How to find out unmarked BLDC motor specs?

Discussion in 'The Projects Forum' started by Rimbaldo, Jun 6, 2016.

  1. Rimbaldo

    Thread Starter New Member

    Jun 6, 2016
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    Hi to everyone!

    I´m new here, and I´m a dentist.

    I´ve been into electronics for a long time, as a hobby always, so I´m not a tech, but I enjoy building stuff.

    Here´s my problem. I have one BLDC 3-phase motor, but I don´t have it´s control box. I´ve searched ebay, and found some PCBs which are general BLDC controllers, and allow a wide range of volts (12-36), allow me to control it´s speed and direction, etc. So, I guess I could build a control box for this motor I have.
    There are no specs for it, and I can´t get it. It´s a replacement motor for a dental device, and there´s no info on what´s inside.

    I do have another one which is exactly the same, with it´s original control box (the one I use everyday)

    So, how can I find out on how many volts is this motor supposed to be driven, it´s current, etc? I know it´s not simple as attaching a multimeter in parallel and in series, because brushless are different..

    Is there a way for me to find out?

    I´ve have a 2 channel oscilloscope soon. I´ve ordered it over ebay, but it may take weeks to arrive to me...

    I have this other complete unit, working, with it´s original control box (sealed, never opened it). Sois there a way for me to "check" the volts, amps from the original controller to find out how much power I need to drive the motor?

    I know it´s easier to buy another original control-box, but i don´t want to spend more than 1000 dollars on it right now...

    I´m sorry if I didn´t make myself clear. English is not my first language..

    Thanks a lot!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    2,379
    One thing to be known is if it has any kind of commutation devices, an old method used be 3 hall effect devices, but if the motor only has three conductors for the stator then it will not have them.
    If you can measure the internal DC supply of a known controller this will give you an idea of the voltage required for a replacement drive.
    What is the physical size of the motor and can you post a pic?
    Max.
     
  3. Rimbaldo

    Thread Starter New Member

    Jun 6, 2016
    11
    0
    Hi! Thanks for your answer!

    Yes. It probably doesn´t have hall effect devices. It has only 3 wires. (In it´s casing there are 2 more separete, but they are definitely to drive an internal led that lights up a handpiece attached to it.

    The motor is inside a casing. But it´s no more than 40 mm long, and probably has a 19mm diameter.

    The power source for the whole unit it rated at 48V DC, 1.25A - 50 to 63 Watts. But it also drives a power led and the LCD of the control box also. I don´t know yet if the whole 48V drives the motor alone...

    I could open it and check for it´s connections, surely.

    But is there a way where I could measure it when the unit is working to check the voltage and current requirements also? Without opening it? I know it´s not so straight forward as it would be with a DC motor...

    Thanks a lot!
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,566
    2,379
    I have never worked with a BLDC motor that small, I would expect the current required would be quite trivial, normally a BLDC motor has two of the stator conductors powered at any one time, as opposed to a identical motor powered as a AC 3ph motor.
    But I would suspect this one is the former.
    The voltage is normally constant level with the switching frequency controls the motor RPM.
    Are you thinking of building something or looking for off the shelf replacement?
    Max.
     
  5. Rimbaldo

    Thread Starter New Member

    Jun 6, 2016
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    I can buy a replacement, but have to be sent to someone in the US and then this someone has to send it to me. The factory doesn´t sell the control box alone as a spare unit. Only the whole set-up. But if the motor fails, they sell spare motors. When I bought it, I bought one spare motor.

    But the whole unit costs close to 1200 dollars. So I´d like to build a controller of my own, to use this second motor..
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,018
    1,537
    A lot of the price likely comes from certification. Not knowing where you are from, medical devices in the USA have to be certified as to their safety. A DIY controller that's not built to "medical" level isolation could be very dangerous to the operator or the patient.
     
  7. Rimbaldo

    Thread Starter New Member

    Jun 6, 2016
    11
    0
    Hi!
    I won't plug it in my dental chair! I already have one plugged there! I want it on my lab!! I won't need the air pressure and water pressure cotrols!

    The lab one I have is bulkier and noisy! This one is lighter, silent, and has got strobg torque. That's why I want it on my bench!

    Thanks again!
     
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