Getting the right windings...

AC, DC, amps, volts and kilowatt. It's all discussed in here
User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

Getting the right windings...

Post by weber » Wed, 01 Aug 2012, 03:06

Next time I take a shower I plan to work on the axial version of the cat-toast motor.

[img]http://images2.wikia.nocookie.net/__cb20060713130824/uncyclopedia/images/8/8b/Cat_toast_swirl.gif[/img]
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

Getting the right windings...

Post by weber » Wed, 01 Aug 2012, 05:10

Hi Chris, I know it's too late now, but just wondering if you saw these YASA motors before settling on the EVO? And if so, what did you think of them?

http://www.yasamotors.com/

They (and I presume EVO) don't use laminations in their stator cores, they use Soft Magnetic Composite (SMC).

http://www.hoganas.com/en/Segments/Soma ... materials/

[Edit: I see you already answered that question here, thanks:
viewtopic.php?p=38310&t=1391#p38310 ]
Last edited by weber on Tue, 31 Jul 2012, 19:14, edited 1 time in total.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Faz
Groupie
Posts: 96
Joined: Tue, 05 Jul 2011, 16:43

Getting the right windings...

Post by Faz » Wed, 01 Aug 2012, 23:43

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


I wouldn't go that far.
Nor would I (or the CSIRO).
CSIRO developed an axial flux motor for solar cars that is proven to be 97.3% efficient.
I would think that would give most IM's a run for their money.

edit: They are actually being offered at up to 98.4% efficiency.
Last edited by Faz on Wed, 01 Aug 2012, 13:46, edited 1 time in total.

User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

Getting the right windings...

Post by weber » Thu, 02 Aug 2012, 04:38

Faz wrote:CSIRO developed an axial flux motor for solar cars that is proven to be 97.3% efficient.
I would think that would give most IM's a run for their money.

Hi Faz. Stiive misquoted me, so now everyone who doesn't know me thinks I'm a complete moron.

What I actually wrote was:
"IMHO, induction motors are more efficient than PM ... when you get up to high-performance-car-type power requirements."

That CSIRO motor, is only about 2 kW, wonderful though it is.

And I'm talking average efficiency, not peak efficiency.

You can prove me wrong there too, but only by going to a PM motor that costs more than 3 times as much as the induction motor.

Axial is good. But IM can be axial too.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
jonescg
Senior Member
Posts: 2939
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Getting the right windings...

Post by jonescg » Thu, 02 Aug 2012, 05:09

Yeah, I think a well designed Axial IM would be a winner. As you say, keep the laminations to a minimum in the rotor to avoid any centrifugal distortion. Given that axial flux DC motors use 8 magnets like trapezoids on either side of the rotor (ala Agni, Perm) and axial flux PMAC motors use trapezoidal magnets in the rotors with trapezoidal coils in the stator (ala MARS, Evo) could you not use trapezoidal shaped coils in the rotor? They would need to be overlapping to some extent, and set in some kind of super-strong epoxy, but the lack of material to concentrate the magnetic field would make it a bit weak. I've no doubt missed something important though Image
AEVA National Secretary, WA branch chair.

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Getting the right windings...

Post by T2 » Thu, 02 Aug 2012, 14:41

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

So which winding is that ?
EVO site was down on the weekend so was AEVA and the following post got lost.

WDG #3 11.79 rpm/volt   i.e. Lo V/Hz What jonescg wants
WDG #4   8.842 rpm/volt   i.e. Hi V/Hz What EVO recommends

Anyone who has followed my posts knows that with similar frame sizes the most power capable machine is always the one with the lowest V/Hz.

On any reasonable bus voltage WDG #3 is the less likely to find itself in field weakening. So power will continue to rise with WDG #3 while WDG #4 will fade and die.

Stiive described WDG #4 with a turnover point of "3000rpm" his own words. As a competent drive guy he would be seeking the most torque for the amp and that's why he went for WDG #4, as did EVO who probably also design drives.

For vehicle performance that is not the best choice.

Use of WDG #3 instead will give the voltage headroom for an increase of 5000/3000 or an expectation of a commensurate 67% more power going from 3000rpm to 5000rpm at constant current but honestly, I don't know what battery system will support that order of power on a bike that is to weigh no more than 200kg. (23rd July)   

Plus a load factor of 90% on 90Kw is equivalent to a 80Kw drain - these must be short races. (also 23rd July) 8 laps of 30secs ?
T2

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

Getting the right windings...

