Do I really need to use a hall sensor on my motor controller

Thread Starter

TommyLee

Joined Sep 22, 2020
7
I want to purchase a new brushless controller for my 40V DC Motor that uses PWM. Do i have to use the hall sensor if the new controller has it? I would like to just use a potentiometer to drive the speed. There is no hall sensor in my motor.
 

MaxHeadRoom

Joined Jul 18, 2013
21,434
What is the make and/or origin of the motor, generally for P.M. AC or BLDC motors, some form of commutation is necessary, either hall or by current sensing.
What type of brushless controller were you thinking of, BLDC?
Max.
 

Thread Starter

TommyLee

Joined Sep 22, 2020
7
What is the make and/or origin of the motor, generally for P.M. AC or BLDC motors, some form of commutation is necessary, either hall or by current sensing.
What type of brushless controller were you thinking of, BLDC?
Max.
Banggood 1592604 brushless controller. Does have a Hall effect connector. My motor. Now with a bad/failed drive does not use hall, must be integrated in the 3 ph coil current.
 

MaxHeadRoom

Joined Jul 18, 2013
21,434
Banggood 1592604 brushless controller.
This would appear to be a BLDC controller not the 3ph AC.
The motors are identical, just the commutation is different.
You would need hall effect or feedback sensors of some kind, motors with encoders have commutation tracks included now, which are much more accurate than the old Hall method.
For operating with commutation method of some kind, you need to know the pole count of the motor, which can be found by shorting the 3 stator leads and revolve the armature one turn and count the 'bumps'.
Max.
 

shortbus

Joined Sep 30, 2009
7,945
The ESC is for a E-bike or scooter. Wouldn't the Hall input be for a throttle/speed control? Many bikes/scooters use a Hall sensor throttle.
 

Thread Starter

TommyLee

Joined Sep 22, 2020
7
This drive is from a lawn mower. I assume that there is no speed control but that is my problem. I am guessing what is used to control the motor. I know that the motor side of the controller is yellow, green, blue PWM with one T1 wire from the battery. I know the power source is a 40V lithium battery black/red. The control of the drive is a ribbon cable with four wires. They came from switches in the handle of the mower. They are just momentary rocker arm switches. One switch for start which is held until the mower starts and then is released. Second switch is held closed with a spring actuated lever if you let go the motor stops. The third switch is a rocker arm switch held closed by extending the folding handle all the way out. I assume that the third switch is a safety device to ensure that the handle is fully extended before running the motor. There is a fourth circuit which drives the led lights. This fourth circuit gets its voltage from the controller and converts it to 5 vdc.
 

nsaspook

Joined Aug 27, 2009
7,594
With proper hardware you don't need Hall sensors for some level (typically with better shaft position sensing you have wider and better levels) of performance with controllers designed for both methods of operation.



PM brushless Motor commutation (a reversing function) is the process of converting a DC supply into a suitable AC signal to rotate the motor at the desired speed, torque and maybe a desired shaft position. To properly commutate the DC source signal across the motor coil(s) as a AC current (reversing polarity) you need to know the proper position of the motor magnets and the field that will be generated by applying the power supply current to the them aligned at angles designed to push and rotate the motor shaft. With a brushed DC motor the brushes are set in a position to provide DC to reversing AC commutation at the correct magnet to coil angles at the correct shaft position. Without brushes this positional data for a external circuit that provides the commutation function must come from something that gives us the motor shaft to coil alignment position.

(Sensored) Hall sensors provide a code that gives us this positional information properly apply polarity and timing for the current sequencing as an AC signal to the motor coils.

http://blog.aerotechmotioncontrol.com/2012/08/08/commutation-and-linear-motors/


The commutation reversing function here of the brushes converts AC from the generator to DC.

(Sensorless) is a little tricky to understand without some basic understanding of induction laws but basically we are looking (sampling with no motor drive) to see the level of push-back (coil cutting flux lines) to our supplied signal as an indication of where the motor shaft is IRT magnets and motor coils. We then use this information exactly like the Hall example above for DC to AC signal commutation.
https://www.allaboutcircuits.com/technical-articles/sensorless-brushless-dc-bldc-motor-control/
Sensorless BLDC motor control—sometimes called sensorless trapezoidal control of BLDC motors—uses back EMF (BEMF) for determining the location of the motor's rotor (the motor's rotating part) with respect to the motor's stator (the stationary part).

A voltage applied across a motor's winding forces the motor's rotor to turn. The movement of the rotor through the motor’s magnetic field, however, is analogous to the behavior of a generator, and consequently the motor not only receives an applied voltage but also generates its own voltage. This voltage is referred to as back electromotive force, or back EMF, and it is proportional to the motor's rotational speed. Back EMF can be used to determine a motor's rotor speed and position—no sensors are required. Controlling a motor by means of back EMF is not a simple task; most sensorless BLDC motors are controlled using a microcontroller, a digital signal processor, or a dedicated driver IC.
Obviously with an already AC signal of the proper type you don't need additional commutation with a motor designed to run with an AC signal.
 
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MaxHeadRoom

Joined Jul 18, 2013
21,434
The BLDC and P.M. 3ph AC motor are practically identical, the difference is in the commutation, in the BLDC, only two winding's are energized at any one time, in the AC 3ph the supply is a 3ph sinusoidal power is applied.
One can be converted to the other, I have done this in the past by converting 3ph to BLDC.
Max.
 

nsaspook

Joined Aug 27, 2009
7,594
The BLDC and P.M. 3ph AC motor are practically identical, the difference is in the commutation, in the BLDC, only two winding's are energized at any one time, in the AC 3ph the supply is a 3ph sinusoidal power is applied.
One can be converted to the other, I have done this in the past by converting 3ph to BLDC.
Max.
Yes, commutation of the DC power source to a 3-phase AC motor drive signal. BLDC block-commutation using Hall coding (two winding's of three are energized at any one time for the positional code duration (100%) using simple DC ON/OFF switching) is just one way to commutate DC power for a BLDC synchronous motor.

Block (trapezoidal commutation, six-step commutation or 120-degree commutation) using a DC switch:

Comparison of Commutation Methods
With Sensor and Sensorless control methods

Space Vector Modulation
 
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