Start Capacitor

[BillyP]

Can you safely substitute a 72-87 microfarad capacitor with a 88-108? It's on a 1HP belt drive fan motor. I've read you can safely go up one size as long as you stay with the same voltage rating or higher.

Thanks

 

[BigE_]

As long as you are going up and not down, you should be fine. Those capacitors are typically rated as +80%/-20% anyway.

 

[BillyP]

Just noticed that the new capacitors I was looking at are rated 125 VAC and the old one is 165 VAC. The only problem there is if I move up in voltage, so does the physical size of the capacitor. I can go a little longer but not in diameter.

 

[tallyho8]

You should not use a lower voltage rating capacitor. Different manufacturers often make capacitors with the same rating in different physical sizes so if your supplier does not have one that will fit, try another supplier.

 

[Tig]

What is the voltage of the motor? Measure the voltage across the capacitor. If it's less than 125V you are ok.
Keep in mind that the first cap failed for a reason. I usually go up in voltage and heat rating so that I don't have to ever fix it again.

 

[BillyP]

What is the voltage of the motor? Measure the voltage across the capacitor. If it's less than 125V you are ok.
Keep in mind that the first cap failed for a reason. I usually go up in voltage and heat rating so that I don't have to ever fix it again.

The fan motor is 220 volt. That's what is confusing me. I have a 1.5hp motor that uses a 189-227MFD 125VAC start capacitor. The 1hp uses a 72-87MFD 165VAC capacitor.

These motors start every 5 minutes, 24 hours a day. I figure that might be the cause of failure? Do they make a heavy duty capacitor?

How do you go about measuring the voltage across the capacitor? They have three wires, one on one pole and two on another.

Another thing, the capacitors are rated at 65 degrees C. There's no way they ever reach that temp because they're pulling inside cooler air over.

 

[Tig]

Do they make a heavy duty capacitor?

How do you go about measuring the voltage across the capacitor? They have three wires, one on one pole and two on another.

You can go up in voltage and heat rating. Although it would seem that you are ok on the heat at 65C if the motor and cap are well ventilated.
Measure across the legs of the cap to see what voltage is across it. It sounds like the cap is wired across 220V. Which does not seem right for a cap rated less than 220V
Unless we are talking p-p and rms values......
I am hoping someone with more motor experience will jump in now.

 

[BillyP]

I finally found a place to order them, thanks to Grainger. The sad thing is because they're 165VAC the price is 9 bucks a pop instead of a 125VAC at 4 bucks. Oh well....

Thanks a bunch

PS
If anyone comes up with a heavy duty/cycle capacitor, let me know.

 

[Tig]

Here are some motor diagrams. One shows a three leg cap but it is not wired as yours is. Leeson Single Phase Electric Motor characteristics and applications
Pictures of your motor spec plate and the cap would help. It sounds like you may not have the original cap on this motor.