BEMF and Hall signals

[The7]

Continued from http://endless-sphere.com/forums/viewtopic.php?f=2&t=4512

Crystalyte 4000: (Updated **)

1) It has 48 stator poles and 16 magnet poles (8 pole-pairs).
This gives 3 stator poles per magnet pole (180 deg).
1 stator pole = 60 deg.
There are 16 stator coils in one phase

2) Hall sensors spaced 2 stator poles ( 120 deg) at the gap between poles

3) The stator poles are skewed for 1 stator pole pitch (60 deg).
** Each coil is wound around two stator poles.
** The back EMF in one stator coil is a tent shape with a point top of 120 deg.

4) The resultant phase BEMF will be 16 times of (3) if the 16 stator coils are connected in series.

5) ** Due to the loaction of the Hall sensors in the gaps, the Hall signal could be configured as -90 deg, -30 deg, 30 deg or 90 deg with repect to the phase BEMF.

6) Since it is Y-connected, the resultant phase to phase BEMF will be 1.732 that of (4). There will be a further 30 deg advance when compared with (4).
Note. 1.732 times is not quite correct because it is not sinusoidal.

7) ** There is 60 deg for the phase BEMF in forward and reverse direction. If the forward BEMF is +30 deg wrt Hall signal, then the reverse BEMF is -30deg.

 

[The7]

MAC-BMC ( Fecther’s 600W motor):

1) It has 18 stator poles and 16 magnet poles (8 pole-pairs).
This gives 9/8 stator poles per magnet pole (180 deg).
1 stator pole = 180 x (8/9) deg = 160 deg
There are 6 stator coils in one phase

2) Hall sensors spaced 3 stator poles ( 480 deg) at the gap between poles.
Spacing 480 deg is equivalent spacing to at 120 deg.

3) The stator poles are not skewed.
So the back EMF in one stator coil is trapezoidal with a flat top of 20 deg.

4) The resultant phase BEMF will NOT be 6 times of (3) even if the 6 stator coils are connected in series.
Instead the resultant phase BEMF is very close to an sine wave with the maximum about 4 times.

5) Due to the loaction of the Hall sensors in the gaps, the Hall signal could be configured as -80 deg, -20 deg, 20 deg or 80 deg with respect to the phase BEMF. (Furthermore -40 deg and 40 deg are also possible). But there is no 0 deg.

6) It is delta-connected, the resultant phase to phase BEMF is same as of (4).

7) With the symmetrical location of Hall sensors, there is no difference in performance in forward and reverse running.

8) **** If the location of Hall sensors are shifted some distance to one side from the gaps, the location is not symmetrical (unless it is moved to centre of the stator pole). Thus the performance in forward and reverse will be not be identical. ****

 

[The7]

GL2 Hub Motor (solarbbq2003)

1) It has 51 stator poles and 46 magnet poles (23 pole-pairs).
This gives 51/46 stator poles per magnet pole (180 deg).
1 stator pole = 180 x 46 /51 deg = 162 deg
There are 17 stator coils in one phase

2) Hall sensors spaced about 1.5 stator poles with one only one at the gap between poles.
Spacing = 162 x 1.5 deg = about 243 deg (say 240 deg).
Then spacing becomes -240 deg : 0 deg : 240 deg.
-240 deg is equivalent to 120 deg.

3) The stator poles are not skewed.
So the back EMF in one stator coil is trapezoidal with a flat top of 18 deg.

4) The resultant phase BEMF will NOT be 17 times of (3) even if the 17 stator coils are connected in series.
Instead the resultant phase BEMF is very close to an sine wave (more sinusoidal the MAC-BMC 600W).

5) The Hall signal could be configured as –81 deg, -39 deg, 39 deg and 81 deg with respect to the phase BEMF. (Maybe it is also as –18 deg and 18 deg). But there is no 0 deg.

6) It is Y-connected, the resultant phase to phase BEMF is about 1.732 of (4). There will be a further 30 deg advance when compared with (4).

7) With the symmetrical location of Hall sensors, there is no difference in performance in forward and reverse running.

 

[fechter]

One note on the BMC motor (same on Puma):

The windings are placed in groups of 3 stator teeth. This is hard to explain, but starting at tooth 1, the winding goes directly to tooth 2 in the opposite direction, then to tooth 3 in the direction of #1. From tooth 3, the wire jumps over to tooth 10,11,12.

When the first coil is energized (tooth 1), the rotor will try to line up with tooth 2, since that is in the center of the group. This has an effect similar to a skewed pole.

 

[The7]

One note on the BMC motor (same on Puma):

The windings are placed in groups of 3 stator teeth. This is hard to explain, but starting at tooth 1, the winding goes directly to tooth 2 in the opposite direction, then to tooth 3 in the direction of #1. From tooth 3, the wire jumps over to tooth 10,11,12.

When the first coil is energized (tooth 1), the rotor will try to line up with tooth 2, since that is in the center of the group. This has an effect similar to a skewed pole.

Do you mean this MAC-BMC motor or Puma hub motor?
Each coil is simply wound on each stator pole (tooth).

It is expected that the BEMF and Hall signal for the Puma are identical in shape and in time displacement because Puma only has only double the nos of poles as MAC-BMC.

 

[The7]

Bionx hub motor:

1) It has 24 stator poles and 22 magnet poles (11 pole-pairs).
1 stator pole = 165 deg.
There are 8 stator coils in one phase

2) Hall sensors spaced 8 stator poles at the gap between poles
8 stator poles = 165 x 8 = 1320 deg => 240 deg spacing

3) The stator poles are not skewed.
The back EMF in one stator coil is trapezoidal with a flat top of 15 deg.

4) The resultant phase BEMF will NOT be 8 times of (3) if the 8 stator coils are connected in series.
The resultant phase BEMF is close to an sine wave.

5) The Hall signal could be configured as –82.5 deg, -37.5 deg, 37.5 deg and 82.5 deg with respect to the phase BEMF. But there is no 0 deg.

6) If it is Y-connected, the resultant phase to phase BEMF will be 1.732 that of (4). There will be a further 30 deg advance when compared with (4).
Note. 1.732 times is not quite correct because it is not sinusoidal.

7) With the symmetrical location of Hall sensors, there is no difference in performance in forward and reverse running.