180 degree commutation with sensors vs standard 120

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Hummie
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180 degree commutation with sensors vs standard 120

Postby Hummie » 30 Nov 2017, 02:35

I heard with sensors you can commutate at 180 degrees with a 3 phase motor vs 120 and therefore get more torque. do people do this? I thought sensors were only a hair more efficient and at the lowest speeds but if this were the case I'd think you could get greater efficiency at any speed if there was a big load.

devin
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Re: 180 degree commutation with sensors vs standard 120

Postby devin » 30 Nov 2017, 16:11

Last edited by devin on 01 Dec 2017, 02:04, edited 1 time in total.

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Re: 180 degree commutation with sensors vs standard 120

Postby devin » 01 Dec 2017, 00:06

found this:

Image

Image Source:

the question becomes: does running a wye motor with 180 degree commutation instead of 120 degree commutation improve the electrical to mechanical conversion efficiency at the same rpm, battery amps and electrical wattage?

it would appear to my untrained eye that utilizing 180 degree commutation could possibly have the effect of lowering effective winding resistance and possibly increasing kv compared to 120 commutation, but at this point it's purely my speculation. in theory lowering the effective winding resistance should give more motor amps for the same number of battery amps, in theory giving more torque, but if the kv increases also as a result, then the KT torque per amp might decrease, so even though it's possibly more motor amps for the same battery amps, if the torque per amp is less, the greater motor amps @ same battery amps might result in the same net effective torque.

if (big IF) the "effective kv" is different in each mode then switching between the 2 modes could be another way to "switch gears" so to speak (besides delta/wye changeover switch) for either a higher torque mode or a higher top speed mode.
Last edited by devin on 01 Dec 2017, 02:31, edited 3 times in total.

Hummie
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Re: 180 degree commutation with sensors vs standard 120

Postby Hummie » 01 Dec 2017, 02:14

i'm still stuck on the old question of why a wye motor doesn't suck with a high load as it seems to only be using 2/3 the teeth and would be more likely to saturate having less iron. I feel like this question has to be answered before getting any more complex especially since ironically people say wye runs smoother with a heavy slow load. I thought somewhere around here someone surprisingly said that with FOC all phases are electrified. maybe I have it wrong in my memory. Last someone told me there was some crazy transformer black magic going on...that was the latest explanation I heard. It seems such basic basic circuitry but somehow not.

devin
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Re: 180 degree commutation with sensors vs standard 120

Postby devin » 01 Dec 2017, 08:49

i'm going to go out on a limb and make a strange prediction that switching from 120 degree to 180 degree commutation increases the "apparent" kv of delta but not wye.

i base this on the fact that when rewinding motors, shortening the conductor length increases the kv, but increasing the conductor thickness doesn't change kv. in the case of delta, we'd be effectively shortening the conductor length of one of the 2 paths the electricity takes through the motor, but in the case of wye, switching from 120 to 180, the conductor length isn't shortened... it's effectively thickened... and thickening doesn't change kv when rewinding motors.

i wouldn't be surprised if i'm wrong-- but i theorize perhaps 180 vs 120 degree commutation can reveal whether a motor is delta or wye from outside measurements based on whether or not there are changes to the "apparent kv."

Hummie
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Re: 180 degree commutation with sensors vs standard 120

Postby Hummie » 02 Dec 2017, 00:32

i'm going to go out on a limb and make a strange prediction that switching from 120 degree to 180 degree commutation increases the "apparent" kv of delta but not wye.
what's apparent vs real. ill assume you mean real would be from generated from the motor and apparent with an applied voltage to the motor. apparent not so appearent

i base this on the fact that when rewinding motors, shortening the conductor length increases the kv, but increasing the conductor thickness doesn't change kv. in the case of delta, we'd be effectively shortening the conductor length of one of the 2 paths the electricity takes through the motor , but in the case of wye, switching from 120 to 180, the conductor length isn't shortened... it's effectively thickened... and thickening doesn't change kv when rewinding motors.Id like to see a visual of the rotor and stator to see what we are talking about in terms of the timing of the fields. I'd have thought we were limited to certain combinations of magnets and teeth by the 120. but there are simulation programs and they're probably pretty right and I could do that. I know you could too. but can you do it on the vesc with sensors and what am I even talking about? ...someone told me with sensors you could do 180 vs 120 as is necessary using the back emf to orient. Does it do 120 or does it do 180 as standard with sensors?


i wouldn't be surprised if i'm wrong-- but i theorize perhaps 180 vs 120 degree commutation can reveal whether a motor is delta or wye from outside measurements based on whether or not there are changes to the "apparent kv."

devin
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Re: 180 degree commutation with sensors vs standard 120

Postby devin » 02 Dec 2017, 04:14


devin
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Re: 180 degree commutation with sensors vs standard 120

Postby devin » 02 Dec 2017, 05:09

after a bit more reading, i have a question— are “FOC” and “180 degree commutation” basically just 2 different words for the same thing? i should bow out of the conversation at this point as im only speculating.

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Re: 180 degree commutation with sensors vs standard 120

Postby rew » 02 Dec 2017, 19:26

No, From what I read above, the "180 deg commutation" is simply BLDC but with an extra motor coil powered up. (Y or Delta does not matter).

But if we think about what we want to achieve.... We have a permanent magnet in an electromagnetic field. We want to set up that magnetic field that has creates the most torque on that permanent magnet. Well... That's exactly what FOC does: It optimizes the D field vector to be just enough, minimizes the Q component. (the D causes the maximum torque per applied current, the Q field vector does not cause any torque).

This way of commutating would improve performance if the motor amp rating of say 15A would mean: The motor wires blow up at 15.1A. That is not the case. So running two coils at slightly less current instead of just one is going to win you very little.

devin
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Re: 180 degree commutation with sensors vs standard 120

Postby devin » 02 Dec 2017, 22:26



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