Same debate again, motor windings!

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sn0wchyld   1 MW

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Same debate again, motor windings!

Post by sn0wchyld » Oct 22 2019 6:37pm

Brought this here so as not to clog a sales thread any more...
original thread:
viewtopic.php?p=1504502#p1504502
Theres a thread somewhere on here that discusses the below issues at length - ill post myself if I can find it, unless someone else does first?
ElectricGod wrote:
Oct 17 2019 12:43am
sn0wchyld wrote:
Oct 16 2019 9:31pm
ElectricGod wrote:
Oct 16 2019 6:52pm
Clearly there is desire for higher voltage. I want this too. I'd have bought 2 of the 24 fet version that worked at 150v max if they existed.
higher voltage controllers (mosfet based) are really only of benefit if you have a slow wind motor that is significantly underutilized at 80VDC, that you cant rewind (for whatever reason)... at least until you get to really big power levels where conductor sizes and breakers can get impractically huge (we're no where near such sizes here). I have one such motor that I haven't yet got round to rewinding (too many projects!) from its 17kv now to ~50kv - a higher voltage controller would be good and save me time/effort, but still not as good as a rewind for higher kv (80VDC mosfets are the highest power density, for example). Runnning 500A conductors really isn't so bad compared to dealing with 300VDC :P. One is just a bit more copper, the other is properly deadly. One is transient, the other is perpetually hazardous.
Not true...depends on what you are doing and why.

1. The hubmonster, when they were being manufactured were put on scooters and ran at 60v. Despite that, this motor does much better at 130v than it does at 60v and might be even better yet at 200v.

2. "Slow wind" indicates low Kv or lots of turns per stator tooth. This means more resistance in the windings compared to motors with a higher Kv.

3. All motors at higher voltage have a broader power band than they do at lower voltages. This is quite advantageous to have. There's excellent reasons why electric car makers use 380v.

4. Some motors due to the iron losses do poorly at higher voltages. I have a couple of large inrunners. They heat up running above 82v. These motors are a bad option above 82v. Others do great at higher voltage.,

5. Any motor is capable of only so much wattage. Current is what heats up a motor, not voltage. So to maximize motor wattage, run it at higher voltage and less phase current so it heats up less.

6. I've done rewinds on outrunners. I always get more copper on them than they had from the factory.

7. I think you need to read up about electricity. Current kills, not voltage. How many times have you been shocked by static electricity? That's voltages in the 100,000 to millions of volts range, but may be 10mA of current. Compere that to 48v and 400 amps...which will cook you to a crisp in seconds

So yeah...150v Nucular controllers would be way cool! I'd be running them at 131v just as soon as I could build the battery pack!

1. The hubmonster, when ...
This is why i mentioned rewinding motors - did you read my post at all? Yes, wound for 150+V they need... 150+V to realize their full potential. Rewind them for 80V will achieve the same as running them at 150V, only your controller will be better, and voltages (marginally) safer.The motor im talking about above is a mini monster after all...

2. "Slow wind" ...
ture, but irelevant when it comes to torque production. If you halve the Kv, you halve the turn count - so you can double the parallel wires, ie halve the reistance. Then you've only gone half as far for each winding, so you end up with 1/4 the reisistance... so the same copper losses per unit of torque produced. I^2R=P after all.

3. All motors at ...
No, read above. if you change the winding, then you end up at the same place. Cars use higher voltages because they have the funds to pay for safety systems, and at the same time 6+kA is hard to manage vs such safety systems. We're not talking about 500kw systems though - not even 1/10th of that. Im guessing you also skipped over where I said 'MOSFET BASED'? IGBTs are a different story/beast, as are the power levels involved.

4. Some motors due to the iron losses do poorly at higher voltages.....
Again, its not about voltage, but about the rpm they hit for a given voltage AND winding. Rewind those large in-runners with double the turns per tooth and they'll do fine at 82+v (assuming the motors do fine at 41V). Their torque capability wont shift at all though.

