# AC induction motor rewinding questions



## Siwastaja (Aug 1, 2012)

Hi,

we are ready to do a test rewind for an industrial AC induction motor. We have a motor, an aluminum frame 7.5 kW nominal 4-pole 50 Hz motor that weighed 50 kg.

We already did strip old windings from the stator, and built a simple winding machine, and will be getting a 22 kg reel of new enamel wire and impregnation varnish hopefully tomorrow.

Getting more power out of industrial motors by "overclocking" has been debated, so we will try it out to see what happens. So I'm not giving any claims here, just what we are going to test. I hope to hear any opinions before we go, for example, would you go for even lower / not so low nominal voltage.

In any case, we'll probably limit ourselves at around 150 Hz, or 3x the original frequency.

To state the actual problem again (why do we need a rewind): As for the original design, 380V 7.5 kW 1500 rpm @ 50 Hz, going to 4500 rpm without field weakening would require 1140V @ 150 Hz and produce 22.5 kW of power. This would require a 1600 volt battery pack, which is practically impossible. 

We will use a 320 V battery pack. Hence, we need to reduce the original voltage by the factor 5.

The motor has 36 stators slots, this is 3 slot pairs per pole pair per phase. There were 3 strands of 0.80 mm diameter wire in parallel, making 34 turns per slot pair (34 turns * 3 parallel wires = 102 wires in a slot).

Do you agree that the right way to go is to reduce the number of turns by the factor of 5, too? This would be 7 turns per slot. Our new wire is 1.18 mm in diameter. In practice, we would test how many wires fit the slot, and parallel as many as possible, probably around 8...10 parallel. There was quite a bit of air in the slots of this motor - clearly it wasn't optimized for maximum efficiency - but we can make a tighter fit to increase the amount of copper there.

Any comments on this design before we go?


Ah, and we have an another one too. It was originally a 2-pole 440V 13kW 3000 rpm @ 50 Hz and has the same frame size despite the higher power. We would make identical windings for this one, thus converting it to 4-pole. I can see that there is less iron in stator in this 2-pole design (slimmer "teeth") but we still want to try it out. But do you see any other problems? Are there inherent, large differences 2-pole vs. 4-pole _in the rotor_?

Any comments appreciated. Will share the results.


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## major (Apr 4, 2008)

Siwastaja said:


> The motor has 36 stators slots, this is 3 slot pairs per pole pair per phase. There were 3 strands of 0.80 mm diameter wire in parallel, making 34 turns per slot pair (34 turns * 3 parallel wires = 102 wires in a slot).
> .............
> Any comments on this design before we go?


I don't get "slot pairs"  You have 9 slots/pole and 3 phase. Each slot has 2 coil sides in it, doesn't it? Total of 36 coils, 2 coil sides per coil, or 72 coil sides, into 36 slots, giving 2 coil sides per slot. Is it lap wound? (all coils identical?) What is the coil span? Did you make a wiring diagram before you stripped it? Got your slot liners and top sticks? 



> Are there inherent, large differences 2-pole vs. 4-pole _in the rotor_?


All else being equal, on the 2 pole rotor, the end rings support twice the current so could be larger. Oft times the motor company uses the same die for 2, 4 or even 6 pole and carries the extra for the higher pole counts. Going from 2 to 4 should not be a problem unless the rotor slots are different. The 2 pole design could use deeper slots which would mess with 4 pole performance. Hard tellin' unless you cut one in half 

Good luck.


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## Coulomb (Apr 22, 2009)

Siwastaja said:


> Do you agree that the right way to go is to reduce the number of turns by the factor of 5, too?


Yes, your plan sounds good to me. The only problems should be the mechanical details of rewinding, and keeping the same winding pattern, as Major has mentioned.


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## Siwastaja (Aug 1, 2012)

major said:


> Each slot has 2 coil sides in it, doesn't it? Total of 36 coils, 2 coil sides per coil, or 72 coil sides, into 36 slots, giving 2 coil sides per slot.


Hm, no no. Both of the motors we stripped have the simplest possible single layer windings. (If I understood you correctly?)

Like this, for the 4-pole motor (drawn with Emetor.com)










... and the identical set of second pole pairs (not drawn above) connected in series with the first ones. (Actually, the connections were accessible so that it could have been modified for half the voltage by changing them to parallel, but it wouldn't have been enough still.)



> Is it lap wound? (all coils identical?)


No, it was a concentric winding. We are going to replace it with lap winding as it seems like a bit less hassle to wind identical windings. Otherwise, it doesn't seem to make much difference? Concentric are easier to machine insert?



> What is the coil span? Did you make a wiring diagram before you stripped it?


Coil span should be 9 slots for lap winding, right? However, as it was concentric, it was 8, 9 and 10, yes?

Wiring diagram as shown above -- it was easy to get as it was single layer winding and not completely gummed up with the varnish.



> Got your slot liners and top sticks?


I thought about using 100 µm PET (Mylar) sheet for slot and phase insulation, and reuse the top sticks from the old windings. Didn't throw them away. However, now I do realize that having a wire and varnish specified up to 200 deg C, that mylar sheet would be the limiting factor... Oh well, we saved most of the slot insulation, too, and most of them are in a good shape. Reusing would at least be ecological .



> Good luck.


Thanks! I think we will need it .


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## Siwastaja (Aug 1, 2012)

Hey, I also came up with a new idea.

As this is a four pole design, I will be probably connecting the identical pole pairs in series, as they were originally. However, since I'm going to have a very small number of turns -- just 7 per slot pair (ah, by slot pair, I'm simply meaning the two slots 90 deg apart in a 4-pole design that share the exact same winding with opposite current directions) or 3*7 = 21 per three adjacent slots (one pole of one phase) -- would it be better to have 14 turns instead of 7 and connect the two pole pairs in parallel instead of series?

Or, would this make any difference? At least connecting them in series guarantees the same current flowing through them.


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## Ivansgarage (Sep 3, 2011)

Here is something i didnt see you mention, The IN HAND TURNS have to handle the incoming current, what does the controller put out 200? 500?
amps? A regular motor can only hanlde 20-30 amps.

You have to do a delta connect for the 3 phases, 4 poles seires,
dont forget the poles s-s f-f (start start) (finish-finsh) when laying the 
4 poles, Notes on my rewind span 1-9 so the first pole starts, slots
123 789 second pole slots 10 11 12 16 17 18 ect

The second phase start slot 789 13 14 15 ect.

You can see more on my web site.


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## PStechPaul (May 1, 2012)

You might want to check the skew of the rotors of these motors. It may be different for the two pole vs the four pole. I've rewound some smaller motors which were actually single phase and I made them three phase with variously more poles, up to 12. I had some strange experiences, but I think I figued out what was wrong. You might want to read though my thread on SED about 7 years ago when I did it:
http://sci.tech-archive.net/Archive/sci.electronics.design/2005-07/msg01591.html


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## Dennis (Feb 25, 2008)

I hope your original motor was not concentric wound, which would make it a pain in the rear. I like lap wound 3-phase motors, but machines can make concentric wound coils easily vs. lap wound coils. So if your motor is below 50 HP then you most likely had an original concentric wound stator before you modified it. My little black book on rewinding motors does not have the information on how to convert a concentric wound stator to a lap wound stator. Good luck.


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## Siwastaja (Aug 1, 2012)

Dennis said:


> I hope your original motor was not concentric wound, which would make it a pain in the rear. I like lap wound 3-phase motors, but machines can make concentric wound coils easily vs. lap wound coils. So if your motor is below 50 HP then you most likely had an original concentric wound stator before you modified it. My little black book on rewinding motors does not have the information on how to convert a concentric wound stator to a lap wound stator.


Why would this be any more difficult than just making the coils identical (practically, like the middle one)? Refer to the picture; over 5 minutes in MS Paint:











All this multilayer stuff is making my head spin. Why it is done . Neither of these motors did have anything special, they were just like the first textbook example with single layer windings with equal number of turns in every slot.

Everything looks _too_ simple to me now. Given all the information, it seems I am probably missing something crucial.

Some sources claim double layer windings can achieve better efficiency, some say it doesn't matter. For example:
http://pe.org.pl/articles/2011/3/16.pdf table 4; efficiency is the same, but single layer has better PF. EDIT: the fractional multilayer
has practically the same efficiency as integer single-layer but with a bit less copper; so I would guess that the core losses might go down a little bit but I2R losses a bit up due to layer insulation in slots leading to less space for copper.


Or:
http://engineering2.dartmouth.edu/inductor/papers/isie2006a.pdf
_
"a well designed multi-layer winding with a sufficient
number of layers can have lower losses than a single-layer
winding. This does not mean that any random multi-layer design
is superior it only holds if the winding is properly designed,
taking into account all harmonics and optimizing the number of
layers and/or the layer thickness."_


The newer of the two motors is manufactured in 2004 in Germany by VEM. It is very difficult to believe this would have any kind of severe compromise w.r.t. efficiency.

Luckily, these motors had simple single-layer windings so I don't have to care about this at all .


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## Ivansgarage (Sep 3, 2011)

This is what i am talking about the inhand turns, this is a ev motor
that is able to handle the amps 500+ delta connection. This pic
is the six leads tyed together delta, see the size of the leads?


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## Siwastaja (Aug 1, 2012)

Yeah, indeed huge leads.

But AFAIK, there shouldn't be any inherent mechanism why lower voltage would be so much more demanding? If the same total copper weight is used, the lower turn count allows more and/or thicker wires to be used. I^2R losses go up in the square of I, but OTOH, the resistance of a wire goes down in the square of the diameter.

Original motor used 3 x 0.80 mm(dia) = 3 x 0.50 mm^2 = 1.50 mm^2.
We hope to fit maybe 12 x 1.18 mm(dia) = 12 x 1.09 mm^2 = 13.1 mm^2,
hence 8.72x increase in area, allowing sqrt(8.72) = 3x increase in current, right? Well this is not quite 5x . Let's hope for the best.


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## PStechPaul (May 1, 2012)

Also consider the skin effect when you are using thicker wire as well as higher frequencies. It is not very significant at 60 Hz but it will be more so at 180 Hz and higher, and PWM waveforms may make it very important. There is a component of AC resistance as well as impedance due to reactance. You may need a good LCR meter or impedance bridge or motor winding analyzer to see just what effect this may have, but in general it's better to use multiple parallel strands of much smaller gauge. You do lose some copper due to the additional thicknesses of insulation, however. I did not realize all the factors when I did my rewinding job, but it was only a learning exercise.


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## Siwastaja (Aug 1, 2012)




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## leong (Aug 22, 2012)

when i was in school my professor did some research... there are other papers on ieee just search "re-rated induction machine" otherwise here is a pdf available from the internet.

http://www.electro-tech-online.com/custompdfs/2010/04/IEMDC202003202.pdf

hth
Leong




Siwastaja said:


> Hi,
> 
> we are ready to do a test rewind for an industrial AC induction motor. We have a motor, an aluminum frame 7.5 kW nominal 4-pole 50 Hz motor that weighed 50 kg.
> 
> ...


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## PStechPaul (May 1, 2012)

leong said:


> when i was in school my professor did some research... there are other papers on ieee just search "re-rated induction machine" otherwise here is a pdf available from the internet.
> 
> http://www.electro-tech-online.com/custompdfs/2010/04/IEMDC202003202.pdf
> 
> ...


That is a very interesting and important paper! It bears out my long-held assertion that AC induction motors can be re-rated to much higher power by overclocking, and this paper shows a 10 HP motor with an effective traction rating of 90 HP! Reading more closely, it seems the actual continuous power has been boosted "only" by a factor of about 3, and the additional boost is by means of 3x torque overload, which is more severely limited to short bursts because of I^2R losses.

Even higher boosting of power might be attained by using thinner and higher quality steel laminations. This may be more easily done for the stator than the rotor, but both should be done for maximum efficiency and power/weight ratio. 

I think it is also worthwhile to pursue the switched reluctance motor, which eliminates the windings on the rotor and increases the maximum speed. I've done some work on this but my experiments were somewhat flawed and I don't have time right now to continue. What I did looked promising, and there are other examples on youtube, but they seem to be either small experimental demos or large commercial motors recently introduced by Siemens and ABB but with little detail as to the construction and drive electronics. From my work so far it seems that I may need a six-legged H-bridge for a full three-phase two-pole stator (six pole pieces), and the rotor may be either 2-pole or 4-pole or more.


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## Ivansgarage (Sep 3, 2011)

Siwastaja said:


> Yeah, indeed huge leads.
> 
> But AFAIK, there shouldn't be any inherent mechanism why lower voltage would be so much more demanding? If the same total copper weight is used, the lower turn count allows more and/or thicker wires to be used. I^2R losses go up in the square of I, but OTOH, the resistance of a wire goes down in the square of the diameter.
> 
> ...


Am I missing something? Don't most controllers put out 100s of amps? Doesnt it take a 100 or so amps
to cruise down the freeway? So how is your 3 17 gauge wires going to handle a 100 or so amps..

So what size wire are you using, it would sure help if you would use circular mils, so what you are saying you will have 3 or 4 wires in hand?
with multi turns. Looks like you are using a 17 gauge wire? Wrong, That will never handle the amps. Smoke....

Would you take a 100 hp motor and run 3 12 gauge leeds out. I dont think so...

I really thought the picture would convince you.


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## Ivansgarage (Sep 3, 2011)

While i am on the subject, your winding machine looks real nice, but(we new that was coming) does not do any good if you wind this right..

Using ALL wires in hand the motor needs to be hand layed, all 4 poles
continuous because the pole connections would be to BIG How many
wires in each coil times two?


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## PStechPaul (May 1, 2012)

It takes about 18kW to maintain reasonable speed on the highway, assuming 300Wh per mile and 60 MPH. At 240 VAC three phase that's about 43 amps per phase. #17 AWG with 90C insulation is good for about 16 amps. So three conductors should be OK.
http://www.armstrongssupply.com/wire_chart.htm

I could not find a good motor winding wire size chart.


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## Dennis (Feb 25, 2008)

PStechPaul said:


> That is a very interesting and important paper! It bears out my long-held assertion that AC induction motors can be re-rated to much higher power by overclocking, and this paper shows a 10 HP motor with an effective traction rating of 90 HP! Reading more closely, it seems the actual continuous power has been boosted "only" by a factor of about 3, and the additional boost is by means of 3x torque overload, which is more severely limited to short bursts because of I^2R losses.



This is actually common. Of course it's possible to take a 60 HZ AC motor and run at at say 180 HZ with proper increase in voltage to obtain a new base speed. The power increase comes from speed though. The torque values will not be higher. In fact, those silly overpriced AC kits you see are nothing more than glorified, 60 HZ, Lesson 3-phase motors that have been wound with fewer turns plus multiple parallel strands of wire for low voltage operation at a higher base speed frequency operation.

In my example above in the second sentence, the 60 Hz motor could simply have some turns removed to keep the voltage level the same as it was at 60 HZ, but allow a new frequency operation at 180 Hz. So you get the full torque benefit and higher speed which means more power. So there you go.


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## Siwastaja (Aug 1, 2012)

Ivansgarage said:


> Am I missing something? Don't most controllers put out 100s of amps? Doesnt it take a 100 or so amps
> to cruise down the freeway? So how is your 3 17 gauge wires going to handle a 100 or so amps..


So let's get down to basics... Cruising down the freeway doesn't take any "amps". It takes watts.

Please start by reading:
http://www.diyelectriccar.com/forums/showthread.php?t=6535
http://www.diyelectriccar.com/forums/showthread.php?t=11708

So you have to get this:
P = U*I

You can have a lot of power by having either a lot of current or a lot of voltage. For non-technical (availability) reasons, hobbyist EV converters prefer high current low voltage systems. OEMs prefer high voltage low current system; they have a bit better efficiency, a bit smaller controller and easier wiring. Going too high in voltage would become difficult again. Somewhere around 300VDC there is a "sweet spot" for a normal sized car. For a microcar, 100V maybe. For a large truck, 1000V maybe.

