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I have a BLDC hub motor (out runner type; 3 phase wires) for my electric bike. It currently has 1 set of hall sensors (3 pieces) and I would like to install a second set (3 more) for spare (in case one of the original 3 stops working).

Current hall sensor's locations: enter image description here
NOTE: on the photo the middle hall sensor is not installed since the photo was taken when replacing it with a new hall sensor.

In the following picture I have tried to indicate which wires serve which purpose: (The wires indicated in red are the motor phase wires) enter image description here The hall sensor-wires indicated in green in the picture go from the outside of the motor (top right in the picture) to the PCB (green circle in the picture) and via traces in the PCB the wires go to the 3 hall sensors. Color coding:

  • Red, Black = 5V DC
  • Brown = Temp. sensor
  • yellow, orange, blue = sensor signal wires

Photo from slightly different angle: enter image description here

There is also 1 wire for a temperature sensor among the wires inside the green circle but Its currently not connected.

There are hub motors which come with 2 sets of hall sensors from the factory and I would like to upgrade mine to 2 sets.

The current set was installed from the factory.

I was wondering where I should put the new set of hall sensors in order for the motor's timing (of the different coils) to remain unchanged (in other words so that I don't mess up the motor's timing), both sets of hall sensors have to be activated at the same time such that if i were to connect them in parallel (hall sensor A (set 1) to hall sensor A (set 2) they would only give 1 signal (if that explanation makes any sense).

Is my only option to either place the new hall sensors on top of the existing hall sensors (not sure if i have enough room for this) or to place the new hall sensors on the other side of the motor (current set of hall sensors are placed on top of the windings on the right side of the bicycle (when the motor is inserted), I could perhaps place the new set of hall sensors on top of the windings on the left side of the bicycle. (if you look at the photo I'd want to place them in the same location but on the side of the windings that is currently laying on the table (on the green cloth)). Any other (better) suggestions for placement of second set of hall sensors are definitely welcome.

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  • \$\begingroup\$ Not so sure if those are hall sensors, they are placed in positions where the rotor permanent magnet is far away. What about the device covered with black rubber and black cable? What's that for? \$\endgroup\$
    – Marko Buršič
    Feb 22, 2020 at 11:18
  • \$\begingroup\$ @Marko Buršič I believe the black silicone rubber is used to keep the hall sensors (I'm quite sure they are hall sensors) in place. the wires leading up to the hall sensors extend quite a way outward and i believe the top of the hall sensors themselves are placed quite close to the outer perimeter of the stator so they would be quite close to the permanent magnets of the rotor (but it's hard to see due to black rubber). I replaced the middle hall sensor some time ago, unfortunately I don't recall part number, will try and find a photo.. IIRC it was a digital hall sensor (replacement part) \$\endgroup\$
    – Maarten -Monica for president
    Feb 22, 2020 at 11:36
  • \$\begingroup\$ @Marko Buršič Also I was running the motor without the wires for these hall sensors attached for some time (because the connections of these wires inside the motor controller had come undone) and it was very noticable that the acceleration of the motor and top speed was drastically reduced and it appeared as if the amount of acceleration was 'luck based' (you had to be lucky to get approximately the right timing since the sensors were not connected). Pretty sure my motor controller can't use back-emf to determine when to fire the coil groups, some controllers can do this. \$\endgroup\$
    – Maarten -Monica for president
    Feb 22, 2020 at 11:39
  • \$\begingroup\$ @Marko Buršič with "the amount of acceleration was luck based" i mean that sometimes the motor wouldnt accelerate under load, even with full throttle, and if i were to release the throttle and re-apply it sometime later the acceleration would be greatly increased. indicating the original timing of the coils firing was off by quite some time (and perhaps slowing down the motor instead of accelerating it because the coils were energized too late)(that last part is just a theory though). The voltage going to these sensors is 5V DC. \$\endgroup\$
    – Maarten -Monica for president
    Feb 22, 2020 at 11:40
  • \$\begingroup\$ @marko bursic I edited my question and added some photos \$\endgroup\$
    – Maarten -Monica for president
    Feb 22, 2020 at 12:57

1 Answer 1

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You can place the other three Hall sensor in the next groove: That is: you rotate each Hall sensor (clockwise or counter colckwise doesn't matter).

The Hall sensors are needed to detect the commutation instant. The important thing is that the sequence be maintained, so the relative position and not the absolute position is the important thing.

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  • \$\begingroup\$ I guess that makes sense since the rotor is rotationally symmetrical so the absolute position of the hall sensor's can't matter. Thanks for your answer! \$\endgroup\$
    – Maarten -Monica for president
    Feb 22, 2020 at 23:45
  • \$\begingroup\$ I'm glad that I could be of assitance :) \$\endgroup\$
    – Ken Grimes
    Feb 23, 2020 at 10:50

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