# Aluminum vs Copper Windings



## JRP3 (Mar 7, 2008)

Size might be an issue as aluminum windings will have a greater volume for the same current capacity, so you'll need a larger housing and end up with a larger motor. Not sure if there is enough copper in a motor for aluminum to significantly affect the price. I don't think current motor pricing is a result of the materials used.


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## IamIan (Mar 29, 2009)

JRP3 said:


> Size might be an issue as aluminum windings will have a greater volume for the same current capacity, so you'll need a larger housing and end up with a larger motor. Not sure if there is enough copper in a motor for aluminum to significantly affect the price. I don't think current motor pricing is a result of the materials used.


100% agree about the increased size / volume of the aluminum windings motor.

Although even with aluminum windings an electric motor will still occupy less space than an equivalent ICE.

Attached is a chart that shows the effects on weight from the two options, taken from the initial three links.

Then attached is a chart also from the initial three links that shows the significant price difference between the materials ... Although you might be correct in that other factors might dominate and prevent it from making a large difference in price.

Then attached is a chart also taken from the initial three links that shows the an interesting relationship in the difference in Ohms between the two materials at different frequencies ... in some ranges of frequencies there is not significant difference in the resistance ... which means if operated in that range , a Al windings motor would not need to be significantly larger ... which would further decrease the weight of the Al options.

There are of course issues to deal with ... significant issues ... but I do see interesting potential to be yet explored.


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## aeroscott (Jan 5, 2008)

at the frequency of 5 to 400 hz is the operating range of motors if we go higher the switching losses go up dramatically . not that al would not work but ive seen a lot of very cheep motors in the junk yard and never seen al wound motor .


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## IamIan (Mar 29, 2009)

aeroscott said:


> at the frequency of 5 to 400 hz is the operating range of motors if we go higher the switching losses go up dramatically . not that al would not work but ive seen a lot of very cheep motors in the junk yard and never seen al wound motor .


5 to 400 hz ???

That is pretty low ... you sure you don't mean khz ( 1,000 hz )?

For example the Zilla and Curtis Controllers operate around ~15 khz ( ~15,000 hz )... way above your 5 to 400 hz number.

It is around ~80 khz that the AC ohms of Al and Cu get pretty close to each other.

Switching losses are an issue ... but even if you do not use the higher frequencies where Al and Cu AC Ohms get close to each other ... even if you never do... Al is still lighter to carry the same current, even in DC.

I would have been surprised if you had seen a Al wound motor ... they are pretty rare... and as long as copper windings dominate , it only makes sense that you found copper windings in a normal junk yard.


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## jehan12413 (Feb 4, 2010)

I think he is referring to the frequency the windings expierence due to commutation. 5-400Hz sounds about right.


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## aeroscott (Jan 5, 2008)

yes motor winding


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## umurali2000 (May 3, 2010)

Interesting and most useful discussion ,...


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## IamIan (Mar 29, 2009)

umurali2000 said:


> Interesting and most useful discussion ,...


I find it interesting myself ... but I'm not sure how useful it will be ... at least until some motor companies begin to exploit it... and I don't see much of that happening yet.

I suspect the initial temptation would be for those companies just trying to reduce costs ... and that runs the risk of marketing a less expensive but inferior design ... which would sadly give the wrong impression to the concept.

I think it is most interesting where a good quality design is used ... the Aluminum based Electric motor of equal performance should be able to be lighter weight... although to maximize the Aluminum motor performance the entire motor should be designed with aluminum in mind, and not just substituting aluminum in a copper design.

I like the concept ... but I don't expect a product on the market like this any time soon.


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## Nickmey (Sep 23, 2014)

IamIan wrote:
> I like the concept ... but I don't expect a product on the market like this 
> any time soon.

Just have a look at the XD-80 80W washing motor. It just failed on me in
a tiny, sink-top washing machine!

I looked for it and was surprised to find it at AliBaba for..... 5 (five) $.
On a closer investigation (on mine and on the net) I discovered that these
aluminium-wound motors are being churned out by the thousands - for
cheap washing machines. How expensive a machine must I buy to avoid getting such a crap motor again? 

Nick


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## Ivansgarage (Sep 3, 2011)

IamIan said:


> 5 to 400 hz ???
> 
> That is pretty low ... you sure you don't mean khz ( 1,000 hz )?
> 
> ...



No Curtis Controllers are about 5-300Hz you need to read more.

