14000 rpm Machines

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Post by Johny »

woody wrote: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.
Yes, interesting. I wonder how many 160 frame motors I ignored a few years back because they "wouldn't fit".
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Post by Richo »

TCMtech wrote: Once you go past that designed spec HP and or frequency numbers you are reaching into the area of limited extra HP due to the iron core reaching its designed magnetic saturation point which is for the most part is a physical dead end limit to how much HP the motor can produce mechanically regardless of how much more electrical energy is forced into it.


So much for break down torque eh.
TCMtech wrote: your motor likely just has a natural limit on how much mechanical power its going to produce and in this case the engineers that designed its magnetic properties probably did not give it much extra headroom before magnetic saturation occurs.


Sure if I ran my 50Hz motor at 51Hz it runs into magnetic saturation.

I think the problem with that web site is there are different people not understanding what the other is doing.

Tell you the truth after seeing red Suzi driving around I would say they are full of it.
Not to mention the ACIM demo Matt and ACmotor gave with 2 ACIM's coupled together - one big one and one small one running past 50Hz.

I do agree there will be core losses although somewhat less significant than what the other website claims.
But once again don't really care about the efficiency.
So the short answer is NO but the long answer is YES.
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Post by Richo »

Johny wrote:
woody wrote: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.
Yes, interesting. I wonder how many 160 frame motors I ignored a few years back because they "wouldn't fit".


Sorry the frame size defines the centre to the OD of the motor body.
So 160 can't be smaller than a 132.
Just the same as a ruler 300mm long can't be smaller than a 150mm one
The frame size does not include any flanges.

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

Johny wrote:Yes, interesting. I wonder how many 160 frame motors I ignored a few years back because they "wouldn't fit".

But if you're going for maximum power-per-mass then won't you automatically be looking only at motors which have maximum stator diameter for their frame-size?
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Post by Johny »

I agree Richo. That contributor has often been shown to be extremely conservative about ACIMs. Most industrial engineers on that forum have difficulty with overrating anything. I have been critisized for threatening the safety of the general public for daring to reverse engineer my controller. It was more the guy with the EV I found interesting. He appears to have found a way to assess the magnetic issues with respect to air gaps etc.

Not only Acmotors experiments - the Tritium tests also support over-frequency ACIMs as being totally worthwhile.
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Post by Johny »

weber wrote:I suppose the rotor diameter might increase with pole-count, while keeping frame-size and mass constant, but if so, so what?
Sorry I'm going back a bit here. The rotor diameter must matter a LOT! It's a lever effect. If the magnetic pull occurs at the outer edge of the rotor, a larger diameter rotor would provide more torque. Did I miss something? Hmm, why can't you partially hollow out the rotor? To what physical depth does the rotor have to magnetise?
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Post by weber »

Johny wrote:Sorry I'm going back a bit here. The rotor diameter must matter a LOT! It's a lever effect. If the magnetic pull occurs at the outer edge of the rotor, a larger diameter rotor would provide more torque. Did I miss something?

Sorry. I only meant it wouldn't affect the fact that a 6-pole can give more power than a 4-pole for the same mass, frame-size and rpm. Yes, it would affect the validity of my windlass analogy.

We could look at the catalog. They don't give rotor diameter, but they do give rotor moment of inertia which is closely related. If the length and density of the rotor was constant, the moment of inertia would be proportional to the 4th power of the diameter. So the fourth root of the ratio of the MoI's should give an approximation of the ratio of the diameters.

I had a quick look and it does look like rotor diameter increases with pole count (for same-mass same-frame (including length)), but I've run out of time today to knock up a spreadsheet to analyse it properly and see if it's anything like proportional to torque or number of poles.
Hmm, why can't you partially hollow out the rotor? To what physical depth does the rotor have to magnetise?
With a two-pole the flux goes all the way through. But the more poles you have the shallower it can be. I think the problem is that the tensile strength of "hollow" tends to be fairly low.
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Post by weber »

I've compared some 2, 4 and 6 poles in the ABB General Performance Aluminium Motors catalog and found that my estimated rotor diameter (fourth root of rotor moment of inertia) only increases by about 20% between 2 and 4 pole and only about 5% between 4 and 6 pole. But the actual diameter might not change at all. The increase in MoI might be purely the result of having more steel and less aluminium. Or the diameter might change more, and be compensated by less steel and more aluminium.

