Connecting mechanical starter relay to single phase reversible AC motor

Discussion in 'General Electronics Chat' started by reaverkin, Aug 12, 2018.

  1. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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    Hello all. I've been researching for weeks trying to learn as much as I can on the subject but have hit a wall. I have an existing setup for a funicular elevator - worked fine for a decade but the motor recently died. Found a replacement motor with identical specs but can't figure out how to wire it up (the wiring is slightly different on the new one).

    The system has two Square D Nema 0 type S mechanical starters with the accompanying wiring diagram.
    upload_2018-8-12_13-39-32.png

    The problem I'm having is that the motor I'm using is a single phase induction-start induction-run motor. I understand that to reverse the direction is a matter of reversing the polarity of starting winding with respect to the run windings, but I can't for the love of me figure out how to map the (3) outputs of the starters to the (6) motor leads as seen below.

    upload_2018-8-12_13-46-15.png

    The starters are wired to 240 with i1 and i2, and outputs O1, O2, O3 (I apologize in advance for incorrect nomenclature or conventions) coming off the bottom of the relays. When latched in the forward position O1 = O2 = i1 and O3 = i2, when in reverse O1 = i1, and O2 = O3 = i2. I've probed the various contacts exposed on the relays to see if there's anything else I could use - but I think most of them are part of the 'latching circuit' and not intended to drive the motor.

    I've probed the motor and P1-2, 3-4 and 5-8 appear to have continuity (although 5-8 behave strangely on the multimeter with the resistant slowing going up - I assume because of interaction with a capacitor).

    It was all working perfectly with nearly identical motor, so i know it's possible - just reached the limit of my understanding.

    I appreciate any insight,
    Shaun
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Should be fairly simple to reverse the 5 & 8 connections the same as it is done with the 3ph motor, the third contact on each would switch the L1, if you obtained a 4 contact contactor you could switch both L1 -L2 which on 240v would be a little more applicable to code etc.
    Max.

    [​IMG]
     
    Last edited: Aug 12, 2018
  3. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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    Thanks for the reply! Yes I can see how a 4 contact contactor would be straight forward - however I was really hoping to get it working exactly as it was before without changing out the relays. When you say it would be simple to switch the 5 & 8, do you mean with a 4 contact contactor or with the existing 3 contact contactor? I can't get my head around how it would be done right now without some additional part. Is it possible to run the starting wiring at 120 but the run wiring at 240? (I did notice two points on the relay that switched between neutral and L2 that I could theoretically use but it seemed like a bad idea :)

     
  4. LesJones

    Well-Known Member

    Jan 8, 2017
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    I don't see how you can say the new motor has the same specification as the old one when one is three phase and one is single phase. There are a few possible problems you may have.
    1 Is you power supply capable of providing the extra current required by the single phase motor ?
    2 Can the thermal overloads in the starter be adjusted for the higher current ?
    3 Are you sure the single phase motor will have enough starting torque for your application ?

    Disconnect the L3 power in wire and make the end safe as it will not be used. (Isolate at the source as well for safety.)

    Connect T2 on the starter to P1 on the motor.

    Connect 4 on the motor to the L1 input on the starter.

    Connect 2 and 3 on the motor to L3 on the starter

    Connect 5 on the motor to T1 on the starter.

    Connect 8 on the motor to T3 on the starter

    This will not totally isolate the motor from the power. One end of one winding will be connected to L1 when the motor is stopped.

    Test first without the mechanical load being connected to the motor. (This is to be shure that if it fails to start it is not due to the starting torque being too low for your application.)
    I don't think you could run the start winding between one phase and neutral. (This would not be 120 volts it would be 138 volts.) Also I can't see any neutral on the diagram of the starter.

    Les.
     
    Last edited: Aug 13, 2018
    reaverkin likes this.
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Where are you? Do you have 240v and N or N.A. style 240v L1 & L2.?
    I have to leave for a while but can sketch the DWG up when I get back.
    Are you using the existing 3 ph to power it?
    Max.
     
