Motor control with SCR NTE5414 or NTE5411 Thyristor

Discussion in 'Homework Help' started by Nara Shikamaru, Nov 25, 2007.

  1. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
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    Hey there!!....i need a little help here!!....i need to control de activation of the RL (DC Fan Motor 12V) in the circuit...but i need to calculate the values of R1, R2, R3, C1, C2 for a wide range of activation adjustment....in the circuit youll find the values that i "miscalculate" cause it doesnt work, i hope somebody could tell how to get the best values for them!!....the signal is
    12VAC 60Hz....Thanx a lot!!.....
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    I am going to move this post to Homework Help.

    If the purple object is the motor, the circuit is laid out incorrectly. The phase control elements and the SCR need to be on the other side of the motor - between the AC source and the motor.
     
  3. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    he there!!...sorry if a posted wrong!!....the purple thing in the circuit is just the Mark that indicates the "center" of the page in the Proteus!!...the Motor is the device next to the AC source....the one with the green LCD.......
     
  4. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Is it my eyes or is the cathode and gate shorted in the schematic?

    I surely hope your professor didn't draw that.

    What is the input AC signal?
     
  5. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
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    3
    Fudge!!....you´re right!!...no..jajaja...it was my mistake!!!...sorry...that cable is not suposed to be there...the circuit obviously is exactly but that shortcircuit ignore it....the proffessor didnt say anything about the AC source....but because RL is a DC Fan motor of 12V 0.2A then i guess i should be 12VAC 60HZ....but those values that you see in the circuit are the ones that i calculated...but they´re wrong....how do a calculate the good ones?...and how do i see in the ´scope the max and min trigger Angles?....
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Which resistor is R3?
     
  7. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
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    3
    oh sorry!!....i didnt see that the Proteus put R3 as R2....R1 is R1, R2 is the Potentiometer (variable resistor), R3 is the resistor to the gate...
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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  9. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    Hey everybody!!...i finally calculated the true values....in this next circuit you can see them R1=2.7K, Pot R2=20K, R3=2.7K, remember that in SCR circuits when using AC sorce the RC time constant varies from Tmin 1mSeg and Tmax 30mSeg....to determine the Min Triggering Angle and the Max triggering angle...with those values in the circuit the Tmin is 2.7mS and the Tmax is 23mS....remember that the AC source is 12VAC 60Hz cause im using a Fan motor 12VDC.....moving the variable resistor R2 you can move the triggerin angles from technically the 2mS and the 23mS....but i need the plot of the graph and i dont know how to connect the oscilloscope and graph in the Proteus...can someone tell me how to connect the `scope and get the Min and MAx triggering values in the graph?....or can someone simulate the circuit in any other software and send me the graphs?...thanx!!
     
  10. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I see you didn't follow beenthere's recommendations in post #2.

    I don't know if you followed the recommendation of post #8 either.
     
  11. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    i didnt followed them beacuse the circuit layout is not wrong....in fact...the second circuit schematic that i upload wich has the correct values i already prove it...and it works....you can stop, activate and control the speed of the fan by adjusting R2....and the second recomendation i look for it...but it didnt help so much...then investigating i read the book Modern Industrial Electronics by Timothy Maloney....and there it explain those kinds of circuits...but not also that...i discover that my teacher got the ciruit from that book!!...thats how i finally knew how to solve the circuit...cause is there!!....and it explains how to calculated for your requirements....the thing is that i need to see the signal on the oscilloscope to see the max and min trigger angles...and i dont know how to put the `scope in the simulation software....neither in real life...the book doest explain that part...that was what my teacher add to the excersise....to see in the `scope if what you calculated is true....greetings
     
  12. JoeJester

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    Apr 26, 2005
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    Where is R2's wiper connected?
     
  13. Nara Shikamaru

    Thread Starter Active Member

    Nov 24, 2007
    92
    3
    Hey JoeJester!!....R2 wiper its connected to the node that goes to R3 and C1...
     
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I don't think a 20k potentiometer has a "wide range of activation adjustment." In fact, your probably using less than 10% of that potentiometer.
    30 milliseconds is way more than one-half of the period of 60 Hz. I would think, and you can correct me if I'm incorrect, that you can only have the motor being initiated from the 12 volt level on the leading edge of the positive half-cycle to the peak of the 12V trailing edge of the positive half-cycle. The SCR will remain on till the signal on the gate becomes negative with respect to the cathode.
    To view those signals on the oscilloscope, you must measure across the motor. If you require a ground, you can insert the ground on the cathode of the SCR and remember Kirchoff's voltage law. The motor voltage drop and the SCR voltage drop will equal the source voltage.
     
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