Thread: Old aircon help.

Originally Posted by rick130

Nope, a run cap for CSR will be 10-15mFd, or on a PSC motor up to 50-60mFd, but that little one will be pretty small.

"The microfarad (symbolized µF) is a unit of capacitance, equivalent to 0.000001 (10 to the -6th power) farad. The microfarad is a moderate unit of capacitance. In utility alternating-current (AC) and audio-frequency (AF) circuits, capacitors with values on the order of 1 µF or more are common."

Ahhhh yea that helps a lot lol!! Yes i had to google that damn it!

Originally Posted by DAMINK

I have to ask.
Curiosity mostly but i guess the stupidity in me also.

What would happen if i bypassed that capacitor or fitted an incorrect one?

Run caps need to be within 5% of correct rating.
No cap it will run slow, draw excessive current and burn out the motor.

Start caps can be varied, but too low and it won't start. In areas of low voltage, e.g. The bush I used to oversize them to get a compressor underway.

Originally Posted by DAMINK

"The microfarad (symbolized µF) is a unit of capacitance, equivalent to 0.000001 (10 to the -6th power) farad. The microfarad is a moderate unit of capacitance. In utility alternating-current (AC) and audio-frequency (AF) circuits, capacitors with values on the order of 1 µF or more are common."

Ahhhh yea that helps a lot lol!! Yes i had to google that damn it!

And run capacitors and start capacitors are different beasts.

A start capacitor is only powered up for a very short time, 1 second or so, and can only tolerate about fifteen starts an hour (Damn, I can't remember!)
Any more and they overheat and go BANG!

A run capacitor helps with power factor correction and so is in circuit continuously.

Originally Posted by DAMINK

I have to ask.
Curiosity mostly but i guess the stupidity in me also.

What would happen if i bypassed that capacitor or fitted an incorrect one?

Geez,that has me stumped....

Bypass,just stand back when you switch it on....

Seriously,bypass it and the motor will probably pull locked rotor current,not the type of thing to do,and trip a breaker.

Use the wrong cap and that could happen as well.Or the motor will run but draw excessive current and/or run too hot.

Bottom line is don't do it,fit the correct part or don't do anything to it at all.

And it should be done by someone qualified.

This will help Everything You Ever Wanted to Know About Capacitors | York Central Tech Talk

Sorry,didn't see Ricks posts above,he has done a better job answering than me......

Hmm, some of you young fellas need to study a bit more theory! A motor start capacitor is traditionally an electrolytic device placed in series with the starting winding and switched out as the motor reaches around 75% speed. Its main function is to increase the starting torque of a single phase motor by providing additional phase shift to the starting winding. Never seen one that had only a limited starting cycle, but willing to accept that some of the junk now being manufactured could well be the case!

A run capacitor on the other hand was traditionally a "paper" device, but now made with better material. It is designed to stay in circuit with either an auxiliary winding, or the start winding if so designed. But its main function is again to provide a phase shift to increase the motor torque.

Getting too old to both argue or explain the theory, so the following is just one of many examples on the Internet. Google Cap start Cap run motors. Cheers. Grandpa!

What is a Capacitor Start Capacitor Run Motor? - its Phasor Diagram & Characteristics - Circuit Globe

I have had to replace the start cap on my drill press as the original had self destructed. The new cap is exactly the same voltage & mf as the old but the drill press struggles to get going at the higher speeds. Once up & running, the drill press is fine.

Any ideas please.

This will help

Everything You Ever Wanted to Know About Capacitors | York Central Tech Talk

This is complete drivel!

The

RUN

capacitor is wired in series with the

start winding

of the motor and stays in the circuit all of the time. They are designed to dissipate heat associated with continuous operation of the motor. The whole purpose of the

RUN

capacitor is to bring the start winding back in phase with the run winding. The start winding is slightly out of phase with the run winding to provide starting torque for the motor. The RUN capacitor also provides “running torque” once the motor is up and running.

Originally Posted by Milton477

I have had to replace the start cap on my drill press as the original had self destructed. The new cap is exactly the same voltage & mf as the old but the drill press struggles to get going at the higher speeds. Once up & running, the drill press is fine.

Any ideas please.

Are you sure the old capacitor was the original factory one? As in have you had the drill press since new?
It sounds like it is not big enough, or the new one is faulty. If it is slow to start it will be drawing a lot more current for an extended time and will most likely cause the new capacitor to fail.