ... see fender schematic for power tube grid balance pot circuit. ... reduce value of plate resistor for experiment your voltage drop and ...
    (alt.guitar.amps)
Loading