More thinner strands vs less thicker strands

[Jellyfish0]

correction
I meant to say both motors would have the same mm² of copper> same amount of copper. NOT SURFACE AREA

Assuming two motors have the same overall surface area of
copper strands and turns, but motor A one has 15 strands while motor B has 25 strands

will there be any meaningful difference between them?

I only read about a theoretical skin effect difference

Example to two motors with identical surface area:

Motor A: 10 strands> each 1mm²
Motor B: 10 strands>each 0.5mm² also
Same amount of turns for both

 

[DogDipstick]

Yes, this is a factor certainly.

It changes alot of things, like power output and rpm/volt speed.

Take the Cromotor for example. Cromotor vs the QS 205V3motor.. both fit in identical shells, both come in 4T variations. Both have the same stator metal thickness, and number of laminations. .

Cromotor is labeled as "4T x 18strands" ( 4T x 18)

Four turns of 18 strands.. ( thick thick wire)... This motor handles 6000w and will burn out fast on a stall event ( locked rotor current). 6000w motor, the kV is rather low for a " 4T" at 8.9 kV.

QS205V3 4T 12kV motor is labeled as " 4T x 30strands" ( 4T x 30)

A QS 204 " 4T x 30 strand" motor is 11.39kV. It has a " 4 x 30".. 4 turns of (and they make most all variations. ) 30 strands... so thinner wire, and a higher threshold tolerance for " locked rotor current"... This motor handles 3000w. Will not burn out on the first locked rotor event.

Here are some other various options of hub motor turn count vs strand count. Chart provided by QS. You can see the various options they sell.

Copper fill means more power but also more hungry motor.

 

[spinningmagnets]

Yes, what ou are describing is the "kV" of the motor, and the major effect is that fewer turns provide a higher top-speed, if the voltage stay the same.

The minor effect is that a few turns of thicker wire has less inherent resistance, because the length of the wire-runs are shorter. The lower resistance means there will be less waste-heat from copper losses.

 

[Jellyfish0]

Yes, this is a factor certainly.

It changes alot of things, like power output and rpm/volt speed.

Take the Cromotor for example. Cromotor vs the QS 205V3motor.. both fit in identical shells, both come in 4T variations. Both have the same stator metal thickness, and number of laminations. .

Cromotor is labeled as "4T x 18strands" ( 4T x 18)

Four turns of 18 strands.. ( thick thick wire)... This motor handles 6000w and will burn out fast on a stall event ( locked rotor current). 6000w motor, the kV is rather low for a " 4T" at 8.9 kV.

QS205V3 4T 12kV motor is labeled as " 4T x 30strands" ( 4T x 30)

A QS 204 " 4T x 30 strand" motor is 11.39kV. It has a " 4 x 30".. 4 turns of (and they make most all variations. ) 30 strands... so thinner wire, and a higher threshold tolerance for " locked rotor current"... This motor handles 3000w. Will not burn out on the first locked rotor event.

Here are some other various options of hub motor turn count vs strand count. Chart provided by QS. You can see the various options they sell.

Copper fill means more power but also more hungry motor.

That's a very detailed answer
Dothe motors you compared have an identical mm² of strands ?
For example:
Motor A: 5 strands 1mm²
Motor B: 10 strands 0.5mm²
Both have equal surface area
And of course same amount of turns

I found this in the forum:

 

[Jellyfish0]

Yes, what ou are describing is the "kV" of the motor, and the major effect is that fewer turns provide a higher top-speed, if the voltage stay the same.

The minor effect is that a few turns of thicker wire has less inherent resistance, because the length of the wire-runs are shorter. The lower resistance means there will be less waste-heat from copper losses.

with same turns, same kv, but different amount of strands which when combined have equal surface area

Motor A: 5 strands> each 1mm²
Motor B: 10 strands>each 0.5mm²

 

[DogDipstick]

That is a good question, and that is the guy to ask certainly.

I dont know .

