Using one H-bridge to drive 3 motors

Discussion in 'General Electronics Chat' started by Dritech, Nov 3, 2013.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi all,

    Is it possible to drive 3 separate motors using one H-Bridge?
    I was thinking of doing something as shown in the attached schematic, but is there something more reliable and efficient?

    (Note: Max. current will be approx. 25A)
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    If you are going to use relays to select the motors, why do you even need the Hbridge in the first place? Just do the reversing/selecting with relays...

    Even if you need to PWM, you can do that with a single transistor (preferably MOS) switch; use the relay for reversing.
     
  3. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi,

    So is there another method instead of using relays?
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    With your circuit all active motors would have to rotate in the same direction at any one time. Is that what you want?
     
  5. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    The motors will not be operating at the same time, so that would not make a difference for my application.

    Is there a type of electrical switching device that can drive approx. 25A in both directions?
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    An H-bridge comprising MOSFETS will do the job.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Are you controlling the RPM or just on off?
    Particularly if you are just on/off you should have some means of detecting stopped motion before reversing.
    Max.
     
  8. MikeML

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    What are you driving the Hbridge(s) from?
    An MCU?
    What is the MCU supply voltage?
    How much drive on the port pins?
    How many port pins can you allocate to driving the motors?
    What is the supply voltage at the top of the Hbridge?
    Can you use FETs instead of BiPolars.
     
    Last edited: Nov 3, 2013
  9. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    -H-bridge is going to be driven from a PIC18F
    -5V
    -I want to reduce the amount of port pins to be used as much as possible.
    -Supply voltage for the H-bridge (hence to the motors) is 12V
    -As an H-bridge I am going to use the BTS7960 (2PCS)

    I don't want to use three separate H-bridges for two reasons; to reduce cost (since the BTS7960 are not that cheap) and to reduce the number of PIC18F port pins required to drive the three motors.
     
  10. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    5

    OK, but to drive three motors I would have to use 12PCS of MOSFETs and 6 pins from the microcontroller. Or is there another way that you know of?
     
  11. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi, are you referring to the PWM? Yes I will be using PWM to control the motor speed.
     
  12. MikeML

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    Since you are hung up on using the Half Bridges, the relays are the best bet. It takes three port pins to control the two half-bridges (the enable signal can be shared), and two port pins (if you use an external two-to-four line decoder) to select the motors.

    You will have to program some serious delays in the code to take care of reversing a single motor, and other delays when selecting a different motor.
     
  13. MikeML

    AAC Fanatic!

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    It takes more than two pins per motor...
     
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