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Post by T2 »

This is a topic for those who have an interest in high speed electrical machines and the gearing systems designed to accept them.


The machine of interest here is going to be the induction motor,.

That being so what is so wrong with PMSMs ? There is no denying that permanent magnet synchronous motors are prevalent in many EVs including the Nissan Leaf and almost all hybrids.
So what is the problem ? Well it is not the supposedly imminent shortage of the rare-earth elements that go into making them. China doesn't have a lock on the supply there are plenty of mines, some now dormant, waiting on the sidelines if demand builds.

The primary problem with rare-earth magnets is to do with their physical properties regarding temperature sensitivity. Should the motor be allowed to get too warm they begin to lose their magnetic properties. This would otherwise detract from the power density attainable hence the necessary liquid cooling.
In contrast the rotors of induction motors will tolerate much higher temperatures.

There is another disavantage with the rotor magnets in the fact that they are always "ON". As a result, when coasting along in an electric vehicle there is always going to be some magnetic drag from the iron laminations forming the stationary stator. This braking effect offsets from the slightly higher efficiency obtained when motoring.
An induction motor ceases to generate magnetic fields when power is off so zero braking effect.

PMSMs in the form of the Axial Flux type are readily available to developers attracted by their comparitively higher torque capability due in part by their larger diameters, I suspect.

However should you want to find an AC permanent magnet motor in the 14,000 rpm range today then look no further than Ebay or the local breakers yard. Thanks to the longevity since initial release, the high population of Prius cars, coupled with a lack of skilled drivers has ensured a steady supply of serviceable transaxles to be available on the aftermarket. Unfortunately it's not all good news.

First, it has proved impossible to spoof the Toyota ECU since so many support signals need to be around at the same time.
Second, although substitute inverter drives have been tried they have been met with limited degrees of success. The more stringent trapezoidal drive requirements of MG1 and MG2 and the algorithms to drive them known only to Toyota has required downrating them and so prevented them from being successful as EV motors.
Third, there is the recognition that these motors have been built expressly to tolerate only limited periods of transient high power demand. A fact that became revealed while testing at ORNL following the teardown conducted in early 2004 for the USDOE.

Before leaving the Prius transaxle, for the purpose of this topic, it should be pointed out that the MG1 shaft has an appropriate gear ratio to the wheel axle and will accept 10,000rpm. Knowledge of that interesting situation seems to be rare among EVers.

Now we have PMSMs out of the way this would be a propitious time to introduce the back story of induction motors in EVs.

A brief history of which starts with GM, no less. Their first experimental AC powered car, the Electrovair II used an induction motor which maxxed out at 13,200 rpm was liquid cooled and ran on a silver-zinc battery pack. The inverters to overcome the lack of available transistors instead used thyristors along with commutating thyristors to turn them off. This was the way it was back in 1966.
The Convair "donor" car was GM's answer to the VW Beetle. Accordingly the induction motor was coupled into the Convair's gearbox which like the VW turned the power through 90 degrees to the wheel axle differential. Mechanically an extremely inefficient process. I have happened to witness dynamometer testing of a VW Beetle transmission and then later after refitting with the front wheel transaxle from a Honda. Big difference indeed.

Mechanical engineering has advanced since with the following vehicles all being fitted with a single ratio gear reducer(s).

The Impact which was built by subcontractor Aeronvironment in 1988.

The short lived EV1 from 1997.

The Tesla Roadster able to reach 100Km/hr in under four seconds using a 13,000 rpm motor.

In my next post I will continue with the discussion of the topic regarding how to incorporate more high speed induction machines into conversions we can afford.

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Post by Richo »

There may be no imminent shortage for rare-earths for magnetics but it doesn't help when countries hoard it bumping the prices up.
The price of rare-earths have gone up.
The only reason a PM motor price has come down is due to volume production and competetion.

I still see no reason to buy one for an electric car since an Induction motor can be bought in most industrial areas.

I still haven't seen any actual specific vaules of losses through a gearbox or diffs (fwd and rwd).
It all seems to be mechanics / tyno testers heresay.

I agree that once there is enough RPM range out of a motor a simple reduction drive is really the best choice.
Still given that there is limited selection (AT1200) it is still up to some mech engineer to design and build a selection for standardised motors.
So the short answer is NO but the long answer is YES.
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Post by Stiive »

T2 wrote: China doesn't have a lock on the supply there are plenty of mines, some now dormant, waiting on the sidelines if demand builds.