5. Any motor is capable of only so much wattage...
You just gave an example where maximizing voltage caused issues... see your own point #4. You can get a motor and match it to a controller with the right voltage. or you can get a controller with the right voltage and match it to a motor. The highest power density controllers are ~80VDC, so its (often, not always) worth getting or rewinding a motor to suit such a voltage, at least until >50-100kw. The relative simplicity of lower voltage is just a added bonus. There's a reason you can easily get a 12vdc switch to break 1000A (12kw) but relatively hard to find a 120Vdc swith to break 100A (still 12kw) and even harder to get a 1200Vdc switch to break 10A (still... 12kw). DC is a bitch to break as voltages rise, it maintains an arc easily and for a long time, particularly when coming from low impedance sources like batteries.

6. I've done rewinds on outrun.....
Not sure your relevance here? more copper fill is almost always good. Not relevant to rewinding to suit different voltages

7. I think you need to read up about electricit....

How do you get current to flow through something, like say... a motor? is it... voltage?
The fact is you need BOTH to be dangerous, because one is dependent on the other - and the quantity needed is dependent on the situation. 400VDC batteries are incredibly dangerous, because 400VDC is enough to get the current flowing through your skin, once the skin barrier breaks down your a dead man, because we are basically sacks of impure (ie highly conductive) water, covered in a thin layer of rather poor insulation (skin). 80VDC is far safer (Though still potentially deadly, ie if your hands are sweaty or you have a cut thats bleeding) because with dry hands you'll probably be fine to touch the terminals, though if you lick them say good by to your tongue. V=IR after all...
Me thinks it is you who need reed up on electricity (particularly low source impedance DC), young grasshopper :P


So yeah...150v Nucular controllers would be way cool!.......
The hubmonster...a 6 phase hub motor does great at double its design voltage (60v). It does fine at more than that. I have a couple of outrunners that do great at better than 40+ over their spec'd voltage. Just depends on the motor.


Again, and hopefully for the last time... only if you cant/dont want to rewind a motor. 150V controllers wont have the same power density as the current batch of ~80V controllers either, they'll be larger per kw (all else being equal). Rewind your motor with ~60-70% of the turns it currently has and run it at 80V with the current batch of controllers, and you'll be in a better place than waiting on a 150V controller - both because you'll have a higher power density controller, an easier/safer voltage to deal with, and you'll be able to get it by next week if you really want/have some time, just buy some wire and your good to go... vs ???? months/years until a 150V controller is developed (if ever).

Not that anybody will ever acknowledge this, but for a while in the 1990's I worked for a company that rebuilt and serviced industrial breakers. The smallest breaker I serviced was rated for 3 phase AC at 120v per phase and 600 amps.
Cool story. I've had electricians working for me that, despite decades of experience in AC and DC systems couldn't hook up 4 lead batteries in 2S2P configuration, calling me in confusion as to why they were getting 0V rather than 24V... despite having instructions, schematics and photographs of built units in hand. Experience is only useful if its relevant and you learn from it... and im unsure what experience with AC mains breakers in particular has with DC batteries, controllers and motors and how they interact WRT the motor windings. They are very different beasts other than the movement of electrons.



Happy to answer if you have further questions, but otherwise ill go the way of sam, and only answer this 'argument' for the sake of other readers. Vasilli, love ya work mate. Hopefully this saves you some work given you're already struggling to keep up with demand!!!

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Re: Same debate again, motor windings!

Post by district9prawn » Oct 22 2019 8:04pm

ElectricGod wrote:
Oct 17 2019 12:43am
5. Any motor is capable of only so much wattage. Current is what heats up a motor, not voltage. So to maximize motor wattage, run it at higher voltage and less phase current so it heats up less.
I feel like this interpretation of voltage and current is where a lot of misunderstanding comes from. Motor torque depends only on phase current. To make X nm of torque requires the same phase current regardless of battery voltage. Of course the battery current is less on the higher voltage system. Controller (mosfet) heating is also based on phase current and not battery current.

EG, if you did indeed mean battery current and not phase current, my apologies.
Neu 8057 6kW left hand drive hardtail with 18 fet Vesc: viewtopic.php?f=6&t=96754

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Re: Same debate again, motor windings!

Post by sn0wchyld » Oct 22 2019 11:11pm

district9prawn wrote:
Oct 22 2019 8:04pm
ElectricGod wrote:
Oct 17 2019 12:43am
5. Any motor is capable of only so much wattage. Current is what heats up a motor, not voltage. So to maximize motor wattage, run it at higher voltage and less phase current so it heats up less.
I feel like this interpretation of voltage and current is where a lot of misunderstanding comes from. Motor torque depends only on phase current. To make X nm of torque requires the same phase current regardless of battery voltage. Of course the battery current is less on the higher voltage system. Controller (mosfet) heating is also based on phase current and not battery current.

