APL
100 kW
- Joined
- Aug 6, 2018
- Messages
- 1,113
Probably not a lot of difference, especially at slow speeds. Fact is, just about anything will 'work'. But It's good to know
about this stuff, to hone in on getting a better efficiency. At any rate, I feel a lot more comfortable about it.
I was going to mention the other side of the motor geometry equation, but ran out of time.
That would be the coil size and placement in a motor,.. my opinion, from what I've read so far anyway.
The coil width, or pitch, would be the same as with the magnets,.. all the slot to slot widths around the diameter of the
motor, added up, to make the 180 degrees.
But theres also 'Coil Span', which is all the coil widths added together,.. minus one.
Engineers have determined that you can diminish harmonics by adjusting coil span. A coil span of 144 deg. will neutralize
5th order harmonics, and a coil span of 154.3 deg. will take care of 7th order harmonics. So by averaging the two together
we get 150 degrees to take care of both.
Most all modern motors are made with 150 deg. coil spans.
That means that on an 18 coil motor, I need to take 17 of them and adjust their size until collectively, they have a 150
degree distance around the stator end to end. Then space all 18 of 'that size' evenly, to get them to fit in the 180 degree
diameter. After the winding size and fill has been determined, the core size would be whatever fits in the center.
I sure hope I have all that right, although it's kind of unclear as to exactly where on the coil the measurements are taken,
(outside, middle, or inside), I guess I'm assuming outside, or center of slot.
I also read something about the tooth overhang, or brim, and that it's used to even out the cogging fluctuations between
the cores, which will induce eddy currents in the magnets and back iron, as they pass over open slots.
It's an attempt to even out the slot gaps magnetically. I'm assuming that that the brim size is half the slot gap, minus
2-3mm so that wire can be placed in the slot, and to avoid magnetic fringing. The radius, or taper, under the brim is to
further even out the transition.
Just my take.
I'll have to re-measure this motors coils, to see if I'm any where near any of this. Not that it matters too much, it's
a little to late in the build to change anything very much, and I'm not that concerned about harmonics.
Like fetchter says, based on observation, were in the ball park. But it's good to know for the next build.
about this stuff, to hone in on getting a better efficiency. At any rate, I feel a lot more comfortable about it.
I was going to mention the other side of the motor geometry equation, but ran out of time.
That would be the coil size and placement in a motor,.. my opinion, from what I've read so far anyway.
The coil width, or pitch, would be the same as with the magnets,.. all the slot to slot widths around the diameter of the
motor, added up, to make the 180 degrees.
But theres also 'Coil Span', which is all the coil widths added together,.. minus one.
Engineers have determined that you can diminish harmonics by adjusting coil span. A coil span of 144 deg. will neutralize
5th order harmonics, and a coil span of 154.3 deg. will take care of 7th order harmonics. So by averaging the two together
we get 150 degrees to take care of both.
Most all modern motors are made with 150 deg. coil spans.
That means that on an 18 coil motor, I need to take 17 of them and adjust their size until collectively, they have a 150
degree distance around the stator end to end. Then space all 18 of 'that size' evenly, to get them to fit in the 180 degree
diameter. After the winding size and fill has been determined, the core size would be whatever fits in the center.
I sure hope I have all that right, although it's kind of unclear as to exactly where on the coil the measurements are taken,
(outside, middle, or inside), I guess I'm assuming outside, or center of slot.
I also read something about the tooth overhang, or brim, and that it's used to even out the cogging fluctuations between
the cores, which will induce eddy currents in the magnets and back iron, as they pass over open slots.
It's an attempt to even out the slot gaps magnetically. I'm assuming that that the brim size is half the slot gap, minus
2-3mm so that wire can be placed in the slot, and to avoid magnetic fringing. The radius, or taper, under the brim is to
further even out the transition.
Just my take.
I'll have to re-measure this motors coils, to see if I'm any where near any of this. Not that it matters too much, it's
a little to late in the build to change anything very much, and I'm not that concerned about harmonics.
Like fetchter says, based on observation, were in the ball park. But it's good to know for the next build.