But there's no way that the 4 pole rotors could be 4/2 = 2 times the diameter of the 2 pole rotors. So the windlass analogy still stands.

Image

[Edit: Clarification: "it" -> "the actual diameter"]
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Post by T2 »

             The Case for the Two Pole Motor

-Weber
4-poles have nearly twice the peak torque of same-frame-size similar-mass 2-poles.

I am asking the question should 2-pole machines be eliminated as candidates for EV powertrains ?

Although I haven't actually performed a side-by-side physical teardown of two machines of similar power and despite my mistaken early impression while working for a major electrical repair company that the faster machines seemed to have the smaller frame sizes, it is possible I have been wrong all this time particularly as my experience was drawn from a particular population of motors that included members with up to sixty years difference in their date of manufacture.

Much as I like to joke that I hate the facts getting in the way of good ideas, but sometimes - after someone points it out - the figures will tell a different story, one that is not always easy to explain.

Consider a 2-pole machine alongside a 4-pole machine. How can these two machines of the same size and weight produce the same power when one of them is rotating at double the speed of the other ? Surely there should be some advantage in the 2-pole machine using the same materials twice as frequently or in actuality, is it that they seem to be used twice as frequently but are in fact not ?

It has been pointed out that the rotors of 2-pole and 4-pole machines have their specified inertia values in almost the exact ratio of 1 : 2 , and given that the cylindrical inertia is described by the expression MR^2 it follows that the ratios of their diameters will be related by the factor of root 2.

May be this is the clue to how the torque reduction is achieved. The 2-pole motor with its smaller rotor will have its peripheral pole face area (and therefore torque) reduced proportionally by root 2, together with a reduction in leverage caused by its diameter - also reduced by the same factor - such that their product will yield exactly half the torque.

The probability is that manufacture begins for both the above machines with the use of identical lamination blanks, simply punching out a smaller diameter center in the case of the 2-pole machine. This would automatically serve to provide the larger amount of back-iron the 2-pole stator needs to complete the magnetic circuit by transporting the flux along the outer edge of the stator between the diametrically opposite poles. Whatever, this sounds like a reasonable explanation of why 2-pole and 4 pole are of similar weight for the same power.

I have to admit I hadn't realized the relevance of rotor inertia until you pointed it out a week ago, thanks.
That said, it probably is not the best of ideas to even rewind a 2-pole stator if other choices are available.

Bottom line is that if you are looking for 3600rpm from 460Vac, from observing the above chart then rather than select, for example, motor type 131-002 rated at 7.5Kw and weighing 43Kgs, it may be more efficacious instead to employ motor type 112-101 rated at 4Kw @ 60Hz and weighing 29Kgs with its terminals wired for 230Vac thus providing an equivalent capability of 8Kw when supplied from a 460Vac source with its rated current at 120Hz.

I may have stated in the past that it is better to purchase for the most torque rather than power. However as the above chart shows overwhelmingly, the most torque productive appear to be the 4-pole machines which renders that statement moot. When the candidates are reduced to only those running at the same speed then it is just as accurate to state that in fact you're purchasing for power.

I am not touching your WINDLASS THEORY because the smaller diameter rotor with 2-poles is a game changer. Plus we both agree that 6-poles don`t appear to deliver on their promise either.
Close inspection of your chart above shows that for machines of equal mass the 6-pole far from having increased torque seems to show a degradation in torque. As you wrote earlier -

Back to motors. Unfortunately, the closer the poles are together the less of that flux density (Bsat) actually makes it across the air-gap to the rotor, which is one reason torque doesn't go up linearly with pole count and why power factor goes down with increasing pole count.


- weber 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.