Post by Stiive » Thu, 02 Aug 2012, 15:11

weber wrote:
Hi Faz. Stiive misquoted me, so now everyone who doesn't know me thinks I'm a complete moron.

What I actually wrote was:
"IMHO, induction motors are more efficient than PM ... when you get up to high-performance-car-type power requirements."


Oh, sorry that wasn't my intention...
Still sounds ambiguous to me though. I don't think the average motor efficiency of an IM is higher than PM at any size/performance. Perhaps you are referring to cost efficiency?
Rgds,
Stiive

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

Getting the right windings...

Post by Stiive » Thu, 02 Aug 2012, 15:14

Faz wrote:
CSIRO developed an axial flux motor for solar cars that is proven to be 97.3% efficient.
I would think that would give most IM's a run for their money.

edit: They are actually being offered at up to 98.4% efficiency.
Pretty sure that it is a switch reluctance motor. They sold the rights of manufacture to Marand Precision. Most solar cars now use this
Rgds,
Stiive

User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

Getting the right windings...

Post by weber » Thu, 02 Aug 2012, 15:23

jonescg wrote: Yeah, I think a well designed Axial IM would be a winner. As you say, keep the laminations to a minimum in the rotor to avoid any centrifugal distortion. Given that axial flux DC motors use 8 magnets like trapezoids on either side of the rotor (ala Agni, Perm) and axial flux PMAC motors use trapezoidal magnets in the rotors with trapezoidal coils in the stator (ala MARS, Evo) could you not use trapezoidal shaped coils in the rotor? They would need to be overlapping to some extent, and set in some kind of super-strong epoxy, but the lack of material to concentrate the magnetic field would make it a bit weak. I've no doubt missed something important though Image

I don't think you've missed anything important, except that they don't need to be coils at all. You would use copper bars arranged like spokes and brazed between a copper ring near the hub and a copper ring at the rim. Or the whole copper wagon-wheel might be cast in one piece or machined out of a disk. You might have three or four bars in the space that was previously occupied by one magnet.

To smooth out the torque and keep it quiet, the spokes would not be exactly radial but would be skewed slightly so the inner end of one was radially aligned with the outer end of the next, although this would reduce its stability under centrifugal force. There would be a prime number of copper bars, say 47 (or at least a number not divisible by the number of pole-pairs or the number of phases).

The inner and outer copper rings would be just outside the field from the stator poles.

Then maybe that SMC stuff, which looks to me like a fancy name for an improved version of powdered iron, can be formed in place between the copper bars, using a hot press. Maybe notches in the copper bars to retain it. Maybe the copper wheel is the structural component here and its inner ring is bolted to a steel hub. Sounds weak. Maybe some copper alloy that's strong but still has better conductivity than aluminium.

The above would be a IM rotor to suit the EVO-type axial with it stator-rotor-stator (SRS) sandwich. The YASA-type with its rotor-stator-rotor (RSR) sandwich needs backing iron on its rotors. So there a vane-laminated iron rotor might work with the copper bars embedded in slots.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

Getting the right windings...

Post by Stiive » Thu, 02 Aug 2012, 15:24

T2 wrote: Anyone who has followed my posts knows that with similar frame sizes the most power capable machine is always the one with the lowest V/Hz.

I'd love to hear/see your reasoning behind this sweeping statement Image. Perhaps this is true for a certain line/brand of motor, or possibly fixed-line driven IMs?, but I wouldn't say this is a given or even a rule-of-thumb for EV specific IMs.

T2 wrote: Stiive described WDG #4 with a turnover point of "3000rpm" his own words. As a competent drive guy he would be seeking the most torque for the amp and that's why he went for WDG #4, as did EVO who probably also design drives.


I wasn't suggesting he use any motor, i didn't even check the specs of the motor and just pulled 300rpm out of my ass. Just wanted to make sure he knew the difference between nominal speed and maximum speed.
Rgds,
Stiive

User avatar
jonescg
Senior Member
Posts: 2939
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Getting the right windings...