That's a very detailed answer
Dothe motors you compared have an identical mm² of strands ?
For example:
Motor A: 5 strands 1mm²
Motor B: 10 strands 0.5mm²
Both have equal surface area
And of course same amount of turns

I found this in the forum:

 

[Jellyfish0]

Assuming two motors have the same overall surface area of copper strands and turns, but motor A one has 15 strands while motor B has 25 strands

will there be any meaningful difference between them?

I only read about a theoretical skin effect difference

Example to two motors with identical surface area:

Motor A: 10 strands> each 1mm²
Motor B: 10 strands>each 0.5mm² also
Same amount of turns for both[/quote]

I clarified my question, the question is about equal mm² and turns but different strands number

 

[liveforphysics]

At motor inverter commutation frequency range, skin effects are irrelevant in ebike sized motors, and being a solid fat bus bar would always be the optimal efficiency and torque and continuous HP etc.

 

[BalorNG]

At motor inverter commutation frequency range, skin effects are irrelevant in ebike sized motors, and being a solid fat bus bar would always be the optimal efficiency and torque and continuous HP etc.

And what about very high reduction ratio middrive?
Also, unless you have square wires, should thinner wires result in better copper fill?

 

[liveforphysics]

At motor inverter commutation frequency range, skin effects are irrelevant in ebike sized motors, and being a solid fat bus bar would always be the optimal efficiency and torque and continuous HP etc.

And what about very high reduction ratio middrive?
Also, unless you have square wires, should thinner wires result in better copper fill?

Even a high reduction mid drive is irrelevant to skin effect in windings. Square winding of the size of the slot is most ideal, with second most ideal being whatever gets the most copper cross-section in the stator slot.

 

[DogDipstick]

with same turns, same kv, but different amount of strands which when combined have equal surface area

Motor A: 5 strands> each 1mm²
Motor B: 10 strands>each 0.5mm²

Friend.. in this scenario... I think you will either half the current and quarter the power .. or something like that.. for the motor that is obviously filled with less copper.



I think mΩ/m is what you need to look at.
5 strands> each 1mm²
20.95 mΩ/m (x) 5 ( strands )
-or-
10 strands>each 0.5mm²
84.22 mΩ/m (x) 10 ( strands )....


V=IR

with same turns, same kv, but different amount of strands which when combined have equal surface areaa

...This statement does not hold true?... Impossibility, ... with same number of turns ( length) but different strand count and surface area of MotorA and MotorB... ...
Give me an example of such a dimension, and I will use a mathamatical proof to show it is impossible for the "5 strands> each 1mm², 10 strands>each 0.5mm²" dimension as to have the same surface area, unless you account for length... of said sample.

Should we account for length, we could then take that to account. But that would provide for a different number of turns between teh motors.... and if copper fill is = to MotorA and MotorB, I think the torque generation per amp is the power dictating factor. Then the amps fed is teh limit.. and this is going to be finite within the mΩ/m of the applicable circuit ( the stator winding).

 

[Jellyfish0]

with same turns, same kv, but different amount of strands which when combined have equal surface area

Motor A: 5 strands> each 1mm²
Motor B: 10 strands>each 0.5mm²

Friend.. in this scenario... I think you will either half the current and quarter the power .. or something like that.. for the motor that is obviously filled with less copper.



I think mΩ/m is what you need to look at.
5 strands> each 1mm²
20.95 mΩ/m (x) 5 ( strands )
-or-
10 strands>each 0.5mm²
84.22 mΩ/m (x) 10 ( strands )....


V=IR

with same turns, same kv, but different amount of strands which when combined have equal surface areaa

...This statement does not hold true?... Impossibility, ... with same number of turns ( length) but different strand count and surface area of MotorA and MotorB... ...
Give me an example of such a dimension, and I will use a mathamatical proof to show it is impossible for the "5 strands> each 1mm², 10 strands>each 0.5mm²" dimension as to have the same surface area, unless you account for length... of said sample.

Should we account for length, we could then take that to account. But that would provide for a different number of turns between teh motors.... and if copper fill is = to MotorA and MotorB, I think the torque generation per amp is the power dictating factor. Then the amps fed is teh limit.. and this is going to be finite within the mΩ/m of the applicable circuit ( the stator winding).