I think you'll find China DOES have a lock on the supply, providing on average more than 90% of the worlds different rare earths.
China this year has also just split their export quota limits into LRE and M/HRE.

It is also estimated that 20% of the worlds import supply that isn't seen coming from China's export quota, has actually been illegally smuggled out of China.

Your right though, there are many dormant mines outside of China, but they aren't necessarily waiting for demand to build, they are waiting for the price to increase further because mining these materials is hazardous, complicated and extremely expensive when trying to extract using 'environmentally friendly' methods; something that is barely considered/adhered-to in China.
So what happens when the price increases enough to make the extraction of rare earth profitable in developed nations? China relaxes their strict export quotas just enough to reduce the price to keep competition at bay.

IMO China will have a monopoly in this market for a long time, all the while forcing companies to bring manufacturing to China and technology-share with Chinese companies in return for the precious materials.

Induction Motor FTW!

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Post by Johny »

Stiive wrote:....IMO China will have a monopoly in this market for a long time, all the while forcing companies to bring manufacturing to China and technology-share with Chinese companies in return for the precious materials.

Induction Motor FTW!
It seems that Toyota may agree with you Stiive.
http://www.treehugger.com/cars/toyota-i ... arths.html

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Post by Stiive »

For reference
http://www.criticalrareearthsreport.com ... e-0811.pdf


You may need to sign-up to view this document, but i'd recommend it.


An excerpt from the report showing China's current dominance in the different rare earths.
Its an old report now though (1 year almost exactly). This is based on trends, but I still think the Chinese government will be able to keep a strong dominance (and it's in their interest to) for longer than what is shown, but atleast it shows their current dominance

Image

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Post by Richo »

Magnets aside 3 factors limiting High RPM machine are:

1. Rotor dia before it shatters from RPM
2. Rotor balance before it wobbles into the stator
3. Bearings

Most stock bearings of smaller machines should cope with 4500-6000RPM.
But better bearings are needed.
Has anybody seen bearings that are suitable for 10-20kRPM?

So the short answer is NO but the long answer is YES.
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Post by T2 »

Richo,

The general answer to your question is to have the rotor balanced when you take the stator in to be rewound as ACMOTOR did for Red Suzi.

In this case the balance before adjustment was found to be -650gm.mm
Following adjustment this was brought down to 30gm.mm @ 6000 rpm

Considering this 24Kg rotor was originally destined for 1450rpm usage, any guesstimates going forwards ?   Probably at least 12Krpm I would say.

Search Members Machines on page 4 for more details on RED Suzi.

Then jump to Page 6 of that topic for the rotor balance discussion - starting Aug 25th 2009.

Specifically for the bearings I would not go further than having them replaced, if the previous wear history is unknown.
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Post by Richo »

For a 14,000 RPM stock bearings I doubt would be good enough.
My motor currently has 6306ZZ.
A quick look suggests stock bearings are ~6500RPM and high speed are 10,000RPM.
Red Suzi's bearings are likely to be bigger and so lower RPM.

So a rotor balance maybe possible.
Bearings not confirmed to 14,000RPM.
Rotor dia not confirmed to check shattering max RPM.
So the short answer is NO but the long answer is YES.
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Post by T2 »

   Richo, have you any data to support rotor integrity problems at high rpm ?
The images I have seen show aluminum rotor bars "seeping" through rotor slots or surface wear patterns that were likely preceded by a partial bearing collapse. These were all on large diameter rotors I would say 250HP and up. Not comparable to 20Kg rotors with five inch diameters anyway.

I share your concern on bearing durability also. These are not three inch bearings. Consider that the components in question will be fitting on a 5/8" shaft and probably have a 5cm orbit which at 200rps corresponds to a surface velocity of 10m/s. Finally the expected lifetime duration at these speeds would be measured in hundreds of hours not in tens of thousands. Again send in the evidence that this is likely to be a problem. In my case I am considering a gear system that has no side load and that should help a lot. It would be helpful to know the price delta between the bearings you mentioned if you have it.
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Post by T2 »

                      We Don't Need No Stinkin' Efficiency !!

I have seen EVers describe the system they are going to build to be the very model of efficiency then have something like a toothed belt to the final gear or an automatic transmission. That something which totally negates all the care taken previously.