20 years and have never seen alum. wire in a motor (3 phase)
Ivan


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## RIPPERTON (Jan 26, 2010)

You wouldn't just use enameled aluminium wire, you would use enameled copper clad aluminium core so the bulk heat carrying and mechanical strength is done by the alu and the current carrying is done by the copper coat.
Cost would not be much lower than pure copper because of more complex manufacturing so only reduced weight would be factor meaning only a racing motor would be designed with this.

http://www.lpmagnetwire.com/products/enameled-copper-clad-aluminum-wire.html


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## IamIan (Mar 29, 2009)

RIPPERTON said:


> so only reduced weight would be factor meaning only a racing motor would be designed with this.


Agreed ... and even then ... it would probably be low on the list of weight saving options... other things would likely be done first.

- - - - - - - - 



Ivansgarage said:


> IamIan said:
> 
> 
> > For example the Zilla and Curtis Controllers operate around ~15 khz ( ~15,000 hz )... way above your 5 to 400 hz number.
> ...


Sense the Spec Sheet of the Curtis Model #1222 Specifically lists that it operates at a PWM of 16khz ... like I wrote about ... The only thing I can think of ... is that although no one is writing it ... you are thinking of the operating frequency of the stator itself (not the controller itself) ... although (I'll completely agree) they do interface ... the #1222 is designed for example for a Stator operating between 0 and 200 hz... while it (the Curtis) itself is operating at 16khz.

Am I guessing correctly ??
Or are you getting the lower hz frequency from somewhere else ??


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## RIPPERTON (Jan 26, 2010)

The enamelled, copper clad aluminium wire is about $6.80 per kilo plus shipping (China) 1.2mm 5% copper and H class enamel.
The non copper enamelled aluminium is $4.50 kg 1.2mm H class.

For non in/stock products they are asking for a minimum of 500kg order.


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## IamIan (Mar 29, 2009)

RIPPERTON said:


> For non in/stock products they are asking for a minimum of 500kg order.


500kg of potentially aluminum based windings , is either a very big motor ... or .. many motors.


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## Antoniodiel (Feb 13, 2015)

Hi guys!
I would add some consideration about this topic. Currently I'm investigating the possibility to switch from copper solid conductor to aluminum solid conductor in a 3-phase AC synchronous electric machine. 
I performed some interesting FEM simulations with the phase current at different frequencies (from 0 up to 1,5 kHz). The feedback of my study is that from 0 up to 270 Hz the copper winding presents significant advantage in terms of Joule losses (-45% down to -2%), from 270 up to 780 Hz the Aluminum winding presents lower Joule losses (only 1-2% compared to copper windings), from 780 Hz up to 1500 Hz the copper windings has a gradual advantage (from 0% up to 250%).

This because the behavior that I'm trying to analyze is not only described by the law of the skin effect, there is also the proximity effect that strongly affect the behavior of the in-slot conductors...


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## mizlplix (May 1, 2011)

Why don't you quit jacking around and go with gold wire? 
___________________________________________________________

1- Better conductor and efficiency.
2-Less needed to do the same job.
3-Conducts heat away from hot spots and is harder to get a burn-thru.
Simply add 1/2 million USD to the budget.

(Just kidding guys)

Miz


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## mizlplix (May 1, 2011)

*The way I look at things I will NEVER run an AC motor beyond 267 Hz.

rpm = 120 x F
 P

120 X 267 (cycles)/ 4 poles= 8010 RPM (Which an AC50 will do)

My motors pull to 4,500 RPM (150 Hz)

So there is not really any aluminum advantage for my usage.
Assuming all of the other problems could be worked out.

Miz
*


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## IamIan (Mar 29, 2009)

mizlplix said:


> *The way I look at things I will NEVER run an AC motor beyond 267 Hz.
> 
> rpm = 120 x F
> P
> ...


You're looking at the wrong frequency.

It is not the frequency of the motor shaft Revolutions .. or the poles .. what you did the math for above.

It is the frequency of the electricity switching itself.

For example:
When your motor is spinning at 1,000 RPMs .. think about how you are able to vary the torque without varying the shaft rotating frequency ... the answer is ... by changing the switching frequency of the electricity itself , allows you to alter the amount of torque and power.

For example:
As mentioned previously ... the Zilla and Curtis were mentioned , which operated (doing the switching of electricity) at ~16khz... even though the rotational frequency is far less than that.


