Car alternator to DC motor

Discussion in 'Power Electronics' started by Mchael1919, Aug 10, 2016.

  1. Mchael1919

    Thread Starter New Member

    Aug 10, 2016
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    I have an old car alternator , is it possible to convert it to DC motor which will have permanent magnets on the rotor , I have seen on the Internet so that it can work in the generator mode , can and in motor mode ?

    The stator's coil acting in bad condition, all three wires are breaking with the coil , I soldered them , can it will be able to do correctly. I questioned a diode , coil and the place where the soldered, and it shows that OK. I'm all that disassembled and pulled out, and when connect stator to the battery , there is no magnetic force of attraction , put the rotor in, or other ferometal and no attractive, whether it is a bad sign , whether there should be a force of attraction, I still don't have magnets and ask from this reason?

    BLDC is probably a better option , but for me, more complicated and more expensive, I also damaged the rotor's coil.

    I am sorry for my bad english. Greetings
     
  2. AlbertHall

    Distinguished Member

    Jun 4, 2014
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    A DC motor has a commutator to connect the rotor coils differently as it rotates whereas an alternator has simple slip rings to connect to the rotor coil but offers no switching action. An alternator could use a permanent magnet rotor but car alternators use a coil to generate the magnetic field.

    No, a car alternator cannot be used as a DC motor though its starter motor could be used as a dynamo.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    PM on the rotor will require electronic commutation of the stator coils, essentially making it a BLDC.'
    Max.
     
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  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Only if P.M. field, the older series shunt wound starter does not make a good generator.
    You would need to exercise the field.
    Max.
     
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  5. AlbertHall

    Distinguished Member

    Jun 4, 2014
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    Older (OK, ancient) car dynamos used a wound field and were self-exciting like current alternators.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Ancient?? in the 2000's they still use series motors? they exhibit the most torque at low rpm.
    You were not talking 'Dynamos' but Starters.
    They were not self exiting, being series motors, the same current flows through both armature and field .
    Max.
     
  7. Mthokozisi

    New Member

    Feb 14, 2017
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    Hello everyone. I understand that the forum is old, but having been working on a project on converting an alternator I thought I could just share a few ideas. Yes you can run an alternator as a motor only if you do the following: 1. Remove the rectifier, connect three wires to the three stator windings and power these through an Esc for RC vehicles/copters.
    2. Connect two wires to the brushes( brushes should be disconnected from the regulator). Power the field(through the brushes) with say 6 volts to create a magnetic field.
    3. Use a servo tester to send signals to the Esc and the alt/motor should run just fine.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Yes it can be done as you describe but alternators have poor performance with regards to efficiency when used as a motor (actually when used as an alternator too). It is much better to use an actual BLDC motor.
     
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  9. MSFTF

    New Member

    Aug 11, 2017
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    I would try putting as much current into the field winding as it can take.
     
  10. Mthokozisi

    New Member

    Feb 14, 2017
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    Thank you for your respones, I chose an alternator because they come cheap a junkyard.
    I think I'd first try to put more current to the field windings to increase torque. I think if one uses a high amperage esc, they can get even more rpm, but they have to consider the windings' amperage. Thank you again. Would using a simple MOSFET circuitry achieve the desired current increament?
    Thank you in advance.
    I've been watching videos on YouTube from guys who've used this altmotor to power e-bikes and gocarts, so l belive this can be a powerful motor.
     
  11. recklessrog

    Active Member

    May 23, 2013
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    Excercise? take it for a walk ha ha. I think you meant Excite :)
     
  12. MSFTF

    New Member

    Aug 11, 2017
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    I think using MOSFETs in a circuit to control the current to the field winding is a good idea.
     
  13. Mthokozisi

    New Member

    Feb 14, 2017
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    Thank you, again for your response. Now my challenge is to build one such circuit. I'd very much appreciate it if anyone can with such a circuit.
    Thanks in advance.
     
  14. MSFTF

    New Member

    Aug 11, 2017
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    You're welcome. I would use a buck/boost circuit. Connect the field winding to +12v and then use buck/boost. Connecting the winding to + instead of - and then doing buck/boost let's you avoid needing level shifting for an Nch MOSFET, or needing to use a Pch MOSFET.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have used a simlple LM311 and power Mosfet for regulation when used as a generator, you should be able to achieve the same ran as a motor.
    Max.
     
  16. Mthokozisi

    New Member

    Feb 14, 2017
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    Thank you again for your help. I'll try to find both a buck/boost circuit and a regulator circuit using LM311 and try both of them. Thank you so much for your valued time.
     
  17. bassbindevil

    New Member

    Jan 23, 2014
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    I'm pretty sure Don Lancaster wrote about using car alternators as powerful stepper motors in one of his columns.
     
  18. tcmtech

    Distinguished Member

    Nov 4, 2013
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    There are a number of YouTube videos on the the conversion and it's not hard to do . Most are using off the shelf BLDC motor driver power control units (30 - 50+ amp) and a 1 - 2 amp DC feed to the rotor to make them work.

    Power output for their size compared to a proper BLDC motor is not so hot, 1 - 2 HP continuous for a 15 - 20# motor, but the bigger issue is the overall rather dismal efficiency given that most cheaper non commercial automotive alternators are at best 60 - 70% efficient so as a motor apparently most have a fairly poor duty cycle at higher output and loads. :(

    For intermittent high output bursts the better ones are actually not bad at all for what little investment is needed to make one! :cool:

    Electric cart.

    ~4KW!

    Starter motor cart way better though!
     
    Last edited: Sep 27, 2017
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  19. Mthokozisi

    New Member

    Feb 14, 2017
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    Thanks everyone. I think for my project an alternator can do. I need the alt/motor to run a convectional alternator to power a 2.5kw inverter through a battery to power a 0.75 kw/5A for water in an offgrid area . So I was thinking that an alternator converted to a motor should be able to move such a load. Bassbindevil would you please send a link to the Don Lacanster forum.
     
  20. tcmtech

    Distinguished Member

    Nov 4, 2013
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    Why can't the inverter run directly off the batteries? :confused:
     
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