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hall sensor arrangement around BLDC motor

Dharmendra Sharma
Intellectual 735 points
Other Parts Discussed in Thread: DRV5013, TIDA-00197

Hi friends,

I am going to make driver for CD_ROM BLDC motor (upgraded-- i had changed the winding and magnets).

It have 12 winding on rotor (each 3 in series and then in STAR(Y))

and also the stator is having 12 magnets at an anguler separation of 30 degree.

Now plse suggest me that

1. at how much angular difference the hall sensors should be connected.

2. which hall sensor would be best for it and also available on TI.

3. any good links for hall sensor to get some info.

Regards 

Dharmendra Sharma

INDIA

  • 0
    TI__Guru** 114905 points

    Hi Dharmendra,

    1) We will research this for confirmation. 

    2) Please look at the DRV5013, which is used in the TI reference design 

    http://www.ti.com/tool/TIDA-00197. In this case, the three hall sensors are placed at 45 degree increments.

    A list of hall sensors currently available can be found at: http://www.ti.com/lsds/ti/sensors/Digital-Hall-Effect-Sensors-products.page

    3) We will have to get back with you on this one also. What type of info are you after?

  • 0 in reply to Rick Duncan
    Intellectual 735 points

    hey Rick,

    Thanks for your quick response.

     My question is very simple. If there are only 3 finding on rotor then we place the hall sensors at 120 degree angular position and If there are 4 finding ion rotor then we place the hall sensors at 90 degree.

    But in this motor there are 12 winding present but seems to be only tree winding because each three are connected in series.

    So I am confused that how I have to place the hall sensors around motor (at 30 degree separation OR 60 degree OR 120 degree).

    As my calculation all three configurations of placing hall sensors are giving the SEQUENCE FOR ROTATING THE MOTOR (001, 000, 100, 110, 111, 011).

    Wan't to confirm Only 3 hall sensors I have.

     

    Thanks,

    Dharmendra Sharma

    INDIA

     

  • 0 in reply to Dharmendra Sharma
    TI__Expert 8885 points

    Dharmendra,

    it is simple equation: Hall sensor needs to be place 120 electric degree apart. So depending on rotor pole of your motor,hall sensor placement in mechanical degree is:

    Theta_mech = 2/P*120

    Best Regards

    Milan-Motor Application Team

  • 0 in reply to Milan Rajne
    Intellectual 735 points

    Hi MIlan, 

    Would u please explain the Theta_mech. Is this quantity doesn't depends on no. of magnets.

    I just founded the 120 degree by heat and trial method (for three winding it should be 120) by looking the direction of the magnetic field generated by each pole and averaging that and looking effect on hall sensor.

    Regards,

    Dharmendra Sharma

    INDIA

  • 0 in reply to Dharmendra Sharma
    TI__Expert 8885 points

    Dharmendra,

    Yes Thetha_mech depends upon number of magent or number of ploes, P.  In your first post, you mentioned 12 magnets, this means P=12 poles.

    So Theta_mech= 2/12*120 = 20 degree, you should place magets 20 degree apart from each other.

    Best Regards

    Milan-Motor Application Team

     

  • 0 in reply to Milan Rajne
    Intellectual 735 points

    Hey Milan,

    Are you sure with your conclusion. does I gonna get the 3 bit pattern like that (101, 100,110, 010,011, 001) in a whole rotation of motor.

    1. Did you have checked the direction of magnetic field for each 20 degree.

    2. and also one more... how taking a step of 20 degree we can complete a whole cycle in 6 steps.

    Regards 

    Dharmendra Shrama

    INDIA

  • 0 in reply to Dharmendra Sharma
    TI__Expert 8885 points

    Dharmendra,

    you need to understand the difference between electric angle and mechanical angle. My suggestion is based your input of 12 pole motor. For 12-pole motor,  60 mehanical degree would be equal to 360 electric degrees.

    All the six step you are mentioning is for electric degree not for mechanical degrees.

    Best Regards

    Milan-Motor Application Team

  • 0 in reply to Milan Rajne
    Intellectual 735 points

    hey Milan, 

    Thanks a lot and the one last question. which DRV hall sensor would be the best for this CD-ROM motor which is going to achieve 36,000 RPM. 

    thus one rotation would take 60*60/36000 sec = 1/10 sec= 100ms. (for change if reading 6 times)

    Thus which sensor would be able respond to quick in time less than 100ms/ 6 (becuse magnetic field will change ate the rate of 6 tomes in a sec).

    Thanks & Regards,

    Dharmendra Sharma

    INDIA

  • 0 in reply to Dharmendra Sharma
    TI__Expert 8885 points

    Dharmendra,

    For 12-pole motor,  hall sensor frequency at 36000 rpm would be = 36000*12/120 = 3.6kHz

    DRV5013 has banwidth of 20kHz which is quite sufficient to cater 3.6kHz ~ 6 times higher. You can go ahead with this device.

    Best Regards

    Milan-Motor Applicaiton Team

     

  • 0 in reply to Milan Rajne
    Intellectual 735 points

    Milan,

    Thanks a lot for this beneficial conversation.  

    Regards,

    Dharmendra Sharma

    INDIA

  • 0 in reply to Dharmendra Sharma
    Intellectual 735 points

    Milan ,

    It was my fault that didn't mention that the motor is out-runner type. The slots are on stator and stable elsewhere the pole are on rotor. :(

    Any modification regarding angle of hall sensor. 

    Regards,

    Dharmendra Sharma

    INDIA

  • 0 in reply to Dharmendra Sharma
    TI__Expert 8885 points

    Dharmendra,

    All the calculation remains same, irrespective of motor is outer-rotor or inner-rotor.

    Best Regards

    Milan-Motor Application Team

  • 0 in reply to Milan Rajne
    Intellectual 735 points

    Milan,

    Thanks a lot for your useful time for discussion.

    Regards,

    Dharmendra Sharma

    INDIA

  • 0 in reply to Milan Rajne
    Prodigy 10 points
    Hi Milan,

    This is a most usable information. I want to confirm my calculation with you.

    My motor has 20 pole. So as per your calculation, i should place hall sensor at 12 degree apart. But it is difficult for assembly. So I am planning to place at 36 degree so that i can get more resolution (i.e. 3 pulses per cycle). Am I right?
  • 0 in reply to Sohan kumar M
    TI__Mastermind 20985 points

    You can place the 3 Hall sensors at 0°, 12°, 24°.  You can also multiply any of those numbers by 4.

    Think of it this way: 12° of physical spacing causes 120° of electrical phase difference (where 120° is 1/3 of a Hall period).  4*12° causes 480° of electrical phase difference, which is the same as subtracting 360° for 120°.

    Hence, you can use spacings of 0°, 48°, 24°.  Or 0°, 48°, 96°.

    Best regards,
    RE