purpose of capacitor

[framehvac]

fat eddy
Member

Registered: Feb 2005
Posts: 334
Thank You BornRiding,

Now that we have gotten over that hurdle,can we now move on to how it looks a lot like a three phase motor.

Would someone please explain what a single phase to three phase converter does and what it does it with.



I can't beleave you don't know that if you don't know then I am not goning to tell you.HaHa So just tell us?

[fat eddy]

Do tell please,

Enlighten me,

I do know the answer very well I want someone else to tell him so that he might beleive it.

[framehvac]

fat eddy
Member

Registered: Feb 2005
Posts: 335
Do tell please,


Can I phono someone?No I will take my 50/50 so give me my 50/50.

[snewman24]

In my edition of MR&A/C,published in 2000, it does describe a run capacitor on pg. 1159 of the glossary as "A device that dissipates heat generated by a motor." This is clearly in error and should have been caught by the editors. What they are trying to say is that the run cap has to be built to dissipate the heat it develops since it is left in the circuit while the motor runs, as contrasted to a start cap which is only energized for a fraction of a second and therefore doesn't have sufficient time to heat up. This is explained in the text on pg. 268.

[oilman52]

Capacitor law...all caps are wired to line voltage. All caps are wired to start winding.

[oilman52]

Anyone believe that one?

[fat eddy]

That is a false statement Oil

[oilman52]

Which cap. shell is plastic? Run or start?

[oilman52]

Caps. are rated how? Voltage,microfarads,amps.?

[framehvac]

snewman24
Professional Member

In my edition of MR&A/C,published in 2000, it does describe a run capacitor on pg. 1159 of the glossary as "A device that dissipates heat generated by a motor." This is clearly in error and should have been caught by the editors.

Thank you.

[oilman52]

All capacitors recive line voltage,also are wired to start winding. Run capacitors purpose is to limit the amount of current draw produced by the start winding.

[mark beiser]

Originally posted by condenseddave
And, Mark, the start winding (And start capacitor) IS deenergized when a motor reaches full load.

This is only true in a couple of types of motors. In the PSC motors used in compressors and fans we see every day, the start winding is energized in parallel with the run winding whenever the motor is running.

The run capacitor is in series with the start winding.

If there is a start capacitor, it is in parallel with the run capacitor, so thier capacitance actually adds.

The start capacitor should be removed from the circuit when the motor gets to about 75-80% of its full speed. Leaving it in to long will cause the capacitor to fail because start capacitors generally have no way to get rid of the heat generated by the current flow through them.

On a PSC motor, if you check with an amp meter, you will have current through both the run and the start windings, but because the currents through the 2 windings are out of phase with eachother, run current + start current does not = current found at common. If you clamp your meter around run and start at the same time, the current will = what you find at common.

Because we have moving magnetic fiends and coils of wire, we also get a fun thing called back EMF being induced. That is the voltage you get if you check the voltage between start and run. This is the voltage you need to know when you are determining what potential relay is needed for a start kit, and determining what voltage rating you need for a capacitor.

[contactor]

i agree with oilman. all caps are wired IN SERIES with start winding. The reference in Mod REfrig.book is a typo. All caps generate thier own heat. run caps generate less @ are oil cooled. Start caps are of paper @ plastic construction. Designed to be used breifly, then drop out of circuit when motor gets to 75% of speed, via a current or potential relay. Anyone ever run into an exploded start cap due to a stuck closed relay? hats because it overheated.