(This is not to say it's wrong to do a 100V 500A system. It is just suboptimal, but still very good compared to any internal combustion engine . Just remember _we_ are not doing such a system here.)

Some DC motors may have design problems with brushes if the voltage is designed too high. With an AC motor, there is no such limit (insulation limit is nearer to 1000V mark and easy to increase). Hence, any sensibly designed AC motor (meant for a normal car) won't be used from a 100V battery pack. It would just be plain stupid to use voltage that low for no reason. Microcar maybe.

I'm after absolute maximum (continuous) of 3x original power (7.5 kW) at 320V battery voltage. This is 22.5 kW. At 320VDC, this is 70A, from the battery. The line-to-line amperage to the motor is lower because there are 3 wires (phases) to share the current, not just two. So we are speaking about 50A average current per lead. This is for max continuous power.

Can 12 (not 3!) parallel 1.18 mm(dia) (or AWG 17), with total area of 13.1 mm^2 support 50A? Yes, very well. They have quite a bit of mass to support short overcurrent peaks, too. The insulation varnish is good up to 200 deg C.

Simply put; trading turns in windings for thicker wire (and/or more parallel strands to reduce skin effect) is trading voltage for current. In theoretical optimum case, the performance is not altered, but as stated before, lower voltage systems tend to be a _bit_ less efficient in practice, but even this is not a general rule.



> Using ALL wires in hand the motor needs to be hand layed, all 4 poles
> continuous because the pole connections would be to BIG How many
> wires in each coil times two?


I have absolutely no problem soldering 24 1.18mm wires together. It will be quite a big "blob" but nothing impossible there. Actually, I will probably bring all 12 winding ends accessible so that the motor can be wired for four different voltages. This needs some heavy duty connections, but nothing special.


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## aeroscott (Jan 5, 2008)

good find , I would think this would apply to switched reluctance motors as well .


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## mizlplix (May 1, 2011)

Sorry, but I just could not resist replying.



> But AFAIK, there shouldn't be any inherent mechanism why lower voltage would be so much more demanding?


It is called the "free lunch" principal. There is no such thing as a "free lunch".

You might be a little young to have seen this, but:

In 1952, Ford was in the middle of changing over from a 6volt DC electrical system to a newer 12Volt DC system. 

The 6volt wiring was of Huge gauge and so it handled the 12volt change over well. 

The bulbs were changed to 12VDC as was the generator and starter.

The first thing you noticed when the two starters were side by side on the bench, was the huge gauge windings on the 6VDC starter. The 12VDC unit was much smaller...almost exactly half as large, with twice the windings.

12 volts-1/2 wire size-twice the windings= same work performed.
6Volts-double the wire size-half the windings= same work performed.

There is a close relationship between voltage and amperage (current).

Lower voltage requires a larger amperage/current to get the same work as a higher voltage. Thus needing larger conductors to handle the increased current.

http://www.allaboutcircuits.com/vol_1/chpt_2/1.html
http://www.sengpielaudio.com/calculator-ohm.htm
http://jersey.uoregon.edu/vlab/Voltage/
http://www.the12volt.com/ohm/ohmslaw.asp

A lot of reading, I know, but worth it, Miz


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## Siwastaja (Aug 1, 2012)

If I try once again;

In A MOTOR, there is a specific amount of SPACE for windings IN THE SLOTS. They are filled with COPPER WIRE. For lower voltage design, there are FEWER TURNS and hence thicker wire and/or more wires can be fitted to the same slot space, for MORE CURRENT. Hence, there is no direct relationship between motor voltage and efficiency or power; instead, these are "minor" optimization things. So in practice, you can decide whether you design a low-voltage high-current motor or a high-voltage low-current motor; within certain practical limits, with a certain sweet spot.

A very good example would be a series wound DC motor using as low voltages as 100V to produce power as high as 50 kW. It is only slightly suboptimal compared to a higher-voltage system, but doable, and many DIY conversions use these. Let me say again that WE are going for a MID-VOLTAGE system, so actually from an EV viewpoint, the current-voltage-power ratio should be quite well balanced near the sweet spot.

This has _nothing_ to do with free lunch. It is just about paying your lunch in U.S. dollars -- you need a few of them -- or in yen -- you need a _lot_ of them, but both have the same value; you can get a lunch for $20 or 2000 yen, and you can get 10 kilowatts with 100V and 100A, or 300V and 33A, or 1000V and 10A.

As I stated above, generally a higher voltage is somewhat better.


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## few2many (Jun 23, 2009)

Wow, I'm not an EE, and I don't rewind ac motors, but I am learning all I can. So is everyone here. This thread is the path I want to take if/when I can start an EV project. Thanks for the info!
I am, however, an accomplished Internet Troll.
That, and its Saturday morn, and I'm bored.


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## Ivansgarage (Sep 3, 2011)

PStechPaul said:


> It takes about 18kW to maintain reasonable speed on the highway, assuming 300Wh per mile and 60 MPH. At 240 VAC three phase that's about 43 amps per phase. #17 AWG with 90C insulation is good for about 16 amps. So three conductors should be OK.
> http://www.armstrongssupply.com/wire_chart.htm
> 
> I could not find a good motor winding wire size chart.


 
Mag wire data 

http://www.coilwinder.com/Magnet%20wire%20data.htm

So 43 amps is the max ever? come on, we no better PS

What is the max amps the controller puts out. Can't believe you guys.
I give up..


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## few2many (Jun 23, 2009)

Looks more like he is considering Cruising volts/amps, not max. Huge difference.


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## PStechPaul (May 1, 2012)

few2many said:


> Looks more like he is considering Cruising volts/amps, not max. Huge difference.


Yes, of course. Most of the time, for normal driving (not drag racing or hill climbing) an average size commuter/family type EV will use an average of about 200-350 Wh per mile. I just used a nominal value and 60 MPH for a ballpark estimate. Actually, using my *EVcalculator*, a 1000 kg vehicle at 100 km/h requires only about 5.5 kW to maintain speed on a level road, and about 19 kW for a 5% grade or accelerating at 0.05 G (1 MPH/sec) at that speed. 15 kW will also provide acceleration of 2 m/s/s at an average speed of 25 km/h, but we are considering a motor and controller that can provide about 3x torque (current) for short bursts, so at 45 kW and average speed of 50 km/h you can accelerate at 3 m/s/s or 6.7 MPH/s which is 0-60 in under 10 seconds. 

Wire will withstand a 3x current overload for 10 seconds with no problem as long as it's allowed to cool for a few minutes. This is why circuit breakers and motor overloads have time delay curves, many of which allow 90 seconds at 3x current and do not trip instantaneously until 8x-15x rated current. 

The wire chart provided by coilwinder.com is helpful but what I'm looking for is the proper size for winding a motor based on current. I realize that this depends on the I^2R losses and the thermal characteristics of the motor and ambient temperature and cooling methods and many other factors, but surely there is a "rule of thumb" for ACIM stator windings based on current and insulation temperature class. The closest I could find was in these FAQs: http://www.mwswire.com/faqs.htm#mw6

*



Q: How do I calculate the amperage for a given round magnet wire?

Click to expand...

*


> A: The formula for current carrying capacity in amperes for copper magnet wire wound into a coil is: d2 x 4869.48 (d = diameter in inches). This formula is pretty conservative, and formulas from other sources based on straight lengths of solid or stranded conductors in ambient air may indicate greater current carrying capacity than this one.


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## aeroscott (Jan 5, 2008)

mizlplix said:


> Sorry, but I just could not resist replying.
> 
> 
> 
> ...


same is true for 12v to 24v , I can start a engine on a bad connection , week batteries and have higher motor efficiency . But in the case of higher rpm's with high number of turns the back emf goes beyond what our battery packs can do(counteract) . If we take that 6v starter added more gear reduction ( for higher starter speed ) and a motor controller . Say we have 24 v pack limit . we can get more speed at higher amps out of the 6v motor then the 12v motor. Some racing dc motors are lower voltage for the same reason ( packs >300v.)


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## Ivansgarage (Sep 3, 2011)

PStechPaul said:


> Wire will withstand a 3x current overload for 10 seconds with no problem as long as it's allowed to cool for a few minutes. This is why circuit breakers and motor overloads have time delay curves, many of which allow 90 seconds at 3x current and do not trip instantaneously until 8x-15x rated current.
> 
> The wire chart provided by coilwinder.com is helpful but what I'm looking for is the proper size for winding a motor based on current. I realize that this depends on the I^2R losses and the thermal characteristics of the motor and ambient temperature and cooling methods and many other factors, but surely there is a "rule of thumb" for ACIM stator windings based on current and insulation temperature class. The closest I could find was in these FAQs: http://www.mwswire.com/faqs.htm#mw6


*
Wouldn't 3 times the current be locked rotor amps? 90 seconds?
no fricken way.

Rule: 300 the lowest to 500 circular mils can handle ONE amp. Most motor
shops will use 500 to 700 circular mils per amp.

We are talking mag wire.........

3 #17 gauge wires = 6156 circular mils divide by 300 the absolute lowest, = 20.5 amps*


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## Dennis (Feb 25, 2008)

I don't know if this will help you, Siwastaja, but my little black book that is very informative has some information that might be of some use to you. I'll quote some passages from it.


*Changing Concentric windings to Lap Windings*

_The first method that we shall explain works best if all the coils in the concentric winding have the same number of turns. This method works with six-group consequent-pole windings and also with 12-group concentric windings that have one coil per slot. The following is a description of this method.

Example: A 36-slot, four pole concentric winding with 40 turns per coil: 40 turns / 1.9 = 21 turns per coil. Most lap-wound, three-phase motors are spanned at 80 percent of full span. The formula for this is (slots/poles) + 1*0.8= (36/4) + 1*.8 = 8. Thus, it is a 1 and 8 span. A four-pole lap winding has 12 groups. Coils per group = slots/groups, 0r 36/12 = 3 coils per group. The data for the new lap winding are 21 turns per coil, span 1-8, 12 groups of three coils. The wire size and connection remain the same. _

_When the coils do not have the same number of turns, the best method to convert concentric to lap is to find the number of effective turns of the concentric winding and then to design a lap winding with the same number of effective turns. To find the number of effective turns, the chord factor must be used. Chord factor tables do not always have enough data for all situations. The following explanation will enable the repairman to understand how these data have been obtained._

_*Chord Factor*

The chord factor is a multiplier used to find the number of effective turns in a coil of wire. The components in determining chord factor are (1) the number of teeth in the stator, (2) the number of poles in the stator, and (3) the span or pitch of the coil, which will determine the number of teeth surrounded by the coil._ _

Each tooth in a stator represents a number of electrical degrees. The formula to determine the number of electrical degrees per tooth is _ _(180 degrees* poles) / number of teeth in the stator = degrees per tooth. The degrees per tooth encompassed by a coil are added to get the angle of the coil. The sine of 1/2 of this angle is the chord factor.

A coil with a small span will have a low chord factor and have fewer effective turns than will a coil with a full span. A coil that is over a full span, for example, a 1-11 span (four-pole, 36 slot stator) will have the same chord factor as will a coil with a 1-9 span. Concentric windings will often be over full span._ _

The following shows how to convert to a lap winding with a concentric-wound, four-pole, 36-slot motor with a different number of turns in each coil. The original winding data are converted to effective turns._ 

```
[B]Span[/B]    [B]Turns[/B]        [B]Chord factor[/B]           [B] Effective turns[/B]
1-9        50      *      .984               =     49.2
1-7        32      *      .866               =     27.7
1-5        12      *      .642               =      7.7
                                                         ____
                                                          [B]84.6 Total effective turns per group[/B]
```
_The next step is to determine the number of coils per group for the lap winding: slots/groups = 36 slots /12 groups = 3 coils per group. A 1-8 span will be used as in the previous example, using the formula (slots/poles) + 1*0.8 = span. The chord factor for a 1-8 span is 0.939. The effective turns of one group from the old winding are 84.6 turns. The number of new winding 84.6/0.939 = 90 turns per group in the new winding, span 1-8. The connection and wire size remain the same.


_*Electric Motor Repair 3rd. Edition*_*
Robert Rosenberg and August hand
ISBN 0-03-059584-3*
_


----------



## Ivansgarage (Sep 3, 2011)

Here is an other chart for wire size and amps.

It says #17 2052 circular mils is rated at 2.93 amps

These rating are at 700 circular mils per amp.

http://www.interfacebus.com/Copper_Wire_AWG_SIze.html


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## Dennis (Feb 25, 2008)

Siwastaja said:


> Hi,
> 
> 
> In any case, we'll probably limit ourselves at around 150 Hz, or 3x the original frequency.
> ...



I knew my little black book would come in handy. Here you go:


_*Rewinding for a change in voltage
*
If a 220 volt motor is to be rewound to operate on 440 volts, use twice as many turns on each coil and one-half the circular-mills area of wire. In other words, if 40 turns of NO. 17 wire were used on the original motor, 80 turns of NO. 20 should be used on the new motor

Some motors rated for 230 volts will not handle the load on 208 volts if loaded to the maximum. The turns must be reduced to the ratio of the voltage change. As an example, 230-volt motor has 40 turns: 230/208 = 1.1, 40 turns/1.1 = 36 turns. If there is enough room, the next larger wire size should be used. An easy way to determine whether there is enough room is to cut the required number of of lengths of wire of this size and fit then into the slot.

*Changes for New frequency*

There are two ways to convert these motors; one keeps the same horsepower for the new speed, and the other keeps the same torque for the new speed (more horsepower). For the same horsepower, use the following formula: old turns*Sqrt(old Hz / new Hz) = new turns. If you want the same torque then it is: old turns*old Hz/new Hz = new turns.
_ 
*Electric Motor Repair, 3rd. ed.
Robert Rosenberg and August Hand
ISBN 0-03-059584-3*


----------



## mizlplix (May 1, 2011)

So, How does your motor run, Ivan?

Oh, I forgot, You dont have any batteries....

If you would work more and stay off the forums, you could afford batteries.

And Yes. My transmission will be in and running before your motor does. 

(Just saying "Hello") Miz


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## Ivansgarage (Sep 3, 2011)

mizlplix said:


> So, How does your motor run, Ivan?
> 
> Oh, I forgot, You dont have any batteries....
> 
> ...


Ya, Real funny Miz, did you think that up your self? or did your wife help you out?

You got that tranny done?


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## PStechPaul (May 1, 2012)

Ivansgarage said:


> Here is an other chart for wire size and amps.
> 
> It says #17 2052 circular mils is rated at 2.93 amps
> 
> ...


NEC ratings (which are very conservative) allow 15 amps for #14 and 20 amps for #12. That wire chart shows 5.87 and 9.33. I have an *ampacity chart* in Excel which uses several ways of calculating ampacity. For wires in free air, the capacity is related to power and surface area, while for bundles it is more related to volume and thus there is a linear relationship between current and cross sectional area. In a motor or transformer, much depends on the thermal resistance from the hottest spot in a bundle to the mass of the motor, and its thermal resistance to the air. 

Here is a time-current curve for a GE MCCB, which shows a trip time of 15-80 seconds at 3x rating. Of course this is not a motor overload.
http://www.geindustrial.com/publibrary/checkout/GES-6108?TNR=Time Current Curves|GES-6108|generic

You can see various motor overload curves here:
http://static.schneider-electric.us...Melting Alloy Overload Relays/30068-index.pdf

But here's a screenshot of one that shows a 90 second delay at 300%:


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## Ivansgarage (Sep 3, 2011)

PstechPaul

This is just to much detail and bs over the in hand turns to supply 
this motor, or any motor for ev use. 

You can post and quote all the engineering and motor data you want, but most of it does not apply to ev motors.

The hard truth is, there is no data on winding an ev motor. 
The few people that have figured it out, (Baldor Hpev) mostly 
through, trial and error will not cut lose with there findings. 
I have spent the last four months picking up bits and pieces. 

