BLDC motor

Discussion in 'General Electronics Chat' started by pazpaz, Sep 19, 2014.

  1. pazpaz

    Thread Starter New Member

    Nov 14, 2013
    19
    0
    Hello all,
    I am using BLDC micromotor from Saeshin
    it RPM range is 500 to 35000
    torque = 4Ncm
    I am using 1KHz PWM waveform with variable duty cycle from microcontroller and giving to motor driver IC
    L6205 and at the OUT pins of the L6205 motor is connected
    Can you tell me the relation between PWM and RPM. suppose I want to generate 5000 RPM then what setting in RPM I should do?
    Regards
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,382
    A BLDC motor is essentially a synchronous motor, so it depends on the pole count of the motor, which will give you the electrical revolutions per mechanical for each revolution.
    Does the motor have any form of electronic commutation? or post a link to the motor.
    Max.
     
  3. faley

    Member

    Aug 30, 2014
    94
    13
    Higher frequency will produce higher RPM in a similar industrial motor.
     
  4. pazpaz

    Thread Starter New Member

    Nov 14, 2013
    19
    0
    Hello,
    here is the link for the motor
    http://saeshin.en.ec21.com/Strong_E-type_Motor_Series--324317_2619598.html
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,382
    They are certainly very high rpm motors, up to 50krpm.
    I would expect those to be 2 pole motors, if so for e.g. at 50hz the rpm would be 3krpm.
    RPM= (50/Pole Pairs) x 60. (50/1) x 60 = 3000rpm.
    Max.
     
  6. pazpaz

    Thread Starter New Member

    Nov 14, 2013
    19
    0
    Hi,
    but I am using 1KHz pulse with duty cycle of 30% ON and 70% OFF which gives me 5500 RPM
    how I should relate this? what is the relation between RPM-voltage-PWM?
    what if I give 50% duty cycle?
    regards
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,571
    2,382
    One way to tell the pole count of a P.M. motor is to short all three stator wires and as you spin the shaft, count the number of 'bumps' felt, this number is the pole count.
    I suggest going to sites such as Picmicro that have rafts of app notes and explanations of controlling both AC sinusoidal and BLDC motors, both motors are virtually identical but the way they are controlled are quite different.
    One e.g. http://www.microchip.com/pagehandler/en-us/technology/motorcontrol/motor-types/pmsm.html
    http://www.microchip.com/pagehandler/en-us/technology/motorcontrol/motor-types/bldc.html
    Also see A-M-C, one of the major manuf. sites for example drives and engineering notes.
    Increasing the DC supply will increase the torque capability of the motor.
    As a general P.S. voltage should be at least 10% above motor rated voltage for PWM drives.
    Max.
     
    Last edited: Sep 23, 2014
    BR-549 likes this.
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