Post by jonescg » Thu, 02 Aug 2012, 18:13

T2 wrote: So ah, yeah. I'll be going with the 140-4 wound motor, driven by a PM150DZ inverter

So which winding is that ?
EVO site was down on the weekend so was AEVA and the following post got lost.

WDG #3 11.79 rpm/volt   i.e. Lo V/Hz What jonescg wants
WDG #4   8.842 rpm/volt   i.e. Hi V/Hz What EVO recommends

Anyone who has followed my posts knows that with similar frame sizes the most power capable machine is always the one with the lowest V/Hz.

On any reasonable bus voltage WDG #3 is the less likely to find itself in field weakening. So power will continue to rise with WDG #3 while WDG #4 will fade and die.

Stiive described WDG #4 with a turnover point of "3000rpm" his own words. As a competent drive guy he would be seeking the most torque for the amp and that's why he went for WDG #4, as did EVO who probably also design drives.

For vehicle performance that is not the best choice.

Use of WDG #3 instead will give the voltage headroom for an increase of 5000/3000 or an expectation of a commensurate 67% more power going from 3000rpm to 5000rpm at constant current but honestly, I don't know what battery system will support that order of power on a bike that is to weigh no more than 200kg. (23rd July)   

Plus a load factor of 90% on 90Kw is equivalent to a 80Kw drain - these must be short races. (also 23rd July) 8 laps of 30secs ?


This is what I got from Evo a couple of weeks back:
Evo Electric wrote:The voltage constant for the AF-140-4 is 1.44Vs/rad, measured in Vpk,line to line. Hence, your back emf is about 150Vpk/1000rpm. Thus, to spin it up to 1000rpm you need a bit more than this in terms of dc voltage from the battery, let’s say 160Vdc. From this point of view you are right that you would need about 800Vdc to spin the machine up to 5000rpm. However, what you would typically do is employ field weakening, which effectively uses current to supress your bemf. Hence, you will find that it is perfectly possible to spin the machine to 5000rpm on a 600Vdc or even lower dc bus. If you dc voltage is about 640Vdc, as I understand from your email, you will be perfectly fine running the AF-140-4 machine.

You are also right that you could potentially use a AF-140-3 machine instead. This would mitigate the need for field weakening but would have two big drawbacks: Firstly, the inductance of the machine is much lower, which translates into a choppier ac waveform and, consequently, magnets which will overheat when operated at higher speeds for a longer period of time. This is difficult to quantify but the risk is very real. Once demagnetised, you will see an irreversible loss in performance, i.e. torque and power will drop significantly. Second, since you have a lower voltage constant on the AF-140-3, you also have a lower torque constant, which means that you need more current to produce torque. For example, the AF-140-4 needs about 350Arms to produce 600Nm whereas the AF-140-3 needs 465Arms to achieve 600Nm.

In summary, I would suggest that you stick with the AF-140-4. The PM150DZ will be able to spin this up to 5000rpm no problem. The only caveat is that you won’t achieve the full 600Nm peak torque the machine is capable of. If you need the 600Nm, you could employ a AF-140-5 machine, which will still spin up to 5000rpm provided the voltage is at least 600Vdc! It will have a lower power output than the AF-140-4, though, since the base speed where field weakening starts is lower compared with the AF-140-4.
AEVA National Secretary, WA branch chair.

User avatar
Richo
Senior Member
Posts: 3685
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

Getting the right windings...

Post by Richo » Thu, 02 Aug 2012, 20:26

weber wrote: Next time I take a shower I plan to work on the axial version of the cat-toast motor.


DONT DO IT Image

The cat will get angry and the toast will get soggy Image

So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Getting the right windings...

Post by T2 » Fri, 03 Aug 2012, 01:55

-Stiive, do you see the third paragraph from EVO's reply to jonescg ?

you could employ a AF-140-5 machine, which will still spin up to 5000rpm provided the voltage is at least 600Vdc! It will have a lower power output than the AF-140-4, though, since the base speed where field weakening starts is lower compared with the AF-140-4.

So by EVO's admission the AF-140-5 has a lower output than the AF-140-4 because its (the AF-140-5) higher V/Hz forces a base speed where field weakening starts to be lower than that of the AF-140-4

Similarly we can say that AF-140-4 will have lower output than the AF140-3 because its (the AF-140-4) higher V/Hz forces a base speed where field weakening starts - to be lower than that of the AF-140-3.

