Electric motor capacitors

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Harold_V
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Electric motor capacitors

Post by Harold_V » Fri Dec 28, 2018 4:33 am

Several years ago I spotted, on ebay, a Rotron blower. I had no clue what that meant, but the price was right (less than $100), and I was willing to bid. It was new, but appears to have been mounted and removed from some project. A little scratched paint around the bolt holes, otherwise perfect. I got the blower (there were no other bids). It's a Rotron Model DR 202 Y9. They're known as a regenerative blower, and are highly precision balanced and silent in operation. It operates with a relatively quiet high pitched whistle, but not much more noise, and I discovered that they're VERY proud of them. https://www.rotronstore.com/category-s/1715.htm

I bid with the idea of using the blower for an air source for a melting furnace that I have yet to build. I put it to use when I anodized the face plates for the lighting system for the house Susan and I built, and it ran without issue. That was about four years ago. I was reorganizing my shop and thought I'd see how it ran, having sat for several years. I was not pleased to find it wouldn't start. I took note that the armature was hunting back and forth a little, and humming, although not very loud. With that observation, I gave the fan a nudge in the proper direction and it started right up, albeit slowly, as it always did. The motor appears to not have a starting winding (it's 120 volt single phase, 60 Hz), as it lacks the familiar click when the starter switch opens, and there's no noise when the motor slows down upon being turned off, as if the starter switch engages. The motor, once up to speed, runs as I recall it did when I did the anodizing. I ran it for a few days at that time, all without issue.

Thinking that the capacitor isn't functioning, I removed it. It does not hold a charge, and has no continuity. That may be due to an open condition of the apparent internal fuse. The capacitor is marked as having been provided by Baldor, their number 61301. It is marked as 6 MFD 370 VAC 60 Hz. Below that information it says Protected 5AFC, with a notation below that line that says 8212. I am aware that bad electrolytic caps have a tendency to bulge, and this one does.

Considering the motor runs fine once up to speed, and that it won't start without assistance, I'm inclined to think the cap is a starter cap. But is it? I dunno. I understand electricity just enough to be dangerous.

Anyone care to lend their thoughts on this matter? And--does anyone have a source for such a cap? I spent a couple hours scouring the net and had no luck, although I have found similar caps, minus the assumed internal fuse.

Thanks for any guidance you may be willing to provide.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

RMinMN
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Re: Electric motor capacitors

Post by RMinMN » Fri Dec 28, 2018 6:47 am

Capacitors in motors are used as phase shifters so the motor will start and run the proper direction. They can be used just for starring the motor or for continuous running. Ones used for starting are usually much higher capacitance that what you have so I would suspect yours is intended for continuous running. The smaller capacitor will give a smaller phase shift so you would get a slower start. I'd probably just use a capacitor with the same rating and not worry about the internal fuse that may or may not be present in the one you have.

rrnut-2
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Re: Electric motor capacitors

Post by rrnut-2 » Fri Dec 28, 2018 8:33 am

More than likely the capacitor is bad. If you can't find one, I can get one for you. We used those Rotron blowers in the foundry for liquidizing the sand beds. They will put out a lot of air. The ones that we had though were 3 phase. And yes, they are proud of them!

Jim B

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SteveHGraham
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Re: Electric motor capacitors

Post by SteveHGraham » Fri Dec 28, 2018 9:14 am

A capacitor shouldn't have continuity. It's made of two conductors separated by a space full of something that doesn't conduct. It can be used to store electrical energy in the form of static electricity. When you shuffle your feet on carpeting prior to touching a metal doorknob, you're turning yourself and the doorknob into a capacitor.

You can get a meter that checks capacitance. I got a Chinese job from Ebay for something like ten bucks, and it works very well.

If the motor will run after you push it, then the run cap must be working, so my guess is that the starter cap is done.

I have found Amazon to be a pretty good place to look for motor caps. They typically list external dimensions as well as capacitances. If you look for a bargain on Ebay, make sure the capacitor is physically the same size as the one you removed, and check the voltage rating as well as the capacitance. You should be able to get something for ten dollars or so.

Start caps are bigger than run caps.

I found a nice page that explains things.

http://www.capacitorformotor.com/starti ... citor.html

By the way, I stayed at a Holiday Inn Express last week.
Every hard-fried egg began life sunny-side up.

TomB
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Re: Electric motor capacitors

Post by TomB » Fri Dec 28, 2018 11:35 am

Given you use to hear a click as speed wound up and down and that it sat for 4 years I suggest that the centrifugal swithc might be stuck on the shaft. I have several in that state.

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SteveHGraham
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Re: Electric motor capacitors

Post by SteveHGraham » Fri Dec 28, 2018 12:46 pm

Or maybe Harold was better at hearing clicks 4 years ago.
Every hard-fried egg began life sunny-side up.