One of the first traps is motor efficiency. There is a general belief concerning the choice of motor types that among AC motors the Permanent Magnet Synchronous Motor has a clear advantage of not needing an external energy source to provide its magnetic field, unlike an AC Induction Motor for example. Then again It cannot be denied that this puts the induction motor at a distinct disadvantage, efficiencywise particularly at low power outputs, to be carrying this overhead for magnetic excitation. Efficiency figures for induction motors generally originate from standards laid down by the IEC and somehow gravitate to the Standards of other bodies. In this way motor efficiency is usually tied to the low rpms associated with the frequency of the National Grid. In that light the induction motor certainly doesn't look good.

Let's discuss this efficiency for the induction motor. In the past I have put forward the statement that the copper loss i.e. the electrical loss in the stator wiring remains constant per unit torque. A statement that was clearly not recognised by many here, initially. And by none still of the hostile crowd at the DIYelectric website and that from recent personal experience. This statement continues to hold whether the motor does 10 rpm or 10,000 rpm. If you accept that premise then it follows that efficiency improves with rpm.

For example a 1500 rpm machine having 92% efficiency.
It must therefore have a loss of 8%, you would agree ?

Now let's increase both input frequency and voltage, and speed that machine to 12000 rpm while still providing the same torque and drawing the same current.

At the finish the motor will be putting out eight times the mechanical power while incurring the exact same copper loss as it did at the start. The same current remember, the current itself was not changed and remained constant.

So if we have the original electrical loss accompanied by an increase of output power of eight times, this can only mean that the effective efficiency must have increased to a figure of 99%.

A figure derived from (800%-8%)/800 = 99%

Some may have noticed my error in that when Power increased from 92% to 792% it presented an actual increase of 8.6 times in mechanical power NOT the eight times which I quoted above. Thanks to whoever pointed that out.

Of course iron loss was neglected here in order to make a point so 99% is not attainable, even so it is more than likely that inside that initial 8% loss, that the copper loss component does indeed exceed the iron loss at the start. The initial iron loss is small but increases by frequency and frequency squared. How significant this is with both new high efficiency and the older machines needs further investigation.
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Post by weber »

I agree with all that you say in your previous post in this thread. I have pointed out in the past that % efficiency can even increases at the same time that the absolute kW losses (including iron losses) increase.
T2 wrote:In the past I have put forward the statement that the copper loss i.e. the electrical loss in the stator wiring remains constant per unit torque.
You need to say what other things you are holding constant when this holds. I assume you mean this to be with constant frame-size and constant mass, as you have said similar in the past.

But it worries me that you still don't understand that you must also hold the pole count constant for the above to be true. Sorry if I sound like a stuck record, but I understand you to still be ascribing the almost-doubling of torque between same-frame same-mass 2-pole and 4-pole motors to be due to some kind of conspiracy on the part of motor manufacturers. This is not the case.

If the problems of leakage flux could be solved for 6-pole and higher-pole-count induction motors then your higher efficiencies and higher power-to-mass could be achieved at rpm that do not require special balancing, special bearings, special rotor centrifugal strength, or special reduction gears.

Some of the ways that this could proceed are: Different flux geometries, particulatly various axial flux arrangements.
Different direction of steel laminations.
Smaller air-gaps.
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Post by Richo »

T2 wrote:Richo, have you any data to support rotor integrity problems at high rpm ?


You may already be a few steps ahead.

Tensile stress = Density x Radius ^ 2 x angular velocity ^ 2

I haven't worked through the math as I haven't measured my rotor dia.
There will be an RPM that the rotor just shatters - not just seep.
I want to be confident that this RPM is far away from the used RPM of a high RPM motor.
So the short answer is NO but the long answer is YES.
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Post by Richo »

T2 wrote:                       We Don't Need No Stinkin' Efficiency !!


Agreed.
An electronic drive will have to run at extreme inefficiencies before it gets anywhere as bad as using petrol.
T2 wrote: In my case I am considering a gear system that has no side load and that should help a lot.
I agree with this.
However I'd still be intrested in the wear life of the bearings with a gear direct on the motor shaft coupled directly to the gear on the diff - FWD cars in mind.
Just for reduce cost bearing wear vs extra gears
T2 wrote: It would be helpful to know the price delta between the bearings you mentioned if you have it.
I did find some ceramic bearing some time ago but this was more to reduce discharge arc build up on the bearings.
I will look for prices on some better bearings for high speed machines.
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Post by jonescg »

Richo wrote: I still haven't seen any actual specific vaules of losses through a gearbox or diffs (fwd and rwd).
It all seems to be mechanics / dyno testers heresay.