You`ve convinced me on that. For industrial applications I cannot see why any but 4 poles should be on the market particularly now that inverters are almost universal for motor control.

as BGA wrote earlier
It may be better to look at 6,8,12... pole machines to be either special purpose or throwbacks to that pre-inverter DOL world in the same way that dahlander designs and start-delta switching are now relics, only found in museums and many manufacturing plants.


- weber
The quantity that would be a "zero sum game", i.e. constant irrespective of pole-count, for a constant-mass constant frame-size motor (if it wasn't for leakage-flux and other flux-path geometry considerations mentioned in the above article) is not the torque but the power at a given electrical frequency. This should come as no surprise because it is exactly what happens with a transformer.


I have to agree, not only that but it would help get the message out if custom order designation became the norm on anything other than 4-pole machines.

By BGA 2008 Oct 3rd.

The motor manufacturer's spec sheets usually put the maximum torque at between 2.5 and 3.5 times the rated torque. 4 Pole types are more torquey than 2 Pole and provide their torque at a more useful speed than do 2 pole types. [depends on the application, of course]
My observation is that 6 and 8 pole have a speed range that is not so useful for EVs and offer diminishing efficiency and power returns.
Cheers
BGA
Torque is cheap !.


Interesting seems You said it all for us, BGA, about 4 years ago.
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Post by weber »


T2 wrote:I am asking the question should 2-pole machines be eliminated as candidates for EV powertrains ?
The short answer is, "Yes, they should be eliminated". The long answer is that there could conceivably be some unusual situations where a 2-pole might be preferred, e.g. if you were going for efficiency/cost or if a suitable 4-pole at half the voltage was not available.

I'm glad to see you've come around to this, although we still disagree on the reasons. That's a nice try with the rotor diameter. But, as I mentioned in my two previous posts in this thread, the moment of inertia (about its axis of symmetry) of a solid cylinder of uniform density and fixed length is proportional to the fourth power of its diameter, not the square of its diameter. You mention mr^2 but have forgotten that m is also proportional to r^2.

I = 1/2 * mr^2
= 1/2 * (rho * L * pi * r^2) * r^2
= 1/2 * rho * L * r^4
where
I is the moment of inertia of a uniform solid cylinder in kgm^2
m is its mass in kg
r is its radius in m
L is its length in m
rho is its density in kg/m^3

So the approximate doubling of moment-of-inertia suggests that the diameter has only gone up by a factor of about 1.2.

Then you suggest that the radius-decrease from 4-pole to 2-pole has a double-whammy effect on the torque by reducing both the lever-arm and the force at the pole face. The lever-arm I grant, but why should the force decrease with decreasing pole-face area. The force is proportional to flux density not total flux, and to rotor bar current and length, (F=BIL) none of which have any necessary relationship to the rotor radius or pole-face area.

So we are left with only a factor of 1.2 increase in torque being explained by the increase in rotor diameter. I suggest this may be just enough to compensate for the extra leakage flux in the 4-pole relative to the 2-pole.

You've probably seen it, but just in case, Coulomb asked some excellent relevant questions in another thread, which I've answered starting with about the 7th paragraph in this post.
viewtopic.php?title=getting-the-right-w ... 149#p39325
Consider a 2-pole machine alongside a 4-pole machine. How can these two machines of the same size and weight produce the same power when one of them is rotating at double the speed of the other ? Surely there should be some advantage in the 2-pole machine using the same materials twice as frequently or in actuality, is it that they seem to be used twice as frequently but are in fact not ?
I assume you to mean these to be driven at the same electrical frequency and so it is the 2-pole that is rotating at double the speed of the 4-pole. In that case the materials are being "used" equally frequently, and I don't understand why the 2-pole would even seem to be using them twice as frequently.

The stator materials cycle their voltage, current and flux in sync with the driving electrical frequency. All that changes with speed are the phase angles between them. The rotor materials change their voltage current and flux in sync with the slip frequency, which has no relationship to the rotational speed.
That said, it probably is not the best of ideas to even rewind a 2-pole stator if other choices are available.