But EVO don't want you messing with the AF-140-3.

Firstly, the inductance of the machine is much lower, which translates into a choppier ac waveform and, consequently, magnets which will overheat when operated at higher speeds for a longer period of time.

Does that make any sense ? Sure the inductance is lower, so raise the chop frequency. I see on BRUSA website they are using 24Khz !

This is difficult to quantify but the risk is very real

difficult to quantify Hmm... speculation on my part but I think they are not too happy about having their machine open to abuse. When saturation kicks in as you speed up the available power will be curtailed above 3000rpm with the other two motors and the heat sensitive magnets will be atomatically protected. On the other hand the -3 motor with the lower V/HZ means you will make 600N-m well above 3000rpm and considerable more power I might add. Look, these rotor magnets will be sweeping through the stator generating some iron loss in the stator irrespective of how much stator current there is so why would you choose the other two motors whose higher back emf will put you into field weakening purgatory ?    

Magnet heating is a problem I read somewhere that 55 deg C is the curie point for the magnets to degrade, they recover when cooled down but it is a red flag to me. As long as jonescg has a good cooling system on the motor - how much does that weigh again ? - this may not be a problem.

Anyway I thought the advantage of a PM machine was the rotor didn't generate any heat. And EVO suggests they may be overheated by some difficult to quantify flux ripple in the stator ? I can appreciate that the -4 and -5 versions will drive the machine into saturation where the chop frequency at 100% duty cycle coalesce into square waves of the much lower fundamental synchronous frequency which obviously will ease the switching stress on the controller but why sacrifice motor performance for that ? Design a better controller with an increased chop rate, the ripple amplitudes will reduce and the heating problem will go away. Or, why not just add reactors in series with each phase to bring the inductance up to some minimum value that the damn controller can handle ?
T2

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

Getting the right windings...

Post by Stiive » Fri, 03 Aug 2012, 02:29

T2 wrote: -Stiive, do you see the third paragraph from EVO's reply to jonescg ?

you could employ a AF-140-5 machine, which will still spin up to 5000rpm provided the voltage is at least 600Vdc! It will have a lower power output than the AF-140-4, though, since the base speed where field weakening starts is lower compared with the AF-140-4.

So by EVO's admission the AF-140-5 has a lower output than the AF-140-4 because its (the AF-140-5) higher V/Hz forces a base speed where field weakening starts to be lower than that of the AF-140-4

Similarly we can say that AF-140-4 will have lower output than the AF140-3 because its (the AF-140-4) higher V/Hz forces a base speed where field weakening starts - to be lower than that of the AF-140-3.


Forgot we were talking about PM axial flux motors Image

I've never really studied the effects of BEMF on PM, but it seems the AF-140-5 would still be more powerful if there is more voltage available (as long as its not maxing out on insulation rating of the windings).
Sure your statement holds true if for a given maximum voltage one motor hits field weakening and the other doesn't, but I still feel the statement was sweeping Image
I say this because IMO you should always size the motor according to your battery specs (i.e. available DC voltage and current), or vice versa. If you choose a motor with a higher V/hz and don't scale your voltage accordingly, of course your going to hit field weakening early and reduced power. By the same token, if you choose a lower V/hz motor and have too much voltage head room in your battery pack, you cant utilize your batteries entire power potential.

Anyway, sorry if I've taken your statement out of context (seem to do that a bit because i don't read entire threads), but I feel selecting the lowest v/hz motor will not always yield the "highest power potential".

Which motor is best for jonescg? No idea, i haven't even looked at any of the motors specs, or even heard of EVO before this thread Image


T2 wrote:Firstly, the inductance of the machine is much lower, which translates into a choppier ac waveform and, consequently, magnets which will overheat when operated at higher speeds for a longer period of time.

Does that make any sense ? Sure the inductance is lower, so raise the chop frequency. I see on BRUSA website they are using 24Khz !



No idea... Don't have alot of experience with PM. Perhaps increasing the sample time of the controller (if possible??) would also lead to a smoother AC. Or make things worse and blow up... no idea Image Makes you wonder why they produce/sell the motor haha
Rgds,
Stiive

User avatar
jonescg
Senior Member
Posts: 2939
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Getting the right windings...

