Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Capacitor start single phase motor

  1. Mar 14, 2010 #1

    I have been given the task to sort out a broken barrier at the entrance to my work. It is a simple enough system, push button to go up/down and a stop button. Within the barrier mechanism is 2 pistons (one for up, one for down) which are controlled by a hydraulic pump. The pump has a single phase capacitor start motor. This is bidirectional to control either of the pistons.

    My problem; the direction of the motor is controlled by an electronic circuit board mounted within the barrier mechanism. This is continually getting wet and failing no matter how much we try to protect it. I now want to build my own system with either a plc unit, or simply relay system, away from the barrier itself to protect from the elements. I am unsure the best way to do this for the reversal of the motor direction. The motor core colours from the built in flex are brown, blue, black, earth, which i assume is switch wire, neutral, switch wire, earth?? Do i need 2 capacitors, one for each switch wire? any help greatly appreciated.
  2. jcsd
  3. Mar 14, 2010 #2
    In a standard FHP capacitor-start motor, there are two pairs of leads, the motor-run leads and the motor-start leads. All you need to do to reverse the direction of the motor is reverse the polarity of one pair. You cannot reverse the direction of a running single phase induction motor (most, anyway).

    Bob S
  4. Mar 14, 2010 #3


    User Avatar
    Science Advisor
    Gold Member

    Are you sure the control unit is not just operating a valve to switch the fluid between the pistons?
  5. Mar 16, 2010 #4

    the motor is continually changing direction for the up or down movement of the barrier. After Don asking, i double checked this. The motor has a pre-wired flex to it with 3 cores and earth. As it is single phase, i presumed it must be two switch wires and a neutral? is my logic wrong here?? please advise, thanks.
  6. Mar 16, 2010 #5
    page 2 of this link shows the hydraulic unit that im on about. And the electronic board within enclosure that has been so problematic. http://www.ecssecurity.co.uk/pdf/info/FAAC%20620%20TRAFFIC%20BARRIER.pdf [Broken]
    Last edited by a moderator: May 4, 2017
  7. Mar 16, 2010 #6
    See page 3 of this:


    Reverse the connections of wires #5 and #8 in illustration on 3rd page to reverse direction of starting coil. You will need a double pole double throw (DPDT) switch to do this. The motor direction could be reversing automatically due to either physical limit switches or excessive torque (hydraulic pump pressure) switches.

    Bob S
  8. Mar 27, 2010 #7
    thanks to all. problem now solved.
    Using a small bank of relays (plc unit was prob not worth paying for) we have now set a system that works ok. The pump needed to be switched over by manually reversing the polarity like bob explained. This was achieved by the way we wired it.

    cheers guys, appreciated

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook