Common circuit for motor and generator

Discussion in 'General Electronics Chat' started by electronicsLearner77, Feb 13, 2018.

  1. electronicsLearner77

    Thread Starter Active Member

    May 26, 2012
    95
    1
    I have a motor schematic for example MCLV-2 Development board. This will drive the motor using battery. The electrical energy is converted into mechanical energy. Now if i drive the motor externally using some other device. Then does the same circuit work as generator converting the mechanical energy to electrical energy that is charging the same battery? Is it possible? If not what are the changes i need to do in schematic? Please help.
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,414
    1,223
    If it's a magnet stator and coiled rotor yes it can be used as s Dynamo.
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    8,625
    1,965
    What motor are you intending to use? The schematic with that development kit is for driving a BLDC motor having Hall sensors and a quadrature encoder. The circuit, or parts of it, might need to be disconnected if the motor is used as a generator.
     
  4. dendad

    Well-Known Member

    Feb 20, 2016
    1,905
    486
    You will probably get power to charge the battery via the FET diodes if you spin the BLDC motor but I would not necessarily recommend it as there is a chance you could damage the circuitry. Although it may be ok. If you were to try it, make sure the FETs are all off so the diodes rectify the motor's AC output.
    Having the FETs connected to the battery and the rest of the drive unpowered then spinning the motor will charge the battery, but do so at your own risk.
     
  5. electronicsLearner77

    Thread Starter Active Member

    May 26, 2012
    95
    1
    Thank you can you please explain me the concept like when it is functioning as motor the mosfet legs will be switched based on rotor position. In the case of generator i still need to switch the mosfets or leave it in OFF state?
     
  6. dendad

    Well-Known Member

    Feb 20, 2016
    1,905
    486
    I think the FETs need to be all off so the internal diodes act as a 3 phase rectifier. Even so, if you blow something up, just know I warned you it may happen.
    Start with 6 x high speed diodes in place of the FETs, wired as the FET internal diodes are, and spin the motor to see what current you get to charge the battery. Put a fuse or even a lamp in line to limit the current for your test.
     
  7. electronicsLearner77

    Thread Starter Active Member

    May 26, 2012
    95
    1
    I will not use the circuit as it is i will redesign it using this as the base circuit. My requirement is it should work as both motor and generator. I have seen an application where they were switching the mosfets in generator mode as well. Is it possible? What are the advantages of working as generator in diode mode FETs Off and FETs are switching. Please advise.
     
  8. dendad

    Well-Known Member

    Feb 20, 2016
    1,905
    486
    I have not done this in my BLDC designs. To do it properly you need to have active components in the circuit to control the charging.
    Maybe Google "regenerative braking" to see how it is done correctly.
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    8,625
    1,965
    A FET when switched on drops a lot less voltage than the FET body diode would, hence less heating.
     
    electronicsLearner77 likes this.
  10. dendad

    Well-Known Member

    Feb 20, 2016
    1,905
    486
    Yes, but in this case, the diodes need to act as rectifiers. The motor will generate AC, not DC, and unless you can sense things to run the FETs as synchronous rectifiers, just keep the FETs off and use the body diodes.
     
  11. electronicsLearner77

    Thread Starter Active Member

    May 26, 2012
    95
    1
    But if i switch the mosfets in generator mode then it will work as motor. Will there not be any problems? Is there any application note explaining this? Please advise. I am not able to understand the concept.
     
  12. dendad

    Well-Known Member

    Feb 20, 2016
    1,905
    486
    Yes. Just keep the FETs off.
     
  13. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,172
    1,115
    An interesting historical curiosity was the Dynastart used on Yamaha RD series motorcycles.

    It was essentially an excited field dynamo with a second set of brushes for operation as a motor.
     
  14. Danko

    Member

    Nov 22, 2017
    469
    169
Loading...