DC Motor Voltage Help

Discussion in 'The Projects Forum' started by Thomas B, Mar 19, 2015.

  1. Thomas B

    Thread Starter New Member

    Mar 19, 2015
    1
    0
    Hi,

    I have a Motor being controlled by a Programmable controller and I need to reduce the voltage to it.
    The output of the controller is 4.8v and the motor is a 3v motor. So i need a voltage drop of 1.8volts before the motor.
    I know this is simple but I'm really stuck can anyone help?

    Thanks in advance.
     
  2. MCU88

    Member

    Mar 12, 2015
    360
    35
    Hello...

    This is not simple since PWM (Pulse Width Modulation) -- is really the only way to control motors.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    two standard diodes in series will drop about the amount you desire.
     
  4. Annanya

    New Member

    Mar 19, 2015
    1
    0
    I think that, though PLC is an industrial computer control system that continuously monitors the state of input devices and make decisions based on the custom programs to control the state of output devices.
    figure shown below illustrates the control circuit and wiring diagram of a 65% tapped, autotransformer, reduced-voltage-start motor control circuit. This reduced voltage startminimizes the inrush current at the start of the motor (locked rotor current) to 42% of that at full speed.

    In this example, the timer must be set to 5.3 seconds. Also, the instantaneous contacts from the timer in lines 2 and 3 must be trapped.
    [​IMG]
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    annanya, that is a nice reduced voltage starter method, but this post is about a small dc motor, not a 3 phase a c motor.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Unless you are speed controlling it where the higher voltage would not matter, I agree with Kermit, two diodes in series.
    Max.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Unless the OP is reversing the motor.

    If the controller uses PWM for speed control, and if you rarely run the motor wide open, I wouldn't even worry about it...

    If the controller is programmable, why not restrict the top speed to only ~75% of what it would normally be. The startup, inrush current to initially start the motor will still apply 4.8V for a second, but then as the motor comes up to speed, the controller will reduce the effective voltage across the motor to more like 3V.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Another couple in reverse parallel.;)
    'Programmable controller' often refers to PLC? No PWM.
    Max.
     
    Last edited: Mar 19, 2015
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