# Sizing starter capacitor



## JHFWIC (Mar 22, 2012)

Try this.
http://www.alpinehomeair.com/related/Emerson Motors - Capacitor Selection.pdf


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## nbsdsailor (Mar 22, 2015)

JHFWIC said:


> Try this.
> http://www.alpinehomeair.com/related/Emerson Motors - Capacitor Selection.pdf


I believe those are run capacitors. I am looking for a start capacitor. Thanks though.


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## wildleg (Apr 12, 2009)

I'd try a 7.5Mfd and see if it worked. otherwise lookup the parts for the furnace, it should be listed there. was the old capacitor bad ? (did you test it ?) are you sure about the rpm ?


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## nbsdsailor (Mar 22, 2015)

Yea I tested the cap. completely dead. It's a fan for a whole house attic exhaust fan, not a furnace.


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## nbsdsailor (Mar 22, 2015)

It is a old Kenmore Sears fan and it is listed as no longer available in the online manual. Kenmore part number 758.640770


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## dronai (Apr 11, 2011)

The 7.5 mf or smaller is probably a good size to see if it gets her rotating. Call Emerson on Monday , and ask in tech support to match for you. If it's too small, the motor will just hum.


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## tonysmac (Jul 10, 2015)

*Capacitor*



nbsdsailor said:


> Hi, I'm hoping I can find some help here. I have a fan that recently had the motor's starter capacitor fail. Unfortunately the capacitor is so old that when I tried to clean the dirt off it the specs came off as well and I have no idea how many microfarads it is. The motor is an Emerson model K5 5HXKWN-8586. single phase 120, 1/3 HP, 5.7 FLA, 525 RPM. I couldn't find a service factor so Id assume 1.0. I'd greatly appreciate it if anyone could tell me the size of the starting capacitor I would need. I tried to find locked rotor amps but it wasnt on the nameplate.


The capacitor you are looking for is a 15 MFD 330 volt run capacitor. I happen to own the same model fan.


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## telsa (May 22, 2015)

tonysmac said:


> The capacitor you are looking for is a 15 MFD 330 volt run capacitor. I happen to own the same model fan.


Fans in that horsepower range are typically Permanent Split Capacitor motors.

This means that the capacitor stays in the circuit all the time -- and hence Run Capacitors are used.

{ Strictly speaking, then, such a capacitor is not a 'start' capacitor. }

The 15 mFd 330 Volt run cap posted above (tonysmac) is exactly what one would expect.

&&&

The typical start cap will have a bleeding resistor installed across the terminals. (very high ohms)

The typical run cap won't. (Since it will bleed energy right into the windings, anyway.)

The typical start cap will have a range of capacitance values in its legend.

The typical run cap will have a single value -- followed by a plus or minus % figure.


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