Any danger to running an AC motor without a run capacitor?

#12

Joined Nov 30, 2010
18,224
You are definitely from a different world than I. When the original design of the house has a single car parking space included as if it was just another large room, but with a garage door on it, it is essentially inside the house, give or take an 8 inch thick concrete block wall. However, I will concede that a floor plan that horrible can be hard to imagine. It seems akin to sleeping with the horse. Probably why the previous owner took out the garage door, blocked up the hole, and subdivided the space into 2 bedrooms.
 

ian field

Joined Oct 27, 2012
6,536
May be wrong in this answer, but, are you sure the capacitor is a "run" capacitor? Most small AC motors use a "start" cap not a run cap. And manually turning the shaft to get it to run makes it sound more likely that it is a run cap.
If it was a start capacitor - the motor wouldn't start without it, usually just sits there humming till the magic smoke comes out.

You can give it a shove, if it starts running, it should run normally.
 

Hypatia's Protege

Joined Mar 1, 2015
3,228
You are definitely from a different world than I. When the original design of the house has a single car parking space included as if it was just another large room, but with a garage door on it, it is essentially inside the house, give or take an 8 inch thick concrete block wall. However, I will concede that a floor plan that horrible can be hard to imagine. It seems akin to sleeping with the horse. Probably why the previous owner took out the garage door, blocked up the hole, and subdivided the space into 2 bedrooms.
Then too it's a matter of "to each their own" -- I've no doubt that I take chances that certain others regard as failing the 'risk vs benefit test' --- That said, 'attached garages', comfortable and convenient though I'm certain they are, inspire me with the 'heebie-jeebies' -- on fire safety grounds alone... Then there are the petroleum distillate and combustion product fume issues:eek:

Best regards
HP
 

#12

Joined Nov 30, 2010
18,224
on fire safety grounds alone
I did once sell a car which committed suicide a few weeks later. It lit itself on fire and burned to the ground with the owner inside the house and unaware.:(
Uncommon as that is, the consequences seem to high to place the bet. That's why I keep my flammables in the shed.

One of my mottoes: If you keep accepting a percentage chance of getting killed, the odds will eventually pay off.
 

shortbus

Joined Sep 30, 2009
10,045
If it was a start capacitor - the motor wouldn't start without it, usually just sits there humming till the magic smoke comes out.
Are you sure about that? I've had single phase motors with bad start caps that would start by spinning the shaft and then applying power. One that was on a bench grinder I did that for years, spin the wheel and flip the switch = running.
 

ian field

Joined Oct 27, 2012
6,536
I did once sell a car which committed suicide a few weeks later. It lit itself on fire and burned to the ground with the owner inside the house and unaware.:(
Uncommon as that is, the consequences seem to high to place the bet. That's why I keep my flammables in the shed.

One of my mottoes: If you keep accepting a percentage chance of getting killed, the odds will eventually pay off.
There's plenty of Darwin Award qualifiers around that haven't claimed their prizes yet.
 

Thread Starter

MrSoftware

Joined Oct 29, 2013
2,188
If it was a start capacitor - the motor wouldn't start without it, usually just sits there humming till the magic smoke comes out.

You can give it a shove, if it starts running, it should run normally.
It must be for combined starting and running. When I plug it in, all it does is hum. If I give it a spin, it very very slowly speeds up, but never reaches full speed. By ear, I'm guessing 50-75% of full speed.

As for the gas in the garage; the gasoline storage is outside, but anything with a gas tank will emit fumes, even when the tank is empty.

I'm not up north, I'm down in S. Florida. You can't really store any equipment outside in a shed, or it will be a useless pile of rust long before its service life should be up.
 

Hypatia's Protege

Joined Mar 1, 2015
3,228
If I give it a spin, it very very slowly speeds up, but never reaches full speed. By ear, I'm guessing 50-75% of full speed.
Given a 'spin' following application of power, a single phase motor might attain full AV under load if the bad cap has been removed from the circuit...:)

Best Regards
HP
 

Thread Starter

MrSoftware

Joined Oct 29, 2013
2,188
The problem was definitely the capacitor! The new one arrived yesterday, and now the fan accelerates super fast and spins faster than I've heard it spin in a long time, it must have been failing for a while. Here are some images of the dead cap. It looks like the cap failed catastrophically, but the potting contained it all. Notice the melted plastic that erupted out the side:



cap1.JPG cap2.JPG cap3.JPG
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Be interesting to know the composition, I suspect it may be Bi-polar electrolytic which tend to run warm when used continuously on AC.
Oil filled paper are the preferred type for this.
Max.
 

Thread Starter

MrSoftware

Joined Oct 29, 2013
2,188
I can hack it open and see what I can find. It was in service basically 24/7 for about 8 years in ambient temps between 60-98F, probably mostly in the 80's (S. Florida garage).
 

ian field

Joined Oct 27, 2012
6,536
I can hack it open and see what I can find. It was in service basically 24/7 for about 8 years in ambient temps between 60-98F, probably mostly in the 80's (S. Florida garage).
You could probably replace it with a PFC capacitor from a fluorescent light fitting - but it probably won't fit the original space, and you may have to parallel more than one to make up that much capacitance.

Disregard any talk of electrolytics, bipolar or otherwise - you know those little party poppers that you pull a string to make them go bang and shoot a spiral of paper across the room.............................
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
They are obviously used for starting larger motors but when using bi-polar electrolytic in an AC circuit the maximum current is a concern for continuous operation.
For the OP's motor, there is no more than 1.5amps for both windings.
Max.
 

ian field

Joined Oct 27, 2012
6,536
They are obviously used for starting larger motors but when using bi-polar electrolytic in an AC circuit the maximum current is a concern for continuous operation.
For the OP's motor, there is no more than 1.5amps for both windings.
Max.
When I was a kid, someone gave me an old regen valve radio. It eventually got too damaged so I took it apart to see what's in it.

In the bottom of the cabinet was a big heavy slab, which turned out to be a flattened massive roll of thin metal foil and waxed paper.

Back then I had no idea what it was, but its obvious it was the main HT smoothing/reservoir cap. Values around 8 - 16uF were typical in those days, but from the sheer size and weight of it I'd guess a fair bit more.
 
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