EG, if you did indeed mean battery current and not phase current, my apologies.
my presumption was this was the 'volt up, gear down' mantra - ie by gearing down less ph amps are required for the same torque output (at the wheel) - and then volt up to compensate for the 'higher' gearing to achieve the same top speed.

Point being you can achieve the same thing by re-winding the motor, keep the same battery, same controller and end up with the same benefits.

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Re: Same debate again, motor windings!

Post by larsb » Oct 24 2019 10:21am

Thumbs up to both of you, nicely explained.
Theres a thread somewhere on here that discusses the below issues at length - ill post myself if I can find it, unless someone else does first?
I’ve thought about doing a thread about ”the myth about the myth” for a long time. The myth thread is this one: viewtopic.php?f=2&t=64907#p974291

I agree on all above from sn0wchyld; winding has to be matched to controller and battery, there is a rated rpm for each motor that has to be reached for full performance. Either with high voltage/low kV or the opposite.

But there is more to add that i realised after winding a bit: winding transitions. A low turn motor (even with same copper fill goal) will have relatively less active vs inactive copper.

1) bunching and stacking of wires in the slots
It will not be possible to get the same copper fill on low turn motors since wires bunch up at the entry and exit of the teeth. More parallell wires, more bunching. It won't be possible to fill the slot entirely either due to the large bundles of parallel wires that cannot be stacked in an optimal way.
7CE8F74F-5D44-4C61-8E63-BDE05D9582D4.jpeg
7CE8F74F-5D44-4C61-8E63-BDE05D9582D4.jpeg (111.26 KiB) Viewed 1925 times
From left to right slot in picture, absolute max theoretic fill factor figures below.
Round wire dia 1.5mm:
58 turns per tooth, pi*1.5^2/4*58*2/267= 77%

Square wire 2.5x1.25:
32turns per tooth, 32*2.81597*2/267= 67%

bundled wire 7x1mm dia:
28 turns total 28*7*pi*1^2/4= 58%

—-> stacking of large bundles will lower fill factor.

The bunching at entry and exit of the teeth is not so easy to value, it’s substantial for the really low turn counts like 1, 2 and 3 turn windings.
Compare 10parallel*3turns winding to 3parallel*10turns and it gets pretty obvious.

2) Teeth winding and transitions between teeth
Torque vs loss comparison for the teeth:
4 turn*1-wire winding, current I for a given torque T
1 turn*4-wire winding, same copper fill, current needs to be 4*I for same given torque T.
4x parallel wires --> 1/4 of the resistance and 1/4 length copper --> total 1/16 of the resistance for the 1 turn winding makes the losses around the tooth the same as the 4 turn. Nothing new from above posts.
A9751881-CE8A-4818-B6C4-D9C97D6672CF.png
A9751881-CE8A-4818-B6C4-D9C97D6672CF.png (10.12 KiB) Viewed 2229 times
Transition wire losses on the other hand.. Length of transitions are the same for both windings so R*I*2 losses for the transitions are 4x higher for the 1T winding than for the 4T winding at the same power output.
(Current 4*I, resistance of transitions R=1/4 --> (1/4)*(4)^2)=4)

It will make a difference in efficiency. For single turn motors a lot, i’d guess several percent at full current. Difference will be decreasing/diminishing with higher turn counts. One might think ”who the hell runs such low turn motors as 1,2,3T?!”
I can name some names here on ES :D
Last edited by larsb on Nov 04 2019 1:03am, edited 5 times in total.
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Re: Same debate again, motor windings!

Post by sn0wchyld » Oct 24 2019 4:57pm

larsb wrote:
Oct 24 2019 10:21am
Thumbs up to both of you, nicely explained.
Theres a thread somewhere on here that discusses the below issues at length - ill post myself if I can find it, unless someone else does first?
I’ve thought about doing a thread about ”the myth about the myth” for a long time. The myth thread is this one: viewtopic.php?f=2&t=64907#p974291

I agree on all above from sn0wchyld; winding has to be matched to controller and battery, there is a rated rpm for each motor that has to be reached for full performance. Either with high voltage/low kV or the opposite.

