Correct sizing for a start capacitor

[Jack Budak]

Hi everyone, I have an older unisaw that has a Rockwell 3 hp single phase motor. The motor model # is 83-651. I run the machine on 220 volts. The other day I tried to start the machine and the motor just hummmmmed. The blade moved but did not rotate. Everything I have read points to a bad start capacitor so I removed the capacitor and one of the 1/4'" spade terminals just pulled right out of the top of the capacitor. So now I know I need to replace it. My problem is that I cannot read one letter on the old capacitor. It had an old paper label that is 45 years old. Does anyone know what the MFD range for this application would be?

Thanks for any help! Jack

[Brent VanFossen]

Jack, I have no firsthand knowledge of this. However, doing a quick google search of "83-651 delta motor capacitor" turns up others who have had similar problems. Perhaps these threads will be useful to you:

http://www.woodworkingtalk.com/f12/3...acitor-155433/

http://forum.woodenboat.com/showthre...citor-Question

[Mark Bolton]

We had a start capacitor issue here a while back that many here helped on though we had the numbers for the capacitor, prior to asking here I had done a bunch of research and most everthing you will read will say that the actual size of the cap is specific to the motors design so there is no generic rating based on HP/KW. That said, I read several places and got it from a local motor shop that 80-110Muf/KW is a range many rely on. Our motor was a 5hp an had a 375Muf start capacitor on it. That is right at the 100/Kw given the motor is 3.72KW. Your 3HP would be in the 2.2KW range.

[Jack Budak]

Hi Brent, I saw the post at Woodworkingtalk. It was the same motor but the MFD 829-995. I am no electrician but it just seems to be really high. I am going to call Delta tomorrow and hope they have the answer. Thanks!

Jack, I have no firsthand knowledge of this. However, doing a quick google search of "83-651 delta motor capacitor" turns up others who have had similar problems. Perhaps these threads will be useful to you:

http://www.woodworkingtalk.com/f12/3...acitor-155433/

http://forum.woodenboat.com/showthre...citor-Question

[John McClanahan]

The way I understand it is the MFD number does not have to be an exact match. If it is a bit lower, the motor will start up slower. If it is a higher number, the motor will jerk more on start up. I'm sure there is a reasonable limit to how far off of the ideal MFD you can go.


John

[Jack Budak]

Here is the fix for my Rockwell (Baldor) motor model # 83651 3 hp single phase unisaw that I run on 220volt. Plugged the new cap in and it runs like a champ. Hope this helps somebody in the future.


start capacitor A-A35406-285S
260-311 MFD
250 VAC
50/60 Hz

[Russell Shelly]

Jack, your hopes have been realized. This is the exact answer I was looking for. I have the same motor and cannot read the MFD rating. You’ve helped me immensely. Thank you!

[Charles Lent]

OK, with the age of that original capacitor, you very likely need a new one. Not only the electrical ratings must be close to matching, but the physical size must match the original, or it may not fit that metal bulge on the motor where it is located.

Also, now that the motor is being serviced, be certain to clean the centrifugal switch that's in the end motor cover, and also assure that the plastic collar that the centrifugal flyweights move on the motor shaft before re-assembling the motor. These too, can cause the problem that you are having. The contacts are sprung together and opened when the motor reaches about 1/2 of it's operating speed. They close again as the motor slows, to be ready for the next start-up of the motor. The contacts frequently pit badly. File off the high spots and get the contact shape back to about normal and it will be fine. A jeweler's file is the best way to do this. Then wipe a very thin layer of machine oil or Mystery oil on the shaft where the plastic ring slides, not much, because you don't want it flying off as the motor spins. If this area of the shaft is rusty, clean it up before oiling too.

So, three things can cause your motor to fail to start correctly. Make certain that you take care of all three before putting your motor back together. Maybe new bearings would be a good idea too. The bearing number is etched into the side caps of the bearing. They are a common bearing, readily available at bearing specialty houses, all of the industrial suppliers like Grainger. Even Fastenal has them. An electric motor shop can handle the job at reasonable prices and even provide the new bearings. Rebuild it once and you likely won't ever need to work on it again in your lifetime.

Charley

[Bill Dufour]

Note it is easy to add leads to a cap and locate it at a distance to make things fit.
Bill D

[Mike Henderson]

OK, with the age of that original capacitor, you very likely need a new one. Not only the electrical ratings must be close to matching, but the physical size must match the original, or it may not fit that metal bulge on the motor where it is located.

Charley

I had a situation where the starting cap failed on a Chinese motor. When I went to purchase a replacement, all of the caps of the proper MFd were physically too large. Maybe that's why the original failed.

So I did what Bill D. mentioned: I attached wires to the cap and attached it on the motor with zip ties. I made sure to cover the contacts on the cap so no one could get shocked. It was about the only way to fix the motor.

Mike

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