Substitute motor start capacitor?

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bluecar5556

Joined Jun 9, 2010
7
I'm working on a 120V window AC unit. I'm trying to add another fan motor. Since it drives both the condenser and evaporator fans, with a shaft coming out of both sides, I need to add another fan for the evaporator side. This is due to relocating the evaporator, evap fan inside my shop and leaving the noisy compressor along with condenser on top of my office in my shop.

It has a 6 uf dual start capacitor wired to the motor with a cap. Below is an image of the electrical diagram and the capacitor.


The cap is on backorder and don't really need a dual start capacitor, since i'll just be using it for the 6 uF portion to power the fan motor.

My question to you is will any 6 uF motor start capacitor work or are they special? Does anyone know where I can find a cap that will work?

The fan motor draws 40 watts, 0.5 A @ 115 V

The capacitor states 55/6 uF 5.6/0.6A
 

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MaxHeadRoom

Joined Jul 18, 2013
23,915
As posted on the other site.
For one, I would not use motor start or run capacitors made in China, they are known to fail early.
The two types are motor start and motor run rated, the start capacitors I buy are usually made by CDE (Cornell Dubillier) and are oil filled paper.
The start capacitors are solid electrolytic bi-polar motor start rated, and are not marked by polarity and only meant to be in circuit for a very short period.
Max.
 

MisterBill2

Joined Jan 23, 2018
9,810
If you are using a separate motor then you will need to use whatever value is specified for that separate motor. In addition, the capacitor for the fan motor in a window unit is a run capacitor, rather than a start capacitor. No start switch or relay.
 

moapys

Joined Feb 25, 2018
3
So - resurrecting (and slightly re-vectoring) this thread: When my garage opener "start" cap of ~55uF died, I had only electronics-style high-voltage axial caps available as emergency spares... A pair of polarized nominal 100uF/400v in series neg-neg yielded a 53uF <measured> non-polarized 'lytic.

Now for the question: At a fraction of the size of its predecessor (less foil, electrolyte-paste, etc), but arguably better voltage and ESR <1.2 ohm measured on bridge> specifications - do we anticipate that this pair will somehow have shortened life? I'd like to think that these good Sprague's would outlast the opener's factory cap - but are there heating/power-dissipation considerations? Ostensibly, not being a "run" cap, a "start" cap is in circuit only momentarily. ...'Thoughts?...
 

MaxHeadRoom

Joined Jul 18, 2013
23,915
Motor electrolytic motor start caps are non polarized, made with solid electrolyte for this purpose.
They can only be in circuit for short duration to avoid heating.
The motor is a PSC, Permanent Start Cap motor where each winding is identical.
If a N.A. replacement is used, you can usually expect a long life.
Max.
 

MisterBill2

Joined Jan 23, 2018
9,810
Many years back the blower on my dad's furnace would fail to start. My temporary fix was to add a string of electronic caps in parallel, a mix of0.47 and 0.1 mFd caps, rated at 400 and 600 volts working. That temorary fix lasted many years and never did fail. Eventually he bought a new hi efficiency furnace and so the blower went out to be a garage fan.
 

moapys

Joined Feb 25, 2018
3
Thanks for the responses, folks; it appears now to be a "science experiment": As this door is not my most used - I'd expect no more than perhaps a dozen operations per month... Once this de-polarized cap solution is run for awhile (or spews its innards across the garage), I'll be sure to let you know!
 
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