But there is more to add that i realised after winding a bit: winding transitions. A low turn motor (even with same copper fill goal) will have relatively less active vs inactive copper.

1) bunching
It will not be possible to get the same copper fill on low turn motors since wires bunch up at the entry and exit of the teeth. More parallell wires, more bunching. This is not so easy to value, it’s probably substantial for the really low turn counts like 1, 2 and 3 turn windings. Compare 10parallel*3turn winding to 3parallell*10turn and it gets pretty obvious.

2) Teeth winding and transitions between teeth
Torque vs loss comparison for the teeth:
4 turn*1-wire winding, current I for a given torque T
1 turn*4-wire winding, same copper fill, current needs to be 4*I for same given torque T.
4x parallel wires --> 1/4 of the resistance and 1/4 length copper --> total 1/16 of the resistance for the 1 turn winding makes the losses around the tooth the same as the 4 turn. Nothing new from above posts.
A9751881-CE8A-4818-B6C4-D9C97D6672CF.png
Transition wire losses on the other hand.. Length of transitions are the same for both windings so R*I*2 losses for the transitions are 4x higher for the 1T winding than for the 4T winding at the same power output.
(Current 4*I, resistance of transitions R=1/4 --> (1/4)*(4)^2)=4)

It will make a difference in efficiency. For single turn motors a lot, i’d guess several percent at full current. Difference will be decreasing/diminishing with higher turn counts.

One might think ”who the hell runs such low turn motors as 1,2,3T?!”
I can name some names here on ES :D
Completely agree - end turn losses are marginal as end turns are still contributing to usefull flux, just not as much, and transition losses are (usually) marginal as they are a small % of the total (even less so as turn counts go up as you say) and the extra losses in both cases are only increased in proportion to delta I... as you still get double the conductor dia, just no longer half the length for those bits, so (fortunately) still no ^2 relationships which hurt so much... Just didn't bother to put all the caviates in as it detracts from the underlying point even as it somewhat undermines it hahah :P trying to explain the Forrest and ignore the trees for now, lest the trees block the view of the forrest.

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Re: Same debate again, motor windings!

Post by Punx0r » Oct 24 2019 5:28pm

sn0wchyld wrote:
Oct 24 2019 4:57pm
end turns are still contributing to usefull flux
Are they?

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Re: Same debate again, motor windings!

Post by sn0wchyld » Oct 24 2019 7:51pm

Punx0r wrote:
Oct 24 2019 5:28pm
sn0wchyld wrote:
Oct 24 2019 4:57pm
end turns are still contributing to usefull flux
Are they?
Yes (well... afaik/iiuc) ... a magnetic field forms around a current carrying conductor. the fact that this conductor makes a right angle turn, or runs 'beside' rather than 'between' some iron doesn't change this fact. If such a turn results in a air gap, then some of this flux inside the coil is wasted, but none the less some will still interact with the iron in each stator tooth, and increase the flux density within it. It is not captured anywhere near as well as it is between each tooth, but it still has some interaction with the rotor, and thus isn't entirely useless/wasted. Imagine a really long stator tooth, one that is wider (measuring along the circumference) than it is measuring axially. Does the section of winding running along the side of the stator tooth contribute nothing to the flux density captured and directed by the tooth? or just less than the sections between each tooth? Alternatively think of a perfectly round tooth - it'll give you a larger effective 'air gap' but no part of the winding is contributing more, or (most importantly) no part is contributing nothing to the flux within the tooth.

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Re: Same debate again, motor windings!

Post by major » Oct 24 2019 8:57pm

Punx0r wrote:
Oct 24 2019 5:28pm
sn0wchyld wrote:
Oct 24 2019 4:57pm
end turns are still contributing to usefull flux
Are they?
No.

Been through this on this forum before. I'm not too familiar with this forum search feature. Some recent white papers on the subject show negligible results. Or study Ampere's Law.

Regards,

major

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Re: Same debate again, motor windings!

Post by Punx0r » Oct 25 2019 4:12am

Sorry, my post was a bit tongue-in-cheek - I thought I was going to have to find that massive, angry ~40 page thread about it from a year or two ago :wink:

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Re: Same debate again, motor windings!