Post by jonescg » Fri, 03 Aug 2012, 04:30

So, T2, what you are saying is, Evo, who build and service high-powered axial flux permanent magnet AC motors, don't know what they are talking about.

Now, almost every business I know routinely exaggerates the capabilities of their goods, and I don't doubt Evo are doing this too. But if I'm not mistaken, you are implying that Evo are trying to sell me an inappropriate motor for some reason which still remains unclear.

When I asked them about the more appropriate motor, they explained to me that the motor with the higher voltage constant was basically better placed to handle the abuse I plan on giving it. If peak power (torque x rpm) occurs at 3700 rpm, and it levels off as you approach 5000 rpm due to field weakening (exchanging torque for speed) then I will probably have the ideal setup - high torque out of turns where rmp is limited, and top speed is only going to be achieved once a lap.

Yet, you are still unconvinced. Fair enough, you have your reasons. Can I suggest that you please write to Malte at Evo - malte.jaensch@evo-electric.com and share your concerns with him? You need not mention my situation, but rather than hearing it from me, you can hear it from the engineers themselves. You never know; you might even land yourself a job with them!

I'm sorry, but I just can't understand what it is that's bugging you!?
AEVA National Secretary, WA branch chair.

Stiive
Groupie
Posts: 295
Joined: Wed, 31 Dec 2008, 08:26
Location: Melbourne

Getting the right windings...

Post by Stiive » Fri, 03 Aug 2012, 05:04

jonescg wrote: So, T2, what you are saying is, Evo, who build and service high-powered axial flux permanent magnet AC motors, don't know what they are talking about.


LOL, common dude that's a bit harsh, he's only trying to put across his experience and thoughts. Worst case is we have a good discussion and all learn a little. Image

jonescg wrote:When I asked them about the more appropriate motor, they explained to me that the motor with the higher voltage constant was basically better placed to handle the abuse I plan on giving it. If peak power (torque x rpm) occurs at 3700 rpm, and it levels off as you approach 5000 rpm due to field weakening (exchanging torque for speed) then I will probably have the ideal setup - high torque out of turns where rmp is limited, and top speed is only going to be achieved once a lap.


Sounds alright to me... engineering is always choosing the best compromise.
However you cannot always achieve constant power after nominal speed, it depends on the motor characteristics and the control, though it is generally stated that torque falls off roughly by 1/f^2.
Rgds,
Stiive

User avatar
jonescg
Senior Member
Posts: 2939
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Getting the right windings...

Post by jonescg » Fri, 03 Aug 2012, 05:17

Yeah, harsh maybe, but I still can't work out what his problem is. I don't mean to be difficult or argumentative, trust me; I am genuinely interested in making sure I get a motor which performs, and if T2 knows something which I should know, I am keen to know also.

I thought Evo's explanation of how employing field weakening allows full utilisation of the motor was pretty good. I know that low inductance motors can give controllers grief, especially ones with relatively low switching frequencies. However the PM150DZ should have the capability.

And don't worry, 8 l per minute cooling with a nice big aluminium radiator should keep things under 55'C.

Last edited by jonescg on Thu, 02 Aug 2012, 19:57, edited 1 time in total.
AEVA National Secretary, WA branch chair.

User avatar
weber
Site Admin
Posts: 2601
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

Getting the right windings...

Post by weber » Fri, 03 Aug 2012, 17:05

T2, how about you leave off badgering poor jonescg and debate me on multi-poles instead. Image

jonescg, I agree with what T2 is saying, about getting 25% more peak power and maybe 17% more continuous power from the lower voltage (-3) winding provided you are not limited by battery or inverter. This is simply because you would get full torque out to the 5000 rpm mechanical limit. To make use of it you would need an inverter capable of 333 A rms at 425 V dc. But overheating your magnets is definitely worth worrying about too. It's a tough call. Did the EVO guys know what inverter you were planning to use, so they knew what its PWM switching frequency was, when they made that call?
Stiive wrote:Oh, sorry that wasn't my intention...
Still sounds ambiguous to me though. I don't think the average motor efficiency of an IM is higher than PM at any size/performance. Perhaps you are referring to cost efficiency?
Thanks Stiive. Not only cost. Wally Rippel explains it here.
http://www.teslamotors.com/blog/inducti ... ess-motors
Richo wrote:DONT DO IT Image

The cat will get angry and the toast will get soggy Image

Thanks for your timely warning Richo! That was close!

There I was with my shower-cap on, shower steaming up the room, cat clutched to my bare chest, buttered toast gripped between my teeth, about to step into the productivity booth, when Coulomb called out from the computer room, "Hey Weber, I think you'd better read this". I was wondering why the cat was struggling a bit and its eyes were as wide as dinner plates.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Getting the right windings...

Post by T2 » Sat, 04 Aug 2012, 11:34

Jonescg let me try to explain what is going on here.

i have explained something which you don't understand.
You have therefore tried denial

So, T2, what you are saying is, Evo, who build and service high-powered axial flux permanent magnet AC motors, don't know what they are talking about

Then you transferred the problem to me personally

I'm sorry, but I just can't understand what it is that's bugging you!?
...but I still can't work out what his problem is.


I have presented ideas which are foreign to you.
You haven't been able to successfully refute them.
You have tried to intimidate me with EVO's expertise.

I have shown you that they are asking you to accept compromise.

Since you are racing compromise is unacceptable.

Since you are laying out a whack of money I think you should be getting a no compromise design.

And I don't think that is being unreasonable.

I am here to help if I can and learn a thing or two also.

T2

User avatar
jonescg
Senior Member
Posts: 2939
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Getting the right windings...

Post by jonescg » Sat, 04 Aug 2012, 16:44

Either it's something I don't understand or something you've not explained very well. Both are equally possible Image

The way I see it, both the #3 motor and the #4 motor have the same mass of copper, and therefore will put out the roughly the same power. One is optimised for higher currents, the other for lower currents. Both motors cost the same, I might add. Something which I haven't got from you is whether or not you think field weakening is a good thing or a bad thing. If it works, and it allows the motor to achieve full speed while still delivering >130 kW, then I can't see the issue. If this is a compromise designed to still give good power while preserving my substantial investment, then I'd say it was a good compromise.

Evo know that I will be using the PM150DZ inverter, and they will be bench testing the motor with this very inverter. They also know that I will be racing it competitively and giving it a >90% duty cycle. So in seeing that there was a risk of overcooking it, they found a compromise which to my mind seems reasonable.

And I think you would have to agree that Evo know more about this motor than either you or I. But wait until the end of the racing season and we'll see how much I know Image

Racing cannot be a no-compromise environment. If it was, I would only be pushing that boundary and burning motors out at a higher level. I could have gone for the AFM130 motor but instead opted for more power, even if it's bigger and heavier how I ride the bike won't change - all because the capabilities are higher and the risk of incineration is lower.

It's a bit like a 1000 cc superbike. One could add bigger injection ports and a supercharger, enabling more fuel to be dumped into the chamber, but this risks blowing the motor up. If done once or twice it will probably survive, but not every lap. So rather than risk a grenade on the track, they limit the size of the injectors as a compromise for reliability. And they still go fast, just more consistently.

Oh, I love the discourse here, even if it gets a bit acrimonious.
AEVA National Secretary, WA branch chair.

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Getting the right windings...

Post by T2 » Sun, 05 Aug 2012, 09:26

- weber I would debate you on multipolar machines but I have nothing to bring to the party.
Although I did peruse Marathon's Premium Efficiency range.

At random I selected 30Hp size regarding torque /mass correlation.

2-pole 499lbs   286 frame Probably some slots are left empty
4-pole 519lbs   286 frame
6-pole 689lbs   326 frame So same power, but larger frame.

I did find one case in the catalog to support your view :
In the 40 Hp size -
6-pole,8-pole both 975lbs but cost $9,175 & $13,697 resp. go figure.
That specific example could lead you to think that more poles equal more torque with no weight penalty. I looked up the frame dimensions and found that the 8-pole is one inch longer, so I'm inclined to think that this single case is a typo error.

IPMs v ACIMs Good Link - Is that Wally E. Rippel by the way ? just kidding.