I have read most of your post and thought you were quit knowledgeable 
on ev controllers and motors, I am a little surprised that you seem to think that 3 #17s would be adequate, for the supply leads, This is the kind of 
misinformation why nobody has ever used or rewound a 3 phase off 
the self motor for an ev. 

How about the coil layout and voltage?
How about the back iron, over saturation?
I say that motor stator he wants to use is a no-no. Not enough back iron.


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## mizlplix (May 1, 2011)

I am far from a motor guru, but in my world, if the wires you have going into the motor will not handle the controller's full output, you are in trouble.

(I Reference to the pic in post # 10 on the first page of this thread, all strands are brought out).

With regards to back-iron, I understandl that your back iron will control the ultimate frequency your motor will run (Top RPM) before saturation happens.

The motor in the pic #10 had a freq. limit of 266 even though the controller was capable of 300 cycles.

Question for everyone: Is there a down side to too much back iron?
(Other than motor weight)

Although I do not build controllers or rewind motors like some of you do, I find this an interesting subject.

Miz


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## aeroscott (Jan 5, 2008)

About 4 or 5 years ago Tesla showed up at the annual ev meet in Palo Alto . I was talking with there motor guy and he said the stator held no secrets , so it was jobbed out to a subcontractor . The rotor on the other hand was where all the secret development was going on . He indicated that as soon as they put it on the market the competition would have it. And they would keep coming up with more developments in the rotor. My Prius main motor looks like a little heavier then 6awg , also no potting resin used (better cooling?) just got called into work unloading 120' wind gen blades from ship.


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## Ivansgarage (Sep 3, 2011)

aeroscott said:


> About 4 or 5 years ago Tesla showed up at the annual ev meet in Palo Alto . I was talking with there motor guy and he said the stator held no secrets , so it was jobbed out to a subcontractor . The rotor on the other hand was where all the secret development was going on . He indicated that as soon as they put it on the market the competition would have it. And they would keep coming up with more developments in the rotor. My Prius main motor looks like a little heavier then 6awg , also no potting resin used (better cooling?) just got called into work unloading 120' wind gen blades from ship.


We are talking ac induction motors, The Prius is a synchronous permanent-magnet AC motor. Big diffrence..


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## aeroscott (Jan 5, 2008)

I don't see the big difference when we are taking about stators .Except the Prius my layout coils a little different .


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## Ivansgarage (Sep 3, 2011)

aeroscott said:


> I don't see the big difference when we are taking about stators .Except the Prius my layout coils a little different .


Well I have to agree with you, there is no difference in any motor. There all round on the inside. You just plug it in, and it turns. Hopefully.


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## PStechPaul (May 1, 2012)

Since we were talking about wire size and current capacity, I ran some tests. 

See my thread at:
http://www.diyelectriccar.com/forums/showthread.php?p=318081#post318081


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## aeroscott (Jan 5, 2008)

mizlplix said:


> I am far from a motor guru, but in my world, if the wires you have going into the motor will not handle the controller's full output, you are in trouble.
> 
> (I Reference to the pic in post # 10 on the first page of this thread, all strands are brought out).
> 
> ...


 I was thinking about back iron thing . As you increase frequency iron needs to be reduced or induction heating will dominate the losses . Switched reluctance have much less iron over the ac induction motors , much less heating . Also square wave means less frequency(10x) then the stepped sine wave of ac induction .


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> nobody has ever used or rewound a 3 phase off
> the self motor for an ev.


Well that's a sweeping statement... We use a rewound aluminium frame liquid cooled 4-pole motor in our SAE car. Motor is wound for about 75kW peak and weights about 60kg using a custom winding.

Plus there's plenty of Aussie's that use rewound industrial motors in their EVs


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## Stiive (Nov 22, 2008)

Here's a picture of the *old*,removed windings from the motor.
This motor is designed/built as an EV motor.


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## Ivansgarage (Sep 3, 2011)

Stiive I thought maybe that would drag somebody out of the woodwork.

How about picks of the new wind, Motor. We have all seen old windings.

What is the new wind? HP, turns, inhand, circular mils, poles, span.


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> Stiive
> 
> How about picks of the new wind, Motor.
> What is the new wind? HP, turns, inhand, circular mils, poles, span.



It's round on the inside.


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## aeroscott (Jan 5, 2008)

PStechPaul said:


> Since we were talking about wire size and current capacity, I ran some tests.
> 
> See my thread at:
> http://www.diyelectriccar.com/forums/showthread.php?p=318081#post318081


 Nice test , I would like to do that test but adding gas cooling specifically He and H . H is used by the big utility generators as a coolant .


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## Ivansgarage (Sep 3, 2011)

Stiive said:


> It's round on the inside.


Does that mean, you don't have one or just not willing to help anyone.


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> Does that mean, you don't have one or just not willing to help anyone.


Just quoting you 

Here is pics of the motor fitted with new windings. Without reading the whole thread, basically what are you after?


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## Ivansgarage (Sep 3, 2011)

Stiive

Well you really need to read the whole thread.
I tryed to explaine that the inhand turns need to be able to
handle the controller max amps, then the whole thread rum amuck.


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## mizlplix (May 1, 2011)

Your picture speaks loads to me. Thank you for posting it. Now lets see if anyone besides me and Ivan know what they are looking at.



Miz


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> Stiive
> 
> Well you really need to read the whole thread.
> I tryed to explaine that the inhand turns need to be able to
> handle the controller max amps, then the whole thread rum amuck.


Well, we use 1.9mm wire, 5 in hand.
The wire is oversized as this is for racing application. Using water cooling, is very hard to get this motor to run even warm, even when pushing 300A RMS cont. We have run on the dyno before with no cooling, and the motor still stays within temp limit.

When my controller is finished, I hope to push the motor further and really test these new windings.


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## Stiive (Nov 22, 2008)

mizlplix said:


> Your picture speaks loads to me. Thank you for posting it. Now lets see if anyone besides me and Ivan know what they are looking at.
> 
> Miz



No worries.


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## PStechPaul (May 1, 2012)

I think the bottom line information is a typical wire size for a paricular continuous current rating of an ACIM. It may be a bit different for an EV motor, but basically the determining factor is the allowable temperature rise for the hottest spot in the windings. The overload capability is based on duty cycle and the maximum ON time is based on thermal characteristics, including mass, thermal resistance, and cooling methods. I'm sure these vary considerably depending on motor size and other issues, but I just don't believe some of the high CM/A figures. My *wire gauge calculator* is based on 0.0037 A/sqmil, or 0.0047 A/CM, or 211 CM/A. This is confirmed by: http://www.mwswire.com/faqs.htm#mw6, and the following shows a good range from wire used for chassis wiring to that used for power transmission: http://www.powerstream.com/Wire_Size.htm


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## PStechPaul (May 1, 2012)

Stiive said:


> Well, we use 1.9mm wire, 5 in hand.
> The wire is oversized as this is for racing application. Using water cooling, is very hard to get this motor to run even warm, even when pushing 300A RMS cont. We have run on the dyno before with no cooling, and the motor still stays within temp limit.
> 
> When my controller is finished, I hope to push the motor further and really test these new windings.


OK, 1.5 mm wire is about #13 AWG, which is rated at 15 amps. I will assume that "5 in hand" means in parallel so that makes it 75 amps, conservatively rated. That would be a continuous rating of about 52kW at 400 volts, three phase. Seems just about right to me.

BTW, found this possibly useful resource on motor winding (from 1920!):
http://archive.org/stream/armaturewindingm00brayrich/armaturewindingm00brayrich_djvu.txt


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## Stiive (Nov 22, 2008)

PStechPaul said:


> That would be a continuous rating of about 52kW at 400 volts, three phase.


Continuous rating is mainly governed by how well you can keep it cool. Better cooling methods = higher continuous rating. Wire thickness is only part of the equation.



PStechPaul said:


> Seems just about right to me.


It is right... It's been working for a year and a bit now


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## Siwastaja (Aug 1, 2012)

I think Ivan accidentally misread numbers given by me and that got the thread sidetracked. At least once he was referring that 3 inhand wires of my 1.18 mm dia (17AWG) wire would not be enough for my case, but the real number given by me was 12 wires, not 3. This makes quite a difference...

The mystical "3 inhand wires" was the ORIGINAL winding. It also used 0.8 mm dia (20AWG) wire.

Please, I would appreciate a lot if you tried to read just a little bit more carefully, if possible. I tried to correct this misreading once, but you probably missed that, too.

Also, in our case, the voltage is around 300V and amperage around 50A - naturally some higher peaks, but they won't last long. This is not a huge conversion or a performance racer.

Please also note that post 14 by Leong shows a reference to a scientific study where they apparently did exactly what is discussed here and actually used it in an EV. Of course it can be bogus. Anything can be. But it makes sense and at least I have no logical reason for denying it, at least yet.

Tomorrow we'll pick up the wire and varnish and are set to go.

Dennis, a big thank you for digging up all that info! This confirms exactly what I was thinking about.


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## few2many (Jun 23, 2009)

Noob question of the day, what are you referring to when you say "in hand"? Is that the number of wires in a coil, or coil set, or whole phase?


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## Ivansgarage (Sep 3, 2011)

few2many said:


> Noob question of the day, what are you referring to when you say "in hand"? Is that the number of wires in a coil, or coil set, or whole phase?


InHand means if you had 10 wires in coil and you had 5 inhand it would
take 2 turns to make up the 10 wire coil. 2 inhand it would take 5 turns to make the coil.


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## few2many (Jun 23, 2009)

Would that be 2 parallel 5's to get 10, or series 5's? Or am I still way off?


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## Siwastaja (Aug 1, 2012)

I don't know the terminology either, but I got the impression that this "in hand" thing means just paralleling wires for more cross-sectional area and current, because there are both physical and electrical limits how thick your wires can be; it would get hard to wind and bend them, and skin effect would affect the motor on higher frequencies. Otherwise, it's theoretically identical to using one thick wire, and the turn count is what counts .

Speaking of the which; now as we got the wire and tested it, we can fit only 7 or 8 parallel strands, not 12 we were dreaming about. But the slot fill is quite good. So as for our calculation, we won't probably be able to run 3 x nominal (3 x 7.5 kW = 22.5 kW) continuously, or at least it would need special considerations in cooling. We would still be happy to have 15 kW at 100 Hz cont. and around 20-25 kW peak for < 10 seconds. But we'll see.

Today we checked out one local rewinding shop -- they seemed to be pretty specialized for voltage, power and frequency modifications, too. They had done many jobs like increasing power 3x, and apparently they were also making their own motors, at least assembling stator laminations. 

He was pretty clear that our aim of going 3x power at 150 Hz should not have any imminent problems, it is just about cooling. He was so excited about our project that we got some insulation materials for free. He had also some realistic opinions on this EV thing, and we were talking about different configurations. It's nice to see that not all rewinding shops are just copying original designs. It _might_ be that at the Finnish tax etc. levels, it is always cheaper to buy a new motor than repair one, and hence the few rewind shops specialize in modifications.


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## Ivansgarage (Sep 3, 2011)

few2many said:


> Would that be 2 parallel 5's to get 10, or series 5's? Or am I still way off?


Inhand is just what it says, in your hand..

2 inhand
If you were to have two rolls of wire and rapped them around something
5 times, you would end up with 10 wires, with two wires out each end.


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## few2many (Jun 23, 2009)

Thats what I'm asking about, the two wires out each end. I know it depends on volts/amps, but would you be connecting the wires parallel for less volts/more amps, or series for more volts/less amps?


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## Ivansgarage (Sep 3, 2011)

few2many said:


> Thats what I'm asking about, the two wires out each end. I know it depends on volts/amps, but would you be connecting the wires parallel for less volts/more amps, or series for more volts/less amps?


The in hand turns are allways connect together 2 wires or 10 wires.
Makes no difference. The more inhand turns the more current you can
feed the motor.

Total turns (wires in slot) and size of wire (circular mils) determines the voltage.


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## PStechPaul (May 1, 2012)

Siwastaja said:


> Speaking of the which; now as we got the wire and tested it, we can fit only 7 or 8 parallel strands, not 12 we were dreaming about. But the slot fill is quite good. So as for our calculation, we won't probably be able to run 3 x nominal (3 x 7.5 kW = 22.5 kW) continuously, or at least it would need special considerations in cooling. We would still be happy to have 15 kW at 100 Hz cont. and around 20-25 kW peak for < 10 seconds. But we'll see.


So if you have 7 parallel strands of #17 AWG you should be able carry 6*7=42 amps per phase. At 240V that's 10kW per phase. So how do you figure you can only get 5kW? Unless you are only running 120V? As a WAG perhaps you have 240 ft of wire for each phase winding, and #17 is 5 milliohms per foot, so the resistance is about 1.2 ohms. With 7 strands in parallel for each winding, the resistance is 170 mOhms, and at 42 amps that is 302 watts per phase. So 900 watts of resistive losses for a 30 kW motor is 97% efficiency. At your 7.5 kW/phase rating at 240V that's 31 amps per phase and 170 mOhms, that's just 163 watts per phase or under 500 watts total, so almost 98% efficiency. 

As a point of reference, I measured my 1.5HP 4 pole 240 VAC motor and the windings appear to be about 5 ohms. Rated current is 4.8 amps. So resistive losses would be about 115 watts/phase or 345 watts total for a 1.12 kW machine, or just under 70% efficiency. That is actually fairly typical for a motor that size. Actually its VA rating is 1995, which indicates a 56% PF. The motor appears to have an inductance of about 80 mH or an inductive reactance of about 30 ohms at 60 Hz but that would just indicate a PF of 16% at no load, which also seems reasonable.

Please explain how these measurements and estimates apply to the calculations on the custom motor in question, or to EV motors in general.


----------



## Siwastaja (Aug 1, 2012)

PStechPaul said:


> So if you have 7 parallel strands of #17 AWG you should be able carry 6*7=42 amps per phase. At 240V that's 10kW per phase. So how do you figure you can only get 5kW?


By applying a safety margin, due to the fact that the cooling is hard to get perfect. In extreme theoretical case, if the wire is located in a perfect thermal insulator, it can carry 0 amps continuous . The reality is somewhere between the "open air" test and zero. I just don't want to get my hopes _too_ high.

I think it's easiest to approximate from the original motor, but you would need to know how hot the windings ran at the rated power. If they ran hot then, and if the slots were quite well filled with copper, the only thing you can do to increase power is to increase cooling. OTOH, if the original windings were running cool before, there might be extra power reserve in the motor design even with the same amount of copper and cooling as before. Stator I^2R losses limiting the max power should come down simply to slot area, slot fill ratio and cooling. 

This motor had about 80% of the usable slot space filled, so we could add some extra copper. We will also drill holes to the motor ends and blow air (through a filter) in the air gap between stator and rotor. This kind of open cooling structure is typically used in many DC motors and some small-sized AC motors. More power in smaller size just requires extra cooling, even if the efficiency wouldn't drop at all in the power-up, and the thermal transfer through the iron to the outer shell is limited.

Thanks for the calculation. 97-98% efficiency calculated from stator I^2R losses only sounds about right, as they typically take up something around 30-50% of the losses IMO IIRC. That would be around a typical 90-93% total efficiency, _if_ the iron works well to the frequencies used.


----------



## Coulomb (Apr 22, 2009)

few2many said:


> what are you referring to when you say "in hand"?


I was going to say "in hand" = "in parallel". But that contradicts the post above.

My understanding is that it is "in parallel". So if you need 10 turns, then with 5 in hand you'll end up with 50 pieces of wire in the slots, but five of them are acting as one wire, contributing only one turn each. To get the 10 "amp turns", you need either one thick wire with 10 amps, or 5 thinner wires with 2 A each ("5 in hand"), to make those amp-turns.