Post by kdog » Oct 25 2019 5:55am

I learnt a hell of a lot from that thread.... One of the best here. I was glued to it. Probs 3-4 years ago now . Time flies (with the right winding).

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Re: Same debate again, motor windings!

Post by larsb » Oct 25 2019 1:37pm

I wanted to check what the transitions do for a higher turn motor. Revolt rv120 has about 12cm of transitions per phase. Let’s pretend it’s star connected for simplicity :D then two phases are active at the same time with 24cm of transitions.

Original winding is 5*12T of 0.8mm dia wires. If we compare some windings and match the current to the same torque:

Resistance is 1.6087 mohm for the 5*12t winding transitions—>
RI2 losses @ 200A (which is about max for this motor) is 64W. System voltage 72V to get to the max rpm.
RV120 winding calc.JPG
Readily available controller combinations marked in blue
RV120 winding calc.JPG (40.88 KiB) Viewed 2076 times
We always say that the turn count can be matched with the correct controller and battery to get same performance but it has some boundaries, eh?

Already with the 6 turn winding it’s harder to find a suitable >36V 400A controller. The real point is that motor winding must be matched with controller and battery and be able to get to the max rpm to get max power - within reasonable volts and amps :D

One thing i thought about:
A normal power/rpm curve has the peak power before max rpm since BEMF lowers the current that flows in the winding. That should mean that it’s possible to use a higher voltage (or higher amp&kV) system with rpm limited by the controller in order to increase max power and have max torque at all speeds. Wheelies at 100km/h :D
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Re: Same debate again, motor windings!

Post by sn0wchyld » Oct 29 2019 6:02pm

larsb wrote:
Oct 25 2019 1:37pm
I wanted to check what the transitions do for a higher turn motor. Revolt rv120 has about 12cm of transitions per phase. Let’s pretend it’s star connected for simplicity :D then two phases are active at the same time with 24cm of transitions.

Original winding is 5*12T of 0.8mm dia wires. If we compare some windings and match the current to the same torque:

Resistance is 1.6087 mohm for the 5*12t winding transitions—>
RI2 losses @ 200A (which is about max for this motor) is 64W. System voltage 72V to get to the max rpm.
RV120 winding calc.JPG
We always say that the turn count can be matched with the correct controller and battery to get same performance but it has some boundaries, eh?

Already with the 6 turn winding it’s harder to find a suitable >36V 400A controller. The real point is that motor winding must be matched with controller and battery and be able to get to the max rpm to get max power - within reasonable volts and amps :D

One thing i thought about:
A normal power/rpm curve has the peak power before max rpm since BEMF lowers the current that flows in the winding. That should mean that it’s possible to use a higher voltage (or higher amp&kV) system with rpm limited by the controller in order to increase max power and have max torque at all speeds. Wheelies at 100km/h :D
great post mate - 5% variance is higher than I'd have thought. That said, its 5% change in efficiency (ignoring transitions and just looking at end turns right? so a underestimation if so) across a kv/voltage/amp range of 6000% - so a relatively marginal change in efficiency for a pretty extreme change in kv etc in anyone's book i think hahah. I was more referring to the benefits of a 80v controller vs a 150v controller, but yes outside of that the ratio can change more dramatically. Interesting too that the benefits from a very high turn count can offset the relatively high switching losses of a IGBT based controller (vs MOSFET). 'tis why I like this forum, even when your wrong (or not quite right) you can learn something.

For interests sake, what is the ratio of transition to 'useful' wire? I'm curious how the net copper losses vary by winding?

I did find a great thread by the way, really great info and changed my thinking on the subject (prompted by major).
viewtopic.php?f=30&t=93145&p=1506819#p1506819

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Re: Same debate again, motor windings!

Post by larsb » Oct 30 2019 12:41am

This calculation is only for the transitions between coils, not endturns. I’ll add in the total copper losses.
For interests sake, what is the ratio of transition to 'useful' wire? I'm curious how the net copper losses vary by winding?
Ride on!

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Re: Same debate again, motor windings!

Post by Hummina Shadeeba » Jan 26 2020 1:04pm

Why would the transition wire losses be any more with less strands in parallel? Id think it would amount to the same copper in transition for the same amount of turns regardless of how many strands it is.

