Science, Physics, Math, & Myth

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Re: Science, Physics, Math, & Myth

Post by liveforphysics » Nov 24 2014 2:08am

kiwifiat wrote:
liveforphysics wrote:Try thinking of what generates the field in terms of amp-turns.

If the tooth has 10 turns with 1 amp of drive current, or 1 turn with 10 amps of drive current, the field in the tooth is 10 amp-turns either way.
Niether Kingfish or I are debating the fact that copper losses between equal fill winding options are equal, the proof is trivial.

John in Cr says this:

"Saying that a slow wind motor makes more torque at the same current is irrelevant, because in that comparison the slow wind makes more heat to produce that greater torque. Apples and oranges comparisons simply don't cut it. Your understanding is incomplete, because you can't ignore copper losses."

And that is misinformation, the copper losses are identical.
His statement is correct. If both motors have identical copper fill, whichever happens to be producing more torque will be the motor generating more heat. This is true regardless of the kV (and hence torque/amp.)

An example of misinformation/myth would be something like Kingfishes lines here:
Kingfish wrote: 21. If Power (P) is the same, we can demonstrate that higher current is less beneficial than higher voltage by using the formula P = I * V = I^2*R = V^2 / R,
22. Therefore higher Current (I) produces more Heat (Q) as loss than can be recovered by other mechanisms within the System, leading to a total loss in efficiency.
23. Therefore motors with faster winds (and having fewer turns) are inherently less efficient than slower winds (and having more turns)…
...
29. In conclusion, the statement “POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS” is inaccurate and can never exist.

kiwifiat wrote: We all agree that 10 amps into a 1 turn motor will yield the same torque as 1 amp into a 10 turn motor all else being equal. However in the context of speed/torque characteristics it is not correct to say that the motors are the same, if the torque constant is different how can you claim they are the same?
If you took a pair of coils, and arranged them in series, and powered them so each coil gets say 10A, or arrange them in parallel and drive it so each coil gets 10A, the motor has no way of knowing the difference. The kV shifts 4x up or down, the performance capabilities of the motor remain identical.
kiwifiat wrote: In terms of system efficiency the higher turn lower lower current wind wins every time.
This is not correct.
kiwifiat wrote: I assume we all acknowledge that the batteries have internal resistance. We all acknowledge the switching semiconductors have resistance. Is anyone going to provide a proof that a system consisting of a power source,wiring, controller and motor that requires 10 amps to provide X tractive force at the wheel can do so more efficiently than the system that requires only 1 amp? Particularly in the context of the vast majority of ebikes that are constrained in Voltage and the maximum continuous discharge current. So given those real world constraints a higher wind motor will deliver more torque, more tractive force at the wheel, better acceleration, better hill climbing ability and better overall system efficiency than a lower turn count motor when constrained by the power supply.
Myth and nonsense. Learn about how a buck-converter works, the motors windings serve as the inductor in the buck converter.
kiwifiat wrote:
There is a very good reason why the engineers who are responsible for designing the tractive systems for the currently available electric cars have not gone with low turn count low voltage high current solutions but rather high voltage high turn count motors and that reason is system efficiency.
BS. Its because lossy IGBTs were once the only practical game in town for switching high power.
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Re: Science, Physics, Math, & Myth

Post by liveforphysics » Nov 24 2014 2:14am

zombiess wrote:What about iron tooth saturation? The tooth is only able to handle so much flux before it reaches diminishing returns and eventually full saturation. What about the Perm magnets generated flux? How much does it take to equal the field of the magnet? How much does air gap come into play?

Any easy ways to measure/estimate the saturation point for a motor?

Its simple, apply current to a phase and measure the force to cog the motor over (like with a lever arm and spring scale.) Keep increasing current until the current/torque relationship ceases being perfectly linear.
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Re: Science, Physics, Math, & Myth

Post by Kingfish » Nov 24 2014 2:35am

tearocks wrote:
Kingfish wrote:7. Torque (τ) = Force (F) * 2 * Radius (r)
This is where I got lost. I'm very new to e-biking, but didn't think classical mechanics had changed that much. :)
Interesting thread nonetheless.
You are correct! A transposition error upon my part - thank you for catching that. :) It should read:
7. Torque (τ) = Force (F) * Radius (r)

Ref: http://en.wikipedia.org/wiki/Torque
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Re: Science, Physics, Math, & Myth

Post by zombiess » Nov 24 2014 3:57am

liveforphysics wrote:BS. Its because lossy IGBTs were once the only practical game in town for switching high power.
Mmmmm.... 1200V SiC MOSFETs. I need to read up more on GaN devices. Once prices come down on these it could get interesting.

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Re: Science, Physics, Math, & Myth

Post by Punx0r » Nov 24 2014 7:39am

kiwifiat wrote:There is a very good reason why the engineers who are responsible for designing the tractive systems for the currently available electric cars have not gone with low turn count low voltage high current solutions but rather high voltage high turn count motors and that reason is system efficiency.
The design parameters for a car are likely to be different to that of an ebike, though. We're mostly concerned with motor efficiency, as motor heating tends to be the limiting factor on an ebike. A 1% absolute increase in system efficiency thanks to reduced controller switching losses would be meaningless, whereas for a 200kW drive system for a car it might mean a worthwhile saving in required battery capacity.