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## PStechPaul (May 1, 2012)

Gold is actually a poor conductor compared to copper, but silver is a little bit better. Silver is about 100 times the cost of copper, and gold is about 50 times higher than silver.
http://www.munknee.com/a-direct-comparison-between-gold-silver-platinum-and-copper/

I don't think any significant advantage in cost can be gained from using aluminum for stator windings, but it is often used for the squirrel cage of the rotor. These conductors are rather large and may carry hundreds of amps, and there might be significant skin effect when running at higher frequencies. It may be practical to overclock up to more than 400 Hz for a motor with 8 poles or more, where 400 Hz might correspond to 6000 RPM. But the greatest limiting factor may be eddy currents and core losses due to the cheaper thicker laminations used in most industrial induction motors.

The switching frequency (typically 12-20 kHz) does not come into play where the magnetics of the motor are concerned. It may even be advantageous to filter out the high frequency components of the base frequency that the PWM attempts to replicate, and a pure sine wave of 5-400 Hz may be best. Some motors and cabling are specifically designed for inverter duty, and they usually have lower capacitance and a higher grade of insulation to withstand the transients imposed by high frequency PWM waveforms.

Torque boost is usually achieved by changing the duty cycle of the PWM to provide a higher V/F ratio, which is essentially a higher voltage driving the stator closer to saturation and perhaps increasing the slip frequency closer to breakdown torque. The PWM frequency might be changed to reduce audible and electrical noise, and perhaps optimizing the efficiency of the inverter, especially with older, slower, IGBTs.


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## aeroscott (Jan 5, 2008)

Point taken on the high frequency to approximate a cycle . 
How about cladding with silver using al or copper core.


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## IamIan (Mar 29, 2009)

PStechPaul said:


> The switching frequency (typically 12-20 kHz) does not come into play where the magnetics of the motor are concerned.


Exactly.

If the switching frequency was increased up toward the ~80kHz range .. as shown above .. That's where Copper starts to loose most of it's advantage over Aluminum.

- - - 

Separate from the high frequency effects ... Aluminum pretty much always has better conductivity per unit weight than copper ... An aluminum wire with the same resistance as copper will be larger , but it will also be lighter .. And Aluminum is stronger per unit weight than copper as well ... For an equal strength it has to be larger , but will be lighter ... But , usually this had a significant con .. that additional size does matter allot in design , due to the reduced magnetic field strength as distance increases.

The nice thing about the benefit at the higher frequencies is that the Aluminum doesn't have to be larger anymore.


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## PStechPaul (May 1, 2012)

The skin effect is not deep enough at these frequencies to benefit from cladding. A more effective method is to use Litz wire, which at these frequencies would just consist of perhaps multiple strands of #22 AWG insulated wire braided so that the current is forced equally into all depths of the conductor. This is, essentially, already done in larger high current low voltage motors where multiple strands of thinner wire is easier to wind, and true Litz wire uses extremely fine wire (#32 to #44 or smaller) with very thin insulation (since there is almost no voltage between adjacent strands), and an overall covering of thicker insulation that can withstand full voltage.

Aluminum wires might possibly be anodized instead of using enamel, as aluminum oxide is an excellent insulator. 

Perhaps in the future we may be able to use carbon nano-fibers and tubules, possibly with silver particles, as high performance lightweight conductors:
http://www.sciencedirect.com/science/article/pii/S0167577X14012415
http://en.wikipedia.org/wiki/Carbon_nanotube

And maybe a motor can be developed using high frequency magnetic materials such as powdered iron and ferrite, with perhaps 200 poles and driven with 6 kHz for 3600 RPM.


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## aeroscott (Jan 5, 2008)

I like the point about size effecting magnetic field strength. The lack of thermal conductively would lead to more hot spots in the conductor with al.


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## major (Apr 4, 2008)

The motor acts as a low pass filter. High switching frequency shows up as ripple on the current waveform and does not contribute to skin effect anywhere near that of alternating current. Use the fundamental frequency for such analysis (50 or 60Hz maybe up to 400Hz) in the armature conductors. The rotor sees only slip frequency of a few Hz in inverter driven EV motors.

The analysis of skin effect in the conductors in a motor is quite different from the classic single round wire in free space. The surrounding magnetic material and flux patterns with the leakage inductance becomes complex. For instance, altering the shape and depth of a rotor bar can increase its effective resistance 3 or 4 fold at 60Hz for line starting compared to running resistance at 1 to 2Hz as done in deep bar or double cage rotors.