I’ve read higher voltage amounts to higher current ripple and losses in the motor regardless. Unless there’s additional bits added to smoothen it

LRK winding of every other tooth seems to allow more wire as it doesn’t have the blockages that come from having to fit two coils in a single slot (and safer with less chance of shorting across phases).

LRK has a higher winding factor amounting to a better magnetic circuit. It does have more endturns and losses there especially with short motors

Square wire is very expensive in any sizes smaller than 15 or 14 awg and also doesn’t seem worth using in those smaller sizes unless you’re obsessively careful as it twists and then produces less fill.
Last edited by Hummina Shadeeba on Jan 26 2020 1:16pm, edited 1 time in total.

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Re: Same debate again, motor windings!

Post by larsb » Jan 26 2020 1:16pm

Please quote where you see this (i don’t mean that)

The 2.5x1.25 wires i have used myself, wasn’t that expensive - if it’s for a business, then probably it is. But then you won’t wind more than 40-50% copper fill anyway since labour will cost too much
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Re: Same debate again, motor windings!

Post by Hummina Shadeeba » Jan 26 2020 1:37pm

Rectangular like you got but longer that could go the full length of the slot top to bottom, and then flatten it on an angle make it triangular. I’ll have to try that. And what I think we’re both calling transitions: the wires going from tooth to tooth, they would be 10x1 triangular ribbon. And could also cool the wide ribbon transits. No?

Then again pressing the ribbon wire to be rectangular twice for each turn could be a huge time suck besides being awkward.
Last edited by Hummina Shadeeba on Jan 26 2020 3:39pm, edited 1 time in total.

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Re: Same debate again, motor windings!

Post by Hummina Shadeeba » Jan 26 2020 3:30pm

I still don’t understand how transitions, the magnet wire connecting wound teeth, transits, will have more losses if a high kv and fewest turns. As you show it with parallel strands with your graph if you added resistance of the wire it will decrease in proportion to the more strands in parallel.
A 10kv motor vs 100kv if they have the same copper should be the same I^2r losses in the transits for a given amount of torque output. Maybe not what you’re saying.

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Re: Same debate again, motor windings!

Post by John in CR » Jan 26 2020 10:24pm

I like to simplify things, and simply put, power = torque x rpm, and the torque and rpm limits of our PMDC motors is determined by its iron core and magnetic circuit. How the copper is wound on the stator (assuming equal copper fill) just sets the voltage and current to get back to the same place (torque, rpm, efficiency, etc), because changes in the winding vary things in direct proportion.

This means there is no such thing as a "higher torque" wind of the same motor, lower Kv motors aren't more capable or more efficient climbing hills, etc. Yes higher turn count motors make more torque per amp, but the long thinner length of copper means lower current for the same heat.
This does come with some caveats:
1. I suspect that some motor manufacturers (specifically some geared hubbies) don't fully understand this and wind different turn count versions of their motors with the same thickness of copper, essentially disregarding copper fill. In those cases of course the higher turn count motors are better and more efficient, simply because they have more copper on the teeth.
2. The limited availability of controllers that handle battery voltage higher than about 95V means that higher Kv motors are generally capable of higher power as long as the rpm limits don't come into play. The voltage limits of readily available controllers makes low Kv motors simply slower and lower power.

I believe that the "end turn losses" thing is blown far out of proportion. This view comes from my 6 phase motors, which are wound as dual 3 phase motors with every other tooth belonging to one 3 phase set. This results in a lot more end turn copper than a 3 phase motor. If the non-productive end turn copper is such a bad thing, then how are these motors capable of 95% efficiency which is unheard of in a hubmotor.

For you guys who rewind motors, you might want to consider going 6 phase with your next rewind for several of reasons. Each controller only needs half the current, making controller selection broader for high power. Winding to higher Kv is easier than for a 3 phase based on something Larsb said above, because to get to a given Kv each tooth gets double the number of turns than if wound as 3 phase, so the copper is easier to bend and fit a high copper fill %. The higher turn count also gives the motor greater inductance, so it's an easier load for the controllers to push.

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Re: Same debate again, motor windings!