Also, isn't the GM volt motor a two turn hairpin design? I only have a recollection of a video of a factory tour.

Car designers have the luxury of starting with a blank sheet for their drive systems. At least for us DIYers the choice is largely whatever Xie Chang happen to be churning out.

From the other thread:77
flathill wrote:
Punx0r wrote:Disagree.

Reductio ad absurdum: following your argument, the best ebike system uses umpteen turns of hair-fine wire and a 1000V battery in order to minimise current. Great, except you now have ~250 tiny cells, a frock-ton of interconnects, a serious risk of lethality and no available controller.

Also, the discharge rate of the battery is irrelevant. Regardless of how you configure cells in series/parallel to form a battery, the power output and capacity is the same.

Like Johnrobholmes said, you're looking for the goldilocks zone.
The number in interconnects will be the same in either case. I agree about the shock hazard, but yes, the best ebike system would use a much higher voltage. Right now 100V is the sweet spot but in the future SiC fets will change the game
That's only true if you use the same cells. In reality, the voltage of each cell is almost fixed, whereas the capacity is highly variable. A high voltage pack forces you to use tiny cells, else result would be enormous and heavy. Staying low voltage, high current you can use fewer, larger capacity cells (if desirable). An infinitely high voltage pack requires an infinite number of cells. An infinitely high capacity packs only requires one cell of infinite size and zero interconnects.

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Re: Science, Physics, Math, & Myth

Post by John in CR » Nov 24 2014 2:53pm

Kingfish,

Time to stop hiding. Are you going to be a man and own up to the glaring mistake you made by leaving the change in resistance out of your analysis? Don't bother trying to change the subject like KiwiFiat attempted, because that's not going to fly. The discussion is otherwise identical motors with different windings, which make the same heat for the same torque. It's time for some posts to be edited too, so others don't make purchase decisions based on the incorrect statements you made.

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Re: Science, Physics, Math, & Myth

Post by liveforphysics » Nov 24 2014 4:53pm

In industrial applications where big motors in a factory have many hundreds or thousands of feet separating them, one quickly finds going to a drive voltage like 480 3p saves a ton of cost on cabling those motors.

In applications like a battery EV however, the battery, inverter, and motors are typically only a few feet apart at the most if the packaging layout was reasonable. A common way to do an EV these days is with an inverter bolted right on top of the motor, and the battery pack power leads exiting just a foot away from the pack.

This makes the cabling cost between running something crazy like a 10kV battery and being able to use tiny wire perhaps 16awg as a result, or running a 10V battery and needing perhaps 8 pieces of 0000awg cabling in parallel. What one rapidly finds out in building EV drivetrains that adding more cell monitoring chipsets to the BMS, and associated BMS support needs like balance tap harnesses adds up to be so much more costly it makes buying a few feet of thick cable become very cheap in comparison.

The choice of pack voltage for a powertrain system is one we know the motor is entirely agnostic towards (as discussed ad nauseam), but there are more players involved in the system than just the motor. One of these players involved is human life safety, both from an assembly and service perspective, as well as customer exposure. Choosing a voltage that is unlikely to result in life-safety issues from shock hazards offers a level of life safety hard to match by just adding more safety covers and large expensive human-touch-blocked connectors and things.

So, we know the motor doesn't care, and the BMS and pack design gets cheaper and removes failure modes as voltage goes down, and we know for life-safety considerations lower voltage is better. Why aren't all EV's running 24v or something then? The controller MOSFET limitations. Right now the sweet spot in controller power density is to leverage the tremendously low RdsOn 100V MOSFETs available. For the same size of controller, going with 150v MOSFETs reduces power density by ~40-60%. Going to the next common step down in MOSFETs of 60V also results in a decrease in power density, though to a lesser extent than going to 150v FETs.

This is why running something like ~20s is about ideal for an EV drive setup in the say ~5hp range to ~200hp range, though the motor itself isn't a factor in that decision which is based around leveraging available MOSFET options, BMS cost and monitoring system complexity, and life safety.
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Re: Science, Physics, Math, & Myth

Post by liveforphysics » Nov 24 2014 6:07pm

John in CR wrote:Kingfish,

Time to stop hiding. Are you going to be a man and own up to the glaring mistake you made by leaving the change in resistance out of your analysis? Don't bother trying to change the subject like KiwiFiat attempted, because that's not going to fly. The discussion is otherwise identical motors with different windings, which make the same heat for the same torque. It's time for some posts to be edited too, so others don't make purchase decisions based on the incorrect statements you made.

