help choosing solid state relay

Discussion in 'General Electronics Chat' started by mobydick, Jun 5, 2015.

  1. mobydick

    Thread Starter New Member

    Nov 19, 2010
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    Hello
    I have an old DC motor that used to drive Tension Test machine
    The motor is 150V 4.5KW
    The block diagram for motor driver :
    block diagram.png
    My problem is the motor rotates too fast .
    I have done some googling and I get that the best way to lower the voltage is to use solid state relay before the rectifier
    I have never used one before and There is lots of types for specific uses (inductive loads, capacitive loads…) and lots of control methods(zero crossing, random turn on,….) and I got confused.

    Any recommendations will be appreciated
     
    Last edited: Jun 5, 2015
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If using a motor on rectified DC you do not need the Cap, Especially using 3ph rectifier where the % ripple is less than 5%.
    This will lower your peak DC.
    An off the shelf SSR generally switches on/off, not variable.
    Another alternative is a 3ph SCR bridge control.
    Max.
     
    Last edited: Jun 5, 2015
  3. mobydick

    Thread Starter New Member

    Nov 19, 2010
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    the capacitor is already installed
    i want to lower the DC voltage even more
    so there is no off the shelve phase control SSR
    is bossible to make one
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What % of the current rpm limit are you looking for?
    The 3ph SCR SSR circuit is one way or a couple of Buck/Boost transformers on two of the transformer outputs.
    Another possibility is to reduce the secondaries by taking equal turns off of each.
    Max.
     
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  5. mobydick

    Thread Starter New Member

    Nov 19, 2010
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    i have never dealt with big motors like this ,so i have no idea what is the current rpm limit
    adding extra transformer will be too expensive
    i want to cut rpm to half or may be more so i need to remove a lot of turns
    adding external component will be the easiest solution
     
  6. MaxHeadRoom

    Expert

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    I assumed automatically it was a P.M. field, it would not be a wound field by any chance?
    Especially in that size of motor?
    If it was, there is a simple answer.
    Max.
     
  7. mobydick

    Thread Starter New Member

    Nov 19, 2010
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    i think it is P.M
    there is only 2 wires to the motor
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    AFAIK: SSR and phase control modules are 2 entirely different things.

    But you can get off the shelf phase control modules. A company I used to work for that made ultrasonic cleaning equipment used them as a cheaper alternative to variacs in a continuously variable generator.

    Unfortunately I can't remember the make - the only SSR I can think of off hand is the Opto22.
     
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  9. MaxHeadRoom

    Expert

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    2 wires to the motor can still mean wound field if the voltage is fixed.
    Yes Opto22 are SSR's, the 3phase SCR controllers are fairly pricey.
    Depending on whether you are looking for variable rpm or just a lower fixed rpm.
    Max.
     
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  10. ian field

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    Could you get away with 3 individual phase controls - if you can find a 3-gang pot?
     
  11. MaxHeadRoom

    Expert

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    I presume you mean three Triac controllers in place of the SCR control?
    It would depend on how the three transformers are connected, Star or Delta secondary?
    One of the down sides with SCR control is miss-firing, especially in the case of power outage etc usually ending up in blown SCR or fuses.
    Personally I would be looking at reducing the AC if fixed rpm is needed, or PWM if variable.
    Max.
     
  12. ian field

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    I just assumed that an off the shelf phase control module would most likely have a triac in it.
     
  13. MaxHeadRoom

    Expert

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    1ph 'Dimmer' style AC motor controllers have a Triac, which agreed you can operate ahead of a bridge.
    But when getting in to 3phase control, the nature of the AC origin has to be known, Star-Delta?
    Most of the first CNC DC servo motor controllers were a 12 SCR bank for reversal capability.
    Now replaced with PWM.
    Max.
     
  14. mobydick

    Thread Starter New Member

    Nov 19, 2010
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    great dissection

    so i should search for phase controller not SSR?
    can't i use DC SSR after the capacitor?

    i will look at it again
    i will also look at the transformers to see the toopolgy

    just a lower fixed rpm



    yes , that what i meant but using SSR(now phase controllers) not pot
     
  15. ian field

    Distinguished Member

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    A solid state relay is exactly that - it switches the power on and off in response to a control signal.

    A phase control module switches on at some point on each half cycle of the AC waveform - the control signal tells it how early or late to fire on each half cycle.
     
  16. MaxHeadRoom

    Expert

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    Check how the three transformers are connected Star/Delta, Star/Star etc, a possible change in the configuration can possibly lower the voltage to the acceptable level.
    Max.
     
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  17. mobydick

    Thread Starter New Member

    Nov 19, 2010
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    Each transformer has 3 yellow and 2 black wires
    1 yellow wire is not connected
    1 yellow wire is connected to an input phase
    1 yellow wire is connected to the other wires from the other transformers

    1 black wire is output to the rectifier
    The other black one is connected to the other wires from the other transformers
    So I guess if the not connected wire is a center tap one the connection will be (Yy)
     
  18. MaxHeadRoom

    Expert

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    They appear to be connected Star-Star so this is the lowest voltage from them unfortunately.
    BUT when they are powered, on one transformer, measure from the star connection on the input side to the 'open' (unused) connection and compare to the other used terminal, you may be able to use the alternative Higher primary connection and lower it that way, probably by half.
    Max.
     
  19. ian field

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    Found it - its a; Hyreg AR2/250-15.
     
  20. MaxHeadRoom

    Expert

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    Looks like it might be an obsolete part?
    Max.
     
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