Hall sensor placement

Hi,

I saw someone on this forum mounting hall sensors on the inside of a brushless dc motor by glueing them between the stator's teeth. If I want to add 3 Hall sensors on the inside of a 14 pole motor, does it still require 17,14 mechanical degrees, or will 120 mechanical degrees also work? I'm asking this because if I want to place them at 17,14 mechanical degrees, 2 of them would be in a slot, but the middle one would be on a teeth, which doesn't work.

Greetings!

Fabbe said:

Hi,

I saw someone on this forum mounting hall sensors on the inside of a brushless dc motor by glueing them between the stator's teeth. If I want to add 3 Hall sensors on the inside of a 14 pole motor, does it still require 17,14 mechanical degrees, or will 120 mechanical degrees also work? I'm asking this because if I want to place them at 17,14 mechanical degrees, 2 of them would be in a slot, but the middle one would be on a teeth, which doesn't work.

Greetings!

Click to expand...

Hi Fabbe,
mount them at 120 degrees is the best option ( they will all fit in the slots), the 17.14 degrees just makes it a little more compact when mounting them externally.

Ok I see, thank you very much!

Another question, if I use winding sequence AabBCcaABbcC does it matter where each Hall sensor should be placed? Can I for instance use this sequence: A H1 a b B C H2 c a A B H3 b c C ? Or is it dependent on the controller type? Is it trial and error then or is there a quick way to determine the right place?

Greetings!

Hi Fabbe,

I dont think it matters which slots you place the sensors in relative to the dlrk winding scheme, (as long as they are spaced 120 degrees -every 4th slot) because you can always compensate by changing the relative phase wire/sensor wire combination to keep the controller happy. (B.T.W. I have not tried this :? )


In the past I have always inserted the sensors between different phases. You can establish where the gaps are by passing a dc current (say 1 or 2 amps) through one phase and check the magnetic polarity of each stator tooth using a compass.

Burtie

Here's my understanding of it.

The Halls need to sense the magnetic field from the rotor. 120 degree spacing is always right, whatever the number of stator poles and rotor magnets. But with certain stator and rotor numbers you can divide the spacing angle.

Since the number of stators has to be a multiple of 3, there should always be a way of mounting the Halls between the stators at 120 degrees.

If they are not mounted on the stator, eg externally, then the spacing can be reduced by the number of rotor pole-pairs. Eg., 14 magnets = 7 pole-pairs. 120/7 = 17.14. Thus, in this case, 17.14 degree spacing gives the same signals as 120 degree spacing. That applies if the Halls are only sensing the rotor magnets; if they are placed where they will also see a field contribution from the stator windings, then the output signals with 17.14 degree are not exactly the same as with 120 degree spacing.

As regards mounting the Halls on the stators at angles other than 120 degrees. I think that can be exactly correct only when there is a suitable common factor between the number of stators and the number of pole-pairs.
Eg., with 12 stators and 8 pole pairs (16 magnets), there is a common factor of 4, so spacing at 120/4 = 30 is possible. Ie, adjacent stator slots.

Nick

> Tiberius , thank you for such a clear , condensed and understandable explanation of Hall sensor placement.

I wish you had written some application-notes by various big companies , they would be so much more easier to read ....

As Einstein said , if you can't explain it to your grandmother you have not understood it well enough 8)