Be kind John. You read his introduction, and I know you have the wisdom to decipher what a strong learning disability "knowing" exerts.
Kingfish wrote: Let me begin by saying that your education level and mine is substantially different. :)
I am an Engineer having multiple disciplines being Electromechanical, Software Development, Multimedia, Manufacturing, and Operations with over 30 years of experience. You can find me on LinkedIn and view my website through the signature link below. I speak with brevity because it’s faster to get to the point so that we can move to the next. Mathematical formulas speak volumes just as a picture is worth a thousand words.
Your education is substantially different John, you had the wisdom not to believe you already knew, and therefore you were able to quickly gain an understanding of electro-mechanical device basics. Had you been raised in his shoes, you also may not have learned foundation principals of electro-mechanical devices.

I agree with you though, for the sake of lowering the BS/misinformation ratio on ES, it would be wise of Kingfish to spend some hours editing to reflect the understanding I think he has perhaps now gained thanks to making this thread targeted just at clearly highlighting his misconceptions so folks could help teach him.
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Re: Science, Physics, Math, & Myth

Post by kiwifiat » Nov 24 2014 6:21pm

liveforphysics wrote:
His statement is correct. If both motors have identical copper fill, whichever happens to be producing more torque will be the motor generating more heat. This is true regardless of the kV (and hence torque/amp.)
That is not the way i read John's comment, I read it that John is claiming that at the same torque output the higher turn count motor has greater losses and that is not true.

An example of misinformation/myth would be something like Kingfishes lines here:
Kingfish wrote: 21. If Power (P) is the same, we can demonstrate that higher current is less beneficial than higher voltage by using the formula P = I * V = I^2*R = V^2 / R,
22. Therefore higher Current (I) produces more Heat (Q) as loss than can be recovered by other mechanisms within the System, leading to a total loss in efficiency.
23. Therefore motors with faster winds (and having fewer turns) are inherently less efficient than slower winds (and having more turns)…
So in your opinion the power companies that transmit power over high voltage lines are idiots because I2R losses in the system are fictional.

liveforphysics wrote:
If you took a pair of coils, and arranged them in series, and powered them so each coil gets say 10A, or arrange them in parallel and drive it so each coil gets 10A, the motor has no way of knowing the difference. The kV shifts 4x up or down, the performance capabilities of the motor remain identical.
Your concept of identical and mine are quite different, Ke and Kt are different. Point me to one peer reviewed PHD thesis on motor design where the electrical loading and torque and speed requirements are not critical design parameters. If I understand you and John correctly they are irrelevant because you keep saying any wind will do as long as the copper fill is the same when as I see it in a well engineered motor design any wind will not do.
kiwifiat wrote: In terms of system efficiency the higher turn lower lower current wind wins every time.
liveforphysics wrote: This is not correct.
So the guy who lives in a hilly area with a 12AH battery is better off in your opinion with a motor that draws the higher current to get him up the hill?
kiwifiat wrote: I assume we all acknowledge that the batteries have internal resistance. We all acknowledge the switching semiconductors have resistance. Is anyone going to provide a proof that a system consisting of a power source,wiring, controller and motor that requires 10 amps to provide X tractive force at the wheel can do so more efficiently than the system that requires only 1 amp? Particularly in the context of the vast majority of ebikes that are constrained in Voltage and the maximum continuous discharge current. So given those real world constraints a higher wind motor will deliver more torque, more tractive force at the wheel, better acceleration, better hill climbing ability and better overall system efficiency than a lower turn count motor when constrained by the power supply.
liveforphysics wrote: Myth and nonsense. Learn about how a buck-converter works, the motors windings serve as the inductor in the buck converter.
I ran an Electronics company for 16 years, i know how a buck, boost, flyback etc SMPS's work and have designed and manufacture many. The efficiency calculation does not concern itself with phase currents but rather the current supplied by the power source so your point is what? I am happy to accept that it is your professional opinion switching losses in the controller and joule heating in the battery are myth and nonsense. Let's agree to disagree on that one.
kiwifiat wrote:
There is a very good reason why the engineers who are responsible for designing the tractive systems for the currently available electric cars have not gone with low turn count low voltage high current solutions but rather high voltage high turn count motors and that reason is system efficiency.
liveforphysics wrote: BS. Its because lossy IGBTs were once the only practical game in town for switching high power.
Not the main reason at all, low turn count low inductance motors at high voltages are almost impossible to control due to extremely fast di/dt which leave insufficient time for the pwm to modulate a wave form. In high power systems I2R losses dominate, low turn count motors exacerbate the problem whereas high turn counts improve matters.

I stand by my advice that if you live in a hilly area buy a motor with a higher turn count because it is better suited to the terrain and the constraints of the vast majority of power packs sold for e-bikes.
“You never know if quotes on the internet are genuine.” - Abraham Lincoln

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Re: Science, Physics, Math, & Myth

Post by liveforphysics » Nov 24 2014 7:00pm

Kiwifiat- You are still failing to get it, perhaps at all levels. This seems astounding, as I don't believe you or Kingfish are incompetent to understand.

I^2*R loss is the copper loss component. If the same amount of copper is around the tooth, it makes the same amount of continuous torque, and continuous power, and the same heat production per amount of torque etc. Likewise, it would be no additional power consumption from a battery to make that same amount of torque/power etc.