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## PStechPaul (May 1, 2012)

I think the standard 211 CM/A formula will be fine for your calculations. Consider that it is used by the NEC to determine ampacity of wiring with 65-90C rated PVC insulation routed in walls which may be packed with insulation, and it is very conservative. I have heard that I^2R losses in motors is by far the major factor, probably 2-3x that of iron losses at 50/60 Hz. Running at 180 Hz tends to make them about equal contributors. 

It might be a good idea to wind thermal switches or sensors such as thermistors in with the windings. You can also measure the resistance of the windings and determine the temperature that way, although it's tricky to do so while the motor is running. However, you can run a separate small copper winding with the power windings and you can do so in such a way as to cancel out the AC component induced by the electromagnetics. Then you can run a small DC current through it and read the temperature by the resistance. Copper is a pretty good PTC sensor. 

There's probably a lot of space among the larger windings. In fact, you might be able to get a higher fill factor by adding several smaller windings in parallel with the larger ones. You might get 10% more copper in there and boost efficiency and power accordingly. If nothing else, it will better conduct heat than air and help transmit it to the iron laminations.

I wonder if it would help to inject thermally conductive silicone grease into the slots?


----------



## few2many (Jun 23, 2009)

On the stator slots, can they be opened up, machined or drilled? Then simply reseal or varnish them? Or are they set how they are, any change ruins the motor?


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## Ivansgarage (Sep 3, 2011)

few2many said:


> On the stator slots, can they be opened up, machined or drilled? Then simply reseal or varnish them? Or are they set how they are, any change ruins the motor?


Any change would ruin the motor. The best thing to do is select
the right motor stator. A 220v 3 phase motor will have a higher amp
rating to begin with, and more back-iron.


----------



## Coulomb (Apr 22, 2009)

PStechPaul, you're saying that 240V and 42 amps gives 10kW per phase, but either the current current (delta) or voltage (wye) will be split by a factor of sqrt(3), so that's 10*1.73=17.3 KVA, and with a power factor of typically 0.85, that's 14.7 kW.

Edit: so those efficiency numbers were optimistic by about 2x (copper losses will be about twice what you stated). There are also iron losses as well, and friction and windage.


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## Stiive (Nov 22, 2008)

Coulomb said:


> PStechPaul, you're saying that 240V and 42 amps gives 10kW per phase, but either the current current (delta) or voltage (wye) will be split by a factor of sqrt(3), so that's 10*1.73=17.3 KVA, and with a power factor of typically 0.85, that's 14.7 kW.
> 
> Edit: so those efficiency numbers were optimistic by about 2x (copper losses will be about twice what you stated). There are also iron losses as well, and friction and windage.


Stiive likes this post.


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> Any change would ruin the motor. The best thing to do is select
> the right motor stator. A 220v 3 phase motor will have a higher amp
> rating to begin with, and more back-iron.


More back-iron = harder to keep cool. Engineering is full of compromises.
You'll notice in our motor there's only about 20mm between the winding slots and the water jacket


----------



## Ivansgarage (Sep 3, 2011)

Stiive said:


> More back-iron = harder to keep cool. Engineering is full of compromises.
> You'll notice in our motor there's only about 20mm between the winding slots and the water jacket


Ya Stiive but most won't have water cooling.

Even my motor is 180000 flux at 200amp and 200 hz, max is 120000 but i got water.


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> Ya Stiive but most won't have water cooling.
> 
> Even my motor is 180000 flux at 200amp and 200 hz, max is 120000 but i got water.


I'd say water cooling is very very very desired in an EV motor. If you have to use an industrial style IM, i'd seriously look into adding a custom water jacket.
That's how they can get the EV motors so small and so light, show me an industrial 150kW induction motor that weights less than 80kg. 

PS, not talking to you directly here Ivan since you already have a water cooled motor.


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## Stiive (Nov 22, 2008)

Ivansgarage said:


> Even my motor is 180000 flux at 200amp and 200 hz


Also, maybe im missing something but i'm a bit confused by this 180,000 value. 
What is this? Wb? . A*turns? Or maybe a parameter particular to your controller?


----------



## Ivansgarage (Sep 3, 2011)

Stiive said:


> Also, maybe im missing something but i'm a bit confused by this 180,000 value.
> What is this? Wb? . A*turns? Or maybe a parameter particular to your controller?


These are flux densitys for my back iron. Over saturation.. = HEAT

tooth density is 193387, Max allowed is 120000
Back iron density is 163228, max allowed is 120000
Air gap density is 92285, max allowed is 55000.


----------



## Stiive (Nov 22, 2008)

Ivansgarage said:


> These are flux densitys for my back iron. Over saturation.. = HEAT
> 
> tooth density is 193387, Max allowed is 120000
> Back iron density is 163228, max allowed is 120000
> Air gap density is 92285, max allowed is 55000.



Ah I c. I thought you meant flux linkage. Makes sense now


----------



## major (Apr 4, 2008)

Ivansgarage said:


> These are flux densitys for my back iron. Over saturation.. = HEAT
> 
> tooth density is 193387, Max allowed is 120000
> Back iron density is 163228, max allowed is 120000
> Air gap density is 92285, max allowed is 55000.


Are these numbers in units of lines per square inch?


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## few2many (Jun 23, 2009)

I recall reading somewhere that the ac50 was 4 pole? I believe it was also wye. Would it be hard to imitate the ac50, since that is basically the target?


----------



## mizlplix (May 1, 2011)

Yah, 4 pole, But if I remember right it is Delta. (I could be wrong on that)

But it has a 7 1/2" long stator/rotor where most motors of that class have a standard 5" stator/rotor. 

It has a really beautiful CNC fan unit on the drive end which pulls axially through the stator/rotor air gap and the case bolt holes and discharges radially through the "C" face drive end cap. 

The rotor is also a twisted design. it is "helical" - and not straight. The rotor laminations are not afixed in a perfect row but twisted one pitch. I assume it was to reduce "Cogging" but I could be wrong. As I asserted before, I am at the student level in the motor theory subject.

All thoeries and speculations aside, the actual usable torque and RPM is amazing. It pulls a little lazy from 0 RPM to about 2000RPM.

@ 2000RPM to 6,500RPM it really shines. 
@ 6,500RPM to 8,000RPMs it gets lazy again, but entirelty useful. 
The last 500RPMs is reaching a bit and of no real use except for that last few MPH on the expressway. 

If you have geared and tired your vehicle correctly, you almost never use that RPM band anyways. At least I would not to run my Powerglide in low gear held in low at that RPM band continually. I would probably cap my continious RPM to 6,000RPM.

For what it is, it is amazingly flexable. It would be a GREAT direct-drive reverse trike motor.

Miz


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## Ivansgarage (Sep 3, 2011)

major said:


> Are these numbers in units of lines per square inch?


Yes Major Stator dimesions were all figured in inches.


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## major (Apr 4, 2008)

Ivansgarage said:


> Ivansgarage said:
> 
> 
> > tooth density is 193387
> ...


So 193387 lines per square inch converts to 3.0 Tesla. Typical steel B-H curves go up to about 2 T and there are mention of 2.2 T. But 3 T is way off the charts. 



Ref: http://en.wikipedia.org/wiki/Saturation_(magnetic)


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## Ivansgarage (Sep 3, 2011)

Major I no what you are saying, When I figured this is was maxed to
200+ amps continuous and 200Hz just wanted to see how bad it was.
I shoud not normaly be running those kind of numbers and I think the water cooling will take care of the rest. The general consenses is,
try it..


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## mizlplix (May 1, 2011)

Ivan, can I bring HotDogs just in case?

Miz


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## Ivansgarage (Sep 3, 2011)

mizlplix said:


> Ivan, can I bring HotDogs just in case?
> 
> Miz


HOT DOGS! You cheapo--- I was thinking more of the lines of STEAK

What happens when you over saturate the iron?
It could be a cataclysmic event an the entire universe could collapse into a monobloc. 

gee hope no body thinks im rude..


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## PStechPaul (May 1, 2012)

OK, here's what happens when iron saturates:
http://www.allaboutcircuits.com/vol_1/chpt_14/4.html

Basically it is a point of diminishing returns, where additional current (or field intensity H) does not produce an appreciable increase in flux density B. All of the extra power is simply wasted as heat, and may also cause degradation of the magnetic properties of the material (mostly for ferrite and permanent magnets), as well as insulation issues. 

The question is, then, why would someone want to oversaturate the iron in an electromagnetic machine?


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## Ivansgarage (Sep 3, 2011)

PStechPaul said:


> The question is, then, why would someone want to oversaturate the iron in an electromagnetic machine?


Why you ask? because we are all elcheapos and dont or wont spend 10-15 k for a siemens motor.. and this is called diyelectriccar..


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## Siwastaja (Aug 1, 2012)

We don't even want to spend 3-4 k for an EVE motor or professional rewinding......

So we DIY it, and pretend we do it just for the fun of doing it!

Anyways, already managed to insert 5 windings (10 slots). Almost two pole pairs! Only 26 slots to go!

It's really pain in the ass . But fun in its own way.

Our first test winding had sides way too long so we redid it smaller, but we might have reduced a bit too much, so now it's a long battle to be able to insert the windings next to each other. But with enough sweat, it seems possible, and of course all this fighting might result in 0.05 percentage point increase in the total efficiency so _totally_ worth it!

Note To Shelf^tm: next time buy thinner wire. Apparently, wire this thick is harder to work with and leaves more air in the windings. I kind of knew it, but thought 1.18mm would still be a good compromise. Take a look at this comparison:

Old winding: 0.8 mm(dia) 0.503 mm^2/wire 102 wires = 51.31 mm^2 -- a lot of space, expectations to add at least 20% more surface area.

New winding: 1.18 mm(dia) 1.094 mm^2/wire 49 wires = 53.61 mm^2 --
only 4.9% increase in surface area -- 9000% increase in pain.


But this is the very first time we are doing anything like this, and with manageable pain, it's succeeding! Had to call it a day anyway. I think we should feel quite happy, at least for now until it is failing.

Yeah. Winding your motor is fun. Really!


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## Ivansgarage (Sep 3, 2011)

Siwastaja said:


> We don't even want to spend 3-4 k for an EVE motor or professional rewinding......
> 
> So we DIY it, and pretend we do it just for the fun of doing it!
> 
> ...


How about some pictures, please.


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## Siwastaja (Aug 1, 2012)

OK, some pictures, showing the first winding being wound and inserted.










The hallway is good for cutting those 16 meter long wires from a single spool. You can see the 7 parallel "in hand" strands.










The first test winding.











Inserting the insulations that keep the wires in place.










Four slots filled... After the picture was taken, more windings were inserted and it's becoming very cramped there.


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## Ivansgarage (Sep 3, 2011)

Looks good keep it going.

You should be using scotch tape to hold the winding together it will
pull off easy. Taking a chance of nicking the wire with zipp ties.

Are you winding 2 pole.


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## Siwastaja (Aug 1, 2012)

4 pole, as you can see from the last picture .


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## alvin (Jul 26, 2008)

Those pics look nice,got any more? And is it 6 slots per pole? Another question, do other phase poles use those same slots?

Alvin


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## few2many (Jun 23, 2009)

Any more pics? Looking good!
http://www.youtube.com/watch?v=BvriKt-RCjw&feature=youtube_gdata_player


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## mizlplix (May 1, 2011)

Siwastaja:

Please update. I can not hold my breath much longer. 

Miz


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## Siwastaja (Aug 1, 2012)

Sorry for non-update. I had a flu but fortunately there are two of us working on this thing...

Having the first pole pair set fully inserted for all phases, it kind of proves it is possible. Still, it's PITA. Have to use thinner wire next time, really! So we have around 60% inserted as of now. We are working on it whenever we have nothing else to do.

We also have two simple proof-of-concept ACIM inverter designs, one on FPGA and one on Atmel AVR 8-bit MCU, both of which turn motors nicely.
Both share the same IGBT module power stage.


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## Ivansgarage (Sep 3, 2011)

Siwastaja said:


> Sorry for non-update. I had a flu but fortunately there are two of us working on this thing...
> 
> Having the first pole pair set fully inserted for all phases, it kind of proves it is possible. Still, it's PITA. Have to use thinner wire next time, really! So we have around 60% inserted as of now. We are working on it whenever we have nothing else to do.
> 
> ...


How about some more pictures, Please


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## tomofreno (Mar 3, 2009)

Siwastaja said:


> Sorry for non-update. I had a flu but fortunately there are two of us working on this thing...
> 
> Having the first pole pair set fully inserted for all phases, it kind of proves it is possible. Still, it's PITA. Have to use thinner wire next time, really! So we have around 60% inserted as of now. We are working on it whenever we have nothing else to do.
> 
> ...


 What IGBTs are you using, and what are their voltage and frequency limits? Thanks for the photos. Very interesting project.


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## Siwastaja (Aug 1, 2012)

Some old IGBTs laying around... 100A 1200V? Driver is ACNW3130.

Physical DC bus design is very temporary and snubbers are missing, but it seems to work, at least at lower currents.










Almost there. One phase left.


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## jdsanderson (Sep 26, 2012)

Wow I just simply put my wire back in the motor as close to how it came out as I could, only I did two in hand instead of one in hand so that it would run on 110 or 220 instead of 220 or 480. After playing around I found that it would be better to run on 220. I used manilla folder to line the irons. A vendor from a motor shop gave me the material to put over the wires and hold the wire and paper in the slots. The only thing that was odd is that I had to shim my end bells so that the clutch did not push it of mag center.

I had my doubts about my little two pole hunk of junk but it pushes the truck down the road and is zippier than I thought it would be. Lots of sticky varnish time frustration and vc tape topped off with red dog.

The motor build can be viewed at "evmaker.tumblr.com" a few pages back.

This is a low budget build. With a home made controller. Don't laugh too hard it runs...so far.


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## Siwastaja (Aug 1, 2012)

IT'S WORKING!!!!!!!!!!!! 

Please see with your own eyes:

http://www.youtube.com/watch?v=M1S_Ey8KgBM


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## PStechPaul (May 1, 2012)

Pretty good! So that's 10 VDC at 6 amps? What is the actual rated voltage and frequency? I see you were able to stop it by holding the shaft. Is that because the torque is limited by the power supply current? Looking forward to testing at higher voltage and power!


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## Siwastaja (Aug 1, 2012)

PStechPaul said:


> Pretty good! So that's 10 VDC at 6 amps? What is the actual rated voltage and frequency? I see you were able to stop it by holding the shaft. Is that because the torque is limited by the power supply current? Looking forward to testing at higher voltage and power!


It was now connected in star not delta, hence the original voltage would be sqrt(3) * 380V = 658V at 50Hz. We did reduce the turns by factor 5, so 132V at 50Hz; by constant V/f, it would be 16.3V at 6.2 Hz we used. At pure sine (no 3rd harmonic / SVPWM yet), this would require DC bus at 23.0 V. Having our DC bus at 12V, and taking the 2*2.5V voltage drop across IGBT's into account, this was driving the motor in 3x field weakening, whereas normally we should use somewhat higher voltage rating at that low frequency to give a stronger field.

Furthermore, as there was no feedback, just constant frequency, it quickly goes below the breakdown torque and stall. Actually, before stalling, it gives quite a respectable torque at voltage this low. My hand was actually *BLOODING*!!! ((but only due to the sharp edge in the shaft keyway, before adding that tape as shown in the video, but let's not ruin a good-looking argument with facts))

Had to leave for some sleep now, but yes, next we will dip varnish the motor and then run it off 230V 16A rectified to 320VDC - this is the pack voltage we'll be using.


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## Siwastaja (Aug 1, 2012)

LOL, we figured out our big mistake...

The motor is wound totally incorrectly. Yes, it is electromagnetically correct, but it just appeared to us that you can wind identical electrical poles in two different ways...

I scribbled it on a pizza carton:









Now that's quite obvious, huh? I think beginners make beginner mistakes. 