Bottom line is that if you are looking for 3600rpm from 460Vac, from observing the above chart then rather than select, for example, motor type 131-002 rated at 7.5Kw and weighing 43Kgs, it may be more efficacious instead to employ motor type 112-101 rated at 4Kw @ 60Hz and weighing 29Kgs with its terminals wired for 230Vac thus providing an equivalent capability of 8Kw when supplied from a 460Vac source with its rated current at 120Hz.
Agreed. Unless you are concerned about small differences in efficiency, or continuous ratings.
I am not touching your WINDLASS THEORY because the smaller diameter rotor with 2-poles is a game changer.
I hope you see now, that rotor diameter is not the game changer you thought it was.
Plus we both agree that 6-poles don`t appear to deliver on their promise either.
Close inspection of your chart above shows that for machines of equal mass the 6-pole far from having increased torque seems to show a degradation in torque.
Apparently you haven't inspected the chart closely enough. It shows a decrease in specific torque from 4-pole to 6-pole in sizes smaller than 132-frame but an increase in specific torque from 4-pole to 6-pole in sizes larger than 132-frame. The bigger they get, the better 6-poles look. If you were doing an EV conversion on a prime-mover for a semi-trailer there would be no question about it, a 6-pole would be the optimum choice.

What I'd like to see, is for some motor-design genius to figure out how to get that changeover point between 4-pole and 6-pole to come down to well below 132-frame size (at low cost). Then we could run them at 300 Hz and they would still only be doing 6000 rpm.

It's tempting to say that since induction motors have been around for over 100 years now, it would have been done long ago if it was possible at all. But inverters/VFDs have only become commonplace in the last decade or two and the desire for high power-to-weight induction motors (as required for EVs) is more recent still. Could be a PhD there for someone.
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Post by T2 »


I assume you to mean these to be driven at the same electrical frequency and so it is the 2-pole that is rotating at double the speed of the 4-pole. In that case the materials are being "used" equally frequently, and I don't understand why the 2-pole would even seem to be using them twice as frequently.

-weber. Here's my viewpoint
Imagine a line drawn across the rotor and parallel to the axis.
When the rotor is turned thru' 360 deg the line will have scanned the entire stator area.
The total magnetizing ampere turns should be the same for both 2-pole and 4-pole machines meaning that the rotor should have swept through an area energised with the same total amount of flux.

The torque should be the same for both rotors which we both agree are oblivious to the speed of rotation. Therefore the higher speed of the 2-pole rotor would have caused it to have accomplished twice the work - so you would think.

If this were a DC motor then a weakened shunt field would be analogous to the 2-pole machine, however when field weakening you are concious of 'ruining' the machine in that you accept the loss of torque capability. In the case above no deliberate 'ruining' is taking place so the specific power should not have been compromised.

Since I am not intending to pursue 2-poles further, I don't want to get too deep in the theory here, so I'll accept what you propose for now.
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Post by T2 »

Apparently you haven't inspected the chart closely enough. It shows a decrease in specific torque from 4-pole to 6-pole in sizes smaller than 132-frame but an increase in specific torque from 4-pole to 6-pole in sizes larger than 132-frame. The bigger they get, the better 6-poles look. If you were doing an EV conversion on a prime-mover for a semi-trailer there would be no question about it, a 6-pole would be the optimum choice.
- weber, I had noticed that the numbers began to trend towards your WINDLASS THEORY but didn't feel the need to comment. The thing to remember is that I am the guy who is going for motors of 49Kgs or less but at double the rpms you are considering. Your interest on the other hand is towards the larger machines with greater than 4-poles that will provide more torque at the lower speeds. I received the message.

My view, OTOH, remains unchanged that motors running at 14krpms are within the range of possibility with rewound stators.
The equally important part of this topic is obtaining the single ratio around 10:1 for the reducer which allows for optimal use of these motors. I have two people looking at two approaches with this. One who has experience with rebuilding gearbox assemblies is examining prospects for obtaining parts that allow the fitting of a custom specific ratio. The other has a machining capability for face mounting a planetary.   
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T2 wrote:The thing to remember is that I am the guy who is going for motors of 49Kgs or less but at double the rpms you are considering. Your interest on the other hand is towards the larger machines with greater than 4-poles that will provide more torque at the lower speeds. I received the message.
Then you have misunderstood me. I too want to maximise the power from motors of around that mass. BTW, the unit symbol for kilograms is "kg". "Kgs" would be kelvin-gram-seconds. Yes, I'm a pedant. Image

You must have missed where I wrote "What I'd like to see, is for some motor-design genius to figure out how to get that changeover point between 4-pole and 6-pole [being the optimum choice] to come down to well below 132-frame size (at low cost)."