A motors resistance climbs at the SQUARE of the number of turns, yet the current demand to make a given amount of torque varies inversely proportional, yet this linear decrease in current decreases heating by the ROOT of current. This makes them cancel each other cleanly, and is why a 1t motor makes torque exactly as efficiently as a 10t motor, despite one needing 10x higher drive current (at 1/10th the average bucked-down phase voltage, so power drawn from the pack is identical).

I was going to break it all down again for you in a long response, but I don't think it needs to be made clearer than the examples already provided in this thread, it just needs them to be read and understood rather than read and replaced by pre-existing confused delusions of knowing.
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Re: Science, Physics, Math, & Myth

Post by Kingfish » Nov 24 2014 7:06pm

John: Hiding? Actually I work for a living, and when I’m not – I play.

Been busy: This weekend I went up to Mt. Vernon and poured beer for a friend of mine at the Skagit Wine & Beer Festival; it was really an awesome experience and I was busy from sunrise to midnight. Sunday I barely had a cuppa joe down my throat before my pals grabbed me and we’re off tinkering in the shop followed with an afternoon filled with the Seattle Motorcycle Expo and Seahawk football. Paint me a red-blooded human. You find fault in that?

John, know that you have had 3 days and yet you still cannot identify which line of the math that confuses you. Who’s craven again? I wrote the proof, not you.



The weekend has passed and I am surprised (in a good way) by the majority of feedback. Let’s try to get a synopsis of this; stop me when you think I have it wrong:

LFP: In theory, yes I understand what you are saying, and actually you are agreeing with my statements up to a point where you go off on a tangent. Your winding thoughts and the way you explain it is correct and as I see it (so long as we avoid changing strand counts/awg size, winding patterns, etc). On that note…

In General: Let us not introduce new vectors; I never committed to a wire size because that pulls in another intangible about a change in strands and fills and gearing and frequency that is beyond the basic premise (not saying we should ignore the conversation; just don’t introduce something new). Similarly – I do not include controller or battery variables. KISS and same-same to be in agreement with the basic premise.

The issue is in trying to make the generalized statement (which I believe to be inaccurately portrayed) and then proving it. In theory – if ignoring enough of the losses, yeah – you’d think it would work, but in reality it falls apart. Where I object is that the individual admitted he parroted an idea, can’t do the math to prove he is right, and in trying to do so his message comes out garbled, yet he yammers away like unwanted religious peoples at the doorstep. That my friends is the definition of a poser, troll, or armchair quarterback; little napoleons dictating from the peanut gallery. There are several on this forum and they have no class.

I do my own study, my own math, my own simulations, I go build test cases to find out if it works and publicize the findings to my team. Sometimes I take the risk, invest, and run the gauntlet with my own money. That is the definition of a professional engineer. There are many here and I get joy from listening to these bright people and reading about their adventures.

Here’s the statement again:
POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS

Allow me to demonstrate why the statement fails, and I can also do this w/o math since it appears to be difficult for some:
  • Presume –
  • Same Motor, except for winds <- the only physical difference.
  • Winds use the same AWG; you said same same same same… therefore everything is the same!
  • I’m going to spin this motor using the same sized Wheel, with the same load (or incline, I don’t care) at the Same Speed!
  • I can run this forward or in regen, and the different winds will absolutely not produce identical power in or out.
    Why? The elephant is in the room!
Can’t move the same mass of motor with different winds and expect the same efficiency; a student could see that it is proportionally different. Therefore copper losses are not identical, nor is saturation linear, nor is the flux density linear. Iron, steel, electric steel, magnets, even the flux in the gap – nearly every physical aspect affected by induced reactionary magnetic fields will differ in a non-linear manner, however slight. The greatest difference is observed between the extremes offered within the series. One more time: Different winding and the subsequent alterations in voltage and current in attempt to balance power, speed, and torque will fail to be equal with other windings because the losses are not linear such that the equation P = V * I will hold true.

It falls apart.

Now if you really want to pick nits, I’d challenge you one more step:

All Motors of the Same Wind, mounted on the Same Wheel with the Same Load at the Same Speed will not consume the Same Power – in reality. Why is that? Anyone that’s ever been an engineer and been part of the manufacturing and production process will tell you that it is impossible for them to be identical due to variances in quality control (in production, it’s called “yield”). My job as an engineer is to design product such that these tiny changes do not accumulate to create something that grossly falls out of spec. There’s a whole history behind this methodology that has its’ roots going back to WWII, and really why our equipment was reparable in the field w/o using a hammer. That’s a different argument that the one above – and yet I can demonstrate those variances.

Anyone ever play guitar? Go to a pro shop and start playing a good quality instrument. Now pick up another of the exact same model and year: A professional, heck even an amateur can tell the difference in tone and attack. A consumer will try many until settling on one that fits right, play right, sounds right.
One more step: Because of the above, not all components will perform the same. They are however very very close and within acceptable margins of error (it’s called “Tolerance”). We care about tolerances when designing circuits and assemblies. We definitely care about tolerances when constructing nuclear bombs. In comparison to electric motors? Meh. (OK – I lied, we do care)

But grossly – on the larger front, and back to the point:
POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS

That’s baloney; different winds of the same series perform differently enough to be well-measured. I can’t make a slow speed (high-wind) motor go as fast as a high-speed (low-wind) without creating unacceptable issues. We all know that, just as common sense says not to take a high speed motor and try to make a hill climber out of it. That’s just nuts, and so is this statement:

POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS

Pick the Motor to suit your application however it fits with the potential that your system (or pocketbook) can offer. :) If it were not true, why make different wind motors at all? <- and thus the argument fails.

Think about it.
Thanks for listening. KF
PS – Luke, are you feeling well? You are such a cool dude in person. :?
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Re: Science, Physics, Math, & Myth

Post by liveforphysics » Nov 24 2014 9:29pm

Kingfish wrote: LFP: In theory, yes I understand what you are saying, and actually you are agreeing with my statements up to a point where you go off on a tangent. Your winding thoughts and the way you explain it is correct and as I see it (so long as we avoid changing strand counts/awg size, winding patterns, etc). On that note…
When a lower turn-count motor is wound, it is still fitted with however much copper the slot holds, otherwise it wouldn't be the same copper fill and of course anything regardless if it has more or less turns would be at a disadvantage if it had decreased copper fill%.

Take a 9C for example, at 6 turns, it has 10 pieces of ~18awg in parallel. At 10 turns, it has 6 pieces in parallel, and each piece is longer. Both have 60 pieces of copper cross section in the slot, both have an identical copper fill%. Despite a 40% kV difference, both have identical continuous torque, continuous power, efficiency, etc.

Have you ever seen a motor where the lower turn-count version is made just by leaving off some turns and calling it a day? Has anyone ever seen that??

Kingfish wrote: In General: Let us not introduce new vectors; I never committed to a wire size because that pulls in another intangible about a change in strands and fills and gearing and frequency that is beyond the basic premise (not saying we should ignore the conversation; just don’t introduce something new). Similarly – I do not include controller or battery variables. KISS and same-same to be in agreement with the basic premise.
Whoa. This isn't new, it's called keeping copper fill% the same, because that's how motors are made. Making up some strange concept where a motor just has windings removed to decrease it's copper fill and then comparing it's uncrippled to crippled performance (through reduced copper fill%).

What would be adding crazy changes in variables to pointlessly mask and confuse the issue would be not keeping copper fill% the same, as it is with all real-world motors I've seen sold.

If you intentionally unwind a motor and leave a bunch of air where there once was copper in the slot, of course the performance goes down! However, this isn't a situation I've ever seen be relevant to anything, because a motor maker would know if they reduce turns, the wire needs to become thicker to fill the same slot.
Kingfish wrote: Where I object is that the individual admitted he parroted an idea, can’t do the math to prove he is right, and in trying to do so his message comes out garbled, yet he yammers away like unwanted religious peoples at the doorstep. That my friends is the definition of a poser, troll, or armchair quarterback; little napoleons dictating from the peanut gallery. There are several on this forum and they have no class.
If John is an armchair quarterback who got it without needing math, who understands it, and shares the correct version of electro-mechanical basics with the forum, he is not the troll misleading folks.

Like myself, I think he is also passionate about seeing the spreading BS and Myths related to motors concluded on ES. For reference to such BS and myths we are both looking to conclude, read your own post starting this thread, towards the bottom it fills up with them.

Kingfish wrote: Here’s the statement again:
POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS
To make this true, copper fill% must also be the same between winds. Just like they are manufactured and sold. Then the statement is true.

If you make up some bizarre fantasy situation where someone just unwinds a turn and doesn't use fatter wire, then yes of course it's a penalty. Can you even find a single production motor where this intentional decrease of copper fill by unwinding a motor stator situation would be relevant?
Kingfish wrote:
  • Presume –
  • Same Motor, except for winds <- the only physical difference.
  • Winds use the same AWG; you said same same same same… therefore everything is the same!
No, the copper fill is what stays the same, nobody is talking about just unwinding copper off a stator and then comparing it's performance... Talk about pointless Trolling to spread misunderstandings...
Kingfish wrote:
But grossly – on the larger front, and back to the point:
POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS

That’s baloney; different winds of the same series perform differently enough to be well-measured. I can’t make a slow speed (high-wind) motor go as fast as a high-speed (low-wind) without creating unacceptable issues. We all know that, just as common sense says not to take a high speed motor and try to make a hill climber out of it.


Actually, as I assume you would already know, if both winds have equal copper fill, both motors would be equally good climbers or high speed motors. No difference at all. The motor doesn't know or care how the amp-turns around the tooth may happen to occur, it has no preference for having 10amps lapping the tooth 10 times, or 100amps lapping the tooth once.

Kingfish wrote:
That’s just nuts, and so is this statement:

POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS

Pick the Motor to suit your application however it fits with the potential that your system (or pocketbook) can offer. :) If it were not true, why make different wind motors at all? <- and thus the argument fails.
Different motor winds exist so folks can pick an option that best suits the controller/battery setup they wish to power the motor with. There is a battery and controller for any winding that will make it perform precisely the same as any other winding sharing the same amount of copper fill%. If every motor was a 1-turn, controllers and phase leads would need to be bigger to handle the increased phase currents. If every motor was a 100-turn, BMS's/safety/management would start outweighing and out-costing the battery.

Motors are offered in differing turn-counts so they can be matched up well with a practical and available controller and battery solution to make a system with the desired performance, not because some magical number of turns is greater or lesser performance than any other with identical copper fill.


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Re: Science, Physics, Math, & Myth

Post by flathill » Nov 24 2014 9:46pm

I think any talk of motors not being identical due to production tolerances is way off tangent.

Luke has given the best example to argue about since the wire sized is fixed and the turn count is changes simply by configuring how the wires are paralleled. This is a real world example and the copper fill will be identical. Please let's keep the discussion on point and use this simple example.

"Lets say we have some motor, and it's wound with 2 pieces of say 14awg wire in parallel, and it's wound with 4 turns around each tooth. If we take this same motor, and re-wind it to have 8 turns of a single pieces of 14awg (identical copper fill %) or rewind it with 2 turns of 4 pieces of 14awg in parallel (identical copper fill).

So, we have 3 winding options for this motor now, each one yielding a substantial difference in kV, but do any have a performance difference?

We know the 8-turn needs half the amount of current to make a given amount of torque than the 4 turn, yet the 8 turn is 50% of the cross section of wire AND twice as long, giving it a 4x increase in phase resistance. This 4x resistance increase perfectly balances the I^2*R difference, both make precisely the same amount of loss per unit of torque produced, both are capable of exactly the same continuous power, continuous torque, etc. Now let's look at the 2 turn, it needs 2x the phase current to generate the same torque as the 4 turn, yet, it's resistance dropped by 4x, because the wire is now twice the cross section and only half as long. It is also capable of exactly the same continuous torque, continuous power, same loss per unit of torque produced, etc. "

SO 3 WINDING OPTIONS WITH 14 AWG WIRE

I will start by assigning phase resistance value to this hypothetical motor. I will use simple value to make the calculations easy. Kingfish will fill in the rest.

8-TURN SINGLE STRAND: Let's make the phase resistance 16 Ohm (2 Ohm per turn times 8 turns). Let's make the Kt ? Newton-meter/Amp. Let's make the Kv ? rpm/Volt.

4-TURN TWO STANDS IN PARALLEL: Given the 8 TURN is 16 Ohms, the phase resistance of this version will be 4 Ohm (1 Ohm per turn time 4 turns). The Kt will be ? Newton-meter/Amp. The Kv will be ? rpm/Volt.

2-TURN FOUR STRANDS IN PARALLEL: The phase resistance of this version will be 1 Ohm (0.5 Ohm per turn times 2 turns). The Kt will be ? Newton-meter/Amp. The Kv will be ? rpm/Volt.

Now show us the math. Is it true? : POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL 3 WINDS GIVEN IN THIS POST. THE COPPER FILL AND TOTAL COPPER MASS IS IDENTICAL FOR ALL 3 WINDS. IGNORE PHASE INDUCTANCE. THE WINDING CONFIGURATION IS THE ONLY VARIABLE.

The wind options should be referred to in shorthand as:

"8-T"
"4-T"
"2-T"

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Re: Science, Physics, Math, & Myth

Post by teslanv » Nov 25 2014 1:01am

liveforphysics wrote:
Different motor winds exist so folks can pick an option that best suits the controller/battery setup they wish to power the motor with. There is a battery and controller for any winding that will make it perform precisely the same as any other winding sharing the same amount of copper fill%. If every motor was a 1-turn, controllers and phase leads would need to be bigger to handle the increased phase currents. If every motor was a 100-turn, BMS's/safety/management would start outweighing and out-costing the battery.

Motors are offered in differing turn-counts so they can be matched up well with a practical and available controller and battery solution to make a system with the desired performance, not because some magical number of turns is greater or lesser performance than any other with identical copper fill.
I would not argue with this statement at all. In fact, I am still trying to figure out what the "myth" is to which John in CR keeps referring. - Is it simply the "name" that has been given to a high-turn-count motor? "High Torque" - If this is the case, what is a more accurate way to describe a High-turn-count motor? "Slow-speed" motor? - Because as someone who wants to market these types of motors, that is the last thing I want to call it. "Slow-Speed" motor would be just as much of a misnomer as "High-Torque"
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Re: Science, Physics, Math, & Myth

Post by Stevil_Knevil » Nov 25 2014 1:27am

Great discussion!

Higher wind count motors exist for good reasons ..I see no myth there.