While it works just fine, it looks ugly. More importantly, the heat transfer will be poor on the areas with three overlying windings. As we want to overclock to _increase_ power, we have no other choice than redo the windings. But now it will be _so_ easy! Luckily, we didn't varnish coat it yet.


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## alvin (Jul 26, 2008)

So yours is wound as a 2 pole motor. 


This is one phase of a 4 pole motor.


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## PStechPaul (May 1, 2012)

Only 12 slots are shown, so I'm assuming you have a 36 slot stator and using 3 physical slots for each phase. So it looks like a 4 pole motor. But I think there is commonly an overlap of phases so the poles are not so sharply defined. Here is a paper describing optimal winding patterns. It is rather technical, but it seems to show that slots may share windings from adjacent phases:
http://lipo.ece.wisc.edu/2005pubs/2005_02.pdf

If you look at a vector diagam of three phase current you will see the three main vectors A, B, and C at 120 degrees, and if you add the opposite vectors A-, B-, and C-, there are now six vectors at 60 degrees. If you look at the A vector, pointing up at 0 degrees, you will see that the B- and C- vectors also have a zero degree component of cos(60) or 0.5 as well as 90 degree components of sin(60) or 0.866, which cancel. So the vector sum of these three vectors is 1 + 0.5 + 0.5 or 2, while the scalar sum of the three vectors is 3.

What I did awhile ago was calculate the vector sum of currents in each slot pair, which I assumed corresponded to the effective ampere-turns on each tooth. For my 36 slot 12 pole motor I used a winding pattern, without multiple phases per slot, of:

1. A 
2. C- 
3. B 
4. A-
5. C
6. B-

Each of these corresponds to 60 electrical degrees, so repeated 6 times this gives the full 360 degrees in six slots, so 36 slots corresponds to 6 cycles or 12 poles, with a sync speed of 600 RPM. As I understand it, at a given phase angle, you may consider the pole tooth between slots 3 and 4 as being wound with a complete loop of phase C with contribution also from B and A-, as well as A and B-. These vectors add up to a phase angle of 120 degrees, or C phase, with the other two current vectors each contributing 50% in the C phase direction. So the net magnetic flux is 1+0.5+0.5 = 2, or 2/3 considering all three phase currents.

Now my 24 slot 4 pole motor was wound as follows:

1. A and A
2. A and C-
3. C- and C-
4. C- and B
5. B and B
6. B and A-
7. A- and A-
8. A- and C
9. C and C
10. C and B-
11. B- and B-
12. B- and A

So there are two pole pairs of 4 poles. The tooth between slots 6 and 7 is fully wound with C and C-, and then to lesser extents by B and B- and A and A-. These add up to a vector sum which I think is also 2. So the field strength is the same, but there are only 2 pole pairs and thus higher RPM but less torque. I think the vector sum may always be 2 for each pole pair, which helps explain why torque is proportional to number of poles. But I think there is greater winding efficiency for smaller number of poles (or a greater number of slots), because there is less overlap of winding belts so less space is needed.

I don't know if this is really correct, but it makes some sense to me, and I have actually wound these motors and determined that they work. I can't really grasp the math as presented in the paper cited above, or others, but on an intuitive level I feel comfortable with this explanation.


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## aeroscott (Jan 5, 2008)

After I wound my first generator , I found I flipped one of the windings . I had epoxied them in with mill spec high temp epoxy . After digging the stuff out and getting new wire it was so easy the second time.


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## Siwastaja (Aug 1, 2012)

PStechPaul said:


> Only 12 slots are shown, so I'm assuming you have a 36 slot stator and using 3 physical slots for each phase. So it looks like a 4 pole motor.


Yes.



> But I think there is commonly an overlap of phases so the poles are not so sharply defined.


Yea, the multilayer stuff.

I think I have finally grasped the idea behind multilayer windings. It is just because the magnetic field caused by the stator is not a perfect point source. Layering does not affect the speed of the magnetic field or anything like that, but it is only to reduce minor imperfections from the rotating field (harmonics; that is, additional fields rotating at different speed from the main field.) 

Having now opened three different but similar motors (7.5 to 11 kW), none of them had multilayer windings. I have also read some papers about the subject; it seems that in some cases, multilayer windings can increase efficiency by removing unwanted harmonics that create small negative torque. It seems the effect is in range of about 1 percentage point or so, _if_ the multilayer windings are done exactly right. If not, they might actually decrease the efficiency. It is about fixing a small imperfection by making a small adjustment how the field is created, and it can go wrong.

So, if the motor is single layer winding to begin with, it seems to me it's the most safe bet to rewind it as single layer, too, if you are not sure how to mathematically model (or simulate) the actual motor with the actual parameters, including the model of stator material. There is also the added benefit of simplicity in single layer windings. OTOH, with careful design, it seems that one could increase the efficiency of a single-layer winding a bit by changing it to multilayer. But we don't want to experiment with that (at least yet.)

PS. We just reconfigured one 4-pole motor to halve the voltage by changing the windings from series to parallel, and tested it up to 200 Hz (6000 rpm minus slip). It just took an hour to do it! Really easy, anyone can do it. Still, it needs a 600V battery pack. You U.S. guys have 230V (in delta) motors, so you are much better off by just reconfiguring. Now as we bought an old, rusty pick-up truck, it seems we are going to put two motors on the same axle (with separate inverters), and the first one might run at 320 VDC (the rewound one) and the second at 640V (the reconfigured one) -- need to build a large boost converter.


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## cts_casemod (Aug 23, 2012)

Siwastaja said:


>


 
That motor seems familiar to me

http://www.diyelectriccar.com/forum...ersion-vw-polo-ac-industrial-motor-78701.html

I have opened mine and I believe I found a way to actually feed it with 208V as there are 3 windings in series. Have yet to try.

Yours looks pretty clean now. 
What sort of power levels do you plan on achieving with it?

Regards


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## Siwastaja (Aug 1, 2012)

cts_casemod said:


> That motor seems familiar to me
> 
> http://www.diyelectriccar.com/forum...ersion-vw-polo-ac-industrial-motor-78701.html


Yes, indeed .



> I have opened mine and I believe I found a way to actually feed it with 208V as there are 3 windings in series. Have yet to try.


Yea, we did that to an another similar motor but a different brand. This Asea would have been OK too, but a third motor we opened would have been very difficult because the connections were quite well hidden. 

It took an hour or so... You'll find 3 series connections, cut them open and you get 6 loose wires, solder them parallel to the 6 existing input wires and you're done. (Just use a multimeter or similar to identify the wires. It's difficult to do it wrong, you would be obviously connecting either wrong phases, or making an obvious open circuit; if not, it just goes right. This is for 4-pole motor.)

From:

U1 ------- [ connection ] -------- U2
V1 ------- [ connection ] -------- V2 
W1 ------- [ connection ] -------- W2 

To:

```
______________________
          |                    |
U1 +------+   [cut]   +--------+ U2
   |__________________|
```
And the same for the other phases...

We finished the mod by adding fiber glass insulation to the new connections and applied some varnish and inserted NTC sensors to the windings. We have tested this motor with no load to 6000 rpm (200 Hz) from 250V DC bus. (This is a huge field weakening so it doesn't go any higher RPM with voltage that low. Need more testing.) Previously it did got to 3000 rpm (100 Hz) with the same DC voltage, so yes, it seems to work as expected at least with low load.

So, yes, you can halve the voltage, and it is very easy. Still, if you are after 3x power at 150 Hz without field weakening, you would need a 800V battery pack. Much more doable than 1600V, anyway, and this is a very easy job to do. If 2x overclocking sounds good enough, this trick should be very usable.

If you could get a 230V/400V motor and halve the voltage for that, it would be enough for most purposes... I think those exists in the USA. Here, everything is 400V/690V, except for very small motors.



> What sort of power levels do you plan on achieving with it?


This is yet to be seen. We would be VERY happy if we got 3x power at 150 Hz, this is for fully rewound motor for 1/5 of original voltage. 

We have drilled holes in the casing ends and will force air through the air gap to cool the windings and the rotor.


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## cts_casemod (Aug 23, 2012)

Siwastaja said:


> Yes, indeed .
> 
> Yea, we did that to an another similar motor but a different brand. This Asea would have been OK too, but a third motor we opened would have been very difficult because the connections were quite well hidden.
> 
> ...


 
Thanks a lot Siwastaja,


I believe, on this one itself it was not particularly easy to get to the wires.


I only plan to have twice the actual power. Just discussing this on another forum, my car will be about or less than 900kg, and being AC I will have regeneration, so I should get about 30 miles from a 6.5KW Lithium pack.


I would like to have 100nm up to 3000RPM. I hardly go above this limit. 
Besides above nameplate your iron losses start to get considerable.


I know mine went up to 3000 connected in star easily. My VFD doesn’t allow for more.


USA... Also talking about that on another topic today... They have everything, we in Europe are quite limited! They also have 110V 3 phase Motors. They use them on some generators or specific motors changing the poles.


I have been thinking in a circuit to change between 2 and 4 poles. I am sure the iron losses at 2x RPM are at least 20%


Now back to the motor, I am kind of confused. Lets talk about coils. If I parallel the coils I will end up with a 208V 2 pole motor. Can you describe a coil diagram of the connection you describe?










I believe if you conect the coils in paralell with the same polarity you have a 2 pole (NN,SS), if you do it with th oposite polarity you have a 4 pole(NSNS), but I am confused now!!

I have no interest in having twice the power above 3000 (up to 6000) lol.


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## Siwastaja (Aug 1, 2012)

cts_casemod said:


> I would like to have 100nm up to 3000RPM. I hardly go above this limit.


Yes, just note that overclocking does not give more torque on low RPM, but just extends the constant torque range to higher RPMs, hence enabling the use of higher reduction gears.

For a direct drive application (with rear differential ratio of just 1:4 or so) like us, this just means extended top speed. We will still need motor big enough to give enough torque. A 7.5 kW 4-pole has 50 Nm nominal and that can be temporarily upped to about 100 Nm with or without overclocking, so we will either need two of these motors or a bigger one.




> I know mine went up to 3000 connected in star easily. My VFD doesn’t allow for more.


Yes, connecting to delta lowers the voltage requirement (or increases the max power given the same voltage) by 1.7x compared to star; connecting the series windings to parallel will do the same at factor 2.0x. Of course you can and should do both.



> I have been thinking in a circuit to change between 2 and 4 poles.


IMHO, this needs special windings designed for this change, I can't imagine how you would reconfigure a 4-pole motor to 2-pole. I can't see the benefit of doing so, either.




> Now back to the motor, I am kind of confused. Lets talk about coils. If I parallel the coils I will end up with a 208V 2 pole motor.


Umm, no? If you have 4-pole motor to begin with, the same current is flowing in the pole pairs that are in series. If you change them to parallel, it makes no difference, the current is flowing exactly in the same way in exactly the same windings; just that half the voltage is enough for same power.



> I believe if you conect the coils in paralell with the same polarity you have a 2 pole (NN,SS), if you do it with th oposite polarity you have a 4 pole(NSNS), but I am confused now!!


No -- the poles that are connected in series in the motor are opposite pole pairs; hence you cannot change the number of poles per phase.

The windings are wound in such a way that the physical angle between the opposite poles is fixed. For a 4-pole motor, it is 90 degrees, for 2 poles it is 180 degrees. You will always have the opposite magnetic pole 90 physical degree away because the very same windings go there to the opposite direction. You just can't change that in a typical motor without full rewind. What you CAN do is to reconnect the _identical_ _pole pairs_ -- a 4-pole motor has two identical sets -- to parallel instead of series. A 2-pole motor has one "set" anyway so you can't reconfigure a 2-pole motor. OTOH, a 6-pole motor has three identical sets so you could reconfigure it to 1/3 voltage.


----------



## cts_casemod (Aug 23, 2012)

In my case I will have 50 nm of the torque up to 3000RPM as My VFD only able to provide 15KW. Later I will get one with at least twice the power to have the same toque (100nm) to match the now improved motor. This is considering a nominal power of 15KW and a peak power of 30KW.

I have to disagree with you on this one.

Considering the windings to be equal and takind DC to make it nmore clear you have

+ Winding one - + winding two -

or you might do it this way

+ Winding one - - Winding two +

They are both in parallel, but the magnetic fields are oposed.

You have NN on the first case and NS on the second, so if two coils are powered at the same time ypou end up with either NNSS (2 Pole) or NSNS (4 Pole).

As you say on a 2 Pole the windings are spaced 180D and on a 4 pole only 90D. So its not phisicaly possible to convert a 2 pole to a 4 pole, but the same is not true for a 4 pole into a 2 pole.
This is possible with half the voltage and the same for a 6 pole into a into a 2 pole with 1/3 of the voltage or even a 8 pole into a 4 pole with 1/2 the voltage or a 2 pole with 1/4 of the voltage.

Of course this is assuming the coils are all equal, but if they are not the half voltage mod is not going to work anyway as the one with less resistance will have the most of the current.


----------



## tylerwatts (Feb 9, 2012)

Wow very interesting information gentlemen. It looks like you are saying you can 'reconnect' the coils in a 4/6/8 pole motor to run the coils in parallel rather than series and thus effectively lower your voltage requirement. 

Does this equally mean that by the same factor you lower the voltage, you can increase the current? So for example taking an 8-pole motor and reconnecting totally in parallel would mean using ~120VAC rather than the ~400VAC BUT would also mean using ~ 200A nominal rather than ~50A previously. This is before over-clocking or pushing the motor harder with extra cooling etc of course.

And as a result, if iron losses are not an issue, you should get ~4 times as much torque from the motor then also. Of course iron losses will be a big factor in this. So maybe conservatively you only double the current, but then overvolt the motor to ~200VAC to extend the torque band and power output.

Am I thinking on the right lines here? Or is this a dream and in reality I'd melt the motor before long and have wasted my time?


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## cts_casemod (Aug 23, 2012)

tylerwatts said:


> Wow very interesting information gentlemen. It looks like you are saying you can 'reconnect' the coils in a 4/6/8 pole motor to run the coils in parallel rather than series and thus effectively lower your voltage requirement.
> 
> Does this equally mean that by the same factor you lower the voltage, you can increase the current? So for example taking an 8-pole motor and reconnecting totally in parallel would mean using ~120VAC rather than the ~400VAC BUT would also mean using ~ 200A nominal rather than ~50A previously. This is before over-clocking or pushing the motor harder with extra cooling etc of course.
> 
> ...


 
Tylerwatts,

You can change the motor specs, however how good the efficiency is will depend. If you have a 4 pole motor and you run it at 200Hz you can make it run at 6000RPM, but regardless your iron losses are going to get big. I believe 10% for each double of the speed (10% at 3000, 20% at 4500, 30% at 6000), but I havent seen any figures and depends on the quality of the motor. Premmium efficiency motors have less losses.

Think of the motor like two bulbs at 400V.
If you have 2 coils in series you have 2 bulbs using 200V at lets say 2A.
If you place them in parallel you have the same 200V, but now you have 4Amps for the same power. So keeping the same current per coil you are not overheating the motor. The voltage is proportional to the speed you get, just like in DC. More Voltage - Mpore top speed.

In an electric motor torque is Amps and Speed is volts.

If you have a 15HP Motor producing 50nm at 1800RPM and you connect the coils in parallel you now have twice the current.
If you raise the voltage you keep the same (doubled as the coils are now in parallel) current, but as you raise the voltage your top speed goes up as well. So, same nm (amps) twice the RPM (Volts) = twice HP.

Now what i am trying to do is change the number of poles on demand.
So to Start I would use 4 poles up to 1500RPM at 100nm and after 3000 I would change to 2 Poles at 50nm. Like I now have twice the speed as a 2 pole I wont have iron losses and I can save one gear as the motor acts as a gearbox.

On a 8 Pole motor I could even discard the gearbox (The motor acts as a 4 speed gearbox - 200nm at 900RPM; 100nm at 1500RPM; 50nm at 3000RPM and constant HP up to 6000RPM @ 25nm).