This approach is complementary to that of increasing the mechanical capabilities to allow higher rpm. We should be doing both. Previously you didn't recognise the existence of the increased-pole-count approach. I'm glad we're on the same page with that now.
My view, OTOH, remains unchanged that motors running at 14krpms are within the range of possibility with rewound stators.

That is obviously within the range of possibility, since the Tesla Roadster motor already does 14 krpm. See mention of "ceramic bearings" here http://www.teslamotors.com/roadster/technology/motor.

Coulomb, please note that, in this newer graph, the Tesla Roadster motor torque is shown as falling off as 1/f^2 just like industrial induction motors *.

Image

[Edit: * Actually, when I look more closely I see it has a 1/f fall-off between 5 and 7 krpm, then 1/f^2 from 7 krpm onward.]
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Post by Richo »

The torque plot of the "compact commuter" looks really suss.
It must have been an old car with serious issues.
So the short answer is NO but the long answer is YES.
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Post by coulomb »

Richo wrote: The torque plot of the "compact commuter" looks really suss.

Yeah, and how the torque curve starts at 2000 RPM and stops around 8000 RPM. I've always thought the Tesla torque plots were very "marketing oriented". It seems odd for a company that's otherwise so technically oriented. And it's not like they have to lie or bend the facts to appear better than the competition.

All gloss and little science, I suspect. A shame, really.
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Post by T2 »

mizlplix has started a thread on the practice of rewinding entitled "AC electric motor rewinding for EV use". Originally I composed this to go on that thread however I want to provide some jottings here to avoid possibly disrupting that thread.
For the same reason I don't post on www.ivanbennett.com/forum, but I still go there. miz only wants craftsmen at his level to participate and certainly not armchair jockeys. Which is great for me, I only have to read there and it keeps me out of trouble !
Accordingly I've rewritten this post:

From what I can see, miz's design is predicated upon a torque monster of a motor matched with an ampzilla of a controller. He has focussed on that one idea and I commend him for it. I am fine with oversized current controllers though they may need horsepower limits if ever battery longevity becomes a concern.
I will comment further two things on that project which are unique, I think.

First it uses a super large motor mostly for visual effect. Anything that encourages an interest in electric traction has got to be a good thing and I specifically mean attracting those people who wouldn't care a rat's... otherwise. Nevertheless this 20Hp frame is one honking machine !!

Second his rear differential has a beneficiary 6.41 ratio on which others have also commented. An unusually high ratio no doubt needed by those lower torque engines of 1930.

These two facts makes his direct drive system viable.

Today, however, you'd be hard pressed to find any modern diff. above a 4.0 ratio nor even a vehicle as light as 1900lbs. In fairness he has written on his site that this vehicle may never see the expressway but will fulfill its purpose of being a general runabout.

That said, most here are aware that turning power through 90 deg. loses 30% of the torque. And a 6.41 ratio is also sub optimal although in this case the use of the OEM rear diff is to preserve some authenticity to the vehicle's original design. I get that.

There is one helpful comment I could make and that is to be wary regarding delta configurations.
Whenever there are slight differences in back emfs of each phase - which should normally sum to zero - then there is the possibility of these emfs to start circulating currents within the mesh. This can cause unexpected motor heating.

There could also be possible problems with the generation of third, fifth and seventh harmonic voltages dependent on the span and distribution of the coils although there are techniques to mitigate those effects by avoiding the usage of certain wiring patterns. It is possible that harmonic distortion could be unsettling to the Curtis algorithms.

For more predictable results the recommended winding is the Y config.
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Post by T2 »

What I am trying to focus on in this thread is with the motor itself.

Clearly the preponderance of direct drives shows that the operation of the electric motor is not understood as well as it could be.

