Air compressor motor capacitor

[Charles in Aus.]

I've been given a really nice Italian made Fiac air compressor that has a defective 60uf capacitor .

There is an obvious bulge in it and the motor will sit and hum until the fan is helped to move . When this is done the motor will spin in either direction .
It is easy to replace , only two connectors and one mount bolt . So when ordering a replacement do I need a start capacitor or a start / run capacitor or are they basically the same thing ?

 

[dr sportster]

Just go by the microfarads that is all you need . The difference is the microfarad range of the caps . Start and run have different Uf specs of two differing ranges. Sellers also separate
the two categories .

 

[dr sportster]

Your 60uf cap is a start type the range of start caps 50--1200 uf the range of run caps is 15-50.

 

[MarkB_MI]

Start capacitors are for intermittent duty, while run capacitors are continuous duty. So you should be able to use a run capacitor in place of a start capacitor but not vice-versa. A run capacitor will be physically larger than a start capacitor of the same capacitance.

When I look up 60 µF capacitors on Grainger, they all seem to be run caps.
60 uF caps

 

[Charles in Aus.]

Thanks !
All I need to know I suppose .
I'm really pleased with it , but of course haven't run it for very long yet . Local electronic shop only carries up to 30uf so I will have to be patient and order one .
The compressor after I cleaned it up a little .

 

[buickanddeere]

(quoted from post at 20:39:59 06/25/21) I've been given a really nice Italian made Fiac air compressor that has a defective 60uf capacitor .

There is an obvious bulge in it and the motor will sit and hum until the fan is helped to move . When this is done the motor will spin in either direction .
It is easy to replace , only two connectors and one mount bolt . So when ordering a replacement do I need a start capacitor or a start / run capacitor or are they basically the same thing ?

As long as the voltage rating is 370V or higher . The capacitance should be 60uf or higher .
Contrary to what some people think here . A 600uf start capacitor is entirely acceptable . No drawback and the motor will start faster and with less current .

 

[bc]

(reply to post at 19:39:59 06/25/21)

You might check with an HVAC supply and get one or at least get one that is close such as a 45 uf or more or get 2 or 3 caps that add up to 60. A start/run cap will have 3 sets of terminals on top, 1 for start, 1 for run, and 1 for the common/ground. You could probably get a start/run cap and just use the terminals for the one with the higher capacitance. Probably can find one off of an old junk air conditioner that may be good. You can hook capacitors up in parallel as long as they total up to at least 60 uf or so and are of the necessary voltage which most will be.

An old HVAC trick when compressors are starting to go bad and pulling more amps, then they add a big jump start capacitor to the start side to get it started faster without pulling too many amps and kicking out your breaker. Those aren't too expensive starting around 12 bux or so. Also called boosters and hard start kits. They wire in at the same terminals as the regular start cap. Whenever you have a motor that hums and starts slow then stick a jump start kit in there and off you go.

Have trouble waking up in the morning? Just put a jump start kit by your bed and touch the terminals on the cap. That will give you a jump start in the morning. Just kidding/don't do this at home kids.

Just remember to short across any capacitor with an insulated tool to make sure they are discharged. That jolt can put a burn on your finger and you will feel the pain. A heart defibrillator has capacitors in it that discharge when switched on.

 

[M-MAN]

Where did you get the 60uf? It's not
showing on the label. Looks way too
small to be a 60.

What caught my eye is it looks exactly
like the capacitors I used to change
regularly at work on jacquard heads.
Same name, shape, color and looks to be
the same size. They were 20. I changed
hundreds of them because some engineer
goofed. The kits I installed had a
mounting plate with a provision to screw
in two for a total of 40.

 

[buickanddeere]

60hz not 60uf

This post was edited by buickanddeere on 06/26/2021 at 10:12 am.

 

[buickanddeere]

Go though the 370V capacitors and install the highest uf that will fit under the cover.

 

[Steve@Advance]

Being the application is on a compressor, which will have a high start load, it is likely a start
cap.

But 60uf is a really low number for a start cap, that is more inline with a run cap. Have you tried
to look up the part number on the old cap?

Any information on the motor? A wiring diagram, a model number you can look up?

A start cap is not real picky about the uf, as long as the voltage is higher than what the motor
operates at, a higher uf will give it more kick.