The electronics are complex thought and there is a compromise as the motor gets heavier the more poles it has. But since we are using 4 pole motors we can take advantage of that at at least change from 2 to 4.

Its all teorical YET.


----------



## PStechPaul (May 1, 2012)

Multi-speed motors exist, both single phase and three phase, but I think they are less efficient and/or larger than a similar spec single speed. Here is a very detailed account (beyond my level of technical comprehension) of the design of a large multispeed motor with 6/10 poles:
http://www.atmos.ucla.edu/~jbortnik/pubs/Machine.pdf

I searched for multispeed AC induction motors and I got lots of hits, but not much detail on the winding patterns. But here is how I would analyze the requirements:

For a single phase ACIM, you may simplify the design by using four discrete poles, wound as follows:

*A A' A A'*

Notice that the pole pairs are 90 physical degrees apart, and 180 electrical degrees apart, so on 60 Hz it will run at 3600/2 = 1800 RPM.

If you reverse the connections for one of the pole pairs, you will get:

*A A A' A'*

So now there is effectively one pole pair and the speed will be 3600 RPM.

But most AC motors are wound with overlap so that the torque is smoother, and the simple switching of the pole pairs may not result in an optimum winding pattern.

Now consider the case of a three phase four pole motor, wound as follows:

*A C' B A' C B' A C' B A' C B'*

The pole pairs are still 90 physical degrees apart and 180 electrical degrees apart, but adjacent poles, such as A to C', are 30 physical degrees and 60 electrical degrees apart. This provides a smoother operation than the single phase motor, although overlapping of windings and rotor design compensate for any deficiencies.

Now consider the same number of slots, but changing from four pole to two pole:

*A A C' C' B B A' A' C C B' B'* 

Notice that the phases for all slots except two have changed, so switching from four to two poles seems a daunting task. Now let me try another method:

*A B C A' B' C' A B C A' B' C'*

This reverses the polarity of one of the windings (which is not the same as swapping the phase drive connections which just results in reversal). In the example above, there is a 120 electrical degree shift between adjacent poles which are 30 physical degrees apart. Thus each 360 degree cycle will result in 90 physical degrees of rotation or 900 RPM, which is an eight pole motor.

I actually experienced this when I wound a 36 slot motor with the phase sequence:

*A C' B A' C B' ...*

This should have resulted in a 12 pole motor, running at 600 RPM. When I first tried it, however, it ran more like 300 RPM, which would be a 24 pole motor. I flipped one phase and it ran at 600 RPM as expected. However, the low speed connection seemed to have very little torque, and not more as would be expected. I think the problem comes from the inherent overlap of phase windings, where the vector sums of the phases around any given pole result in very little contribution to the direction of angular torque. This also may explain why smaller motors with higher number of poles have lower power than a two pole motor of the same size. For larger motors with more slots, the windings can be more efficient with less overlap. 

Anyway, that's how I see it. I comprehend things on a visual and intuitive basis more than mathematical, so I may not have this exactly right. But it seems to work out from practical experience. If you can understand the math in the link I provided, maybe there is a better way to analyze the problem and provide a good way to achieve an efficient multispeed motor. 

I found something called a Dahlander connected motor which can provide two speeds:
http://www.lmphotonics.com/InductionMotor/dahlander_motor.php
http://www2.schneider-electric.com/...cal-know-how/low-voltage-minus-1kv/ect207.pdf

Here is a catalog of various motors, including many multispeed types. It is interesting to check the differences in efficiency and power for the Dahlander connected types. They even have a 2/8 pole type with separate windings. See series BP. The largest is a 4 kW 2 pole/ 1.1 kW 8 pole in a 132M frame. A single speed 2 or 4 pole motor in the same frame is 7.5 kW, 6 pole is 5.5 kW, and 8 pole is 3 kW.
http://skemman.is/stream/get/1946/10642/25652/9/motor.pdf


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## Siwastaja (Aug 1, 2012)

Status update.

We finally finished and varnished that 7.5 kW Asea motor. The varnishing process was surprisingly easy, we wanted to dip varnish it but had only 5 kg of varnish so we plugged the holes in the motor casing with silicone and filled the motor with the varnish, with rotor removed. Then drained it and cured the motor in oven. Nice result.

The motor did spin nicely, we got to around 100 Hz, but unfortunately we blew up two IGBTs. I guess the gate drive circuitry is at fault, it wasn't a proper one for high power. Hopefully this is the cause, and designing proper gate drive modules would prevent further blown up IGBTs.

As a power supply, we used rectified 230VAC which becomes 320VDC, just right to simulate our future battery pack.


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## cts_casemod (Aug 23, 2012)

Siwastaja said:


> Status update.
> 
> We finally finished and varnished that 7.5 kW Asea motor. The varnishing process was surprisingly easy, we wanted to dip varnish it but had only 5 kg of varnish so we plugged the holes in the motor casing with silicone and filled the motor with the varnish, with rotor removed. Then drained it and cured the motor in oven. Nice result.
> 
> ...


Great work!

If you can get your hands on some Inteligent Power modules. No hassle with the gate drivers and they go off if a fault is detected. I find them much easier to use, just +/-15V Power supply and 5V TTL signals from the uP. 

What controller are you using?


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## Siwastaja (Aug 1, 2012)

cts_casemod said:


> Great work!
> 
> If you can get your hands on some Inteligent Power modules. No hassle with the gate drivers and they go off if a fault is detected. I find them much easier to use, just +/-15V Power supply and 5V TTL signals from the uP.


Any recommendations? I have been looking at those modules, but all I've seen have been either too expensive or useless, or usually both. 

Well anyway, it shouldn't be too difficult to do properly either, these drivers just were meant for a different project with different power ratings.



> What controller are you using?


A simple & quick & dirty DIY, V/f control on FPGA. No FOC/DTC as of yet.


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## mizlplix (May 1, 2011)

I feel your pain....

Miz


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## cts_casemod (Aug 23, 2012)

Both Fuji and Mitsubishi have similar pinouts.

Usually to find the best deal I contact some chinese companies and ask them what they have in stock. Some are new, some are refurbished. You might find something on eBay but I find it not worth the hassle as you end up paying more for a specific model.

The 300Amps 600V can be found for about $300 Delivered and you are safe up to 200Amps @ 400V peak (100HP). They are more expensive but for 7 IGBT's, no need for drivers, no messy wiring, single heatsink contact point (great for water cooling) and protection against short circuits/overcurrents, as long as you read the datasheet and avoid noise/inductance/peaks on the DC BUS you should be safe.

I did a project with smaller IGBT's once and it ended up being more expensive. I had to design a PCB for the drivers and the inductances and RFI were a problem I am happy to avoid again, not to mention the expense each time some blows up!
Place capacitors everywere the first time you run the thing (including the 3 phase output) and take a look with the scope, they are burnt either by too long on/off cycles (low gate current) or voltage peaks that last a few ns.

End of story:
A few isolated +/-15V power supplies (that you need anyway)
A few optocoupers for isolation
Done!


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## Siwastaja (Aug 1, 2012)

Nah, not much pain at this point. After all, we were blowing up some free IGBTs .

But maybe if they weren't free we wouldn't have recklessly used these gate driver boards .

Unfortunately, our IGBT resource is far from unlimited. I think we have only two similar 1200V 200A half-bridge modules for replacement left, so it would be nice not to blow them again. We do have a lot of single 1200V 200A modules, but half-bridge modules are practically a must to maintain a proper layout.

BTW, 300A 600V half-bridge modules cost about $100 / piece when bought _new_ and are of current technology, so I wouldn't pay much for old stock.

I guess these older IGBT half-bridge modules need negative gate drive more than new IGBTs, or single IGBT in a chopper type configuration. We didn't have even that, and there's always some inductance between the driver pin and internal gate in the IGBT module. Also, we had a dirty bootstrap power supply to the drivers, and all three phases were powered from one supply. Yes, it was a quick setup used for a 2 kW compressor.

On the plus side, it had optoisolated gate drivers and used differential signaling to drive the LEDs (so, negative voltage across the LED when off), so I think this was not part of the problem.

IMO, the best and simplest power supply for gate drive modules would consist of small +/- 5V and +12V isolated DC/DC modules (which are easily available), connected in series, to give -5/+17V gate driver supply. Total of six power supplies needed. Then on/off gate drive resistors, gate pulldown resistor and a gate clamp zener.

But need to take a look at modules with integrated gate drive.


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## cts_casemod (Aug 23, 2012)

I am far from having them free lol.

I used to be able to source most of my components cheap (not free, but cheap) but since coming to London it has been impossible to. Everyone here makes easy money here selling scrap, scrapyards dont sell to the public... I find myself importing rather than looking into the local market. In fact 90% of my conversion time is spent on finding suitable parts at a decent price.

There is not much difference in newer IGBTs to say "older" in fact the Smart modules I use are 10 years old and you can still find new stock being used on industry. Of course you have more options these days with smaller footprints and lower losses but the real world difference isnt much.
My experience is with the fuji 6MBP75RH120 and similar. 

Always use a brake IGBT as well, otherwise during decelleration the Bus voltage will go to high. Not so much of a problem with a battery (if good) but on rectified mains I've had a small prototype powered by 72V reaching 400V.

I always use a minimun of -5 to switch the gate off, ideally -10 to and use two isolated power suplies one for high and other for low side (3 and 4 gates ea) I am also starting to replace optocouplers with digital isolators as they offer many advantages and a smaller footprint.

Problem with smaller DC DC modules is the low output capability. I prefer to use an isolated power supply straight from HV DC bus, any centered tap 12V SMPS can be made into a +/-15V Power supply with little modifications. I am not sure what frequences you are using but for a quiet motor (at least 10Khz) there is a noticeable loss charging the gates.


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## cts_casemod (Aug 23, 2012)

Hum, this conversation has gave me a great idea,

Instead of using contactors on each of my battery packs (Amperage limited, 24V @ 1A power supply required for each) I will keep the bi-polar fuses but use a IGBT as a switch. A cheap Isolated DC DC and a pull down resistor will be enought as its only on/off operation so the master can safely output 12V @ 1 or 2 Amps for the DC-DC and a small fan on each pack if required.
I can even do a low frequency PWM for the precharge.

IGBT is much smaller so with a bit of luck a small charger can be made to fit inside the box.


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## Siwastaja (Aug 1, 2012)

cts_casemod said:


> I can even do a low frequency PWM for the precharge.


In precharging the capacitor bank, only the inductance of the wires will limit the current -- or the discrete resistor typically used.

If you were thinking of using only single switch and no resistor, you would need very _high _frequency and low duty cycle for the PWM in order to limit the peak current.

Or maybe it would work with very very low duty cycle even with low frequency, but is the precharging then fast enough? Worth trying at least.

Is the conduction loss of 2 - 3 V OK? I think a good mechanical contactor would have much less.

I would still use a mechanical contactor as an extra safety measure in the battery box; it would isolate the pack in case of any failure causing control voltage to be lost -- and that can be done automatically in any detected failure case. Heck, you could (and really should) include an RCD in such high voltage system, and it'll need a contactor anyway so you can share it.


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## cts_casemod (Aug 23, 2012)

Siwastaja said:


> In precharging the capacitor bank, only the inductance of the wires will limit the current -- or the discrete resistor typically used.
> 
> If you were thinking of using only single switch and no resistor, you would need very _high _frequency and low duty cycle for the PWM in order to limit the peak current.
> 
> ...



Hi,

I guess we have to try. The simplest bet is to make the BMS activate a smaller IGBT/Mosfet with a series resistor and when the output voltage is 80% of the battery voltage close the main switch, but I am really wondering if I couldnt just use the IGBT in the linear region, they can usually cope with a good 300W at least, that would be a fast precharge.

Thats a tricky one, not ideal really. By my calculations:

I will still have a main contactor, the IGBTs would only isolate the individual packs (4).

A good IGBT can do about 2V under load or even less (1.5V) at low load, so lets say 2V drop in 144 is not that bad. I could simplify the wiring and its much cheaper.


So roughly 24V at 1Amp for each contactor is an overkill, I need 2 power supplies (640 to 14.4 and 14.4 that the BMS takes back to 24) so that would be a drain each time the car is on (including charging and being stationary with the DC-DC on) of about 96Watts per hour plus losses on the power supplies ~ 130Wph

With the IGBTS for my 10Ah battery, lets assume a voltage drop of 2V at 10Ah (same as 2V at 30Amps for 3C, 20minutes) = 80Wh per charge overal losses, no matter what time they are on so I am still better with them. 

In fact the other day I was looking at the overal efect of the DC DC converter drawing 40Amps with the AC on at 14.4V and it can drain the pack real fast! Thats not something most discuss but it does have a big efect on the range.

I thought that myself before but In regards to safety If the control voltage is lost the IGBT gate goes to GND with a pull down and the packs are isolated. In an overcurrent the BMS will cut, if it shorts the fuse will burn, the packs are isolated from the chassis so cant really think of much else that could fail


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## cts_casemod (Aug 23, 2012)

If you never worked with smart modules here is a good chance to get a good one at a decent price http://www.ebay.com/itm/Mitsubishi-...004?pt=LH_DefaultDomain_0&hash=item27ceaf5e64


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## Siwastaja (Aug 1, 2012)

Just a quick update.

Our first conversion, a cute '88 Suzuki Alto, using the rewound motor, is moving. We got it up a hill and back down using regen.

So far, using 36V 60Ah lead-acid . Going to up the voltage step by step while measuring voltage spikes.

Motor coupled to transmission: http://i.imgur.com/fbxz9GEh.jpg
SLA batteries (in the box) and the inverter prototype: http://i.imgur.com/VybJ5FHh.jpg . That's all, very simple so far...


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## electro wrks (Mar 5, 2012)

Siwastaja said:


> Just a quick update.
> 
> Our first conversion, a cute '88 Suzuki Alto, using the rewound motor, is moving. We got it up a hill and back down using regen.
> 
> ...


It looks like you're using elongated motor case bolts, with spacers, to mount the motor to the adapter plate. They're probably 6-8mm diameter-possible too small to handle the torque reaction of the motor. The force on the bolts has been changed from mostly shearing to mostly bending- increasing the deflection-possible permanently so as you increase the voltage. the spacers look to be too small a diameter, also.

You might consider increasing the diameter of the spacers and /or tying the motor base(it looks like it's still attached) to the adapter plate with a bolt-on bracket. Great project. Keep going.


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## Siwastaja (Aug 1, 2012)

electro wrks said:


> It looks like you're using elongated motor case bolts, with spacers, to mount the motor to the adapter plate. They're probably 6-8mm diameter-possible too small to handle the torque reaction of the motor. The force on the bolts has been changed from mostly shearing to mostly bending- increasing the deflection-possible permanently so as you increase the voltage. the spacers look to be too small a diameter, also.
> 
> You might consider increasing the diameter of the spacers and /or tying the motor base(it looks like it's still attached) to the adapter plate with a bolt-on bracket. Great project. Keep going.


The spacers (diameter is 16 mm) are only for alignment and careful (hopefully! ) initial testing. The plan is to make a proper motor mount.


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## Siwastaja (Aug 1, 2012)

Going around a bit. Regen is very strong, which is good, because we have the original brakes working only in one wheel 

See: http://www.youtube.com/watch?v=1IIr5P2l4vM

Driving with frequency (= speed) control by turning a pot in the rear seat is actually kind of fun. 

Gonna implement a simple slip control (will be very simple) to make a proper acceleration/deceleration pedal next. And up the voltage, first to about 100V, later to 320V.


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## cts_casemod (Aug 23, 2012)

Siwastaja said:


> Going around a bit. Regen is very strong, which is good, because we have the original brakes working only in one wheel
> 
> See: http://www.youtube.com/watch?v=1IIr5P2l4vM
> 
> ...