Generally the electric motor is not appreciated from the angle that it is a magnetic device.

In the same way that an arborist can tell you a lot about the care and pruning of trees without much regard for the tree being an organism powered by photosynthesis.

The objective of applying a magnetic machine to an automotive application should recognise that the rated magnetic torque is limited to the dimensions of that machine. For that reason the major advantage of high rpm capability should be exploited to the max.

The imagined fears of bearing breakup and rotor fragmentation at high speed may not be as problematic as some would propose. The only way to do that is to get some machines made up with specifically low values of V/Hz and find out. Since ACMOTOR performed some groundbreaking rewire work several years ago not much has changed here.

Using Siwajasta's motor rewind as an example.

1) Originally the machine had a certain copper loss at 9.2Amps while delivering rated torque @ 1500rpm.
2) After the rewind the motor required 46amps to provide the exact same rated torque @1500rpm.
3) The copper loss incurred by the stator winding is the same for both cases.
4a) Therefore "copper loss is constant for rated torque and is independent of the V/Hz ratio".

Their V/Hz of 660/50 (13.2) and 460/60 (7.6) make easily available off-the-shelf motors impractical for use with the lower voltage battery packs especially when frequencies approaching 400Hz are contemplated.

In the case above a rewind of 5 : 1 was accomplished. This resulted in as much as 132Vac required per 50Hz which allows only a headroom of double that frequency on 360Vdc. The useful rated motor power from this frame size was only raised by a factor two.

In order to get more revs and therefore even more power the V/Hz must be lowered by a factor of 10 times at least from the original values.
In support of this claim the lower semiconductor voltages of more than 25 years ago recommended Eaton corporation to specify 68Vac @240Hz for their winding on a 4-pole machine.

The equation Motor Torque = V/Hz times Motor current, infers that as the motor's V/Hz goes down we must mitigate this by allowing the current to rise up in order to maintain the original torque.

Statement 4a) should make clear that although current may have to be increased by ten times the actual heat dissipated in the copper of the new stator winding will still remain exactly the same as before.
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Post by Richo »

T2 wrote:In order to get more revs and therefore even more power the V/Hz must be lowered by a factor of 10 times at least from the original values.


So a 4-pole typically 1,500RPM is now 15,000RPM.
Don't forget you still need RPM overhead past the peak.

A motor set for a 7,000RPM peak still can run up to 12,000 RPM to match a vehicle for optimum performance.

And still I say off the shelf bearings will be the limit.
and these are likely to be open bearings.

Find me some bearings then I'll worry about copper loss or magnetic saturation.
So the short answer is NO but the long answer is YES.
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Post by TooQik »

These babies look like they'd do the job...

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Post by T2 »

In order to get more revs and therefore even more power the V/Hz must be lowered by a factor of 10 times at least from the original values.

So a 4-pole typically 1,500RPM is now 15,000RPM.
Richo - not exactly.

First the V/Hz has to be reduced just so as to place the inverter bus voltage within a reasonable value, which could be anywhere from 100Vdc to 400Vdc. As a matter of safety I don't advocate anyone should be dealing with 650Vdc power rails (for 460Vac) supplied directly by Li-ion cells. Even Tesla doesn't do that.

Then the V/Hz ratio is further reduced to allow "overclocking".
It is this second part that gives us the increase in motor power.

As an example (now that you've got me writing about it), Siwajasta made a 5:1 winding adjustment but only gave room for 100Hz working - a 2 to 1 power advantage in actual returns - when working from 360Vdc.

If you consider the "Impact" car from c.1990. Its V/Hz was 0.74 which caused it to go constant power from 6600rpm. It finished the 0 to 60mph in 8.0 secs with a motor speed of 9500 rpm. IMPACT used a 400V Pb-acid supply. GM provided the data except for the V/Hz which was calculated from their figures. Source material is from the Feb 1990 AEVA newsletter and a VHS video obtained from GM-Canada Marketing.

A rewind on each of the Impact motors reducing their V/Hz to 0.5 would have raised their power from 57Hp to 85Hp at 9900rpm. In which case it would have been possible to maintain their original torque through to 60mph instead of causing it to decline from about 42 mph onwards.