Aluminum has proven rather effective for cage rotors where it can be cast IMO. It has served industry well and been fairly efficient. Many EV motors can and do use Al rotors. There has been a push recently to change to copper bar rotors in industry to squeeze out a percent or two efficiency points. Copper helps the EV ACIM torque density as evidenced by Tesla. 

Using aluminum for winding motors has many problems. I'm sure it has been tried over and over again. I don't see it happening. I don't think you could actually show a performance or cost improvement when all design aspects were fully analyzed. 

Odd lately I've started seeing copper heatsinks replacing aluminum ones in high density power electronics


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## aeroscott (Jan 5, 2008)

Makes me think of the heat pipes so common for cpu's these days , copper except for the fins.


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## mizlplix (May 1, 2011)

My hand held programmer reads out motor Hz in real time. The last time I read it at full RPM it was 157 Hz. 

It was an 8" diameter rotor. 4,500 RPM is pretty fast. (I even had it custom balanced to run that fast.)

Directly from the Curtis manual:


> The Curtis AC controllers can output a sine wave from 0 – 300Hz and drive 2, 4 or 6 pole motors. This equates to a theoretical maximum speed of 12000 rpm for 2 poles, 6000 rpm for 4 poles and 3000 rpm for 6 poles.


Was what I was referring to and seems to perform that way.

Miz


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## IamIan (Mar 29, 2009)

mizlplix said:


> My hand held programmer reads out motor Hz in real time. The last time I read it at full RPM it was 157 Hz.


Your hand held might not see the high switching frequency that is here... But it's there none the less.

Like only seeing the very slow frequency of ocean tides , and being unable to see smaller faster frequencies of individual waves on shore.

As Major already well said:


major said:


> The motor acts as a low pass filter. High switching frequency shows up as ripple on the current waveform


- - - - - - 

For windings of equal resistance ... Aluminum has to be about 80% more volume (that's pretty big) .. unless AC resistance dominates and you can get up near that ~80khz range .. than the size difference gets vanishingly small .... But (again for equal resistance) ... The Copper has to be about 82% heavier .. unless AC resistance dominates (at those higher frequencies when the AC resistance is about the same , copper gets hit twice and would have to be about ~147% heavier for the same resistance).

- - - - - - 

Copper vs Aluminum use in motors (specifically) and windings in general is not new concept ... pros and cons have been debated and studied allot .. and continue to be .. it is far from a 'closed case'

Some Examples:

Selection of copper versus aluminum rotors for induction motors
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=968162

Fabricated aluminum rotor construction for induction motors 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=324505

Selection of copper against aluminium windings for distribution transformers
http://www.academia.edu/2165728/Sel...minium_windings_for_distribution_transformers

High performance control in ultra-low speed range of inverter-fed linear induction motor using vector control scheme 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=298977

The effects of various magnetic materials on lamination design for stator–rotor diecasting of induction motors for electric vehicle applications
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=5147841

Preliminary study of using anodized aluminum strip for electrical motor windings 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6995808

Solar Plane Propulsion Motors With Precompressed Aluminum Stator Windings 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6802418

Fabricated Aluminum Cage Construction in Large Induction Motors 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=4157872

A Wavelet/PSO Based Voltage Regulation Scheme and Suitability Analysis of Copper- and Aluminum-Rotor Induction Machines for Distributed Wind Power Generation 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=6205350

Comparative performance analysis of aluminum-rotor and copper-rotor SEIG considering skin effect 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=4800134

The study to substitute aluminum for copper as a winding material in induction machine 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=5352008


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## mizlplix (May 1, 2011)

Understood, but I am like an aborigine. If I can't see it, fight it or screw it, it don't exist for me....(heh)


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## IamIan (Mar 29, 2009)

mizlplix said:


> Understood, but I am like an aborigine. If I can't see it, fight it or screw it, it don't exist for me....(heh)


Nothing really at all wrong with that PoV ... It still gets the job done.


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## major (Apr 4, 2008)

IamIan said:


> Your hand held might not see the high switching frequency that is here... But it's there none the less.
> 
> <snip>
> 
> As Major already well said:


Thank you. My point was that switching frequency is irrelevant to the discussion and the frequency Miz reads on his handset is relevant. It is the frequency of AC in the motor winding. If the switching frequency contributes at all to conductor loss in motors I suspect it would be so small as to be considered noise and a theoretical footnote which could not be experimentally verified.

I was able able to pull up only one of your numerous references without joining IEEE and paying fees. It concluded that Al foil windings on utility transformers were cost effective below 170KVA with 2007 metal prices. It would be a stretch to form an analogy of that to an EV motor IMO.


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## IamIan (Mar 29, 2009)

major said:


> Thank you. My point was that switching frequency is irrelevant to the discussion and the frequency Miz reads on his handset is relevant. It is the frequency of AC in the motor winding. If the switching frequency contributes at all to conductor loss in motors I suspect it would be so small as to be considered noise and a theoretical footnote which could not be experimentally verified.


You're welcome .. I differ slightly... ~98% agree.

Basically on two points:

#1> This discussion is about potential benefits for aluminum use in motors (in general) and in the current carrying windings (specifically) .. as such ANY aspect / property / etc .. of Aluminum that could (even theoretically) offer a benefit is completely 100% relevant to this thread / discussion... Lower AC resistance counts.

Caveat:
I'm still agreeing Copper has many pros .. and Aluminum has many cons .. and I'm not claiming aluminum will automatically be better in any possible application , nor design... in most designs today Copper's pros out weigh it's cons .. etc... I don't intend to give any kind of 'anti-copper' impression.

#2> Is probably just a minor point / semantics:
But ... Technically , no .. I don't agree ... the AC in the windings is the switching frequency in the windings .. that is what creates the other 'emergent' / 'aggregate' / or 'net' lower frequency.

For example:
My thoughts and self awareness etc ... are also an 'emergent' / 'aggregate' / or 'net' effect of the neurons , synapses , etc ... in my brain .. but that doesn't mean those neurons / etc are not there , or not happening .. or that the 'emergent' effect somehow happens without that 'lower' level to create that 'upper' level 'emergent' effect.



major said:


> I was able able to pull up only one of your numerous references without joining IEEE and paying fees. It concluded that Al foil windings on utility transformers were cost effective below 170KVA with 2007 metal prices. It would be a stretch to form an analogy of that to an EV motor IMO.


Sad part of our world today .. sorry .. lots of information is behind pay walls. 

But .. If you are going to 'pay' for just one (if any) of them .. maybe the biggest bang for the buck .. to explore the concept of this thread / discussion ... would be ... The one I link to bellow .. it goes about with a fairly fair and honest look at the pros and cons of both copper and Aluminum .. and then comes up with design method that produces a proof of concept motor for testing that shows a design that plays to Aluminum's pros and shows it is possible to produce competitive (even superior performance) results when doing so.

Caveate:
I'm not saying someone couldn't go out and equally purpose build a motor to exploit the benefits of copper as well .. This is just an example of the Aluminum 'side'.

Solar Plane Propulsion Motors With Precompressed Aluminum Stator Windings
http://ieeexplore.ieee.org/xpl/arti...&searchProductType=IEEE Journals Transactions

A few highlights:
(I shouldn't get in trouble for that much) 

The main take away from that is probably .. that by carefully compressing the aluminum it is possible to gain enough additional 'fill-factor' to cover the additional volume Aluminum windings need for a net superior performance device ... and they didn't even exploit the high frequency effect... which could (in theory) be designed to stack.


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## major (Apr 4, 2008)

IamIan said:


> ... the AC in the windings is the switching frequency in the windings ..


I think you are pretty much alone in your thinking about this. The normal view is depicted on this diagram:










I lifted it from Wikipedia. It shows the AC or Alternating Current in the green trace clearly swinging back and forth between polarity, or from positive to negative, or alternating from one direction to the other direction. The blue trace labelled pulsating is what I referred to as ripple which in our case is superimposed on the fundamental AC. The current clearly does not alternate or change direction at the switching frequency but does change direction at the fundamental frequency. That is AC.

Within the context here, motors, another clue is how all the characteristic motor equations relate frequency to speed (RPM). In all equations, they use the fundamental AC frequency, and never the switching frequency.


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## IamIan (Mar 29, 2009)

major said:


> I think you are pretty much alone in your thinking about this.
> 
> The current clearly does not alternate or change direction at the switching frequency but does change direction at the fundamental frequency. That is AC.
> 
> Within the context here, motors, another clue is how all the characteristic motor equations relate frequency to speed (RPM). In all equations, they use the fundamental AC frequency, and never the switching frequency.


