Results 1 to 9 of 9

Thread: Got an Electrical Motor Question

  1. #1
    Join Date
    Feb 2008
    Location
    S E Washington State
    Posts
    3,777

    Got an Electrical Motor Question

    The motor on my son's Rigid bandsaw (that I store for him) has a problem. When I turn on the switch it sort of just hummms. The shaft turns freely if I turn it by hand. Is this a starting compositor or brushes or? This doesn't have over 5 or 6 total hours running time on it I wouldn't think. It is about 7 or 8 years old. I don't know much about electric motors.
    "We the People ......"

  2. #2
    Join Date
    Nov 2006
    Location
    Villa Park, CA
    Posts
    1,407
    IF it's an induction motor as opposed to a universal motor, the problem is probably either the starting capacitor or the contacts on the starting switch (which cuts in the starting capacitor) is fouled by dust.

    If it's an induction motor, try blowing it out with compressed air.

    A test. Disconnect the belt (if it's belt driven) and give the motor a good spin. While it's spinning, turn the power on and see if it starts. It doesn't matter which way you spin it.

    If there's no belt, it's probably a universal motor.

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

  3. #3
    Join Date
    Feb 2008
    Location
    S E Washington State
    Posts
    3,777
    If I spin the motor then turn on the switch it starts. So that is a starting cap. problem, correct. Now the question, how hard is that to change? Is the capacitor going to zap me? What little I know I remember capacitors store electricity and can do a person in.
    "We the People ......"

  4. #4
    Join Date
    Dec 2007
    Location
    Tellico Plains, Tennessee
    Posts
    4,353
    I'm not an electrician and have both a healthy respect and fear of electricity... I've been zapped hard enough to knock me backwards onto my keister and seen guys that have been cut by an electrical charge running on the surface across their hands.... I'll change switches and wire plugs, but not a lot else... as I remember what little electrical training I did get, which ain't much, I think you are right about the capacitor holding a charge. The trick is, make sure you don't cross two points of contact simultaneously... no path, no shock. I think the start capacitor is in a little capsule on top/side of the motor and should be relatively easy to change. Don't take my word though, get more competent advice.
    Chuck
    Tellico Plains, TN
    https://www.etsy.com/shop/TellicoTurnings
    My parents taught me to respect my elders, but it's getting harder and harder to find any.
    If you go looking for trouble, it will usually find you.

  5. #5
    Paul,

    As Mike said...it could be the starting capacitor or it could also be the centrifugal switch.

    Typically there is a centrifugal switch ( looks similar to a set of mechanical ignition points in an old car but without the weights) at the one end of the motor. You can removed the end cap and blow it out with an air compressor. I have recently seen those starting caps at both ends of a motor.....capped end...and shaft end.

    The switch closes when the motor is turned off and it puts the starting capacitor in the circuit. The next time the motor is turned on, the starting capacitor causes the motor to start in a specific direction. Once the motor attains approximately 80% of it's rated speed, the centrifugal switch opens, removing the capacitor from the circuit.

    If sawdust gets into the housing, it can clog the switch preventing it from closing when then motor is turned off, and thus the capacitor isn't in the circuit and the motor won't start the next time power is applied.

    Check the motor and verify that nothing is preventing the centrifugal switch from functioning. It can be located at either end of the motor.'

    Then you can probably get a capacitor of similar value at a motor shop in the Tri-Cities area.

    Good luck!
    Ken
    ------



  6. #6
    Join Date
    Feb 2008
    Location
    S E Washington State
    Posts
    3,777
    I took the end plate off and blew it out real good with a compressor. But what I didn't do was work the centrifugal switch manually open and closed. Must have knocked more dust out. But everything back together and started it and it about jumped off the table. I really appreciate the help. So I will remount it on the band saw and see what happens. Thanks for all the input. I just maybe back in business again.

    By the way, any one that owns one of the Rigid band saws the motors are no longer manufactured so you it you need to replace the motor for some reason, look elsewhere.
    "We the People ......"

  7. #7
    Join Date
    Nov 2006
    Location
    Villa Park, CA
    Posts
    1,407
    As Ken pointed out, before you change the starting cap, blow out the centrifugal switch. If there's crud in there it'll act just like a bad cap.

    Regarding safety - you can short the two wires of the cap before working on it to discharge it (if it has any charge on it). Keep the screwdriver (or whatever you use) on it for a little while, maybe 10 seconds, just to make sure it's fully discharged.

    While a cap can store enough electricity to get your attention, it's very unlikely to kill you unless you have some heart rhythm problems.

    Mike
    Last edited by Mike Henderson; 09-26-2011 at 06:21 PM.
    Ancora imparo
    Go into the world and do well. But more importantly, go into the world and do good.

  8. #8
    Join Date
    Feb 2008
    Location
    S E Washington State
    Posts
    3,777
    Thanks, Mike. All back together and operating. Just wish I had asked the question before I dismounted the motor and switch. I did unnecessary work. But hey, I'm cheap labor and I will know better next time.
    "We the People ......"

  9. #9
    Paul,

    I would expect those contacts on the switch could become pitted just like the contacts on a set of ignition system points and stick as a result too. I have not observed that but I suspect it's possible.

    Glad you found the problem and fixed it.
    Ken
    ------



Similar Threads

  1. Electrical Question
    By Michael Tulak in forum Off Topic Discussion
    Replies: 9
    Last Post: 05-04-2015, 08:55 PM
  2. Electrical Question
    By Sayer Fancher in forum Off Topic Discussion
    Replies: 11
    Last Post: 12-13-2014, 06:17 PM
  3. Electrical Requirement for 1 1/2 Hp Motor
    By Mike Turner in forum Turning Tool Questions and Show & Tell
    Replies: 3
    Last Post: 07-27-2012, 02:51 AM
  4. Electrical question
    By Bob Gibson in forum Off Topic Discussion
    Replies: 9
    Last Post: 08-27-2011, 03:30 PM
  5. Electrical question
    By Ned Bulken in forum Carpentry and Construction
    Replies: 22
    Last Post: 06-02-2007, 01:00 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •