Getting the right windings...

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Post by jonescg » Tue, 17 Jul 2012, 06:14

Hi All,

I have placed a deposit on an Evo AFM140 motor. Upon Evo's recommendation I chose the #4 wind, which has a Ke of 1.08 Vs/rad.

For those of us who prefer to work with rpm/V, this equates to 8.842 rpm/V.

The mechanical limit of this motor is 5000 rpm, or 565 V rms. Since most inverters aren't as efficient at turning a DC Bus into AC, multiplying by 1.5 is a safe bet. This means I need to be running a nominal 850 V DC!

Surely the #3 wind would be better for me? It has a speed of 11.79 rpm/V, meaning top speed occurs at 424 V rms, indicating a nominal battery pack voltage of 636 V (which is what I have planned).

Why are they recommending the slower motor? I have queried them about it, so I will hopefully find out soon.

Cheers,
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Post by Richo » Tue, 17 Jul 2012, 20:44

Are you sure you can run on that voltage?
I thought that the max voltage anywhere on the bike was suppose to be ~500V.

The #3 wind does sound better suited.
Probably has to do with extra power losses the lower the voltage.
But I doubt it would be enough to be worried about.
So the short answer is NO but the long answer is YES.
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Post by jonescg » Wed, 18 Jul 2012, 00:34

Another forum has suggested this is all correct, but the inverter should be able to engage in field weakening so as to get the last 20% out of it - in theory it should trade torque for speed... Still a bit confusing.

Oh, 700 V is the maximum. Suits me Image
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Post by jonescg » Wed, 18 Jul 2012, 04:16

Yep the answer was field weakening. The inverter under normal conditions will spin the motor up to a base speed of 3750 rpm, but provided the inverter is able to, it adjusts the timing of the waveform such that 'field weakening' occurs. This reduces the back EMF at the expense of torque. Since the motor speed increases the total power output remains fairly constant.

So in short, Evo assured me I will be able to spin this sucker up to 5000 rpm without any worries Image
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Post by T2 » Thu, 19 Jul 2012, 13:25

What's up with all this high voltage stuff ?

Can you tell me why EVO can't wind this motor
with a lower voltage ?

They know it's for a race bike do they not ?
Yet they are OK for field weakening.
Sorry but there is no reason they should OK that.

If you go all the way to providing 636Vdc there is no reason that you should be in the field weakening zone between 3750rpm and 5000 rpm

You are building an extreme machine and should not be accepting compromise otherwise it is not the motor that should be referred to as a sucker.

I have taken the time to examine their website and I am confused too. What they have is an overrated machine which they have to liquid cool in order to keep alive.

I believe that a high speed induction motor is equally capable and efficient in this situation although I would be looking at 9k rpm of course. A WS 200 controller could give you that. Plus if you have bothered to read around here you would know that rpms are the key for small frame size motors not voltage.

I am just concerned about who is feeding you and Geerant all this stuff to unload an $11,000 motor like it was a way to a get rich quick scheme.
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Getting the right windings...

Post by PlanB » Thu, 19 Jul 2012, 15:11

The EVOs are down to $6.3k now T2. What inverter you got in mind for 636v Chris?

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Post by jonescg » Thu, 19 Jul 2012, 17:31

Calm down T2...

What's with the high voltages? Less current that's what. High currents = heat and heat is bad news. All PMAC motors worth their salt are liquid cooled nowadays. And if you can find me an induction motor which is good for 100 kW continuous and it fits in the frame of a motorcycle, I'm all ears. PlanB - they are 5750 GBP, or roughly $9k before customs, GST and shipping.

I will be using a Rineheart PM150DZ inverter. I decided not to use a Tritium inverter because it simply doesn't have the DC bus capability to run these power levels. The #3 wind motor would still only get up to about 3700 rpm on a Tritium because it cannot exceed 320 V rms output. the #3 wind needs ~420 V rms to achieve full speed without field weakening. To the best of my knowledge (and James will confirm) they don't employ field weakening, so the best I can get out of this motor on a WS200 would be 80-100 kW max. I need something close to 90 kW continuous. However I will hopefully catch up with James tomorrow in Brisbane so I am open to being proven wrong though; an extra $4k would be nice.

And why are we going for big expensive AC motors? Because I burned through 5 under-powered DC motors, which cost me as much as one big AC motor. And an industrial induction motor of equivalent power weighs about 100 kg. No thanks.
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Post by Faz » Thu, 19 Jul 2012, 20:32

jonescg wrote:And if you can find me an induction motor which is good for 100 kW continuous and it fits in the frame of a motorcycle, I'm all ears.
+1
Axial Flux Permanent Magnet motors seem to have the best available power to weight of any electric motor out there. I don't think you will find an Induction motor that comes close.

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Post by Richo » Thu, 19 Jul 2012, 20:51

Given my 4kW induction motor weighs the same (40kg) I get less than 1/2 the power 70kW pk vs axial flux 167kW.
I'd have to set the peak power of my motor to near 13,000RPM and probably have a max RPM of 16,000RPM to do the same job.

Even Tesla's induction motor (AC-150) only has approx the same performance and weight of the AFM-140.
And I bet you can't pick up one of those up for under $10,000.

If you want light weight performance then induction motors aren't it.
So the short answer is NO but the long answer is YES.
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Post by T2 » Sun, 22 Jul 2012, 16:41

High currents = heat and heat is bad news

First there is nothing wrong with higher currents with appropriate sized cabling and terminations. Plus who is to say that fewer larger terminals are more problematic than a plenitude of smaller ones ?

Second if we consider even a 96V-120Vdc system and 550Amps, those 550 Amps will exist only in the motor windings and the three short leads from the controller. The battery current OTOH will be significantly less than that most of the time as you should know.

The dimensions of a bike mean that we are only discussing about a few feet of heavy cable anyway. I happen to have seen a partially disassembled race bike and there seems to be precious little of that orange cable.

Plus the fact that resistive losses are only incurred for a short period during acceleration since the majority of time the bike is cruising, coasting or braking where average currents are considerably lower, reduces the need for thick cabling.

100 kW continuous   I think you really meant to say 100Kw peak which you can get from a 35Kw AC motor.

But Continuous ???
First the 80Kw Prius at 1312kg cruising at 160km/hr draws 36Kw continuous on the dry flat, checked by a scan tool.
So your bike at 300Kg - I am assuming - will draw what exactly .......more than a Prius?

Second what is meant by continuous power on a bike ?
Even if you had 100Kw continuous power that sort of power would deplete a 10Kwhr pack in about six minutes.

Image Apparently the heatwave we are having here got to me the other night and my left frontal lobe didn't temper my outbursts like it should. I apologise therefore for the over the top comments which I have now seen fit to remove.    
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Post by jonescg » Mon, 23 Jul 2012, 04:18

T2, I'm never really sure how to take you, but your knowledge of my bike is just so profound and insightful, I really wonder why I didn't just hire you to build it for me. Your powers are wasted here!

High currents = more heat except with appropriate cable sizes. How often do you hear folks suggesting you go down a cable size? Wire is a remarkably good heatsink and if it doesn't sink fast enough, the heat goes back into your components. Not worth it. Reduce the currents first so it's not a problem.

I was running a ~110 V system using my pair of Agni motors. Comically, they were rated for 15 kW continuous 30 kW peak. as a pair, 30 kW continuous would have me circulating so slow I'd need a calendar to record laptimes. I was pulling 400 A from the battery pack regularly. Like, every corner exit kind of regular. The motor was getting so much current on occasion it melted the armature solder. It's fair to assume that this was too much current too. The battery currents were simply too high for my liking. Volt up, and wear gloves I say.

As for the dimensions of a bike, yes, every cubic centimetre of the bike is being utilised by a necessary component. But if that component is at serious risk of being cooked because of a high current, I'll use 50 mm2 cable thanks, and I don't care if it takes an extra 20 mm2 to do it. Can't comment on the super-dooper speaker cables you mention, I'm not a true audiophile.

100 kW continuous. Yes you read it right my friend. I want a bike which is good for 100 kW continuous. Even if the battery is not big enough to supply this I want a 100 kW continuous motor.

Why? Because I will be riding this bike with the throttle to the stop on the exit of every corner for 8 laps. The duty cycle for max power is literally 90%. I don't give a stuff what the peak power rating is - it might as well be made up. If a motor is rated for an hour of 100 kW output, it will be more appropriate for the thrashing I intend on giving it than the 12 second burst they claim as peak. Continuous is the new peak, my friend. Continuous means it won't burn up when used at that level. So even if I use it at half that level half the time, and 150% for the other half I know it won't incinerate in a race.

My bike will weigh no more than 200 kg. It will be geared for a top speed of 220 km/h (I want to make the most of the long straights at Eastern Creek and Philip Island).

"Listen I don't care if you seem to have more money than sense just don't get up on AEVA and spout your nonsense here; and if EVO can't wind that motor to YOUR specs allowing you to use a safer voltage and a more supported controller then perhaps they don't deserve your business."

Nice one. I really like the more dollars than sense bit. I don't know how many electric vehicles you have built, or electric race bikes you have built and raced in particular, but I am quietly confident I have a bit more experience on track than yourself. Lower rated stuff which sells for lower prices and has lower tolerances will disappoint unquestionably. It literally fails upon first use. I don't want this. If it costs me 10 grand to prevent catastrophic failure, then I will pay ten grand.

Who is the "we" in "we burned out 5 motors"? Me. And my awesome friends who helped me work the late hours to rebuild the bike with motors I purchased with my own money, between race meets. How on earth you assumed this was someone else's money I don't know, but reading and comprehension have never been your strong points. Why did we (I) go through five motors? Because the motors were paired up. You burn one, replace it, and because you couldn't balance the motor shims overnight between races on the floor of the pits, they remained out of balance and I cooked another. The pair of new balanced motors worked a treat and I won the following two races.

You don't need to lecture me on how crap Agni Motors can be under racing situations - trust me I'm way ahead of you there. But it's not like I could whip an induction motor out and repair it between race meets. Everything about last years bike was custom, commuter, and totally inappropriate for racing. Lessons learned, hence the new, more powerful race bike for 2013.
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Post by Richo » Mon, 23 Jul 2012, 20:41

T2 wrote: 100 kW continuous   I think you really meant to say 100Kw peak which you can get from a 35Kw AC motor.


And how big would said 35kW AC motor be?

My tiny 4kW motor spinning at 13,000RPM already weighs the same (40kg) and would do ~35kW continuous.
It has a smaller OD but is longer.

I don't know if it really practical to fit a much bigger motor on a race bike.

Did you have a motor 35kW in mind or did you dream it up?
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So the short answer is NO but the long answer is YES.
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Post by Stiive » Mon, 23 Jul 2012, 23:18

jonescg wrote: For those of us who prefer to work with rpm/V, this equates to 8.842 rpm/V.

The mechanical limit of this motor is 5000 rpm, or 565 V rms. Since most inverters aren't as efficient at turning a DC Bus into AC, multiplying by 1.5 is a safe bet. This means I need to be running a nominal 850 V DC!


This value will only be up until the nominal speed of the motor, not maximum speed.

What is the nominal freq of the motor? Say its 100Hz and the motor is 4-pole then the nominal speed would be 3,000RPM.

The motor should be designed to have maximum voltage at nominal freq, therefore 3000/8.842=340VRMS would represent your maximum voltage. Therefore using your "1.5x" logic, you could get away with a ~500V DC bus.

Field weakening represents the control of the motor above its nominal speed (over-speed) where voltage is already at its maximum. To continue to increase the speed the frequency still needs to be increased. Because the flux is proportional to the voltage/freq, the flux (or field) decreases, hence the term field weakening.

Hope this helps
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Post by T2 » Thu, 26 Jul 2012, 05:41

-Richo
        Yes, at 13krpm your motor would be capable of a nominal 35Kw

That would be with a V/Hz that can support that rpm without field weakening which you want to avoid with a racing machine.   

Original 4-pole/phase induction motor rated at 4Kw @1500rpm 50Hz
Ambient temp 40deg c, with 80 deg c temp rise at rated hp

It is generally agreed here that power   = P x (wdg ratio)^0.7
                                                  4Kw x 9^0.7
                                                  4Kw x 4.65
With derated current to compensate
for the increased iron loss at 433Hz        19Kw continuous
This figure assumes 40 deg ambient when the temperature of the frame has reached 120 deg c. Until that limit is reached the nominal rating specified below can probably be safely applied.

Same copper loss as original machine        36Kw Nominal(limited time)
Theoretical 300% overcurrent.              108Kw 30 Secs

Gear changing at 13000 rpm would be out of question. OTOH unlike racecar and motorcycle engines and AGNI armatures, which have time limits in seconds on their highest rpms, an induction motor can hold its top rpm indefinitely. As a demo I once took a 3600rpm 60Hz machine from stores. It was equipped with ball bearings with no special rotor balance and it ran straight out the box for 40mins at 7200rpm, no problem. Only the 120Hz limit on the controller prevented further exploration. Admittedly a 1 Hp rotor is fairly small but a 5Hp would only be about 70% larger in dia.

I am looking at an image from Sept '98 of an extreme machine at the Electrical Drives group at Sheffield U. in England. It weighs 12Kg and is said to deliver 100Kw @ 20,000rpm.

Three cables emanate from the non drive end which are as thick as and look exactly like pork sausage, as the best way I can describe them !

The image also shows, anchored in the corner, the 300kg motor, equipped with an outsize industrial blower, used in the load testing.

Unobtanium aside, your 4Kw 1500rpm machine in an L184T frame should weigh in at (60lbs) 27kgs not 40Kgs. And that's alumininum construction in a Totally Enclosed Fan cooled [Brook Crompton OCT '89] frame.

edit : better explanations on the power predictions of overclocking as some people have referred to it.
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Post by T2 » Thu, 26 Jul 2012, 11:31

-jonescg
I looked at the Agni website. They are quite informative but somewhat short on electrical drawings. They entitle product lines "The 95R Series Motor". Uh HUH but does that actully mean that it's a "series motor" ? Eventually I found a picture which shows only two motor terminals. Finally I came across a reference regarding the handling of the magnets. That was the giveaway that DC permanent mag motors was their business. An electrical drawing would have cleared that up instantly.

BTW jonescg did you have the correct grade brushes for the +ve terminals and for the -ve terminals. Different grades depending on the actual polarity of the connection ? Certainly new to me.

I assume both machines wired in series. The 400A limit is my first concern. Accelerating away in current limit every time is what I expect but if the needle stays buried for too long could reflect on the fact that the gear ratio in use is too hard for the motor.

You certainly need to be able to see a voltmeter across the armature itself to ensure a good rate of rise. Feeling and seeing acceleration may have different reactions if the rpm doesn't seem to be punching through the 3000rpm level soon enough. You are correct I've no track time on me but I drive stick and can usually fend off the non-stick driver with the more powerful car when the need arises. That's all you need to know.   

Secondly an rpm gauge to signal a changeup when reaching 5500 rpm would be useful. I would use a tooth wheel and 2 wire magnetic sensor feeding an LM 2907 tach chip from National Semi's Linear catalog. Put 1 microfarad across input to quell noise. Must have used thousands of these on pcbs over the years.Very versatile. You might use them to trigger a tone generator chip when you need to change up. They have an pulse integrator and comparator coupled to a 50mA led driver already built in.

The motor termination bolts look awful light for carrying the frequent 400A surges, and I sure don't like those open style lug crimps they use under the end cover. And they might have stressed the importance of copper washers on perhaps both sides of the lugs (which should be of the ring type) and also recommend the use of brass rather than steel for all the terminal nuts.

With PM motors regen is a natural.
Did the Agni controller have regen capability ?
Dynamic braking resistors for extreme braking when pack overvoltage cuts the regen ?
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Post by Richo » Thu, 26 Jul 2012, 21:04

T2 wrote:your 4Kw 1500rpm machine in an L184T frame should weigh in at (60lbs) 27kgs not 40Kgs. And that's alumininum construction in a Totally Enclosed Fan cooled [Brook Crompton OCT '89] frame.


Brook crompton W-DA184T-S is 1800RPM 3kW(2.5kW@1500RPM) BDT290% 29.4kg - Aug 2002.
Given the next size up W-DA213T-L 1800RPM 5.5kW is 45kg my 4kW 40kg sounds about right.
Yeah there were better motors around in the 80's when MEPS wasn't an issue.

So please throw those old cattledogs out.

The motorbike has no gearbox.

So the short answer is NO but the long answer is YES.
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Post by weber » Fri, 27 Jul 2012, 18:52

It isn't more rpm as such that is required for getting more power out of a motor of a given mass, it is higher frequency. So if you double the frequency and double the number of poles you should have double the power at the same speed. However you don't get quite double the power as higher pole-count motors as less efficacious in terms of newton-metres per pole per kilogram. Why is that?

Why did Tesla Motors use a 4-pole 12,000 rpm motor instead of say a 6-pole 8,000 rpm or an 8-pole 6,000 rpm? The advantages of lower rpm are less likelihood of your rotor exploding from centrifugal force and less need for precise balancing or special bearings and lubrication, and less need for gearboxes with huge reductions and their attendant loss, less inactive mass in the copper at the ends of the windings, lower friction and windage losses. Surely the reduced newton-metres per pole kilogram isn't enough to negate all of those benefits? Or is it?. Or is there some other reason no one is talking about taking an industrial 6-pole induction motor and getting it rewound for 50 V or less (nominal at 50 Hz)?
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Post by woody » Fri, 27 Jul 2012, 19:54

Industrial 6 and 8 pole motors seem to be less efficient (from the catalogues)

I think with higher pole count you get less of the circumference to cram the windings in, they have to overlap.

It seems that many 4 poles are wound with "consequent pole" windings to allow more space per pole.

I think bigger diameter is the way to go, axial flux, we just the the entire industrial world to get on board to get the price down :-(
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Post by T2 » Sat, 28 Jul 2012, 15:30

-weber, the first part of your statement said :
It isn't more rpm as such that is required for getting more power out of a motor of a given mass, it is higher frequency.

Nope, I have to disagree. But I thought you were on the same page with me earlier that for any given frame size its nominal torque can't be changed with a V/Hz rewind as it depends on the ampacity of the slot. That being so, then Hp can only be the product of torque and rpm.

Also another clue could be that the equation for electrical power does not have a sinusoidal component which is line frequency dependent. I am thinking of this one.

P = V x I x cos(phi)

The rotor chases after the synchronous rotating flux field which moves at the same speed around the stator in a 2 pole/phase with 50Hz excitation as it does in a 4 pole/phase with 100Hz excitation.

Only a 3D program with FEA can really show whether the 2,4 or even 6 pole machines display better use of that flux field and answer that question of which has superior magnetic coupling to yield more torque. If I'd have to guess I'd say that would probably turn out to be a 2nd order effect at best.

What we do know- from discussions here - is that the copper loss is constant for a specific torque, therefore the faster the rotor turns the more efficient the copper circuit becomes in relation to the magnetising losses, because we are producing a lot more power without a commensurate increase in the copper loss.

If we can select laminations so thin that the iron loss does not significantly increase as much as the power with respect to RPM then motor efficiency could be said to increase with speed.

And that is why 6 and 8 pole machines seem less efficient because they assume a universal 50Hz excitation. So you are comparing slower 1000rpm and 750rpm machines to machines that run at the faster 1500rpm and then ask why they are less efficient ?

But we know from international catalogs that a 4-pole used on 115 Vac 60Hz shows better efficiency than when run at 100Vac 50Hz even though the V/Hz are mostly the same.

It would be interesting to propose an experiment to see just what happens when all three pole types are run at 1500 rpm with appropriate frequencies and voltages just to see if the efficiency figures change beneficially for those machines with the greater number of poles.

I do not have a bias against high pole numbers and low frequencies. As an aside I believe the Queen Mary II has multi-pole pod drives that max out at 13.8Hz and these are multi-megawatt machines, so when direct drive is necessary these low frequencies must indeed be workable.

Although in the industrial world with increasing numbers of inverters being used I have to wonder whether there is much of a market for other than 4-pole 3 ph machines today.     


So if you double the frequency and double the number of poles you should have double the power at the same speed.


I'd say that is an easy question with a hard answer. The magnetic fields set up by the rotor and the stator are always identical, in synchronism and with the same shape and amplitude.
I'm going with the fact that it is the area of overlap which provides the torque. So narrower double frequency waves provide only half the torque but there are twice as many so you end up with the same torque.
Now ask me to prove it mathematically !!

-richo thanks, but no thanks. I'm not throwing out any of my cattledogs anytime soon.
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Post by weber » Tue, 31 Jul 2012, 14:06

What is wrong with this forum!!!? It seems that it is never available when I want to post something. I had to prepare this response offline and just keep trying until I could post it.
T2 wrote: -weber, the first part of your statement said :
It isn't more rpm as such that is required for getting more power out of a motor of a given mass, it is higher frequency.

Nope, I have to disagree. But I thought you were on the same page with me earlier that for any given frame size its nominal torque can't be changed with a V/Hz rewind as it depends on the ampacity of the slot. That being so, then Hp can only be the product of torque and rpm.
I do agree with your last two sentences above. But you seem to be ignoring the fact that, for a given frame size and mass, torque can be increased by increasing pole count. Check your induction motor catalogs, particularly for frame sizes greater than 132 mm (NEMA 215 I think).

So to get more power out of a motor of a given mass you can either increase rpm while keeping torque constant (what you have been talking about) or you can increase torque while keeping rpm constant, by increasing pole-count. What both of these have in common is an increase in electrical frequency.

This is just like a transformer. Rewinding the motor for a different voltage is analogous to changing the turns ratio. We agree that doesn't change the power rating at the nominal frequency.

How do you get a lot more power through a transformer of a given mass? Answer: You use a higher frequency. As the iron losses increase with frequency you have to use thinner laminations and then powdered iron in a non-conducting matrix, and then ferrite. You also have to use Litz wire to avoid skin effect. Compare the weight of a 50 Hz transformer with the weight of a 20 kHz transformer with the same power rating. It seems that a given mass of iron lets you put through a fixed amount of energy per cycle (approximately). An inductor in a switching power supply certainly does this. It stores a fixed amount of energy equal to 1/2*LI^2 where L is its inductance and I is its saturation current. The faster you can cycle it, the more power you can put through it.
What we do know- from discussions here - is that the copper loss is constant for a specific torque,
That's only true for a given pole-count. By increasing pole-count you can increase torque without increasing copper loss.
therefore the faster the rotor turns the more efficient the copper circuit becomes in relation to the magnetising losses, because we are producing a lot more power without a commensurate increase in the copper loss.

If we can select laminations so thin that the iron loss does not significantly increase as much as the power with respect to RPM then motor efficiency could be said to increase with speed.
Sure. The efficiency increases even though the losses increase, because the useful output increases faster than the losses do.
And that is why 6 and 8 pole machines seem less efficient because they assume a universal 50Hz excitation. So you are comparing slower 1000rpm and 750rpm machines to machines that run at the faster 1500rpm and then ask why they are less efficient ?
I didn't actually say anything about efficiency in the post you were responding to. I was talking about torque per pole per kilogram, which I referred to as an "efficacy". But of course higher pole-count motors are less efficient too (at nominal speed), although the larger the motor, the less difference you find in efficiency between different pole counts. And what you say may well be true -- that if we increase the frequency in proportion to the number of poles, the efficiency may well be nearly constant. But the torque per pole will still decrease with pole count just the same.
It would be interesting to propose an experiment to see just what happens when all three pole types are run at 1500 rpm with appropriate frequencies and voltages just to see if the efficiency figures change beneficially for those machines with the greater number of poles.

I think you just proposed it. It would be more interesting if someone would do it. Image

I now believe the reason why higher pole-count induction motors of the same mass have lower torque per pole is, as I think you implied, that as the poles get closer together, more flux takes a short-cut through the stator and doesn't pass through the rotor.

As Woody said, axial flux is one way (maybe the only way?) to get around this, and once we do, we can go to higher pole counts without losing so much torque per pole. What is the axial flux version of a squirrel-cage rotor? I'm guessing it is a disk with near-radial (slightly spiralled) rotor bars with shorting rings at the centre and periphery.

So how do we make a 16 pole axial-flux induction motor with a ferrite core and Litz rotor-bars, that doesn't fly apart? Actually, with "only" 16 poles, there is no need to go to ferrite and Litz wire since it would only need to go to 400 Hz or so, just many thin copper rotor-bars and stator-strands and thin iron laminations.

Is there a way to reduce the flux leakage in a 16-pole radial-flux (conventional) induction motor?
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Getting the right windings...

Post by jonescg » Tue, 31 Jul 2012, 18:08

So ah, yeah. I'll be going with the 140-4 wound motor, driven by a PM150DZ inverter Image

Axial flux is the way to go, and PMAC is the best power to weight around. I have thought about an axial flux induction motor design, and concluded that yes, something like trapezoidal coils would work. But hey, I need the really high continuous power ratings, and I need it ready by next March. So prototype motors are out of the question Image

And Will, yes this forum desperately needs to go on a real server. Lots of options out there, can't see why we can't get something happening soon.
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Getting the right windings...

Post by weber » Tue, 31 Jul 2012, 19:06

jonescg wrote: So ah, yeah. I'll be going with the 140-4 wound motor, driven by a PM150DZ inverter Image
Sorry about the thread drift, Chris. I wasn't suggesting an induction motor for your bike. PM is definitely the way to go. I was just talking generally. Mainly responding to T2.

IMHO, induction motors are more efficient than PM and can have similar power to weight when you get up to high-performance-car-type power requirements. And they have an advantage that you don't have to worry about cooking your magnets, so they can run at higher temperatures. And your driven wheels won't lock up if the inverter fails. And they are a lot safer to deal with when disassembled -- no crush injuries or fractured magnets from steel tools getting too close.
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Getting the right windings...

Post by Stiive » Tue, 31 Jul 2012, 19:14

weber wrote:
IMHO, induction motors are more efficient than PM


I wouldn't go that far.
In small motors i think PM is the way to go (such as on a bike) because you cant beat the power/weight and efficiency, but in larger vehicle IMO the benefits lie with IM, esp copper rotor IM.

Cost is the biggest factor, but also you cant beat the IM in terms of overload and pure ruggedness Image In a full-size EV, the small increase in performance of PM is easily negated
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Getting the right windings...

Post by weber » Tue, 31 Jul 2012, 19:44

Stiive wrote:
weber wrote:
IMHO, induction motors are more efficient than PM

I wouldn't go that far.
Stiive, you have misquoted me by quoting only part of my sentence.
In small motors i think PM is the way to go (such as on a bike) because you cant beat the power/weight and efficiency, but in larger vehicle IMO the benefits lie with IM, esp copper rotor IM.
Please re-read my previous post. I said exactly that (except I didn't mention copper rotor, but agree with you about those too).
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Getting the right windings...

Post by weber » Wed, 01 Aug 2012, 01:10

Stiive, I see my sentence was ambiguous. As someone famous once said, if something I wrote can be read two ways, and only one of them is correct, then I meant the correct one. Image

Chris, since your original purpose in starting this thread has been satisfied, I hope you don't mind if it continues as a discussion of high power-to-weight induction motors for EVs generally.

I got into my productivity booth (that's Coulomb-ese for a nice relaxing hot shower where no one will bother you) and put my neural CAD system to work designing how I thought an axial flux induction motor (AFIM) should be put together. A fascinating puzzle that I wanted to have a go at before seeing the solutions others had come up with.

The trickiest part, I found, was figuring out how to orient the steel laminations (in both the stator and the rotor). Because they not only have to have the flux passing through them edge-ways so it doesn't induce eddy currents, but in the case of the rotor they have to couple the torque to the shaft and resist expansion by centrifugal force, of not only themselves but also the radial copper rotor-bars and their inner and outer shorting rings.

I decided the laminations should be in the axial-radial plane, i.e. oriented as vanes, not as disks or concentric cylindrical rings, and so the varnish between them would have to be wedge-shaped. It might be powdered-iron filled epoxy. The rectangular rotor stampings might span from half-radius to full-radius of the rotor. They would meet at their inner edge and at their outer edge they would have gaps equal to their thickness. At their inner edge they would all be welded to a solid steel disk that is coupled to the shaft.

I decided it might be best to leave the rotor-bars exactly radial (for centrifugal reasons) and skew the stator slots (and hence stator laminations) instead. Because the stator laminations would also be in the vane-like orientation, magnetic flux could not travel tangentially around the stator to close the magnetic circuit. It could only travel radially and axially. So the stator laminations would need to wrap around the outside of the rotor and present poles to both sides of the rotor. The stator laminations would be stamped in a C-shape, with the rotor laminations fitting in the gap. This would have the side-effect of helping to contain the pieces of a centrifugally-exploding rotor.

Slots in the stator would be formed by short laminations, i.e. with a bigger gap in the "C".

Then after I got out of the productivity booth I went looking on the web and found this great survey paper by Zahra Nasiri-Gheidari and Hamid Lesani.
A Survey on Axial Flux Induction Motors

I was astounded to learn that AFIM laminations for both rotor and stator generally consist of a long strip of motor steel wound around and around in a spiral, with slots having to be machined in it at great expense. And this is so weak and unstable that for high speeds the rotor is typically just made as a solid disk -- too bad about the eddy currents. See pages 301 and 302.

Can anyone see anything fatally wrong with my idea of radial, vane-like laminations? Of course the stator can be the same for a PM machine or an induction machine. I wonder which way EVO's stator laminations go.

Here's a video of an AFIM by an Aussie inventor, Paul Evans. It is intended as a wheel motor and it has a partial stator that looks like a brake caliper. I notice the rotor bars aren't skewed and I wonder if the stator teeth are not skewed either and that's why it's so noisy. Either that or the rotor is scraping on the stator. Information elsewhere indicates that the stator is double-sided but I can't tell which way the laminations go, if any.



[Edit: Spelling. Added that Evans' stator is double-sided]
Last edited by weber on Tue, 31 Jul 2012, 17:03, edited 1 time in total.
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