I was thinking more about the switching frequency in terms of the voltage .. and in the current fluctuations caused by that changing voltage ... still seen as the ripples (even with the filtering) .. but I agree the current (amps) themselves are not changing direction (alternating) at the rate of the switching frequency.

I guess that led me to the mental error  of thinking the high ~80khz range was not as far away .. but .. if it has to be the frequency of the current (amps) reversing (changing direction) .. than yeah .. ~80khz is very far off from current motor / controller designs ... and that would make trying to exploit that Aluminum benefit (most likely) very difficult... MUCH more so than I originally was thinking.

Thanks for correction. 
(Learn something new everyday)

- - - - 

Does lead me to a different thought though.

If (in some prototype) the current doesn't reverse direction ... and only changes/fluctuates say (for example) up to 100v and down 1v .. than back up ... but never reverses direction ... wouldn't one still be able to make use of the changing/fluctuating magnetic field for motor rotation/torque ?? ... ie .. if the entire AC wave form is off set upward so the bottom never crosses zero and never reverses direction.


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## Antoniodiel (Feb 13, 2015)

About your discussion, let me add some considerations. 

Yes, basically Major is in the right.. 



> The current clearly does not alternate or change direction at the switching frequency but does change direction at the fundamental frequency. That is AC.


But the switching frequency strongly affects both the Joule and the iron losses, due to the harmonic content that introduces into the phase current waveform.

In past I did some analysis about the impact of a 12kHz switched current on the iron losses of a 8 poles, 3 -phase AC synchronous electric machine. My study highlighted a +10% of iron losses amount compared to a perfect sinusoidal phase current feeding.


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## major (Apr 4, 2008)

Antoniodiel said:


> But the switching frequency strongly affects both the Joule and the iron losses, due to the harmonic content that introduces into the phase current waveform.


Yes, no argument as to the increase in iron loss. But that is unaffected by Al vs Cu, unless more iron is needed to compensate for the increased volume due to Al windings. A big component to the higher harmonic increase seen in the iron is minor loop hysteresis loss. This would not be present in conductor loss attributed to harmonic content due to PWM. So the increased conductor loss due to PWM vs sinusoidal excitation would likely be less than that measured in the iron. Then, the difference in that already small quantity, between aluminum and copper would be even a smaller amount. And that is what I referred to when I said it was probably on the order of noise and too small to measure. I am not saying it does not exist.

I have no problem with the use of any material which can do the job. Aluminum wire included. But let us be smart about the application. In your typical automobile, be it fossil fuel or battery powered, how much wire is used for all the accessories? It could be about the same mass of copper as used to wind the motor. Why then pick on the motor? Why not change all those other wires to aluminum? 

I'm certain this has been explored many times by automotive engineers over the past 100+ years. And they have undoubtedly proven to their accountants and managers that copper is best choice for their products. The materials for motors will undergo similar scrutiny. Maybe some premium application like that aircraft motor which can command a high enough price as to justify more costly methods needed to utilize lightweight materials will eventually filter down to cars. But for now, I don't see a reason to rewind your EV motor with aluminum wire 

And, Antonio, thanks for chiming in on the subject. I am by no means trying to discourage you. Good luck with your investigation and tell us more about the synchronous machine if you're allowed.


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## PStechPaul (May 1, 2012)

I found some additional information related to the topic of motor drive efficiency and VFD switching frequency:

http://www.vfds.org/vfd-controlled-induction-motor-efficiency-measurement-447038.html

http://ecmweb.com/harmonics/4-1-1-variable-frequency-drives

http://www.eng-tips.com/viewthread.cfm?qid=306303

http://www.mhw-intl.com/wp-content/...earing-Failures-in-AC-Motor-Drive-Systems.pdf

http://www.baldor.com/support/Literature/Load.ashx/BR1301?LitNumber=BR1301 (Line and load reactors)

http://www.apqpower.com/products/low-voltage/pwm-voltage/load-reactor


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## IamIan (Mar 29, 2009)

major said:


> Maybe some premium application like that aircraft motor which can command a high enough price as to justify more costly methods needed to utilize lightweight materials will eventually filter down to cars. But for now, I don't see a reason to rewind your EV motor with aluminum wire


+1

- - - - - 



PStechPaul said:


> I found some additional information related to the topic of motor drive efficiency and VFD switching frequency


Thanks.