Volt up, gear down.
Simple.
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Re: Science, Physics, Math, & Myth

Post by Miles » Nov 25 2014 1:34am

This is the myth:
One false and oft-repeated conclusion is that therefore the 409 is a higher torque motor than the 406 because it can produce the same torque with fewer amps, or likewise more torque with the same amps. This is not the case. All 400 series motors can deliver exactly the same torque at exactly the same efficiency. The lower winding count motors just need more current to do this, but because they have fewer turns of a shorter length of heavier gauge wire, they can handle high currents with minimal loss. To use a concrete example, lets compare a 404 with a 408. The 408 has twice the number of turns than the 404, so the copper wire in the windings has 1/2 the cross sectional area and twice the length, for a total of 4 times the winding resistance of the 404. For a given torque output, the 408 needs only 1/2 the amps, but because it has 4 times the resistance the net electrical loss (I2R) is exactly the same.
http://www.ebikes.ca/learn/hub-motors.html


There almost seems to be a will to not communicate........ :|

Arguments "from authority" are so pathetic....

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Re: Science, Physics, Math, & Myth

Post by teslanv » Nov 25 2014 2:48am

I get it now.
But as a business major, I'm going to tell all Y'all engineers and motor experts to suck it. I'm calling high-turn-count motors "High-Torque" just to spite you. :twisted:
Long live the "Myth!"
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Re: Science, Physics, Math, & Myth

Post by Punx0r » Nov 25 2014 6:52am

Probably best to just specify them by winding configurations (wire size/count/turns) and Kv and Kt.

If someone can't look at the different Kv & Kt numbers for two motors and realise which one will spin fastest or produce the most torque for a given input voltage/current then they probably should seek help in selecting their motor. I see it as the equivalent of not knowing volts from amps from amp-hours and expecting to intelligently select or configure a battery. We don't (yet?) see batteries marketed as "high speed" or "high torque" ;)

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Re: Science, Physics, Math, & Myth

Post by John in CR » Nov 25 2014 7:12am

Stevil_Knevil wrote:Great discussion!

Higher wind count motors exist for good reasons ..I see no myth there.

Volt up, gear down.
Simple.
There aren't any good reasons if you're talking about hubmotors.

Volt up and gear down is a great thing to do with a given motor, but changing to a higher turn count is NOT gearing down. Gearing down multiplies torque and with a hubmotor that can only be accomplished by reducing wheel diameter. A higher turn count doesn't do anything useful. The myth is the belief that increasing the turn count in the windings increases torque, allows you to run a larger wheel, or climb hills with greater efficiency. This myth is repeated so often that many accept it as fact, yet none of these things are true.

Why does it matter if the motors are the same regardless of the winding count? It doesn't for the people running modest power and speed, because they can get to exactly the same position with any winding, but they are being sold the idea that they get more torque and more low speed efficiency with the new "high torque" wound motor. All they had to do was lower the voltage and get to the exact same position, so they were ripped off by a falsehood. Where it really matters is for those attracted to ebikes for performance, and more more more is what we want. Look at the people with 40-50mph ebikes chomping at the bit for higher voltage controllers not yet available, but all they need is a lower turn count motor to get to exactly the same place. MXUS is so brainwashed by the myth that they are resisting winding a motor with 3 turns instead of 4, when a 3 turn would be right in the sweet spot with just enough inductance that it would serve everyone's needs with fast or slow determined by voltage. As you approach 100V, speed and power that blows what's commonly available out of the water is easy and cheap, just low hanging fruit ripe for the pickins, and those who want better low speed efficiency can simply run a lower voltage and still get the same torque they would with the slow wind motor by running the proper current.

A practical problem with low speed winds is that they are easier to burn up. They have lower current limits, which means less margin for error, and we don't even know what the current limits are for any of our motors. Add high power controllers and phase current multiplication to the mix and the result is exactly what we've seen, burned up higher turn count motors because they were easily pushed into saturation. Most were pushing relatively light loads. In the meantime, I'm not aware of a single low turn count motor burning up. I'm not saying they can't get cooked, just that it's harder, since it's harder to get to those current levels.

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Re: Science, Physics, Math, & Myth

Post by John in CR » Nov 25 2014 7:14am

Punx0r wrote:... We don't (yet?) see batteries marketed as "high speed" or "high torque" ;)
Good one. :lol: Thanks for the laugh to start my day.

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Re: Science, Physics, Math, & Myth

Post by John in CR » Nov 25 2014 7:28am

liveforphysics wrote:Be kind John. You read his introduction, and I know you have the wisdom to decipher what a strong learning disability "knowing" exerts.
I know I shouldn't let myself get dragged into the fracas, but when he left the other thread to start this one leaving the gem below, I feel that I'm keeping my sarcasm on a pretty tight leash.
Re: MXUS 3000 Hub Motor

Postby Kingfish » Thu Nov 20, 2014 7:11 pm
John, you have fallen on your sword and missed this by a wide frippen mile. I can't believe you actually posted the equation P = I^2R :lol:

I love that Astro reference! Keep hittin' the Kool-Aid if it makes you feel good. It's pointless for me to continue questioning you when you have done yourself out so well. I almost feel pity.

OK everybody... shows' over.
We all now know John is not an engineer or a scientist.
No doubt he has credibility in other areas, but certainly not in motor theory.

Thank you for clearing that up.

For the record - I am an engineer, I do know my math, and there's a very high probability that you or your kids are using product that I developed.