 
Once you have the thing running you'll only need the hydraulic brakes for emergency stops and to keep the car from rolling after it has reached a stop. I was amazed by how powerfull regeneration is, much more that you can actually accelerate. I was able to spin wheels on 3rd gear with rain just by letting the motor regenerate to a stop too fast and I have broken a few bolts on my provisional mounts.

If you are running on V/Hz you'll controll the aceleration and braking force only with one pedal. Its actually quite usefull for the parking manouvres.

My experience: get an encoder to read shaft speed and command the ammount of slip (Positive for aceleration and negative for regeneration). This is the best compromise between torque and V/Hz mode and will be my next mod to my Polo. Too much and the motor will just overheat and loose power, also sudden changes can change the speed too quickly causing the car to stop too fast or draw excessive ammounts of current during aceleration.

I I am curious about your inverter setup. What are you using?


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## Siwastaja (Aug 1, 2012)

cts_casemod said:


> Once you have the thing running you'll only need the hydraulic brakes for emergency stops and to keep the car from rolling after it has reached a stop.


And for bad weather! This is very important here especially at this time of the year. The snow melts from traffic, and refreezes to a shiny layer of ice... If you drive an RWD, you need to be VERY careful and even avoid motor braking in an ICE car because losing the traction in rear wheels instantly causes the rear to drift. Not as bad in FWD, but still, braking through the differential is not as good as applying the same braking force to both wheels.

So, the regen needs a limit switch with maybe four options: Full enable, rain, icy roads, full disable.

A 4-motor system would be great for this reason, you could always have full regen.



> My experience: get an encoder to read shaft speed and command the ammount of slip (Positive for aceleration and negative for regeneration).


This algorithm should do the trick. It's nearly the same as FOC once you open up the mathematical gibberish behind the FOC:

1) Measure shaft speed, calculate the corresponding frequency[e.g.: 1500 rpm (measured) -> 50 Hz (corresponding frequency)]​2) Set the drive frequency to that * slip factor[e.g.: 50 Hz * 1.05 = 52.5 Hz]​3) Calculate voltage for nominal torque from linear V/Hz[e.g.: 76V for 50 Hz (in the motor "nameplate") -> 79.8V for 52.5 Hz]​4) Multiply this voltage by the torque input, ranging from 0 to 3.[e.g.: pedal fully pressed: 79.8V*3 = 239.4V] (getting all out of the motor)
[e.g.: pedal somewhat pressed: 79.8V*1 = 79.8V] (giving nominal torque of the motor)
[e.g.: pedal in coasting position: 79.8V*0 = 0V] (coasting with no regeneration)​5) For the regen direction of the pedal, beyond coasting, change the direction of slip.[e.g.: Go to step 2) but use 0.95 for slip factor: 50 Hz * 0.95 = 47.5 Hz]
[note: the "torque" pedal, or two separate pedals, need to go through the "zero" position to give zero voltage when changing the slip direction. Some low-pass filtering is needed anyway to prevent jerks.]​6) Command these frequency and voltage values to the inverter module.

Something like 10 lines of code, and the result should be very close to FOC; the main idea is the same after all, to keep the slip optimal and to adjust the field strength by adjusting the voltage according to the need for torque, to maximize the power factor, instead of having constant V/f which causes slip to get too low under light load and too high under heavy load.

A bonus feature: If the voltage limit of the pack is reached, you can still get more torque by increasing the slip factor, allowing the motor to slip more, drawing more current. This may become important at higher speeds, when passing cars.

All of this needs practical verification, but it will be done by us... as soon as possible....



> I I am curious about your inverter setup. What are you using?


150A1200V IGBT half bridge modules with ACNW3130 gate drivers (not up to task, better ones will be used) and Terasic Altera DE2 FPGA development board. This is the meat inside: http://pastebin.com/3WraCSLJ


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## cts_casemod (Aug 23, 2012)

And for those reasons we've chosen AC! The more I drive it, the more I like it!

It is true that it helps with the weather but bare in mind that at the same time if you dont have a 4WD/AWD the motor wheels will be overloaded if the hydraulic brakes are used without modification. Sure its better that a locked wheel but what will the advantages be in regards to a good ABS pump I dont know yet

I need to add field weakening to my VFD. It outputs a constant V/Hz and sometimes if the motor is not under load (cruizing)so it would be more efficient to keep the frequency reducing the field (Voltage)

I was thinking like center of pedal 0 slip, pressed full load, aceleration and released full load regeneration. So to take off you would simply fully press and the controller would keep a constant slip above the actual frequency that could and would vary when you reach constant horsepower or are using field weakening. On the contrary if you wanted to reduce speed you just release the pedal a bit and once you're happy with the speed you go back to the center. This would gradually increase/reduce instead of trying to regenerate back to zero or acelerate suddenly causing the motor to go out of sync. 

Field weakening Its actually quite complex and I dont believe most industrial VFD use it. They have torque mode, but true torque mode is not driveable either, so you'll need to come out with a way to take advantage of both. I would start with Vhz and slip controll because other that some energy savings field weakening is not going to matter too much.

For your motor and your setup 150Amps is not enought.

I have 100Amps IGBT and I can only use my motor in star mode, so I can only have full current up to 1000RPM or so. This is because 150 Battery amps is enought but the motor amps can be as much as 500. 

I plan to have the motor running at nominal voltage with 208VAC in Delta mode (see my re-wire) but the smart module protection disables the module as soon as I load the motor (runs fine unloaded) due to this reason. I will upgrade to 200 or 300Amps so I can have 80 Battery amps but 200 or 300 motor amps (80*356=28BHP or 55BHP if using 650V with a 1200V IGBT).

Not sure what voltage yours is now but you originally quoted that you wanted to reduce from 660 to a factor of 5, lets say 150Amps @ 150V @ 1500RPM (60BHP peak @ 320V @ 3000RPM) you will need at least a 200Amps IGBT. However, if you plan to use torque boost you WILL need more, so say 300Amps.

You might also consider using inteligent power module. they are expensive, but virtually indestructable, so its a good investment. Just something for you to consider.


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## toyolla2 (Jun 21, 2010)

Siwastaja, this has been an interesting thread even though it did get side swiped towards the end. Also it appears to be missing a summary, as usual I suppose. So here goes.

In post #1 you asked :

_I hope to hear any opinions before we go, for example, would you go for even lower / not so low nominal voltage ??_
One thing that got overlooked in the ensuing discussion is that this should not be a discussion of voltage but a discussion of V/Hz.

We can write and propound all we want about winding voltages, 2-pole or 4-pole, switching networks for pole-changing and star-delta configuarations but generally speaking it all comes back down to having the correct ratio of Volts per Herz in the first place.

Generally AC induction motors are sourced from the industrial world of 60Hz electro-mechanical power offerings of predominantly 4-pole machines. In this environment mechanical power is not welcome even at 1800 rpm and oftimes the preference is for a maximum of one quarter of this speed at point of use. Moreover Industrialists happen to prefer process machines to come with two inch thick steel side frames to accomodate large bearings that will survive 24/7 working with a three shift manufacturing operation, so it should come as no surprise that their attached motors with cast iron fames are never viewed in a negative light. There is also a preference to use the highest voltage available. My experience from a population of 300 machines averaging 80Hp is that only one client elected for the lower 230Vac. I don't remember the 175 amps which came with that as being particularly unmanageable either.

Not surprisingly Siwajasta's candidate machine came with an unwieldy 660Vac/9.2A nameplate which is somewhat inappropriate for the average EV constructor to accomodate.

For three times ( i.e. 4500rpm @150Hz ) overclocking from the nominal 380Vac - motor configured for delta - and from a 320Vdc bus will be needing a X 5 turn reduction. So 34 ( bundles of 3 #20awg wire) were replaced with 7 (bundles of 7 #17awg). 

It may be of trivial interest but in each of the stator slots effectively 102 wires were replaced with 49. It should be pointed out that since the cross section of each replacement 17awg wire is twice that of the original 20awg wire then the slot fill percentage was relatively unchanged by this procedure. I agree that since the 17awg has the disadvantage of being 9000% more unwieldy than expected !! that a more flexible wire size will be used next time. 

Incidently orig calcs from Post #1 were based assuming 380Vac delta, but later on at Post #105 after the rewind, testing resumed with *STAR* ???

No matter, in star config 3 of #20 awg were required to carry 9.2 A, after the rewind it is expected that 7 of #17awg should be capable of (2 times 7)/3 times 9.2 amps. Or 43 amps.

So to recap the initial Volts/Hz (star config) of 660/50 viz. 13.2 were moved down to 132/50 viz. 2.64 following the rewind.

I have to comment that 132Vac at 1500 rpm is still an inconveniently high voltage - since you were asking back then.

As a general point of principle you need to consider winding for a Volts/Hz ratio below 1.0, requiring 50Vac or less at 1500rpm. Otherwise you are either doing something exotic (read expensive) or settling for low performance. 

One symptom of a drivetrain when the motor V/Hz is placed too high has already been pointed out by Miz who has noted that the drivetrain starts to get "lazy" towards the latter end of the rpm range. The cure here is to raise the pack voltage when that is an option. OTOH going to a lower ratio gear will slow the motor down and restore motor torque. But the motor is now producing less torque at the wheels with that lower gear. Is that what you want ??

It should be mentioned that there is a symptom of a drivetrain when the motor V/Hz is placed too low, in which case the drivetrain seems to be "lazy" over the whole of the rpm range while sitting in current limit !! Moving to a higher gear ratio will solve that problem. In other words "to make the road look easier" will improve the acceleration.


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## Siwastaja (Aug 1, 2012)

Hi,

We did indeed make one mistake when we determined the ratio of 1:5. We sure designed the system to run at 320 Vdc, but we didn't add any leeway for voltage sag and getting out more than the nominal 50Nm at 4500 rpm, even for very briefly.

Naturally, you cannot run 3x voltage with 3x frequency AND 2x current for a very long time; it's impossible to cool.

But you still need the voltage to allow that to be present _when_ you need that acceleration very briefly.

Voltage reserve is needed for upping frequency (speed), sure, but voltage reserve is _also_ needed for upping current (torque).

Currently we have a 96V pack and get max speed of 50 km/h, with _good_ acceleration up to 30 km/h. Upping that to the designed 320V would make good acceleration up to 100 km/h, but maybe only to 80 km/h in reality (increased drag). So in order to get the good acceleration up to 120 km/h, we would need to go to about 450-500 volts.

Expressed in terms of power, our 96V pack pretty much limits the power to 10 kW. 320V would then be 33 kW, which is more than what we wanted for _continuous_ power, but for a peak value of a few seconds, not too great for joining a freeway.

(No drive algorithm is going to change these basic laws.)

So next time, if we are going to rewind a 380VAC 4-pole industrial motor for 320V DC, the reduction should be something like 1:7 instead of 1:5. Also, the reduction could be even higher so that the motor would be driven in star for 320VDC instead of delta, so that there would remain an option for lower battery voltage (190VDC in delta).

I'm also rethinking the 320VDC choice. Maybe we should just go higher, in which case the motor winding would be just perfect. We happen to have those 1200V IGBT modules.....


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## cts_casemod (Aug 23, 2012)

I think it would also be important to note that an increase in voltage and hence frequency will also lead to lower efficiency due to core losses. There is a reason they are rated for 50Hz, above that eddy currents, and iron losses increase by the square of the speed, so if the power is not really needed (only on peaks to overtake, etc) it could make more sense to go with a lower speed, where the voltage mod wont give much more power, but instead will use more current and here we have a balance, because operating at a lower voltage will increase this current way too much, stressing the power components and the batteries, that would themselves be another source of losses.

So While it may seem tempting to reduce the voltage, the current issue should be taken into consideration because we are now trading low speed torque by high speed HP.


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## toyolla2 (Jun 21, 2010)

Siwa, I agree with much of what you wrote. I was pondering on your statement regarding a suspected problem :

_but we didn't add any leeway for voltage sag _
But _voltage sag _is not usually a problem until battery current begins to equal the motor current.

Then I noticed that later you wrote 
_Currently we have a 96V pack and get max speed of 50 km/h, with good acceleration up to 30 km/h._

This is a different problem which is caused by that (insufficient) rewind ratio that left you with 132Vac @ 1500rpm ( as I surmised in my previous post ) So this result is much to be expected.

Personally I would stick with 96Vdc otherwise BMS issues with 320Vdc i.e. the monitoring of 90 cells may overwhelm the project. Something to consider.

With a Curtis controller on 120Vdc each phase winding would need to consist of only ONE bundle of 102 #20awg wires to be laid in each of the 12 slots for that phase. For nominal torque current will have to increase by 34 times the original 9.2A consequently 312 amps will now be required for nominal torque ! 
Of course the *I* ^2 losses remain constant as ever since the path length is 34 times shorter and the effective conductor cross section area has increased by 34 times. The motor torque should now be expected to hold up beyond 5000 rpm since the new V/Hz 13.2/34 = 0.39. or 19.5Vac per 1500 rpm.

I have seen one motor prepared this way. The wires exited the motor as three long bundles each appearing to be loosely shrink wrapped with zip ties added for grip. I had never realized why until now but at low voltage it is likely propitious to avoid unecessary terminations between motor and controller.

At full load motor case temperature rise should not be problematic as it will be entirely due to stator iron loss. I am banking on this motor meeting 1E3 specs for efficiency then iron loss should not present a problem. Premium motors from SEW Eurodrive meet 1E3. 

cts_casemod may be aware that high efficiency types like 1E2 and 1E1 are no longer sold within Europe, North America, Australia and the UK for new equipment. For that reason iron losses when running above 60Hz should avoid the extreme losses of hysterisis and eddy currents of the past.


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## cts_casemod (Aug 23, 2012)

toyolla2 said:


> cts_casemod may be aware that high efficiency types like 1E2 and 1E1 are no longer sold within Europe, North America, Australia and the UK for new equipment. For that reason iron losses when running above 60Hz should avoid the extreme losses of hysterisis and eddy currents of the past.


 
And what exactly is your point?

IE2 can and it is still sold as part of new equipment as long as it is powered by a VFD it still meets the nergy efficiency rules. That may change in the future, but for now it is very hard and there are only a few models of IE4 many of which are variable reluctance drives, so we should see some boost on this type of motors in a near future.

That leaves us with IE3 that can be used with or without a VFD.

But there is a very small number of motors that claim any data other that the nameplate, so the losses are irrelevant here. Now my point is that the problem is not at say 120Hz is more if you run the motor at 240Hz or 5800RPM, plus there will be more losses on the drivetrain in general. Both the lamiations and the core material are not suitable for this, and then, of course, bearings play into account. High speed bearings have a metalic seal and do not provide enough protection for an automotive environment. Standard rubber seal bearings *should* not be operated above 4500-5000RPM.

But the poster has the same model of motor as I am using and I believe it is a IE1 model. IE2 and above are physically larger, so unless you buy a new motor I cant see why you are pointing out IE2 and above. In fact, if you can live with motor rewinded for 115VAC this can be sourced from china cheaper that what a rewind would cost and IE3 Ready. I am seriously pondering this for my conversion. That would give me decent aceleration up to 60KPH and contant torque thereafter (I currently have a maximun speed of 60KPH in second gear at 127Hz but my power starts to fade above 30KPH when the motor pasts the nameplate speed).


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## toyolla2 (Jun 21, 2010)

My point is that the coefficients for both hysterisis and eddy current losses are *significantly lower *today as a result of more stringent energy standards. Also if you are going to all the trouble of performing a rewind it may well be smarter to begin with a newer machine rather than an older less reliable design.


I would look for IE3 certification as a first requirement and not accept just anything that happens to be lying around. I agree only a subset of info appears on the nameplate, whilst information from online catalogs pertains to 60Hz working which is not too useful either. 


