Tester running on 3 phase - help

Discussion in 'The Projects Forum' started by Man_in_UK, May 6, 2010.

  1. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
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    I make repairs to machine controllers.
    To make things simple to explain we will say for now that these machines use a 3 phase motor that has to run in both directions. There are limit switches to tell the controller when it has reached the end of its travel, then the controller switches 2 of the phases around to make the motor run in reverse.

    I would like be able to test these controllers from a single phase supply. I have built many similar testers for single phase controllers as it is easy to use the output voltage to drive a motor/cam cluster (didn't need motor reversing on those ones), but, I cannot think of a way of getting a motor to run in both directions on mains AC.

    Any ideas ?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    If you mean to reverse a single phase AC induction motor then you will need to reverse the wires of the starting winding internally unless it is a special motor which has extra wires for this purpose.

    If you are going to make a tester then you don't need to run motors but indicators that show the output of the controller works.
     
  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    You must be doing something else than commanding a starter. Mechanical starters with interlocked reversing starter, or VFDs simply need a command.
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    I am guessing you are testing the motor and guides outside of the command module (Aww, Apollo 13 reference) ;)

    Am I close? You want to have a 3 phase supply that reverses any 2 phases at the end of travel to reverse the motor.

    So you need only 2 relays that switch 2 of the legs to 2 of the leads. Should be easy.
    The reverse signal can energize the relay coil to swap the phases.
     
  5. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
    132
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    Mik3, Indicators will show that there is power in the right places but without a motor hitting switches at the correct intervals, it is almost impossible to tell if the controller is starting & stopping other functions correctly.

    Retched, yes your right. But I don't need to reverse the phases, the controller does it.


    I think I will need to go into a lot more detail about what the controller does.The machines use about 13 solenoids & 3 motors. When a start signal is detected 1 solenoid is pulsed that lets a machine part drop(part A). A switch detects the the drop is complete. At this point a motor is run forward for about 2 seconds until a limit switch is hit, then the motor stops and reverses back to its start position(detected when another switch is hit). The reversing action of the motor raises part A back to its home position and its waiting for another start signal. I have left out a lot of stuff but this shows the idea.

    The controller starts, stops and reverses motors and solenoids independantly after it has got its start signal. What I need to do is to take a controller into a workshop (with single phase supply) and get it to perform its normal routine.
     
  6. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
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    Sounds like an older relay logic machine. Your control circuits will surely be single phase, if not DC, and as long as your starters engage you don't need motors connected. Your description is sequential and just as well, as single stepping through the functions will provide the best evaluation.
     
  7. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    As long as the mechanical load on the motors is not very high, you can produce an approximation of three phase by connecting a motor run capacitor from the third terminal to one of the AC lines. That will give a phase shift and set a direction.

    You still have the problem of being on 240V rather than 415, but a lot of small motors can be linked for two different supplies. You may find you can reposition the jumper links in the motor terminal box to suit the lower voltage.

    If the test rig motors still have difficulty starting on load, try connecting a spare three phase motor of some sort so it's running all the time (while you are using the test rig). The back EMF from that will improve the three phase supply to the other motors and help them start properly.
     
  8. Man_in_UK

    Thread Starter Senior Member

    May 13, 2008
    132
    0
    This thing is a long was from a relay logic machine, the controller does loads of clever stuff. I just missed out 95% of it to try and make the point about reversing a 3-pase motor.

    BUT

    You have put an idea in my head and now I think I am there. The controller PCB runs of 26vac, that then sends control signals to the high voltage 3-phase switching board. I wanted to do my testing after the high voltage board so I know its outputs are good. If I do my testing via the 26vac controll signals, I got loads more options.

    I thank you Getdevice, its going to work.
     
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