Good luck with that myth busting.
~KF

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Alan B   100 GW

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Re: Science, Physics, Math, & Myth

Post by Alan B » Nov 25 2014 7:57am

As in all math, physics or engineering areas there are many ways to look at the same thing. Frequency, time, voltage, current, power, AC, DC, RF, Magnetic, Electrostatic perspectives. Mapping between perspectives is not always simple, and it is easy to argue over the meaning of language, choosing a piece of a statement or a small inaccuracy to twist into something larger, ignoring or changing the context. Good sparring for the debate teams. Looking for a way to win, or withdraw and somehow save face. A myth from one perspective is true in another and both views may be accurate and even consistent with the proper mapping function. Marketing adds its own twists, making certain views and statements more popular and others less.

About 60 years ago we built an accelerator based on motor-generators and mercury vapor tubes to convert 12KVAC incoming power (how would you like to manage a 12KV motor) to 15KVDC at 5KA to operate the main magnet, 20 years ago we built one that used 480VAC input and used 1KVDC for the main magnet, and newer designs are likely to reduce the voltages further due to life cycle costs of systems including maintenance and personnel safety issues. Technology advances tend to enable and safety to encourage lower system voltages. Superconducting magnets push the voltage requirements even lower. It is strange to work on a 5 Tesla magnet where the voltage drop is zero across the magnet, but nonzero across the cables feeding it and the 15V 500A power supply needed to drive them, as well as to worry about taking the stored energy out of the magnet safely in various situations, and keeping it cooled to 5K continuously for a year or more of operating between maintenance cycles, plus dealing with the sudden energy release when it quenches, or the emergency of ice blockages in the cryogenic piping. :)

At the end of the day the little things become big drivers - tons of copper in a vehicle fleet, fleet energy usage, safety, insurance and workers comp, public perception, losses in useful turns vs inter-turn conductors, cost of managing N cell batteries, cost, safety and availability of materials, size and weight, number of connections to deal with when manufacturing and servicing, failure rates and service costs, etc.

Perhaps it is not so much a myth, it is just a statement from a particular perspective, which must be understood to properly evaluate the statement.

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Re: Science, Physics, Math, & Myth

Post by madin88 » Nov 25 2014 9:43am

John in CR wrote:MXUS is so brainwashed by the myth that they are resisting winding a motor with 3 turns instead of 4, when a 3 turn would be right in the sweet spot with just enough inductance that it would serve everyone's needs with fast or slow determined by voltage. As you approach 100V, speed and power that blows what's commonly available out of the water is easy and cheap, just low hanging fruit ripe for the pickins, and those who want better low speed efficiency can simply run a lower voltage and still get the same torque they would with the slow wind motor by running the proper current.
im with you John, but we do not know the nominal or max RPM of the MXUS 3000 motor (before eddy current losses starts to add big amounts of heat).
by the upgraded e4bikes V2 with 0,33mm lams things are better, but with the stock one and its 0,5mm lams?
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Re: Science, Physics, Math, & Myth

Post by John in CR » Nov 25 2014 11:51am

madin88 wrote:
John in CR wrote:MXUS is so brainwashed by the myth that they are resisting winding a motor with 3 turns instead of 4, when a 3 turn would be right in the sweet spot with just enough inductance that it would serve everyone's needs with fast or slow determined by voltage. As you approach 100V, speed and power that blows what's commonly available out of the water is easy and cheap, just low hanging fruit ripe for the pickins, and those who want better low speed efficiency can simply run a lower voltage and still get the same torque they would with the slow wind motor by running the proper current.
im with you John, but we do not know the nominal or max RPM of the MXUS 3000 motor (before eddy current losses starts to add big amounts of heat).
by the upgraded e4bikes V2 with 0,33mm lams things are better, but with the stock one and its 0,5mm lams?
As long as they aren't using cheaper that typical steel it should be fine. I base that on motors I have. That includes a 2 turn motors of quite similar construction with 40mm stators that have a no-load current of slightly over 4A at 80V at about 1250rpm, and that's with the air drag of spoked moto wheels. The motor I have with 56 magnets and 63 slots (vs 48 and 51 slots) and 0.5mm lams does start to exhibit more heat at those rpm, so I'm pretty sure that's dancing with the iron limits. With your 22.5" wheel 1000rpm is 67mph, and they said the Kv of the 3T is just over 12rpm/v. Without some aero treatments I think trying to push more air than that may be a bit of a strain on the 3000, but that's very bike dependent.

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Re: Science, Physics, Math, & Myth

Post by teslanv » Nov 25 2014 12:42pm

Alright, so on Low-turn (21X3T) motors, how would you deal with the small phase wires to get enough current to the windings without overheating the phases?

Obviously you run heavy gauge wire from the controller as close as you can to the motor/Axle, but at best you can get what about 10AWG through the bearing? - Even with a very short 10AWG conductor through the bearings, if your phase amps are up in the 200A-300A range, it's going to be cooking that 10AWG wire, no?

And then if you solve the phase wire issue, you still need a controller capable of outputting that much current. Everything has to get bigger with the higher current needs of a low-turn motor.

I'm looking for practical solutions, not something I have to Mod the heck out of.
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