Post by Punx0r » Jan 27 2020 4:31am

Having a high ratio of end-turn length to active winding between the stator teeth intuitively would seem to favour long stator motors, yet it's interesting to observes that many high-efficiency BLDC motors are slim, panacake style construction. So there's definitely more to it than "do all you can to minimise end turns". Weighed against that must at least be that a pancake style motor inherently produces torque more efficiently, with torque increasing with the square of diameter, but only proprtionately to length.

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Re: Same debate again, motor windings!

Post by thepronghorn » Jan 27 2020 3:36pm

Hummina Shadeeba wrote:
Jan 26 2020 3:30pm
I still don’t understand how transitions, the magnet wire connecting wound teeth, transits, will have more losses if a high kv and fewest turns. As you show it with parallel strands with your graph if you added resistance of the wire it will decrease in proportion to the more strands in parallel.
A 10kv motor vs 100kv if they have the same copper should be the same I^2r losses in the transits for a given amount of torque output. Maybe not what you’re saying.
Transitions are a fixed length whereas tooth windings and end turns vary in length based on the cross section of copper you are winding with.

The reason turn count doesn't matter in tooth windings and end turns is because changing cross section of copper changes both resistance per length of wire and the length of the wire needed to wind. This is critical because losses are I^2R.

If you wind with 2x copper cross section, I for same torque is 2X, R is 1/4X since the copper is 1/2X resistance per length and the length needed to wind a tooth is 1/2X - 1/2*1/2=1/4. P=I^2R=(2*I)^2*1/4R

Since the transitions are a fixed length, they are only 1/2X the resistance from the increase in copper cross section, so losses are 2X instead of the same.

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Re: Same debate again, motor windings!

Post by Hummina Shadeeba » Jan 27 2020 5:08pm

with fewer turns, its shorter wire, and more of that wire is wasted in transits. Ok I get it thanks! never heard that before.

Someone was saying with lrk winding it’s also less transits as even with DLRK winding two teeth beside the wire must come across the stack to bottom of next tooth and bungs it up. Not a transit per say but maybe even more a loss. Makes sense and Lrk seems the best for many reasons.

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Re: Same debate again, motor windings!

Post by John in CR » Jan 27 2020 8:19pm

Now that I too understand what the "transitions" are, that's what is bigger % of the copper on my motors wound for 6 phases not end turns. I have one apart right now and will try to remember to take a pic tomorrow. The high efficiency despite having long transitions slathered with a thick epoxy to prevent loose strands tells me it's just not a big enough effect to worry about. That makes sense too, since the phase wires are essentially transitions as well.
Last edited by John in CR on Jan 28 2020 9:59am, edited 1 time in total.

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Re: Same debate again, motor windings!

Post by Hummina Shadeeba » Jan 27 2020 8:49pm

how do you know your motor is high efficiency? lets see it and explain then.


LRK winding seems the best winding to do when looking at winding factor in simulator http://www.bavaria-direct.co.za/
and does have advantage with less transits.. or having to go to the bottom again of a new tooth causing an out of alignment wire bunging it up. just one big wrap up down up down up down..without concern for whats beside. in my experience I can get way more copper on. it starts to get out of hand literally and the coils will collapse before it runs out of space. it fits in the slot but your on your fourth row and it ...would be nice to peg it there against itself with some fast glue and then could build off itself without collapsing.

lesson learned from above, which makes total sense if what I wrote is the same as your math. very neat and intuitive or something really.

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Re: Same debate again, motor windings!

Post by John in CR » Jan 28 2020 10:08am

Hummina Shadeeba wrote:
Jan 27 2020 8:49pm
how do you know your motor is high efficiency? lets see it and explain then.
The factory tests reports showed over 94% peak efficiency, and that was with tire losses on the dyno. Of course no one believed that back in 2012. I've been running them at extreme power since then, higher than anyone on the forum until Rovi blew his double wide QS 273 after just a few runs. Running high power (20-30kw) pushing over 200kg loads in a mountainous country without heat problems was proof enough for me that the factory claims were correct. Then along came Miles' very useful motor comparison excell spreadsheet, which calculates power, losses, efficiency, etc, so I measured the vital stats needed, and the spreadsheet predicts even high peak efficiency, especially at higher voltages. Go check it yourself.

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Re: Same debate again, motor windings!

Post by Hummina Shadeeba » Jan 28 2020 12:17pm

What about it makes it high efficiency?

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