Brushless DC motor control

Discussion in 'The Projects Forum' started by T2Manf, Nov 5, 2014.

  1. T2Manf

    Thread Starter New Member

    Nov 5, 2014
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    Hello,

    I am very new to electronics and am really just learning about transistors and some basic sensors. I am looking to create a simple circuit using a hall effect sensor and a transistor to turn on and off a single coil to make a very simple BLDC. I have been successful in wiring the Hall effect ( 1751 948E) and also getting my transistor (TIP115) to work...separately. The problem is when i try to use the output from the hall effect to switch the transistor. The output from the hall effect is 3 mV and is not sufficient to saturate the transistor. I need help in creating a circuit to amplify the 3mV to switch the transistor or any suggetions on how to do this. Any help would be great. Thank you for your time :)

    A
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The output of the Hall sensor is open collector NPN, so it should be simple to use a pull up resistor in the collector and get full voltage swing on the output.
    Can you post the circuit you have?
    Max.
     
  3. T2Manf

    Thread Starter New Member

    Nov 5, 2014
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    Thank you for the help :) I have to go to class this afternoon so i wont be able to test what you have suggested until later. But if i understand correctly, i place a lets say 10k resistor from the hall effect output into the base? This increases r and thus increases V? So if i measure the current from the output of the hall effect i should be able to calculate the size of the resistor if i ant 3V going to the base pin? Thank you again
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You require a pull up resistor from hall output to +ve, value dependent on what +v you are using.
    Your diag also shows the base and emitter shorted? Consequentially the transistor will never switch.
    Max.
     
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    To quote you, " using a hall effect sensor and a transistor to turn on and off a single coil to make a very simple BLDC." Don't be discourage if your single coil motor doesn't turn.:) A BLDC needs more than a single coil to rotate. It in the very least needs three phases, sets of coils working separately. Each phase needs a pair of coils opposite each other, with a opposite polarity on each coil.
     
  6. Rasmus Ørndrup

    New Member

    Nov 6, 2014
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    Shortbus is right here. You won't be able to drive your BLDC through these sensors either. You'll (in most cases) need a uController to calculate on the signal which the Hall sensor gives. The uController then turns on or off transistors/mosfets on the bridge running the motor.
    I'am currently having problems running a BLDC from BEMF signals for which i have opened a thread. You can see a design in the thread wich should give you an idea: http://forum.allaboutcircuits.com/forums/the-projects-forum.6/

    You'll use the Sensors to find out when to commutate the motor, instead of the BEMF i am using.
    Hopefully you can use this.
    Depending on "how" new you are to electronics, you might want to buy an actual 'bldc esc' to control the motor.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  8. T2Manf

    Thread Starter New Member

    Nov 5, 2014
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    Sorry i said coil i meant pair of coils :) I am pretty sure i should be able to make this circuit work. Perhaps i dont understand the transistor well enough. I want my coil voltage to be across the emitter and collector while i use the out of the hall in the base to switch the transistor? And i will use a pull up resistor to boost my out put from my Hall effect. The big issue i fear is that the output fromt he hall effect is only around 3mV.
     
  9. T2Manf

    Thread Starter New Member

    Nov 5, 2014
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    SO i have updated my circuit once again but no luck. This time hall effect out put to base with 10K pull up. +9v in series with anLED and 330ohm resistor to the collector. Base pin in series with 10K resistor to ground.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The main thing is to get the swing on the Hall sensor output from 0v to +v, a 300 ohm resistor/led combo should do it, does the LED light?
    Max.
     
  11. T2Manf

    Thread Starter New Member

    Nov 5, 2014
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    No the LED does not light up, i think that i might have shorted the transistor at one point or another i am going to purchase a new one tomorrow and try again.
     
  12. T2Manf

    Thread Starter New Member

    Nov 5, 2014
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    So i think the problem is that im using the wrong type of hall effect. The one i have varies its voltae with magnetic field but im looking for an on off bipolar hall effecy any suggestions?
     
  13. MaxHeadRoom

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  14. T2Manf

    Thread Starter New Member

    Nov 5, 2014
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    Finally got it to work. Turns out Hall effects allow for the lfow of current like a transistor so i had to have my load powered by VCC i was trying to power my load with the out put :p. Once i got this working it was simple enough to add the transitor to the ciruit and now i have a hall effect switch an LED and a transitor which has the coils attached to it!!!! Thanks so much MaxHeadRoom. You helped me a lot if nothing else but just keeping me motivated. I consider this the first real ciruit ive built so thanks !!
     
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