start capacitor sizing

[acmebunny]

I need to replace a start capacitor on a 1.5 hp Emerson motor. My problem is there are no numbers on the capacitor to find a replacement. I contacted Emerson and the were not helpful. I have tried to find a formula to match a start capacitor to the motor with no success. I hope someone on this site can help me out. The specs from the motor data plate are as follows.


Emerson model ks63yzcgp-2232
CAT MC-82, HP 1 1/2, RPM 3450, SF 1.0, v 115/ 230,
hz 60, ph 1, code J, amps 22/11, amb 50 celsius,
TIME RATING cont, insul class A, sa no 22922
MFG No L74 7

Special Service class motor on a small 2 stage compressor.

Any help on what size capacitor or how to size one is appreciated

Thanks,

Drew Vance

 

[busbar]

I am ashamed to admit I know anything about this, but the Maytag repairman is my dad.

The start capacitor is likely rated at 110V, and the size only affects starting torque until a centrifugal switch opens up. For dual-voltage motors, the start circuit is served from one main/run winding—so it sees 115V whether 115- or 230V powered. Select a starting capacitor that has the same physical size as the old one. If the new one is of a lower rating, you’ll sacrifice some starting torque. If it’s larger, the start winding will run a bit hotter, but that’s usually only an issue for a few seconds.

 

[SteveKW]

160 mfd is the most common cap in that size of a motor.

 

[coingy]

Acmebunny,

For the custom fit method using busbars physical size method. First make available the capacitor leads and both sides of the start winding. Apply power to both the start and run windings with the rotor locked. The voltage across the capacitor and the start winding should be recorded. The voltage across the capacitor should be 10% higher than the voltage across the start winding when the right sized capacitor is used. The voltage should be read quickly as possible as the values will change as the windings get hot.
Hope this helps.
Cheers, Coingy

 

[acmebunny]

Thanks for all the info. However, I am still left somewhat confused. If I measure the case like Busbar suggest I get these dims, 4 3/8" L x 1 7/8 D. The lowest MFD for 115v I can find so far is around 400mfd in this case size. According to SteveKW post, the Cap should be around 160mfd. I also saw roughly this number on a woodworking bulletin board for a 3 phase 1 1/2 motor.

It is a very old motor I am working with, Mid to late 70's. Are any of the following scenario's possibe. The caps were in much larger casings for the mfd output back in the mid 70's? The moter MFG (Emerson) used a 220v rated cap? Or, A little motor like this one might just have a cap over 400mfd?

Thanks agian for any input.

Drew

 

[coingy]

Acmebunny,

It could have a capacitor of size up to 800 mfd.

Cheers Coingy