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## major (Apr 4, 2008)

IamIan said:


> Does lead me to a different thought though.
> 
> If (in some prototype) the current doesn't reverse direction ... and only changes/fluctuates say (for example) up to 100v and down 1v .. than back up ... but never reverses direction ... wouldn't one still be able to make use of the changing/fluctuating magnetic field for motor rotation/torque ?? ... ie .. if the entire AC wave form is off set upward so the bottom never crosses zero and never reverses direction.


Kinda off topic, but WTF. Sure. Fluctuating fields can be used without changing polarity completely or crossing zero so-to-speak. But because magnets always come with 2 poles (North and South), it better utilizes the magnetic structure and coils in the motor to have them swing full negative under one pole and then, in the next half cycle, swing full positive under the opposite pole. Reluctance motors are the exception. The principle involves the magnetic force of attraction acting to close a gap. This is an attractive force regardless of direction of flux. So switching coils off and on can be as effective as reversing coil polarity.


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## liveforphysics (Jan 16, 2014)

It doesn't matter what the current control PWM frequency may happen to be. Skin effect is based on current alone, and the current in the windings is not beyond the commutation frequency. 

If you switch voltage at 100kHz or whatever to drive a 400-500hz commutation frequency, you only have the skin effects of the current waveform alone. 

Using clad conductors buys you nothing. 

As aluminum has a greater conductivity per unit of mass than copper, for a motor with the right geometry it could enable more power per motor mass, but less power per unit of volume.


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## Tesseract (Sep 27, 2008)

One other thing y'all seem to be ignoring is that capacitively-coupled currents between adjacent windings and through the bearings (ie - common mode) go up with PWM frequency.


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## major (Apr 4, 2008)

Tesseract said:


> One other thing y'all seem to be ignoring is that capacitively-coupled currents between adjacent windings and through the bearings (ie - common mode) go up with PWM frequency.


Hi Tess,

May I guess why this phenomenon is relevant to the topic? Aluminum conductors require a greater cross section than copper to offer equivalent resistance for the windings. That will mean aluminum conductors have greater surface area which then will increase capacitance. So countermeasures must be considered when analyzing the change in conductors. 

maj


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## Tesseract (Sep 27, 2008)

major said:


> ...May I guess why this phenomena is relative to the topic? Aluminum conductors require a greater cross section than copper to offer equivalent resistance for the windings....


Yep, though I confess I did not bother to consider whether my reply was actually topical ahead of time. I just noticed that everyone seemed hung-up on the currents through the windings while totally ignoring the voltages across them (or, more precisely, the dV/dt of the voltages).


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## PStechPaul (May 1, 2012)

One of the links I posted addresses the issue of capacitive coupling of high frequency components through the frame and shaft of the motor and causing early bearing failure. A combination of common mode and normal mode chokes on the motor leads from the VFD will take care of that, and also possibly allow the use of ordinary cables and standard motors rather than those specifically designed for inverter duty.


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## major (Apr 4, 2008)

*Carbon?*

I've heard some talk about carbon nanotube wire about half the resistance of copper.


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## IamIan (Mar 29, 2009)

*Re: Carbon?*



major said:


> I've heard some talk about carbon nanotube wire about half the resistance of copper.


I've read about two different directions for CNT (carbon Nano Tube) wire.

One is just slight variations in the CNT structure .. which AFAIK still has lots of problems ... 

"a big drawback for CNTs is that a kg of copper is 2.5 times more conductive than a kg of CNT"

But

"is 10 times lighter than copper and 30 times stronger"

One property counters the other.

- - - - 

The other option I've read about is a hybrid that combines copper into the CNT structure ... CNT-Cu .. AFAIK these folks have made the most CNT progress... but it isn't replacing copper as much as it is .. improving copper with CNTs.

I've read talk about the A/cm^2:

"Thus for a given cross-section of electrical conductor, the CNT-Cu composite can withstand and transport one hundred times higher current compared to metals such as copper and gold."

- - - - -

Which is pretty interesting ... not quiet a super conductor ... but doesn't need all that super low temperature stuff .. but still , a massive potential improvement ... if they can find a trick to make them 'cost effective' .. and not just a lab curiosity.


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## RIPPERTON (Jan 26, 2010)

anodized alloy wire is good for 240C but low voltage motors.

http://www.lp-industry.com/products/oxidative-aluminum-wire.html

ECCA
enamelled copper clad aluminium. Getting prices now.

http://www.lp-industry.com/products/enameled-copper-clad-aluminum-wire.html

ECCA windings save 4.8 kilo on a 40kg motor like the EVO AF140


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