Electric Brake

Discussion in 'General Electronics Chat' started by rajahariya, Feb 11, 2010.

  1. rajahariya

    Thread Starter New Member

    Jul 24, 2009
    5
    0
    Good Day Guys..
    I am trying to develop a circuit which will stop the active(running) DC motor immediately like a brake as soon as power is cut off.
    But I don't know how to do it.:confused::confused:

    Motor Configuration: 12V DC, 300 RPM
    Supply: 6~24V variable, 2.8 Amperes
    Switch: Push to ON DPDT switches.

    So please help me how to do it or please provide me a circuit if u can.
    Thank You.
     
    Last edited: Feb 11, 2010
  2. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    What type of DC motor is it?
    shunt, series wound, compound, permanent magnet?
    What type of inertia is developed by what the motor shaft is turning.
    If you aren't sure, let us know the make and model of the motor and if a datasheet is available, we can come up with a solution to your conundrum.

    Typically, DC motors are stopped by the "Plug" or "Dynamic" braking method.
    This is done by simply reversing polarity. We need to know how the field is wired in relationship with the armature to safely and effectively stop your motor.
     
  3. cjdelphi

    New Member

    Mar 26, 2009
    272
    2
    If it's an electric car as it you break, the the wheel becomes a break as you put energy back into the batteries via the means of breaking, as it breaks the energy/watts gets stored in the batteries.
     
  4. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Many motors will break hard if the power input is simply shorted. ( disconnect the power source first ) Currents will be high, heat will be disapated ( sp ) in the motor, you may get more or less breaking than you want. This is a way to drive the voltage across the motor and current thru it to 0. A reverse voltage can also drive the current to 0, but if held too long the motor will reverse. Look up regenerative motor controller circuits where the breaking energy is put back in the battery.
     
  5. rajahariya

    Thread Starter New Member

    Jul 24, 2009
    5
    0
    Thank You Sir russ_hensel for your reply..
    But can u tell me the how to do so.
     
  6. rajahariya

    Thread Starter New Member

    Jul 24, 2009
    5
    0
    Thank You VoodooMojo

    My DC motors are permanent magnet DC motors.
    I dont no much about it.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Here is one simple way to brake the motor when power is removed:

    [​IMG]

    If the power goes off, the relay coil de-energizes and the motors' terminals are effectively shorted together.

    However, it is an over-simplified version. If power is later restored, the motor will start up again. This could be dangerous for a person working on the motor.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    This is an improved version:

    [​IMG]

    RLY1 has been made into a self-latching relay. Pressing S1 initially energizes RLY1's coil, which closes the upper contact. When S1 is released, current flows through D1 and S2 to keep the relay energized.

    D1 is there to prevent S1 from powering the rest of the circuit.

    D2 has been added across the relay's coil to take care of the reverse-EMF when the coil is de-energized, otherwise the reverse voltage rating of D1 may be exceeded, destroying D1. D3 is on RLY2 for the same reason

    When S2 is pressed or power fails, RLY1's coil is de-energized. S1 must be pressed to turn the motor on again.
     
  9. awright

    Well-Known Member

    Jul 5, 2006
    84
    7
    How fast is "immediately?" Is the 300 RPM you mentioned the speed of the motor rotor itself or the output of a gearbox? 300 RPM is exceptionally slow for a common PM motor and you won't get much braking action at that speed. The braking action resulting from shorting the terminals of a PM motor is directly proportional to rotor speed decreasing to zero at zero speed. For most common PM motors current generated at 300 RPM and resulting braking action will be very low. If the rotor speed is high and the 300 RPM is at the output of a gearbox you will get more braking action with shorted terminals.

    If rotor speed is high it is possible that slamming a direct short across the motor terminals could produce more braking action than you need and could overstress the motor and the load. I would recommend experimentation with low value (a few ohms) power resistors across the terminals instead of a direct short until you find the value that results in the minimum acceptable deceleration of the load. The lower the deceleration that you can accept the lower the stress on the hardware and the lower the potentially damaging current surge through the motor. The required power rating of the resistor is dependent upon the amount of energy in the spinning load and the rate at which it must be dissipated in the resistor.

    Can you describe your motor and load in more detail?

    awright
     
  10. rajahariya

    Thread Starter New Member

    Jul 24, 2009
    5
    0
    can i have a simpler version. means is it possible 2 use with only switches???
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Two versions:

    [​IMG]

    The one on the left uses a SPDT toggle switch to change the motor +V input between +12v and an incandescent bulb used as a load resistor. This is a more gentle brake than simply shorting the motor's positive lead to ground.

    The one on the right simply shorts the motor's +V lead to ground.

    Neither will stop the motor instantly, however, it will stop much more quickly than if the power were simply disconnected.
     
  12. rajahariya

    Thread Starter New Member

    Jul 24, 2009
    5
    0
    Thank You Sir..
    its working is proper till now.

    But I wanted to brake instantaneously.

    I have developed some part of the circuit I will post it tommorw, than please try to correct the ckt pls...
    Thanx a lot sir.......
     
  13. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    Not possible, forces would be infinite. Pick a time > 0.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    As Russ_Hensel says, stopping the motor instantly is not possible, as the motor would be destroyed. It would be like stopping a car by driving it into a very large block of concrete - even then, that is still a de-acceleration rather than an instant stop.
     
  15. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    If you incorporated a mechanical brake in conjunction with SgtWookies design, you would improve the braking speed. However, the negative acceleration aspect can not be eliminated. Even if you stopped the shaft instantly, the forces would be transfered into the housing. Destruction would follow.
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Although probably not viable by electrical means, a mechanical solution was used in mid last century. (Man, are we getting old or what) Check here.... http://www.tinyclutch.com/spring-clutches/
    and go about 1/2 way down the page to "Single / Fractional Revolution Clutch" and see what may solve the OP's problem.
    We used something similar to disconnect the motor pulley from the driven shaft based upon a solenoid releasing a collar that controlled the wrap spring. The tab on the stop collar also acted as a stop for the driven shaft, stopping it instantly. Think of a Friden mechanical tape reader....We had two versions. One stopped the output shaft every 180 degrees to allow time to read the sense switches with the pins up and the other after 360 degrees of rotation where the external circuits could read the sense switches on the fly. These dogs were a real bear to align and set timing on. The main shaft carried multiple cams to indicate through auxiliary switches to indicate shaft position.
     
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