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BigDumbDinosaur
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Re: Electric motor capacitors

Post by BigDumbDinosaur » Fri Dec 28, 2018 1:25 pm

TomB wrote:
Fri Dec 28, 2018 11:35 am
Given you use to hear a click as speed wound up and down and that it sat for 4 years I suggest that the centrifugal swithc might be stuck on the shaft. I have several in that state.
Please re-read Harold's original post. He said nothing about the motor having a starting switch.
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John Hasler
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Re: Electric motor capacitors

Post by John Hasler » Fri Dec 28, 2018 1:34 pm

If there is only one capacitor and it is 6 mfd it is most likely a run capacitor. Blowers don't usually need start capacitors because of the very low starting torque. It should read open circuit but the needle on your VOM should move off zero more slowly than it does when you touch the probes together. That can be hard to see with a VOM and a 6 mfd cap, though.

Capacitor-run induction motors will run with no capacitor if you spin them up though they may not develop full torque.
If you spin them up backwards they will start and run that way.


The capacitor is almost certainly bad. Replace it. Just find a 6 mfd 370 VAC cap that will fit.
Last edited by John Hasler on Fri Dec 28, 2018 1:36 pm, edited 1 time in total.

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BigDumbDinosaur
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Re: Electric motor capacitors

Post by BigDumbDinosaur » Fri Dec 28, 2018 1:36 pm

RMinMN wrote:
Fri Dec 28, 2018 6:47 am
Capacitors in motors are used as phase shifters so the motor will start and run the proper direction. They can be used just for starring the motor or for continuous running. Ones used for starting are usually much higher capacitance that what you have so I would suspect yours is intended for continuous running. The smaller capacitor will give a smaller phase shift so you would get a slower start. I'd probably just use a capacitor with the same rating and not worry about the internal fuse that may or may not be present in the one you have.
It sounds as though this motor is using a single capacitor to produce the starting and running phase shifts. The capacitor's 6 µF rating is enough to induce some rotation at startup, which is practical, since a blower is essentially a loadless start. However, it's definitely a low-torque startup, so a loss of capacitance would be consistent with the symptoms described by Harold.
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Harold_V
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Re: Electric motor capacitors

Post by Harold_V » Fri Dec 28, 2018 4:37 pm

SteveHGraham wrote:
Fri Dec 28, 2018 9:14 am
A capacitor shouldn't have continuity. It's made of two conductors separated by a space full of something that doesn't conduct. It can be used to store electrical energy in the form of static electricity. When you shuffle your feet on carpeting prior to touching a metal doorknob, you're turning yourself and the doorknob into a capacitor.
I understand the basics of a capacitor, and I'm aware that they don't have continuity, but those I've checked will generally behave as a conductor, albeit briefly, while the capacitor is charged. Once charged, yeah, no continuity, but it will then display voltage, with the meter slowly falling as the charge dissipates. I use an old analog meter (a Triplett) and that has been consistent with several caps, save for this one.
snip

If the motor will run after you push it, then the run cap must be working, so my guess is that the starter cap is done.
It has but one capacitor, thus my question about its purpose. I'm not smart enough to know for certain, but logic told me it was for starting due to its behavior.
I have found Amazon to be a pretty good place to look for motor caps. They typically list external dimensions as well as capacitances. If you look for a bargain on Ebay, make sure the capacitor is physically the same size as the one you removed, and check the voltage rating as well as the capacitance. You should be able to get something for ten dollars or so.
Thanks for that thought. I'll turn to that when I next address the issue. Right now it isn't needed, but I'd like to put it away knowing it's functional. It's a wonderful device, one I'm happy to own.
I found a nice page that explains things.

http://www.capacitorformotor.com/starti ... citor.html
Thanks for the link. I'll give it a go as quickly as I'm finished with my daily review of the board.
By the way, I stayed at a Holiday Inn Express last week.
I didn't. I stayed home. Want to give me a clue what the significance of that comment is? I'm slow picking up pretty much anything that isn't real obvious. Sort of a black and white person, if you haven't already figured that out. :-)

H
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Harold_V
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Re: Electric motor capacitors

Post by Harold_V » Fri Dec 28, 2018 4:50 pm

Jim,
Thanks for your offer to provide the cap. It is appreciated, and in keeping with your willingness to help.

From all indications, I should be able to source something that works without intruding on your generosity---reserving that option for the next time I'm at an impasse.

I really appreciate the comments that have been provided by you folks. I'm not secure in my assessments where electricity is concerned, so it's very helpful for me to read things that help guide me in my thoughts. I will get this issue resolved, and it will be because of the willingness to share that is found on this board. A great group of people, if I must say so myself.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

armscor 1
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Re: Electric motor capacitors

Post by armscor 1 » Fri Dec 28, 2018 5:09 pm

I bought good quality self healing Caps from a reputable electronics supplier for my ceiling fans, no more problems, steer away from the cheap imports, they just don't last.

I replaced my single phase motors on my 2 lathes, milling machine, drill press and compressor to 3 phase motors using VFD's, no more Cap problems.
The full load current on my compressor with single phase motor was 16 Amps, with 3 phase motor and VFD the full load current measured at input to VFD dropped to a mere 6 Amps!!!

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