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Thread: Delta 50-720 DC Startup Capacitor Rating

  1. #1

    Question Delta 50-720 DC Startup Capacitor Rating

    I need some help, folks. The capacitor on my 50-720 Delta dust collector melted down over the weekend. It is such a loss that I can't read any of the numbers on the can. I have searched everywhere on the machine, in the manual, the internet, and also called Delta. I can't find a mfd rating anywhere. I found another Chinese 1HP, 115V, 3500rpm motor that had a start capacitor with a 270 mfd rating, so I picked up a similar capacitor from Grainger. When I installed the capacitor, the motor would start, but wouldn't reach full RPM. If I left the motor to run, it would slow down until it popped the breaker.

    Anyone have any idea what start capacitor rating this thing uses? I would really like to avoid pulling the motor and taking it to a shop. The motor does work. Without the capacitor, I can give the motor a good spin, flip the switch, and it will start up. It takes an extra second or two to reach full RPM, but it does and will hold the RPMs.

    Many thanks.

    Regards,

    Ken

  2. #2
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    hp, voltage, rpm?

  3. #3
    Quote Originally Posted by Bill Dufour View Post
    hp, voltage, rpm?
    I think that's specified in his post (1HP, 115V, 3500 RPM)

    The only advice I can offer is to look at someplace like ereplacementParts.com and see if they list your model. If so, they may have information on the cap.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  4. #4
    Thanks Mike. Yes I was already on that website and others. No one stocks it, no on has pictures, no one has specs.

  5. #5
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    [QUOTE=Mike Henderson;2789611]I think that's specified in his post (1HP, 115V, 3500 RPM)

    I read that as the motor he borrowed a cap from. I have no idea if it is the same hp or not. The size of the cap will vary depending on motor hp and maybe rpm.
    Bill

  6. #6
    Both right. I got the cap specs from a motor with the same HP, RPM, volts, and amps as the one on my dust collector. I have read that too high of a MFD can result in the capacitor becoming part of the circuit when the motor is running. I am guessing that is what is happening. I could get a lower rated cap, and keep trying until one works. But I was hoping I might get lucky and someone will have replaced a cap on theirs or would be willing to look at the cap on their machine for me.

    Ken

  7. #7
    Quote Originally Posted by Kenneth Casper View Post
    Both right. I got the cap specs from a motor with the same HP, RPM, volts, and amps as the one on my dust collector. I have read that too high of a MFD can result in the capacitor becoming part of the circuit when the motor is running. I am guessing that is what is happening. I could get a lower rated cap, and keep trying until one works. But I was hoping I might get lucky and someone will have replaced a cap on theirs or would be willing to look at the cap on their machine for me.

    Ken
    The cap should be taken out of the circuit by the centrifugal switch once it gets to 50% to 70% of full speed RPMs. You might check your centrifugal switch and see if it's stuck. One "rough" way to check it is to start the motor without the cap by spinning it. Then turn it off and let it coast down. You should hear a distinct "click" as the centrifugal switch resets. If you don't, take the motor apart and clean the switch.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  8. #8
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    You will not only need to clean the switch contacts, but also the shaft and slide ring parts of the centrifugal mechanism that operates the switch. The switch itself is in the end case of the motor. The centrifugal mechanism is on the same end of the motor but on rotating part around the shaft. Two spring weights move a collar around the shaft as they swing out at speed. This collar slides on the shaft and pushes against the switch mechanism to operate it. Usually, the shaft needs cleaning and the application of a thin coat of light weight grease, like Lubriplate. Be careful to only apply a very thin coat, since excess will fly off when the motor spins.

    Charley.

  9. #9
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    Do modern motors still use mechanical start switches?
    Bill

  10. #10
    Quote Originally Posted by Bill Dufour View Post
    Do modern motors still use mechanical start switches?
    Bill
    If by "start switch" you mean the method of taking the starting capacitor out of the circuit when the motor is up to speed, then, yes, modern single phase induction motors still use a mechanical centrifugal switch.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  11. #11
    Thanks Mike and Charley. I finally had time this evening to pop open the motor. I could not find a centrifugal switch. I looked at each end of the motor and did not see anything on either end of the shaft. Attached are a few pics.

    IMGQ9892.jpgIMGQ9895.jpgIMGQ9896.jpg

    Thanks. Ken

  12. #12
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    Looks like you do not have a start cap. What you have is a run cap which will have very different, lower, value then a start cap.
    Your motor is a permanent split capacitor motor. It has a low starting torque but a fan is low torque to start anyway.



    The capacitance value of run capacitors is usually lower than the capacitance of start capacitors, and is often in the range of 1.5 F to 100 F. Choosing a wrong capacitance value for a motor can result in an uneven magnetic field, which can be observed as uneven motor rotation speed, especially under load. This can cause additional noise from the motor, performance drops and increased energy consumption, as well as additional heating, which can cause the motor to overheat.

    Read more http://www.capacitorguide.com/motor-starting-capacitor/
    Last edited by Bill Dufour; 03-22-2018 at 9:54 PM.

  13. #13
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    You have run capacitor motor. for one hp I would guess 10-15 mfd.
    Bill D

  14. #14
    Thanks Bill. After the motor ran at half speed with the new capacitor, I pulled the capacitor and would start the motor by giving the top fan a whirl then hit the start switch. It always built up to full RPM and held it. I have run it this way several times over the past week. If it didn't have a run capacitor at all, would it still run like it does?

    Ken

  15. #15
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    Quote Originally Posted by Mike Henderson View Post
    If by "start switch" you mean the method of taking the starting capacitor out of the circuit when the motor is up to speed, then, yes, modern single phase induction motors still use a mechanical centrifugal switch.

    Mike
    Mike, that's generally correct however I have some single phase machines that have 2 contacts in the start push button.

    One latches the run contactor, the other closes the start capacitor contactor that does not latch.

    Once the machine is up to speed you release the start button.

    Nice thing about that system is that you never have to take the motor apart to service the starting system.........Rod.

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