Back in '95 he was still working for Aeroenvironment Inc. He and Joel Wacknov gave a technical session at the Hyatt Regency in Long Beach for POWERSYSTEMS WORLD 1995. I was busy working for a client in L.A. at the time but hadn't read my latest copy of PCIM and missed out although I note that they were asking several hundred dollars to register for even one session. Their particular session was entitled "Design Decisions and Parameter Selections dealing with Traction AC Drives" subjects included "multiplicity of drives (single versus multiple) transmission types.... A rigorous treatment will also be provided regarding gear type and ratio selection, motor type and base speeds."

A few years earlier Wally had played an important part in the design of the Impact EV at Aeroenvironment Inc. This vehicle happened to be of a twin induction motor front wheel design for thems that might be interested.

So I've been pecking around Evo-electrics website. Heck, they don't give you a lot of info to go on.
Unless you decide to use 600Vdc there is no torque graph to give guidance on motor performance, that's if you had decided to use a less stratospheric voltage like 320Vdc and would be curious as to how peak torque would pan out past 2150rpm for the most recommended motor, the AFM-140-4, for instance.

Knowing that most of their clients would be using somewhat less than that wouldn't you think they should at least publish the performance that is to be expected on 320Vdc ?
This would save speculation regarding the 60sec and 18 sec torque ratings and the expected power ratings at top speed.

I was able to get good correlation between quoted torque figures and the torque constant, Kt. However although they mention nominal torque and nominal power they leave you to detemine what nominal speed is.

Well on 320Vdc it turns out that at the base speed of 2150rpm you can't get the advertised power of 75Kw but only 49.5Kw with the -4 motor.
Calculations with the -3 motor with the 2850rpm base speed gives the much better result of 65.6Kw as I would have expected. But then again it's still shy of the 75Kw of course.

I then investigated the AF-130-4 and -3 series.These motors weigh in at 30Kg being 10kg lighter than the AFM-140 series. They allegedly pump out 64Kw with base speeds of 2850 and 3800 for the -4 and -3 variants respectively. The -3 piqued my interest as it is close to the 5000rpm limit.
I noticed that even though this range of motors is specified as having a top speed of 8000rpm, the base speed chart has footnotes discouraging its use above 5000rpm, strange that.

Again I proceeded to investigate its usage with 320Vdc since the torque graph shows only for 600Vdc. Although torque for this series is 145N-m rather than 220N-m these motors seem able to throw out a healthy 43.3Kw and 57.7Kw respectively. The torque drop off from 3800 to 5000rpm would probably be less significant for the AF-130-3 than all the other choices considered so far. Peak torque of 250N-m should be manageable for 60secs.

Then I came across an anomaly. Using the torque constant Kt of 0.8 A/N-m the -3 required 181 amps which with root3 times 232Vac came to 72.7Kw not 57.7Kw as expected. However resetting Kt = 1.01 N-m/Amp and everything balances out. In which case only 143amps should be needed to produce the rated 145N-m instead of the 181 amps mentioned previously.
Similarly the AF-130-4 should have a Kt = 1.35 N-m/Amp not 1.07 N-m/Amp by my reckoning.

Also if AFM-140-3 has the same base speed as AF-130-4 of 2850rpm then how come their Ke's are different when working off the same 320Vdc supply ? They are 0.81Vs/rad and 0.86Vs/rad resp. I would put all this down to documentation errors which don't detract from the operation of the motor or drive. As a general rule shouldn't motors with the same Ke have the same Kt also however they are built ? I think they should.

How come base speeds are quoted for no load current ? These are synchronous machines fitted with feedback tachs, they should therefore hold the same rpm irrespective of loading, no ?

Why does the AFM-140-4 motor suffer a torque drop from 220N-m to 180N-m on its way to base speed at 4000rpm ?
It could be assumed that this 20 % torque drop at constant current is due to rotor skew, however for the Peak Torque plot there is not even an ounce of torque drop off for that curve until the exact moment it passes above the 4000rpm base speed ? Makes you wonder if they did that test.    
More later.
T2

T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

Getting the right windings...

Post by T2 » Sun, 05 Aug 2012, 11:18

-jonescg if you have decided on 600Vdc and the AFM-140-4 then it would appear that you have restricted your rpm range to 4000rpm.

I therefore assume a multi-ratio gearbox is in use.