  6. LesJones

    Well-Known Member

    Jan 8, 2017
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    Hi Max,
    In post #4 I have assumed thet the TS is in the USA from the fact that his phase to phase voltage is 240. Also the fact that he thinks the phase to neutral voltage is 120 as it would be with the 120 0 120 domestic supplies were the centre tap of the transformer is neutral. Also the fact that the new motor can be configured for 240 or 120 volts.

    Les.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I had assumed that but wanted clarification, his starter is NEMA 0 rated which is 3HP and 18A cont at 120vac.
    If he is using it on N.A. 240v then strictly speaking requires switching both L1 & L2, and may require the 4 contact version contactor.
    If 120v the contactor is still within rating. But the type S is non-reversing (2 single contactors) if I read it right this is what is used, it would be preferable to use a mechanical and electrically interlocked reverser.
    Max.
     
  8. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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  9. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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    Sorry for not being clear about this: the wiring diagram shown corresponds to the starters but was not how it was setup. The old motor was indeed a single phase capacitor start, capacity run motor with nearly identical specs:
    upload_2018-8-13_12-35-44.png
    (note that this is not the exact label from the old motor, its a label I found on the web corresponding to the same model - a Leeson m6k17fb3h)

    I made the ridiculous mistake of not being careful about un-wiring the old one and noting how it was connected (i had falsely assumed it would be straight forward to hook back up).

    So in this respect the load and power requirements are the same. I'm in North America so my L1 is +120v and L2 -120v.

     
    Last edited: Aug 13, 2018
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Can you post a clearer pic of the (Leeson) motor plate?
    Was just one of L1 or L2 switched previously?
    Max.
     
  11. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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    Just wanted to follow up. Drawing Les's suggestion out on a piece of paper and staring at it for a second made me realize that indeed as Max suggested this should be straight forward BUT I think what had been throwing me off here is there is a mistake in how the relays are wired - my T1 and T2 are supplying L1 and L2 in both forward and reverse and only L3 was being switched. I omitted mentioning that a wiring problem was a possibility in the original post because it was only while replacing the motor I took the opportunity to inspect and clean the contactors and undid some wires and was certain I had reconnected them the same way (which obviously i did not). Appreciate your help.

     
  12. MaxHeadRoom

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    If 5 & 8 are supposed to be interchanged I dont's see how you would achieve an interchange of two conductors with one contact?
    Max.
     
  13. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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    Based on Les's suggestions this is my understanding of how it should work. Note however I think the electrician may have reversed L2 and L3 from what the diagram implies (photos are below):

    Inputs | Voltage | Connect to motor lead
    L1 | +120 | (4)
    L2 | +120
    L3 | -120 | (2,3)?

    Outputs | Connect to motor lead | Forward Voltage | Reverse Voltage
    T1 | (5) | +120 (L1) | -120 (L3)
    T2 | (P1) | +120 (L2) | +120 (L2)
    T3 | (8) | -120 (L3) | +120 (L1)

    So T2 is 'passed through' and T1 and T3 are switched.


    Here's a clearer picture of the the specs for the previous leeson motor, with what appears to be identical wiring to the new one.

    upload_2018-8-13_14-37-9.png


    I'll also include pictures of the starters as they were (i was at wise enough to take pictures prior to touching them) - which may be useful to future readers with similar projects.
    upload_2018-8-13_14-33-3.png


    upload_2018-8-13_14-33-3.png


    upload_2018-8-13_14-33-21.png
    upload_2018-8-13_14-33-44.png
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Rather than take pictures of wiring that is not, or has limited numbering, making a reverse engineered print would have been better.
    No marks to the electrician for neatness there!:(
    It looks like I may have been right with only one 'live/feed conductor' switched and 5 & 8 swapped?
    Max.
     
  15. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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    Hey Max, I think you are correct. I won't be at the location until the weekend but will do so asap!