But a run cap needs to be sized correctly or the motor will overheat or be under powered.

 

[Charles in Aus.]

So the discussion has raised doubts as to the value of the capacitor . It only has two contacts so I'm assuming it is a start capacitor as has been explained to me .
The label has disintegrated and there are no other markings on the canister . The parts manual I thought was for it is for a smaller model the supplier has made an error in their site so i cant rely on its information .

The specification plate on the motor does mention 60uf though .

So is it a safe bet to replace the defective one with a 60uf start capacitor ?

 

[guido]

Charles in Aus,

Start capacitors are usually mounted on
the top of the motor.

The two on this one are under the covers,
and look like the one that I put in between
them. They are dry start capacitors.

Yours is an electrolytic capacitor, and
yes you can replace it with one of the
same capacity.

If you need to use two to get to 60 you
can use two, and they are used in parallel
to add the capacity, voltage will stay the
same,

Guido.

 

[deanostoybox]

If it is supposed to be a run capacitor and you replace it with a start capacitor just don't be close by when you turn it on.

 

[Charles in Aus.]

I will try and ring the local agent for Fiac again on Monday . Hopefully I can speak to someone who knows what they are talking about this time . Last contact sounded like he was playing video games at the same time as answering the phone .
Besides that it seems that 60uf is the most likely candidate , thanks to all for your advice . I will report back
once it's installed and hopefully the machine works properly .

 

[MarkB_MI]

I think the motor markings are pretty conclusive evidence it needs a 60 &mic;F capacitor. And since it doesn't have separate start and run caps, I'm inclined to believe it's a run capacitor. As I noted previously, I don't see any 60 &mic;F start capacitors and you can safely replace a start cap with a run cap.

If it is, in fact, a start capacitor there will be a centrifugal switch mounted in the end of the motor.

The stud mount isn't common, but I see plenty of 60 &mic;F stud mount capacitors online so you shouldn't have much trouble finding one.

 

[M-MAN]

Motor plate clearly shows a 60uf is
required. An internet search for the
60uf stud mount capacitor shows plenty
of them and many specifically for the
little compressors. Any 60uf run cap
will work but the stud mount will make
it easier.

Stud mount capacitors were used
extensively in Italian, French,and
German industrial machinery. The British
used them also.

 

[John T]

Charles, NO they typically are NOT the same thing.........I would suggest replacing with a capacitor of the same rating (Uf and voltage)
regardless of what it may be called. What you describe makes me think the problem may be EITHER A capacitor orrrrrrrrrrr A start
winding,,,,,,,orrrrrrrr A centrifugal start switch problem, yet due to the capacitor you show obviously more like a capacitor problem, try
that FIRST

In a typical single phase split phase motor........... If everything is in place and working correctly a START capacitor (If so equipped)
and start winding are both in place ONLY TEMPORARY for start up until such time the centrifugal switch opens taking BOTH out of the
circuit. If they were to remain in place and it had a START capacitor (say the centrifugal switch failed to open) it and the start winding
could overheat and be damaged. If the centrifugal switch failed to ever close any START capacitor (if so equipped) or start winding
wouldnt be in place and the motor would sit there and hum and not start until you manually gave it a good spin in either direction.

Ive seen non capacitor single phase motors, capacitor start motors, capacitor start and capacitor run motors, capacitor run but I hesitate
to say from here what you have.......

Heres is a good place to get help and purchase motor capacitors or other related equipment

https://www.grainger.com/?gucid=N:NSaid:MS:CSM-
2296:8DK268:20500731&ef_id=973438806bc617920ad75858166520fe:G:s&s_kwcid=AL!2966!10!79508582020848!62050107369&gclid=973438806bc617920ad7585
8166520fe&gclsrc=3p.ds&msclkid=973438806bc617920ad75858166520fe

DISCLAIMER its been yearssssssssss since I was an Electrical Engineer at the Century Electric Motor Company so noooooooooooo warranty on
any of this, things have changed......

Best wishes be safe be happy

John T
Graingers

 

[Charles in Aus.]

I managed to speak to a technician from the air compressor agent today .
It is a start/run capacitor and it is 60uf .
I've ordered one that should be here in a few days, I'll post a follow up..

 

[buickanddeere]

A three terminal cap is popular on air conditioning . Rather uncommon with open frame AC induction motors .