Permanent-split capacitor motor question

Discussion in 'The Projects Forum' started by ipanos, Jan 6, 2015.

  1. ipanos

    Thread Starter Member

    May 7, 2010
    12
    0
    Hi all,

    I have a question about a motor I own, which came from a pump and I am planning to reuse on a wood lathe.

    Trying to identify the type of motor, I believe it is a permanent-split capacitor motor. Please verify that if possible based on the following images:

    http://oi58.tinypic.com/23so7q.jpg
    http://oi58.tinypic.com/xbeo48.jpg
    http://oi61.tinypic.com/2ey80u9.jpg
    http://oi61.tinypic.com/10dys5h.jpg

    The motor is rated to operate at 2800RPM, 1Hp. I am trying to figure out whether there is a reasonably efficient way without sacrificing too much torque to control the RPM, especially close to the rated RPM (i.e. 70-100% of the rated 2800RPM). Also, is it possible to soft start this type of a motor?

    Thank you in advance for any contribution.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,566
    2,379
    Very difficult to vary the RPM of 1ph induction motors, there are some VFD's out there for 1ph motors that have permanent run cap style in place, but split phase motors have a reputation for dropping out of run when loaded at low rpm.
    You may be better off to look for either a DC T.M. motor and controller or use a 3ph motor with VFD.
    Max.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    KB Electronics makes a series of variable frequency drives called KBVF :http://www.kbelectronics.com/Variable_Speed_AC_Drives_Inverters/AC_Drives_Chassis.html

    It is claimed that they are suitable for PSC motors. I had a PSC motor that I wanted to control and noticed some fine print in the manual that said the KBVF had to be factory re-programmed to run PSC motors. I have used KB drives for many years for both DC and 3-phase, so I called. They will not send you a programmed chip nor let the user do the programming. Minimum order was 100 for the PSC version. You can try a triac controller (aka light dimmer). Harbor Freight has an inexpensive one. But, they don't work well. For one thing, you need to start at a high rpm, then reduce. They won't start at low rpm, and even when you start them at high rpm, power at low rpm is severely reduced as Max said. You will need high torque.

    If you can find a KBVF-24D that has been programmed for PSC motors, that might work. I couldn't get a free sample to try -- guess I am too honest. ;)

    John
     
  4. ipanos

    Thread Starter Member

    May 7, 2010
    12
    0
    Thanks guys.

    In simple words it is not possible I guess. I will reduce the speed with a cone pulley system which will also give me a fair amount of torque on this motor. The problem is that going low (below 300RPM) is making the system fairly bulky (1/2 inch drive pulley, 8 inch on the spindle), plus the intermediate steps on a 5 pulley system (I don't really wanna have more than 2 on the drive and 5 on the spindle) is giving big steps with large intermediate gaps. So I was hoping to combine mechanical and electrical means but I failed to find a satisfactory circuit diagram after quite some research on line. So I thought to ask the experts here...

    Can one tell from the images above if I was right to assume it is a PSC one? I couldn't see any centrifugal switch in there, there is only one cap which I guess it is a run one due to low capacity and high volage ratings and a squirel cage rotor, but that's my way of thinking without being an expert on the matter.

    I was hoping to use this motor, other than it is free, it is powerfull.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,566
    2,379
    It most definitely looks like a single start/run single cap motor, otherwise you would see the Centrifugal switch, although there are also external types, It does not seem the case here.
    Max.
     
  6. ipanos

    Thread Starter Member

    May 7, 2010
    12
    0
    Thanks Max!
     
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