I used the wrong term, by surface area I meant to say mm²

 

[Chalo]

I used the wrong term, by surface area I meant to say mm²

The same cross-sectional area of the same kind of copper will give the same motor performance, regardless how many strands. Thinner strands are easier to wind onto the stator, but the relative volume of varnish on the surface of fine magnet wire can limit the total mass of copper you can fit into the slot.

 

[ZeroEm]

This is a question! Fewer turns you would be able to run more amps because more copper.
Don't want to suggest the total copper fill is different, just that your not using up space with turns. Always new the wire was shorter thus less resistance.

 

[Chalo]

This is a question! Fewer turns you would be able to run more amps because more copper.
Don't want to suggest the total copper fill is different, just that your not using up space with turns. Always new the wire was shorter thus less resistance.

This is accurate assuming that the voltage is fixed. If both the voltage and the number of turns are configurable, then you can trade one against the other until current/torque reach the saturation point. Less copper fill means less maximum torque regardless of voltage. Past that point you can't linearly trade more amps for fewer volts to make the same power as you can from the motor with more cooper fill.

 

[ZeroEm]

Correction on last thread "new" is known. A little dyslexia and as my brain ages. Always struggled with grammar, thank the powers that be for spell check.

Always wondered about everyone's fixation on low T motors! Understand it better. Still see it as a tuning feature unless you want all out speed and amps. My normal riding want to be at mid rpm's at 15 mph and willing to trade top end speed for take off torque for the given amps. Have good throttle control. What I hear is a low T motor with max amps makes the throttle twitchy or is this not true?

 

[spinningmagnets]

I've always heard that the motor is at its most efficient at around 80% of its top RPM.

That being said, when choosing between two kV's for a motor, liveforphysics has persuaded me that the low-turn count option is better (for most applications).

Use fewer turns of the thickest wire that will fit. This means on a practical scale, if I typically cruise at 28-mph, a low turn count version will be capable of perhaps 50-mph at full-throttle.

I would likely never use that capability, and during cruise the motor would be spinning at a slightly lower RPM than is the "most" efficient.

That being said, the motor will run cooler due to the shorter length of the turn-runs. This is a key early-onset heat, because...hot copper has more resistance than cool copper.

This is also the reason that thinner laminations are a benefit. When you are just cruising along at a constant speed, the laminations convert some of your battery watts into waste-heat. The lower that constant background heat is, the more "headroom" you have when you want to apply high amps to accelerate.

The cooler the motor starts out, then the more power the motor can take before it gets hot, and the state of being hot causes enough additional resistance in the copper that the same power input causes more heat than before.

With enough power, you will only need to apply full-power for a short while to achieve the speed you are accelerating to.

Having thin laminations and short wire turn-runs helps the motor start off as cool as possible, and remain as cool as possible when applying high power for a short while.

 

[ZeroEm]

by spinningmagnets » Dec 21 2022 8:40am

I've always heard that the motor is at its most efficient at around 80% of its top RPM.

That being said, when choosing between two kV's for a motor, liveforphysics has perduaded me that the low-turn count option is better.

Fewer turns of the thickest wire that will fit. This means on a practical scale, if I typically cruise at 28-mph, a low turn count version will be capable of perhaps 50-mph.

I would likely never use that capability, and during cruise the motor would be spinning at a slightly lower RPM than is the "most" efficient.

That being said, the motor will run cooler due to the shorter length of the turn-runs. This is a key early-onset heat, because...hot copper has more resistance than cool copper.

This is also the reason that thinner laminations are a benefit. When you are just cruising along at a constant speed, the lamintons convert some of your battery watts into waste-heat.

The cooler the motor starts out, then the more power the motor can take before it gets hot, and the state of being hot causes enough additional resistance in the copper that the same power input causes more heat than before.

With enough power, you will only need to apply power for a short while to achieve the top speed you are accelerating to.

Having thin laminations and short wire turn-runs helps the motor start off as cool as possible, and remain as cool as possible when applying high power for a short while.

Would never disagree with either of you two. My experience is limited, working on that.

