Replaceing a motor starting capacitor in a 1hp single phase motor.

[acrosteve]

I am rebuilding the 1hp Dayton motor on my 1917 SB, and want to replace the capacitor. Is is a 540-648 uf 110v capacitor.

I can find one of those, but the capacitance range was a little surprising to me. I am used to seeing specific values, not a range.

But, I can more easily find a replacement cap that is 600uf.


Are there any specific reasons why the fixed value cap would not work?


I would prefer to get everything from one source, and surprisingly, Amazon has both bearings and a 600uf cap in stock at pretty decent prices. I would not have looked there, but google turned up a result.
MSC has a good price on one of the bearings, but they are sky high on the other.


Thanks

 

[L Vanice]

Maybe 540-648 is another way of saying 594 +/- 54. I find eBay is a good source of new ball bearings and capacitors. And yes, I have been surprised to find things on Amazon that I had not expected. Larry

 

[Bill D]

Not sure why the odd value but it is almost 600 +/- 10 %.
Bill D.

 

[9100]

A motor starting capacitor just has to get the armature turning the right direction. Starting capacitors with a wide tolerance are common. It is mostly a cost reducing measure, just as a wide tolerance in a machined part usually reduces cost. Note that running capacitors are better quality and to tighter specs because they are in the circuit all the time the motor is running while starting capacitors are only connected for a few seconds and just give the motor a kick. They need to be about as accurate as the pull on a starting rope you use to start your lawnmower.

Bill

 

[Anvil Jenkins]

And if there is nothing WRONG with the existing one...I might buy a SPARE but keep using the OEM one, maybe of higher quality than many import ones avail now ??

Bill

 

[sticks]

Think of start caps like carbon resistors, where the 'range' in this case amounts to a 10% tolerance. I managed to crush a dangling start cap when setting up my big mill's head & didn't want to wait for mail order to get 'er up & running. Grainger isn't like other supply houses here (MESCO, Mid-States Bolt) with a its formal sitting room & a counter vs those who are more open and will let you walk into the back with a counterman once in a while.

Stopped by an electric motor shop in town & was surprised to find the price for 110v 400mfd like the online sources. The guy was confused as to my intentions and knowledge of what value was needed till I showed him the original. These aren't really hen's teeth & it's rare to pay a whole 10 bucks for one wherever you find them. That said, depending on how big or not your town is, and who's local, you might find one just around the corner.

Your source will want to know the usage planned for, as these are non-polarized and use-specific. What I've been surprised to learn is that 220v motors typically use a 110v cap, and 440v a 220. Maybe that's an Asian thing, but someone here can explain the reason better than I can. 110v is the smallest rating I've seen, & matching a motor's higher voltage may get you one that's too large for its OEM enclosure. btw: This is an easy fix & often why otherwise-good 1ph motors can be had for a song.

 

[sticks]

Geez, how do you get a double-post without 'leaving a page'...????

 

[acrosteve]

And if there is nothing WRONG with the existing one...I might buy a SPARE but keep using the OEM one, maybe of higher quality than many import ones avail now ??

Bill

I am restoring my 1917 SB and got to the point of checking out the motor before mounting it. Well, it did not do so well. It looked like it was definitely turning slower than 1,700 rpm and it was making a bad sound. It could have been the centrifugal switch, but I did squirt some contact cleaner on and around it and tried it again, but it still sounded sick.

So, I did what I do - took the damn thing apart.


I did not really check the existing capacitor, but I figure if I got the motor apart, I am going to put in new bearings and a cap.

Since my initial post, I did find some Dayton brand caps on ebay for <$10 with free shipping. While I would prefer to get it all from one place, I will probably just go with the best individual options.

I figure i will spray the centrifugal switch with some dry teflon lube.


Thanks for the good discussion - makes sense.

 

[Anvil Jenkins]

I am restoring my 1917 SB and got to the point of checking out the motor before mounting it. Well, it did not do so well. It looked like it was definitely turning slower than 1,700 rpm and it was making a bad sound. It could have been the centrifugal switch, but I did squirt some contact cleaner on and around it and tried it again, but it still sounded sick.

So, I did what I do - took the damn thing apart.


I did not really check the existing capacitor, but I figure if I got the motor apart, I am going to put in new bearings and a cap.

Since my initial post, I did find some Dayton brand caps on ebay for <$10 with free shipping. While I would prefer to get it all from one place, I will probably just go with the best individual options.


Thanks for the good discussion - makes sense.

If the switch is staying "closed" all the time, it will exceed the duty cycle of the cap, and the cap can go "BOOM"(result is a hatfull of tinfoil confetti and a shattered plastic case of the cap)....I have seen them do it on start/run cap phase converters where the relay contacts welded shut. Start caps are only made to run a short time, that is how they are 10x to 20x the mfd of a run cap, all about duty cycle :-).

Bill

 

[acrosteve]

Well, I only ran the motor less than 30 seconds at a time while it was on the tailgate of my truck. Heck, the cap is probably good, and all the trouble was in the swtich, but while I have it apart, I might as well replace the parts.
If i had a megger, I would check that out too.


The motor is an aluminum Dayton, I am unsure of the age. I suppose it is worth putting $35 into.

I figure I will chuck of the armature in my other lathe and give it a spin to check the switch. Wonder at what RPM it should kick in?

 

[atomarc]

"Kick out"! The switch is closed at rest and opens on speed taking the start cap out of the circuit. Don't know what speed that happens at though...as long as it happens it ain't too critical.