I have heard that a front wheel drive transmission is more efficient than a rear wheel drive, and that losses amount to about 17% from flywheel to drive wheel in a FWD. Possibly closer to 23% in a RWD car. Again, this is from a guy who works on transmissions, and where he got it from I don't know... Still he knew more about it than me so I'll go along with it Image
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Post by T2 »

I have heard that a front wheel drive transmission is more efficient than a rear wheel drive, and that losses amount to about 17% from flywheel to drive wheel in a FWD. Possibly closer to 23% in a RWD car.

I have first hand dyno experience with that using my field controller where a VW rear transaxle was replaced by a Honda transverse FWD modified for rear wheel usage. The dyno results showed a 20% improvement.
BTW the reason for the VW Beetle engine transmission being mounted inline and not transverse was simply because in keeping with all other engines of the time it had to accept a crank handle at the rear.

DETROIT (Reuters) - General Motors Co and Ford Motor Co are jointly developing nine- and 10-speed automatic transmissions to improve the fuel economy of their models, Automotive News reported on Friday Sept 28th 2012.

@ Richo, although I have seen considerable expertise expended in the construction of motor adapter plates, no one to my knowledge has investigated the feasibility for replacing all the gearsets inside a manual box with a single set ratio that would lie somewhere between 1st and 2nd gear.
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Post by T2 »

you must also hold the pole count constant for the above to be true.

Weber, I'm coming around to your style of thinking. The windlass is a good allegory for the multipole effect - I'm still looking for a magnetic solution that explains to my satisfaction.

My experience is that I noticed 2 poles are smaller perhaps because hi-speed fan cooling allowed designers to downsize slightly. All other indicators are that more poles equal more torque for the same length stator. The diameter of these machines seem to increase with more poles - therefore pole area appears to increase. But if pole area is the only driver then everyone would agree that if you simply stretch a stator lengthwise this will also give more pole area and with the same effect.
The key would be if power still goes up if you install more poles in the same diameter stator. A 36 slot stator could support a 4 and 6 pole winding perhaps something to try. My next post will have to address that possibility.

But you are running a 2-pole in the MX-5 what exactly was the thinking there ? Can't find your decision process on it even though I read the whole forty pages odd some time ago and just did a re-read of the salient ones over again.

As I see it you couldn't get the V/Hz below 4.6 despite 230Vac in delta on 50Hz so you used the extended speed range of a two pole machine in lieu of voltage (even more so now that you are now sticking with just 375Vdc) ?

Finally would you now be more enthusiastic about rewinding for a lower V/Hz but with a 6 pole - assuming there would be a next time ?
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Post by Richo »

When I had my car Dyno'd for a baseline they were claiming ~24% loss.
But I suspect that this was for a RWD car.
The extra losses being the 2 uni joint and the Diff gear changing the torque through 90degrees.

I hadn't really considered stripping the existing box and modifiying to a single custom gear of my choice.
Two reasons for this:
1. I would want to put in a higher torque motor which is likely to kill the exisiting gearbox.
2. Using a larger motor (132 size vs 112) I want the extra room from a custom slim line reduction drive.

Still - keeping with the low cost approach stripping the original gearbox is an option.

So the short answer is NO but the long answer is YES.
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Post by weber »

T2 wrote:I'm still looking for a magnetic solution that explains to my satisfaction.
Hmm. But isn't the summing of the torques from all the poles fundamentally a mechanical thing?

[For other readers, the windlass analogy that T2 refers to appears here:
viewtopic.php?title=getting-the-right-w ... 149#p38378]

Although I must admit, the fact that the power throughput of a given mass of iron and copper in a transformer or inductor, is nearly proportional to electrical frequency, makes me feel comfortable about finding that the same applies to motors.
My experience is that I noticed 2 poles are smaller perhaps because hi-speed fan cooling allowed designers to downsize slightly.
Yes. There would be a small effect from that. But Woody and others have compared Tmax or breakdown torque, which has nothing to do with cooling and they still show that 4-poles have nearly twice the peak torque of same-frame-size similar-mass 2-poles.
All other indicators are that more poles equal more torque for the same length stator. The diameter of these machines seem to increase with more poles - therefore pole area appears to increase.
Same frame-size means same machine diameter, so I don't know what you mean here. We've shown that torque nearly doubles by going from 2 poles to 4 poles while keeping the same machine diameter and close to the same mass.