     
  16. LesJones

    Well-Known Member

    Jan 8, 2017
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    I found this web page that shows the internal connections of a dual voltage single phase motor. (We don't have dual voltage single phase motors in the UK so I did not know how they were connected internally.) The start winding only runs from 120 volts. When the motor is connected for high voltage it gets the 120 volts from the junction of the two main windings which are in series. I think the links between L1 and L2 are wrong. I think L1 and L2 should be be +120 and -120 (Even though the + and - are DC terminology I know what you mean.) L3 gets it feed from the junction of the two main windings (2 & 3)

    Les.
     
  17. LesJones

    Well-Known Member

    Jan 8, 2017
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    Another thought. As I now know that the start winding only ever has 120 volts fed to it the original way it was wired MAY have fed the L3 input of the contactors from the neutral rather than from the junction of the two main windings.
    I agree with Max that it would be a good idea to trace out a schematic of the wiring as it is at the moment. It will help us understand how it worked originally.
    The fact that L1 and L2 are linked makes me think it was possible that the start winding was being fed with 240 volts.

    Les.
     
    Last edited: Aug 14, 2018
  18. LesJones

    Well-Known Member

    Jan 8, 2017
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    I was trying to think of a way to avoid leaving the motor live when stopped. This was the first idea I came up with which leaves it connected to neutral.
    140818_01.jpg


    This works by reversing the polarity of the main winding instead of the start winding.
    I then realised that if terminal 8 on the motor was connected to the junction of the two main windings (Terminals 2 & 3) instead of neutral it would totaly isolete the motor when stopped. If this diagram does not make sense then I will draw it properly. The big "X" below L1 and L3 is just showing where the polarity reversal happens.

    Les.
     
    Last edited: Aug 14, 2018
  19. reaverkin

    Thread Starter New Member

    Aug 12, 2018
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    Ah clever! This method does seem familiar in that I do think the neutral was being wired to the old motor.
    So if I'm reading this drawing correctly I infer the following states (can you tell I'm a software guy? :):

    Output | Forward | Reverse | Motor input
    T1 | -120 | -120 | 5
    T2 | -120 | +120 | P1
    T3 | +120 | -120 | 4
    Neutral: 0 | 0 | 8

    and then 2, 3 are alone together (?)

    I'll try this without load and see i it works! I had found diagrams similar to the link you had posted above such as this:
    upload_2018-8-14_13-14-23.png
    But I wasn't sure if it accurately reflected my motor (and the numbers are different I think with 1= P1, 2 = 4 maybe). Funny - looking at it now I realize that the purpose of the run capacitor isn't to drive the run windings (as I thought), its for continuous use of the start-aux windings! And I guess the difference between them is that there's less of a phase shift with start capacitor so it acts like a 'lower gear' and provides more torque. But thats me guessing - a topic for another conversation.

    ps: Yeah I realize it would be more apt to describe the two voltages as -90 degrees and +90 degrees but glad the meaning was conveyed :)
     
  20. LesJones

    Well-Known Member

    Jan 8, 2017
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    NOTE The sequence I have labled the "T" terminals is T2 | T1 | T3 I think you assumed T1 | T2 | T3

    Output | Forward | Reverse | Motor input
    T2 | -120 | -120 | 5
    T1 | -120 | +120 | P1
    T3 | +120 | -120 | 4
    Neutral: 0 | 0 | 8
    This leaves neutral connected to the winding when the motor is stopped which is reasonably safe but may not conform to regulations in the USA. If you connect motor terminal 8 to motor terminals 2 & 3 (Centre point of main winding.) then in the stop position the motor windings are not connected to any supply wire. This point will be at about neutral potential.
    The schematic you posted in post #19 is the standard one for capacitor start capacitor run. It is the dual voltage motor that I was not familiar with. I imagined the start winding would be in parallel for low voltage and in series for high voltage.

    Les.
     
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