DC Motors / Generators, The difference ?

Discussion in 'General Electronics Chat' started by raminee, Jan 7, 2013.

  1. raminee

    Thread Starter New Member

    Jan 7, 2013
    4
    1
    Can someone explain to me what is the difference between a DC Motor and a DC Generator device ?

    From my old school day I remember that if you have current and a magnetic field then you get motion. Or if you have motion and magnetic field you get current. So basically if you have two of the parameters then you can get the third.

    I ask this question because I am playing around with a brush less DC Fan that I have yanked out of a desktop PC. I want to spin the fan so that I can get current out of it. But someone told me that this is not made to generate current.

    I am confused as to why the DC fan can not be used to generate current ?
    It seems you need a different device if you want a DC motor and a different device if you need a DC Generator. But in my head the devices should be the same. Why is there a difference ?

    Any explanation so that I can understand the differences would be appreciated.

    Raminee
     
    BershaM likes this.
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,982
    3,718
    Brushless motors are actually three-phase devices so there is some significant hidden circuitry in your fan. it would be more straight-forward for you to start with a traditional brushed motor. This will produce an AC signal. You can rectify it with a diode and flatten the pulse with a capacitor to get your DC back.
     
  3. raminee

    Thread Starter New Member

    Jan 7, 2013
    4
    1
    I agree with what you said.

    So if we go with a brushed motor then can we say that it is both a motor and a generator ?

    Raminee
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,982
    3,718
    Yes, notice when you spin the motor, it goes freely. If you add an LED or low value resistor, it gets harder to spin. The extra effort is the electric power you are generating.
     
  5. raminee

    Thread Starter New Member

    Jan 7, 2013
    4
    1
    So I should be able to generate electricity by spinning a brushless motor as long as I take care of the three-phases effect by a custom designed circuitary?
     
  6. BReeves

    Member

    Nov 24, 2012
    412
    64
    Have you tried it? Connect a volt meter to your motor and spin the fan with an air hose. This will tell you real quick if it will act as a generator.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,982
    3,718
    Try your volt meter in both DC and AC volts modes. Let us know what results you get, I am interested.
     
  8. raminee

    Thread Starter New Member

    Jan 7, 2013
    4
    1
    When I spin the fan all I get is a voltage reading. But NO current reading.

    I assume the PC fans have built in circuitry that take in current and convert it to motion. So I am not surprised that I do not see current coming out of it.
    But given the right circuitry I should be able to get current flowing when I spin the fan. Am I right ?

    I guess what I am trying to get at is that if current is supplied to a device to get motion then it is a Motor. If motion is given to a device to generate current then it is a generator. At the end of the day the device is the exactly the same. It is the manner that it is used that differentiates whether it is a Generator or a Motor.
     
Loading...