I suppose the rotor diameter might increase with pole-count, while keeping frame-size and mass constant, but if so, so what?
But if pole area is the only driver then everyone would agree that if you simply stretch a stator lengthwise this will also give more pole area and with the same effect.
Stretching stator and rotor lengthwise will give proportionally more torque, but of course that's at the expense of proportionally more mass too, so I don't see the relevance.
The key would be if power still goes up if you install more poles in the same diameter stator. A 36 slot stator could support a 4 and 6 pole winding perhaps something to try. My next post will have to address that possibility.
I assume you mean "if power at the same rpm still goes up ...". But that's exactly what the catalogs show. Particularly when going from 2-pole to 4-pole. The problem is that when you go from 4-pole to 6-pole (with the same motor diameter) you get far less than the 50% increase in torque (and hence peak power at the same rpm) that you might expect. This is the problem I'd like to see solved.
But you are running a 2-pole in the MX-5 what exactly was the thinking there ? Can't find your decision process on it even though I read the whole forty pages odd some time ago and just did a re-read of the salient ones over again.
Sorry about that. I guess it appears in various other threads, but not our main build thread.

Most recently here:
viewtopic.php?title=getting-the-right-w ... 149#p38418
As I see it you couldn't get the V/Hz below 4.6 despite 230Vac in delta on 50Hz so you used the extended speed range of a two pole machine in lieu of voltage (even more so now that you are now sticking with just 375Vdc) ?
Yes. That's right.
Finally would you now be more enthusiastic about rewinding for a lower V/Hz but with a 6 pole - assuming there would be a next time ?

Yes. Except for two things:

1. These high-output 132-frame motors from ABB (131-008 and 132-007) appear so outstanding in power-to-weight for an under-$3000 induction motor that I am worried that a rewinder might fail to reproduce it. Particularly since I have heard that one rewinder, on being told about my motor, said that it was impossible to get 22 kW (continuous DOL industrial rating) from a 132-frame. But fortunately Woody has shown that it is possible to get custom-voltage windings direct from ABB, using the "X" voltage code.

2. There is no comparable high-output 6-pole available from ABB in a 132-frame, or at least it does not appear in any catalog.

So what we would probably do in future is order the 132-007 4-pole wound for about 100/58 V (star/delta) at 50 Hz.
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Post by Richo »

Would you really want to go bigger than a "7.5kW" 132-frame anyway for a high speed machine?
Even at 10,000RPM this would be say ~200kW peak.
I'm sure if you need 400kW you could fit in 2 motors Image

SKF 6306ETN9 is an open bearing claiming 14,000RPM as the limiting speed.
Not too keen on using an open bearing.
I'll keep looking...
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Post by weber »

Richo wrote: Would you really want to go bigger than a "7.5kW" 132-frame anyway for a high speed machine?
Even at 10,000RPM this would be say ~200kW peak.
I'm sure if you need 400kW you could fit in 2 motors Image

Good point. Except, what has "need" ever had to do with it? Image
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Post by woody »

weber wrote: Same frame-size means same machine diameter
I'd say "Same frame-size means same _MAXIMUM_ machine diameter".

I have an 11kW 160 frame 2-pole which is a smaller machine diameter than my 132. The flange is bigger - the 160 looks like a top-hat in proportions.
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Post by BigMouse »

woody wrote:
weber wrote: Same frame-size means same machine diameter
I'd say "Same frame-size means same _MAXIMUM_ machine diameter".

I have an 11kW 160 frame 2-pole which is a smaller machine diameter than my 132. The flange is bigger - the 160 looks like a top-hat in proportions.


Really? It must have tall feet on it (unless it's a flange mount only). The frame size is the distance from the feet to the centreline of the shaft in mm.

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Post by woody »

Sorry, it's flange only.
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Post by Johny »

This is kind of related - at least of interest to those reading this topic.
This guy is home rewinding an ACIM for his EV.
http://ivanbennett.com/ev-motorwinding.html

And here is the discussion thread on CR4 where he indicates that the stuff on his blog is incorrect. Of particluar interest are the comments on saturation.
http://cr4.globalspec.com/thread/80804/ ... =cr4digest

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Post by weber »

woody wrote:I'd say "Same frame-size means same _MAXIMUM_ machine diameter".

Good point, since the feet aren't an essential part of the "machine".
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