Have two speed goals, 15mph and 28mph. The paved trail system here with all the turns and little hills limits me to around 15mph any faster then it feels like a road racing course and popping up on walkers is not good for our image.
The legal road speed here is 28mph and have my trike speed limited to that. Had my 1500w leaf motor wound 7T, so running 72v, 40a in a 26" wheel. Top speed is 32mph, 28mph is 87.5% and 15mph is 46.9%

Take off or acceleration = 7T 8.86 kph/s vs 4T 5.85 kph/s

Higher speeds maybe in the next build for out of town riding. 35mph + or if was pushing the motor to thermal limits, better battery and higher amp controller 80a +.

Here is some eye candy -

4T and 7T 100%

motors at 28mph

motors at 15mph

Note: Before spring will put a 5T edge in a 24" wheel and see how I like it. Have everything just need to assemble.

 

[spinningmagnets]

I am still learning, and if something works for a builder, I don't need to understand why to believe it.

Years ago, there was a discussion about...is it better to have a high top speed, and constantly run at half- throttle, or make the top speed your normal cruise speed and run at full throttle?

When it was hard to source high-amp cells, many builders here ran 2x 36V = 72V. Also, there was not much selection when it comes to motor windings. Retailers often carried just two windings, and you had to order the one for a 20-inch wheel to get the high-kV / low turn-count model.

LFP is firmly on the lower volts / higher amps team. I suppose every configuration has its place...

 

[ZeroEm]

Would have stuck to 48/52v, wanted a bigger battery, more range. It seem easer to get a 72v battery most of them are bigger than l 48v. Have a 72v 25ah. Now could do a pair of 52v or 48v. More amps and faster motor. Wanting to try a 6T, might as well get a 4T and 6T, then don't need to mount the motor just swap cores.

 

[Hummina Shadeeba]

i believe if the motor is the same in every way except instead of using a single thick wire two or more thinner are used, as is typically done by manufacturers so can be wound by machine, the thicker wire motor will better transfer heat off the wire and run cooler. The more thin wires used the harder it will be to get the heat from the wire to the stator or the open air.

using multiple thinner wires ends up comparatively messy and produces less inductance per turn around the tooth. ideal being the highest inductance produced with lowest resistance.

 

[liveforphysics]

The inductance is only different beyond commutation frequency ranges of laminated iron core stators.

It's not the PWM frequency the inverter uses to control current that matters for the stator winding inductance, it's the commutation frequency, which for most ebikes is under 400-500Hz, with a peak of perhaps 800-1kHz for super high RPM situations. The inductance difference between a bar and stranded (or litz) is simply irrelevant at these sizes.

 

[Hummina Shadeeba]

The inductance is only different beyond commutation frequency ranges of laminated iron core stators.

im saying when I do a messy job of wrapping the wire around the teeth as opposed to doing it neat and orderly it will show a lower inductance on my L/C meter and the motor ends up with a higher kv despite the same amount of turns of wire wound on the teeth.

 

[Hummina Shadeeba]

The inductance difference between a bar and stranded (or litz) is simply irrelevant at these sizes.

You mean at those "frequencies" instead of "sizes"?


you woke me from my ev sleep telling me the measurements of wattage, amp.. on the vesc weren't accurate; how can you tell what commutation frequency is most suited to the motor. How do you pair a motor to an esc? the vesc is somewhat adjustable. Is adjusting the wave shape to match the motor a goal?

 

[liveforphysics]

The inductance difference between a bar and stranded (or litz) is simply irrelevant at these sizes.

You mean at those "frequencies" instead of "sizes"?


you woke me from my ev sleep telling me the measurements of wattage, amp.. on the vesc weren't accurate; how can you tell what commutation frequency is most suited to the motor. How do you pair a motor to an esc? the vesc is somewhat adjustable. Is adjusting the wave shape to match the motor a goal?

I meant sizes, because of the physical thicknesses of the bus bars used in small stators not letting them ever get thick enough for skin effect to matter. If you're doing motors with stator slots large enough its whole inches across the slot, you may run into skin effect related issues eventually in going solid bar type windings. At ebike sized motors, skin effect isn't a thing to sweat.