It should be recalled that 42mph is the Half Kinetic Energy point here, consequently that final 18mph is the toughest part of the ramp so to leave 56Hp on the table because of a stator winding deficiency seems rather sad. In retrospect the designers were probably looking at the motors from the electrical rather than the magnetic standpoint which is the point I am now emphasizing.

      
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Post by coulomb »

T2 wrote: A rewind on each of the Impact motors reducing their V/Hz to 0.5 would have raised their power from 57Hp to 85Hp at 9900rpm. In which case it would have been possible to maintain their original torque through to 60mph instead of causing it to decline from about 42 mph onwards.

Maybe the lead acid pack couldn't take that sort of power, or would have led to a lowed life. Also, lower V/Hz means more A per unit torque, so the controller would have had to have been capable of more current, increasing the cost, especially 20(?) years ago when the Impact was being designed. I vaguely recall the EV1 controller using bipolar transistors, or something like that, for example.
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Post by T2 »

Don't forget you still need RPM overhead past the peak.

I envisage peak being a standard 60mph since this is a recognised performance benchmark.
Constant Power from there to 110km/Hr or 70mph should be sufficient for manoeuvering into the center lane for cruising and keeping clear of heavy vehicles. Legal limits for trucks here are now limited to 104Km/Hr ( 65mph ) by Provincial Law.

Another thought which probably should be in the chit chat forum but for commercial EV manufacture..

This next one may not be a popular suggestion but I believe that for EVs, electronic speed limiting should be in place at the previously mentioned 110km/Hr or 70mph for both range and battery longevity reasons. Aerodynamic losses being what they are sometimes EV drivers need to be saved from themselves !

What about personal responsibility you may ask ? Well, pictures of the DVP highway in Toronto this week, after a cloudburst dropped 126mm of rain, show a dozen or so drivers didn't get off the road in time (out of literally hundreds who did) as it gradually turned into an Aqueduct.

A 70mph top limit might also garner a reduction in insurance rates just for that reason and now I come to think about it risk of theft. Sure, it may easily do 0 to 60 in under eight seconds but not if it comes at the cost of a 70mph top speed.
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Post by T2 »

Maybe the lead acid pack couldn't take that sort of power, or would have led to a lower life
I agree, back in 88/89 lead acid was the only choice but at least they were more enduring than those of today.

Going larger than TO-247 style you could get 500V mosfets with Ids of 44A or if you wanted 200A then Vds was only 100V. Sure IGBTs were available but not in the more useful high current range. Those were still the province of thyristors in those hockey puck packages.

Too_Qik - I searched the link and found that greased bearings with steel balls, not ceramic, were also good to 18000rpm. It depends on the inner bearing diameter for 35mm shafts they are OK. It appears not unsurprisingly that the allowable rpm is inversely proportional to the bearing diameter.
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Post by Richo »

T2 wrote: As a matter of safety I don't advocate anyone should be dealing with 650Vdc power rails (for 460Vac) supplied directly by Li-ion cells. Even Tesla doesn't do that.

And the only reason I'm doing it is because 400Vac is an industrial standard and the standard IGBT's as designed for this.
The extra DC voltage overhead is to account for the loss under full load (battery internal impedance)
So the output of the inverter will be 400Vac under full load.

But TBH why bother for a full rewind to a specific voltage?
Why not just rip out all the windings and put in busbars.
Then whatever the final V/Hz works out to make the inverter accordingly.
This would be back in the realm of sub 100V for a "good" system and could use mosfets.

Achieving high RPM would be much easier.

[EDIT]

Oh and I also don't recommend using high voltage for a self conversion unless you work in the electrical industry and know exactly what you're doing.
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Last edited by Richo on Thu, 11 Jul 2013, 10:51, edited 1 time in total.
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Post by Richo »

T2 wrote: Too_Qik - I searched the link and found that greased bearings with steel balls, not ceramic, were also good to 18000rpm.


I had a look and they may show promise.
I will pull out some standard size bearings for comparison shortly.
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