In which case I have to ask why you didn't spring for the AFM-140-3 which gives you 5000rpm reach. Then make the 20% change in the final sprocket. That way you swap rpms for extra torque and maintain full power all the way up to 5000 rpm.

Of course if you have a battery system that would be overwhelmed by supplying this extra power then maybe you have to consider rebalancing your system.

First the EVO motor won't have the inadequate bus barring that dispensed power to the brush gear inside the case like the Agni motor did. It is also water cooled. Overheating of any severity is much less likely to be a problem.

Personally I would think that if fresh ice chilled water were to be pumped around inside the motor before every race that even having a radiator system would be an unnecesary addition. In the span of the race I doubt the motor will dissipate enough power to bring the total thermal masss to 55 deg C. It would be interesting if you could do a work up on what the math looks like on that. Need specs on your battery system though. It would be appreciated if you could be a bit more forthcoming on your system regarding both those items. Gearing and Kwhrs that is.
As for writing to EVO. Tell them to read this thread and see for themselves what we are discussing. I am sure they are quite willing to sell you a system more powerfull than you need, particularly after you came away from a bad experience with Agni.

I know very little about bike racing. One thing I've heard is that 10Hp electric is equivalent to a 30Hp gas because of the better throttle response.
T2

User avatar
coulomb
Site Admin
Posts: 3721
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

Getting the right windings...

Post by coulomb » Sun, 05 Aug 2012, 16:18

T2 wrote: Why does the AFM-140-4 motor suffer a torque drop from 220N-m to 180N-m on its way to base speed at 4000rpm ? ... however for the Peak Torque plot there is not even an ounce of torque drop off for that curve until the exact moment it passes above the 4000rpm base speed ?

I think that's because the drop-off is for continuous torque, which is based on how much heat the motor can continuously get rid of. As the speed increases, the iron losses increase, and there is a fixed rate that the heat can be removed, so there is less "thermal head room" for I^2R losses, so the continuous current has to reduce, so the continuous torque has to reduce (both as the motor speed increases).

For peak torque, it's short term, so it doesn't matter how fast you can take away the heat; it won't be enough to keep the motor safe long term. So the peak torque is about melting the windings, or winding insulation, or twisting the axle, or similar current- or torque- induced effects. None of these depend on motor speed, so the peak torque curve is ruler-flat.

That's my guess.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
coulomb
Site Admin
Posts: 3721
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

Getting the right windings...

Post by coulomb » Sun, 05 Aug 2012, 16:28

T2 wrote: -jonescg if you have decided on 600Vdc and the AFM-140-4 then it would appear that you have restricted your rpm range to 4000rpm.

I therefore assume a multi-ratio gearbox is in use.

No, I believe Jonescg has stated that he'll be relying on field weakening to extend the speed beyond the 3800 or so RPM that he can get with his pack. It will be approximately constant power above that, which will be enough power for the straights. The oil burning competition will be using gearboxes that will do much the same thing, but with more mass and higher losses.

Yes, if he used the lower Kv motor, he would get more power at higher speeds, but remember he is running the motor at something like a 90% service factor; that means that there is very little room for overloading it. The lower Kv motor would probably give more power on the streets, where the power demand is much more peaky; on the track, the lower Kv motor is likely to burn out. These are expensive motors, so understandably, racers want to minimise the number of lessons learned the hard way. This thread is about trying to figure out what is likely to work best, on paper where it is much less expensive than on the track.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
coulomb
Site Admin
Posts: 3721
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

Getting the right windings...

Post by coulomb » Sun, 05 Aug 2012, 16:37

T2 wrote: Personally I would think that if fresh ice chilled water were to be pumped around inside the motor before every race that even having a radiator system would be an unnecesary addition. In the span of the race I doubt the motor will dissipate enough power to bring the total thermal mass to 55 deg C.

These are not 400 m <10 second drag races; these are 5 or 7 laps at minutes per lap. Ten minutes with something like 5 kW loss (wild guess, could be much more) would be plenty energy to boil many litres of water. I think a radiator is still needed.

[ Edit: several litres -> many litres. Think of two 2.4 kW electric water jugs running for 10 minutes! ]
Last edited by coulomb on Sun, 05 Aug 2012, 06:40, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

Post Reply