Electronic – BLDC sensors placement

brushless-dc-motorsensor

I am having some trouble in reversing the direction of a sensored 10KW BLDC motor.
Motor has 36 stator teeth and 40 magnets (20 pole pairs)

Apparently the hall sensors position is set for CW direction, and when rotating the motor CCW, the timing is wrong and efficiency is low.

Timing cannot be adjusted in controller (Kelly controller), so I am re-positioning sensors.

The problem is, that while for CW rotation sensors are placed inside stator slots(see image below),
CCW sensor position - in slot

…for CCW correct position (measured with an OSC) position never matches a slot.
Motor manufacturer tried to place sensors for CCW rotation like this (illustration, ignore zip tie):
sensor on top of stator teeth (please ignore zip tie, this was for testing)
This looked ok unloaded, but was creating a lot of heat and consuming too much power as I increased load.
I assume this is because the sensor is placed halfway between magnets and one coil, and therefore shows zero reading when coil polarity is same and stronger than magnet passing in front of it – Can anyone validate this theory?

The new placement I am experimenting with to solve this is under the magnets on the bottom side of the motor, with the 3 sensors 6 degrees apart on one small plate, facing the magnet narrow end:
bottom sensor board
sensor board front

Haven't tested this under load yet, but unloaded test shows the following behavior:
While testing unloaded at 20v, RPM increases as current increases up to around 2A, then when increasing throttle more, current drops to around 1.8A, and RPM increases as you increase throttle up to the expected max RPM for voltage.

This also happens on the CCW motors with sensors on top of stator.

On CW motors, current gradually increases to 3A for max RPM.

Can anyone tell why this is happening?

I would appreciate any comments on this arrangement and possible solutions.

Best Answer

Apparently the hall sensors position is set for CW direction

Placement of such sensors are direction agnostic as electrical machines are 4quadrant electromagnetic devices.

If this is sensor related I strongly suspect the sensors are wrongly placed. Maybe intentionally biased to provide phase advance in the CW direction (thus phase retard in the CCW direction)

What is more likely is any offset within the controller or wiring of the sensors to the controller is wrong.

Can you state why you think the sensors are wrong

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