Stuart

 

[Duak]

Sticks asked why a 115 V cap was used with 115/230 V motors. Like most things it's to save money by taking advantage of something or other. Most dual voltage motors have two 115 V run windings and one 115 V start winding.

For 115 V the run windings are wired in parallel to the line with the start winding thru the centrifugal switch and start cap.

For 230 V the run windings are wired in series. The circuit node where the two windings connect to each other and not to the line is at half the line voltage ie. 115 V. IOW, the run windings act as an autotransformer and step down the line voltage. This node connects to the start winding thru the centrifugal switch and start cap. The current thru each run winding is probably not the same, but for the time it takes to start the motor it shouldn't make one whit of difference.

Hope I'm making sense,

Cheers,

 

[9100]

Sticks asked why a 115 V cap was used with 115/230 V motors. Like most things it's to save money by taking advantage of something or other. Most dual voltage motors have two 115 V run windings and one 115 V start winding.

For 115 V the run windings are wired in parallel to the line with the start winding thru the centrifugal switch and start cap.

For 230 V the run windings are wired in series. The circuit node where the two windings connect to each other and not to the line is at half the line voltage ie. 115 V. IOW, the run windings act as an autotransformer and step down the line voltage. This node connects to the start winding thru the centrifugal switch and start cap. The current thru each run winding is probably not the same, but for the time it takes to start the motor it shouldn't make one whit of difference.

Hope I'm making sense,

Cheers,

Quite so. The voltage applied to the starting winding is about the same either way. If the motor runs, but very slowly, Wrap a cord around the shaft and give it a good pull after or simultaneously with turning on the power. If it spins up to speed, the probability is that the contacts are dirty or fried, the capacitor is bad, or the starting winding is open. Check the contacts first. They should be closed at rest and open when the centrifugal mechanism operates them.

Somewhat OT, many years ago I took an oath to never run a lathe with a single phase motor again. If you have to, have a separate start/stop switch positioned so you can slap it. Have the reversing switch separated. If you reverse a three phase motor while running, it will come to a stop and then accelerate in the other direction, unwinding the necktie you have been so foolish to be wearing, or at least giving you time to get the switch back to the off position. If you have a reversing drum switch on a single phase motor and hit it too hard, the motor just keeps going the same way.

Bill

 

[atomarc]

So the moral of the story is...only wear a necktie if you have three phase as your disposal! Good thing to keep in mind.

Stuart

 

[acrosteve]

Good info.

I put the armature in my lathe and verified that that part of the switching mechanism is working. However, I did find that the actual switch is acting flakey. I cleaned it up the best i could without taking it apart. It did improve, but I am not convinced. I might check around with a local re-builder for a replacement.

Here is the motor nameplate


For those who have never seen inside.

Switch is on the left.


Here is the mechanism on the armature.

 

[adama]

My experience with most capacitor start motors, once the centrifugal switch fails it can be damn near impossible to find a replacement. Comes a point were a new motor is just less hassle. 1hp single phase motors are pretty cheep. Its even easier swapping motors on things like lathes, were they have nice adaptable motor mounts too.

 

[Anvil Jenkins]

My experience with most capacitor start motors, once the centrifugal switch fails it can be damn near impossible to find a replacement. Comes a point were a new motor is just less hassle. 1hp single phase motors are pretty cheep. Its even easier swapping motors on things like lathes, were they have nice adaptable motor mounts too.

Can you use the same relay you use to build a start/run static phase converter, I think it is a voltage sensing relay ??

Bill

 

[acrosteve]

Yea, I know 1 hp motors are considered disposable, but I am cheap. :lol:

I did a quick look for the switch on line and did not find anything.

I think I am just going to clean the contacts of the switch with some emery cloth, and slap it back together and see what happens.

 

[9100]

Yea, I know 1 hp motors are considered disposable, but I am cheap. :lol:

I did a quick look for the switch on line and did not find anything.

I think I am just going to clean the contacts of the switch with some emery cloth, and slap it back together and see what happens.

If you have the space, the way to clean these contacts is to cut a strip of about 400 grit wet or dry paper that is twice as wide as you need and fold it lengthwise. With the contacts open, slide the strip in between, then hold them closed and pull it out. Repeat as needed. That way you are forming parallel mating surfaces. I said that in another thread a while back and got the usual flak about conducting grit and all that, but I have been doing it since 1959 with no problems. Just be sure to blow the dust out.

Re neckties, that isn't a theoretical issue with me. On one job, I was in the engineering department and expected to meet the dress code, but working on machinery, not lathes, but custom production equipment powered by small motors driving bicycle chain. I was able to grab a shaft and stall a motor, but after the third time I got rolled up in a chain, I quit wearing ties. I don't care for clip ons and bow ties look silly on me, so I just wore white shirts with the collar open. That brought a lot of harassment from the upper rank, but my response was that their job wasn't getting hung for.

Bill

 

[acrosteve]

10-4. I had already done as you suggested, but not sure what grit I used. Just something I had laying around.


Got it all put back together last night and it works just fine with the original parts. So I went ahead and shot a coat of paint on it.

I had made an offer on an ebay capacitor, but the guy declined. And i am impatient and as mentioned previously, cheap. Once I determined it was the switch, I did not ahve many reservations about re-using the cap.

I am not surprised at the switch. Previous life of the lathe was spent in an extremely dusty shop at the limestone plant at my work. When the lathe was put into storage several years ago, someone did tape up most of the vents in the motor, but it still sat for a long time.

I hear you about a dress code. Some of those are enforced with little common sense.