Electric motor direction

Discussion in 'Power Electronics' started by CyrGT, Sep 23, 2016.

  1. CyrGT

    Thread Starter New Member

    Sep 23, 2016
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    Can you explain this? I have an RC boat motor that rotates one way when connected directly to the battery but when I connect it to the toy PCB it turns the same direction but with reverse voltage. I followed the tracks on the PCB and the MOSFETs links the negative battery pole to the positive motor pole and positive battery pole to negative battery pole. The motor turns one direction when conected to the battery and in reverse if the battery voltage is reversed.

    So what kind of trick can make a DC motor behave like this?
     
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Simple bridge rectifier.
    Guarantees same polarity regardless of supply.
    Max.
     
    Last edited: Sep 23, 2016
  4. Alec_t

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    Sep 17, 2013
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    Most (all?) DC brushed motors will do that.
     
  5. CyrGT

    Thread Starter New Member

    Sep 23, 2016
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    I know it's was not clear, but I specified that to rule out the posibility of a full bridge rectifier inside the DC motor. I tested the PCB with a standard toy DC motor and the same phenomena happens.

    My theory is that the PCB senses the back EMP from the motor and uses PWM to send current just at the right time to make the motor turn in the opposite direction that it would if the same polarity was applied in DC.

    If anyone knows what that is and how it's called I would apreciate it since I find the idea quite unusual and interesting.
     
    Last edited: Sep 23, 2016
  6. ThomasWinfrey

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    Sep 26, 2016
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    I think so.
     
  7. MaxHeadRoom

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    I cannot see that happening without at least a small exercising of the motor, as until the rotor starts to turn nothing can be detected.
    Max.
     
  8. ThomasWinfrey

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    Sep 26, 2016
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