purpose of capacitor

[jgb123]

what is mechanical purpose of the run capacitor and the start capcitor?
Start provides starting torqe and run capacitor provides current for compressor operation. is this correct?

[framehvac]

Start Capcitor electrical storage device used to start and run circuits on many electric motors.

Run Capacitor a device that dissipates heat generated by a motor.

[jgb123]

Originally posted by framehvac
Start Capcitor electrical storage device used to start and run circuits on many electric motors.

Run Capacitor a device that dissipates heat generated by a motor.

can any one verify this info as being correct?

[framehvac]

Yes I will.HaHa

[jgb123]

Originally posted by jgb123

Originally posted by framehvac
Start Capcitor electrical storage device used to start and run circuits on many electric motors.

Run Capacitor a device that dissipates heat generated by a motor.

can any one verify this info as being correct?

meant to ask " can anyone else verify this as being correct?"

[condenseddave]

Originally posted by jgb123

Originally posted by framehvac
Start Capcitor electrical storage device used to start and run circuits on many electric motors.

Run Capacitor a device that dissipates heat generated by a motor.

can any one verify this info as being correct?

Close enough.

[contactor]

you @framehvac could both get help from an electronics course. Learning fundementals is essential before understanding the rest.
there is no mechanical job of a capicitor.its electro-magnetic. It doesnt release heat either

[jgb123]

Originally posted by contactor
you @framehvac could both get help from an electronics course. Learning fundementals is essential before understanding the rest.
there is no mechanical job of a capicitor.its electro-magnetic. It doesnt release heat either

So what is the purpose of a run capacitor and a start capacitor in a condensing unit in relation to the compressor? did not think it absobs heat from the motor.

[condenseddave]

OK, the start cap's purpose is to cause a phase angle shift during the starting of the motor to increase the efficiency of the start winding, it, and the start winding, have to be out of the circuit when the motor is at full speed, or will burn. This is often accomplished with the potential relay, but could also be done with a centrifugal switch.


The run cap does the EXACT same job, but is left in the circuit during motor operation, charging and discharging constantly. It DOES reject heat, but only it's own heat, created by that constant charging and discharging, not that of the motor winding. The run caps are usually built tougher, to take higher heat, but are not heat sinks.

Happy?

Hey, you asked............

[condenseddave]

Originally posted by jgb123

Originally posted by contactor
you @framehvac could both get help from an electronics course. Learning fundementals is essential before understanding the rest.
there is no mechanical job of a capicitor.its electro-magnetic. It doesnt release heat either

So what is the purpose of a run capacitor and a start capacitor in a condensing unit in relation to the compressor? did not think it absobs heat from the motor.

Often, in a condensing unit, the run cap ill be for the fan motor.

The compressor will be started with a start capacitor and potential relay.

[jgb123]

Originally posted by condenseddave
OK, the start cap's purpose is to cause a phase angle shift during the starting of the motor to increase the efficiency of the start winding, it, and the start winding, have to be out of the circuit when the motor is at full speed, or will burn. This is often accomplished with the potential relay, but could also be done with a centrifugal switch.


The run cap does the EXACT same job, but is left in the circuit during motor operation, charging and discharging constantly. It DOES reject heat, but only it's own heat, created by that constant charging and discharging, not that of the motor winding. The run caps are usually built tougher, to take higher heat, but are not heat sinks.

Happy?

Hey, you asked............

Thank you for the info, so the run capactor remains in the circuit to keep compressor running after the compressor reaches full speed, correct. would this be a way of explaining this on a test, still in school and studying for exam.

[condenseddave]

On a capacitor-start-capacitor-run motor, which is not real common for a compressor, yes.

A Permanent Split Capacitor motor is the most common application for the run capacitor.

In the PSC motor, the run cap actually assists in starting the motor, and then increases the efficiency of the motor while it's running by causing the phase angle shift.

[justinothertech]

Some of these replys give that "deer in the headlight" look.

[BamaCracker]

Capacitors make use of certain laws of electricity to decrease the amount of power consumed.

Here's a good website for calculations and formulas:
http://www.nepsi.com/formulas.htm

The pertinent term to lock in on is "power factor correction." This term means you are trying to mathematically offset some of the electrical inefficiencies of the system by adding capacitors.

Once you understand the losses associated with induction loads, you'll begin to see how the capacitor offsets some of those losses. This "offset of loss" equals a reduction in usage, and therefore a lower bill for large consumers (factories, hospitals, etc..) but for the design engineer of the HVAC system, it means lower amp draw, allowing smaller wires, both in the motors, and feeding the motors.

Here is a website that explains it much better than I can, and (combined with the formulas you get from the first website I posted) allows you to calculate power correction factors as if you had taken the class in college.


http://www.lmphotonics.com/pwrfact.htm

[Big Ed]

The Start cap is used as a switch. To get the compressor motor moving you need a large set of windings .There are two sets in the motor. At start both winding are working to get the motor spinning .Once it's up to speed running both would pull too much of a load then what it needs, so the start winding have to drop out. A cap will allow electricity through it at discharge but as it builds up a charge, resistance increases through it preventing electricity to pass . The cap is used here as a switch....


The run cap as I understand aligns the phase to make the motor run more efficant making more motion then heat.....

[Edited by Big Ed on 02-26-2005 at 08:30 AM]

[cde72]

Thoughts on this are like a**holes, everybody has one, so heres mine... On a single phase motor, the electric is in phase, so instead of the poles repeling, they match up, and they match up in sequence, in essence, not moving the rotor... When you use a capacitor, you shift the sine wave, taking the electric out of phase, giving you poles that repel, giving you rotor rotation.... A start capacitor is used when a motor will start under a load, it'll shift the sine waves further apart, giving the motor much more starting capability... The start capacitor is designed to fall out of the circuit when the motor is reaching full speed by use of a PTC or a potential relay...

[fat eddy]

Frame,

Run cap cools motor ?

I'm just goona let that one go, go back to basics read them and reread them at least once a year. There is no replacement for basic sound fundamentals,fundamentals are the key to the field. Without them you are lost.They will never let you down.If you can't apply fundamentals and work out a problem ,then you are applying them wrong.A run cap is virtually the same as a start cap it just has less capacitance.

[schmuck]

The capacitors do need to cool. Thats why they are strapped to the side of the unit by a metal band. Don't you just hate to see em dropped in the unit hanging with black tape all over em?????

[fat eddy]

Schmuck,

That is as bad as his original post. Possibly even worse. At least he had some Idea that there was an electrical purpose for the thing.

[mark beiser]

Oh god, everyone that doesn't understand the basics of electric motors, leading and laging currents, induction and rotating magnetic fields, please take an electrical class that covers AC motors!

The capacitor isn't there to switch anything, or to dissipate heat, and the start windings of a compressor doesn't drop out when the compressor gets up to speed. A start capacitor will, but the start winding and run capacitor stay energized.

The run capacitor, in conjunction with the start windings having more turns of smaller wire, causes the current through the start windings to shift out of phase with the current through the run windings. In most cases, the current through the start windings will lead the current through the run winding. This causes the magnetic fields generated by the windings to rotate. The rotation of the magnetic fields in the stator act on the magnetic fields induced in the rotor to cause it to spin.

There are whole books on this subject, read one.

Reading some of these responses makes me wana run around in circles like the mupet Beaker screaming EEEEEEP! EEEEEEEP!

[Edited by mark beiser on 02-26-2005 at 10:59 AM]