One exception is the inertia constant (Jmot). This parameter gives clue to the size of the rotor. I have to credit WEBER for observing that for the *same* Kw output, 4-pole rotors have larger diameters than 2-pole rotors. Giving yet another reason why you should never rewire a 2-pole stator into a 4-pole if the strongest torque happens to be your requirement.


As you wrote only IE3 machines can now be imported as separate items the intent of which is to get us off the slippery slope of short term gains landing us with the long term pain of the energy costs to run those machines. A regulatory vote that speaks well in their favour, and something we in the EV community should be looking to capitalise on.


At the risk of laboring the point I have noticed that the extended stack lengths of these newer machines have caused them to become larger and heavier. It is therefore well founded introspection that alongside the possible use of thinner laminations stator losses are going to be less significant than before and this will continue to hold even as frequencies rise. Core materials in the rotor are less important since rotor frequencies are below 5 or 6 Hz generally and copper rotor cages will probably become the norm. 


There is nothing special about 60Hz current except that in the past there was a race to the bottom to determine the thickest and cheapest laminations that could be tolerated at that frequency. Improvements made to date "raise all boats" and the use of these machines should be contemplated at the higher frequencies. 


This still leaves the big question of how much are the losses at 300Hz ? Something which has to be tried. 200Hz full load tests as reported on AEVA "104V motor" have proved promising. In this particular case a 4-pole 375W motor rewired for 104Vac delivered 1500 watts without overheating on 415Vac.


Sometime after I read that particular thread I coined the phrase "copper loss is constant per unit torque". This is the free lunch that never receives the publicity it deserves. It also validates a further observation that by creating a stator winding with lower V/Hz you can literally "wind a motor for power". 


Last but not least it follows that if iron loss was not a factor we could say that as an induction motor speeds up then its efficiency improves ! 

Depending on the iron loss coefficients, that statement could be truer than most people would want to believe. Bottom line - to advise against building one of these low V/Hz machines on what is probably an outdated belief in my opinion is to leave a golden opportunity on the table.


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## cts_casemod (Aug 23, 2012)

toyolla2 said:


> My point is that the coefficients for both hysterisis and eddy current losses are significantly lower today as a result of more stringent energy standards. Also if you are going to all the trouble of performing a rewind it may well be smarter to begin with a newer machine rather than an older less reliable design.
> I would look for IE3 certification as a first requirement and not accept just anything that happens to be lying around. I agree only a subset of info appears on the nameplate, whilst information from online catalogs pertains to 60Hz working which is not too useful either.


 
My Particular motor does use a big ammount of power just reving high with no load. I plan to remove the flywheel as it is actually a dead weight, but after its up to speed I see no reason for the big power use, other than iron losses and I am not following a V/Hz ration above 1500RPM, if I would this would be worse.

As with laminations, how much of the percentage is lost in the laminations at 60Hz? Say a 2-3% improvement in newer motors? even so, that could mean that even a high efficiency motor at 300Hz could loose as much as 25% on the laminations alone. And iron losses are constant regardless of the load on the motor - they are there if you are using 2% of 150% torque and they increase both with the voltage and frequency. Thats why reluctance motors are one step ahead, because given the right control with a single polarity there is a reduction in the core losses.



toyolla2 said:


> Sometime after I read that particular thread I coined the phrase "copper loss is constant per unit torque". This is the free lunch that never receives the publicity it deserves. It also validates a further observation that by creating a stator winding with lower V/Hz you can literally "wind a motor for power".
> 
> 
> Last but not least it follows that if iron loss was not a factor we could say that as an induction motor speeds up then its efficiency improves !
> ...


 
Coper losses are not constant, they increase by the square of the current so if 1A would yeld a loss of 1W, 2Amps would do 4W and 4Amps 16Watt. In the past this losses were 90% of a motor loss and manufacturers designed the motor to work at 90C at rated power. Imagine on a cooled motor with the windings at 90C how much power was being wasted!

But that only depends on the thickness of the material used, not on the frequency and not on the voltage and while working at low 50/60Hz frequencies I think this is the main work being done by manufacturers - Increasing the copper area, hence a bigger motor with less I^2.R losses. Why would they care a lot with iron losses when they are neglectable at 50/60Hz!? That is exactly what I am pointing, while increasing the voltage will keep the copper losses at a minimum, since you are looking for low torque and high RPM (And HP = torque times RPM) increasing the voltage will increase the iron losses and increasing the frequency will ALSO increase the iron losses, so we have two constants of losses. Of course with a very smart inverter you could dynamically adjust the voltage so the voltage losses would be reduced, and proportional to how much torque you were demanding.

Efficiency, neglecting iron losses, should improve when less torque is required. It is not directly proportional to speed. I can work at 6Hz with 50nm or 600Hz with 50nm with the same copper efficiency neglecting iron and static losses. But this is not true al high frequencies, where iron losses are higher than the copper losses and no one seems to know much about it. Same with transformers, as the frequency increases the meterial is changed.

So all I am saying is that if you are rewinding a motor for the highest power - Go ahead to as low of a voltage as you can, however if you are doing it for economy there should be a sweet point where the motor will operate the most with the highest efficiency, leaving no more that the essential for short moments when extra power could be required


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## toyolla2 (Jun 21, 2010)

Thanks for responding CTS. When I read the following I realised that you are not comprehending what I have written :

_Coper losses are not constant, they increase by the square of the current so if 1A would yeld a loss of 1W, 2Amps would do 4W and 4Amps 16Watt. In the past this losses were 90% of a motor loss and manufacturers designed the motor to work at 90C at rated power. Imagine on a cooled motor with the windings at 90C how much power was being wasted!_


If you don't accept the first statement that "copper loss is constant per unit torque", then the other statements become meaningless.

Let's try to get to first base using Siwajasta's motor 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".


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## cts_casemod (Aug 23, 2012)

toyolla2 said:


> 4a) Therefore "copper loss is constant for rated torque and is independent of the V/Hz ratio".


Neglecting iron and friction losses yes, I agree.



toyolla2 said:


> 4) Therefore "copper loss is constant per unit torque".


Now I dont 
If someone asked me to rephrase that I would say "_the copper losses increase linearly with torque_" or if I had two units of torque I would have double copper losses.


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## PStechPaul (May 1, 2012)

It may be better to use the term "conduction losses", which include copper losses in the stator and the rotor (which may actually use aluminum), and also losses in MOSFETs and/or IGBTs. The percentage of overall losses due to conduction can be reduced by using a higher voltage and frequency (generally with a fairly constant V/F), and adjusting for different amounts of slip may reduce the rotor losses. 

Also, generally, torque is proportional to current and speed is proportional to voltage, but of course if you rewind the motor the V/F ratio will probably change. Most rewinds are for lower voltage and higher current, but the conduction losses in the stator will remain fairly constant because the ampere-turns will not change very much. A higher fill factor may boost efficiency, and at higher frequencies it may be best to use multiple strands of thinner wire to reduce skin effect. But thinner wire also has a greater proportion of cross sectional area for insulation, so that must be factored in.

Higher currents and lower voltage may cause greater conduction losses in the external wiring and the controller. IGBTs, especially, have higher losses at low voltage because of their relatively fixed voltage drop, usually about 2-3 volts, which is a lot of power at several hundred amps. 

Conversely, lower currents and higher voltage, with higher frequency, causes less conduction losses, but then you may have more iron losses in the motor and switching losses in the controller.


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## toyolla2 (Jun 21, 2010)

CTS - thank you for calling me on 

4) "copper loss is constant per unit torque" 

Shortly after posting I began to see how this statement could be misinterpreted. So I replaced it with a corrected version I'm calling 4a for now.

I have always referred to rated torque in my discussions and 1.0 p.u. abbreviated to the term "per unit" always seemed to allude to that.
I agree of course that up to rated torque the copper loss will be proportional to the square of the stator current. However at this moment I'm only concerned, I think we're all concerned for that matter, with just the rated current and rated torque. So scrub 4) we'll go with 4a) from now on. 

This summer I hope to get started on a motor with a combined integral reducer. A test load will be provided in the form of a 22Kw DC generator.
The original plan to use a the stator of a single phase motor was stalled over issues with rotor suitability. I am on the hunt for a IE3 machine and drawing from Siwajasta's experience, as I wrote in post #140, I shall probably construct a single turn winding.


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## cts_casemod (Aug 23, 2012)

PStechPaul said:


> The percentage of overall losses due to conduction can be reduced by using a higher voltage and frequency (generally with a fairly constant V/F), and adjusting for different amounts of slip may reduce the rotor losses.


We were particulary discussing losses due to the rewind. Being copper fairly constant we win *free* horsepower, but I was pointing out that iron losses increase due to the new higher frequencies.

Iron losses depend on the mmf induced on the motor. When steel is polarized behaves like a magnet, so when power is removed it does not go all the way down to zero. There is an excess energy required to take it back to zero when the input voltage reverses polarity on the second half of the sine wave and so on. Just like a capacitor. It blocks DC but acts as a short circuit as frequency increases.

While they increase with voltage (and frequency), this is related to an overal increase in the mmf. It is the same for a 12V or a 13.000V motor. 

Field weakening helps and thats the greatest advantage of Series DC over induction the motor naturally balances field weakening optimizing economy and torque at any load condition.

With an ACIM VFD it is usual to spit a constant V/Hz based on maximun torque required, reducing slip and rotor losses.

Thats why a fixed V/Hz ratio is crap:

Too less and you have great slip under load so higher copper and rotor losses, poor aceleration but good economy at part load.

Too much results in good performance at high torque levels and low rotor losses, however at part loads hysterisis, magnetic losses and a percentage of the copper losses increase, because there is current on the stator that is not doing any usefull work, instead the motor is dragging itself and requires more energy to acelerate (or it will not accelerate past a certain point). 

In fact most VFD have something called "FAN LAW" that changes the V/Hz curve and makes for a more economical motor, problem is, on a car, its not only the speed of the car that requires a given HP, but how fast and with how much torque you want it to be able to accelerate.



So the point is, neglecting iron losses just output a constant V/Hz proportional to the speed for the maximun torque required and increase the voltage to archieve power at twice or more the rated RPM, efectively doubling shaft output power. On a real world there are other losses and while we now have a motor with 2 or 4 times the nominal power, the losses are also higher and a more refined electronic control is required to take advantage of this while keeping economy to a maximun. Otherwise the efficiency will suffer.​


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## cts_casemod (Aug 23, 2012)

toyolla2 said:


> The original plan to use a the stator of a single phase motor was stalled over issues with rotor suitability. I am on the hunt for a IE3 machine and drawing from Siwajasta's experience, as I wrote in post #140, I shall probably construct a single turn winding.


 
New ABB motors have a switched reluctance rotor for IE4 levels. If this was powered with DC you could cut the losses at high frequency, effectivelly taking 100% advantage of the rewind. They wont sell to you but the idea can be used.

I just dont believe getting an IE3 would help a lot. First you are carrying extra weight due to the larger construction of the motor, second at higher frequencies the iron losses would still be there, altough less. Think of it as a capacitor. A 1uF capacitor attached to the 60Hz line wont draw much power, but the same capacitor at 400Hz will! The higher efficiency is just a 0.5uF capacitor in our example.

Also, based on a 4 switch inverter , the inverter design would be 33% more efficient, so you could gain maybe 2%, plus another 2% because simple PWM can be used, instead of sine PWM.

I Think Paul was working on something like that. I would also like to try it. I will have a new 5.5KW induction motor for my tests next month.


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## toyolla2 (Jun 21, 2010)

PSTechPaul re the first paragraph, 


sure I agree, I think you're referring to the Thevenin equivalent model for the ACIM with the rotor impedance transformed into the stator circuit.


Later I see you move to discuss controller slip strategy. 


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 that is 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 the 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 work several years ago not much has changed here.


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## bhamguyspecv (Sep 25, 2013)

This has to be the most informative post on the workings, improvements, and use of AC motors ever made. I registered on this forum for this post alone, and I've spent 6 days at work trying to read all the posts and cram the information in. Holy wow, hats off to all of you who contributed. I really thought motor redesign and customization was a lost art.

I have been kicking around the idea of a DIY EV for about 10 years now, and I am more encouraged now than I have ever been! I can't, in my good conscience, use a DC motor and I am willing to build and scrounge to get the components I want even if it takes a LOT longer. I don't want something that'll putter me down the road, I want an electric that I can eventually make somewhat exciting to drive, and will run freeway speeds. My round-trip to work is about 60 miles a day mostly interstate.

That being said, please forgive me for being an amateur among the rocket scientists. I used to work at a pipe foundry in the electric shop, and I have assisted in the rebuild of about 30-40 squirrel cage 3ph motors ranging from 20hp - 150hp 230/480v but I am by no means an expert on the subject.

Reading from the prior posts, I saw the Chorus harmonics motor which shows to be promising.

I remember learning about Nikoli Tesla years ago and how the polyphase system was envisioned by this mastermind to "combine 2 500hp generators to make 1 1000hp motor". Am I to assume that the chorus motor is a 17phase motor?

I have been trying to shop for a good AC motor to do the conversion with on a thin budget, and I am coming up completely empty handed as far as the existing market goes. Anything that fits the output requirements in the industrial line is too bulky and ESPECIALLY too heavy (looking at 20-30hp). Light/compact EV oriented motors cost a small fortune.

My understanding is that using the 3phase system, we are essentially packaging 3 motors into one shell. With the cost of high current IGBT's and the lack of required standards in the EV industry (theres no power company that offers just 1 or 3 phase power in X volts), why not rewind a motor for more than 3 phases and use more but smaller IGBT's? It seems the price of the IGBT's increases exponentially with voltage/current capacity. Would it not be more efficient to rewind a motor for 6 phases and running 150-200 amps each phase? (6 pack of 200a igbt's found about $200 vs $1800 for 1000a) That could potentially yield a very nice savings.


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## Siwastaja (Aug 1, 2012)

bhamguyspecv said:


> This has to be the most informative post on the workings, improvements, and use of AC motors ever made


Thanks for the kind words.




> I remember learning about Nikoli Tesla years ago and how the polyphase system was envisioned by this mastermind to "combine 2 500hp generators to make 1 1000hp motor". Am I to assume that the chorus motor is a 17phase motor?


Multiphase indeed may provide some improvements by better utilizing the iron by providing more equal flux and by reducing unwanted harmonic frequencies, but these improvements will most likely be rather minor. It will be worth it only if you find a way to make it without increasing the complexity and cost.



> My understanding is that using the 3phase system, we are essentially packaging 3 motors into one shell.


No. You just create a rotating magnetic field on a coordinate system where you have three axes. You need a rotating magnetic field to build a motor, and you can do it by using two coils (x axis and y axis) so that they can together support full rotation. (This is called two-phase motor.) But having three axes instead of two have several electrical benefits. Having more than three, however, can only be a minor optimization, and actually brings back problems from 2-phase motors that 3-phase solved.




> With the cost of high current IGBT's


They are not that expensive anymore. You can build a 100 kW capable bridge for $300.



> and the lack of required standards in the EV industry (theres no power company that offers just 1 or 3 phase power in X volts),


W h a t ??




> why not rewind a motor for more than 3 phases and use more but smaller IGBT's?


Here are some of the reasons:

A lot more wires, a lot more connections on the control side, more expensive gate drive grand total, more complex control.




> It seems the price of the IGBT's increases exponentially with voltage/current capacity.


Not true, it increases quite linearly. The large devices actually include smaller devices paralleled.



> Would it not be more efficient to rewind a motor for 6 phases and running 150-200 amps each phase? (6 pack of 200a igbt's found about $200 vs $1800 for 1000a) That could potentially yield a very nice savings.


Why compare a 200A 6-phase bridge to a 1000A 3-phase bridge? The latter provides 2.5 times the power.


Multiphase has some point in it but it's not any kind of silver bullet and if you see it solving power or budget problems, the explanation is more simple; you have calculated wrong and need to double check the numbers.


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## bhamguyspecv (Sep 25, 2013)

Here's what I was afraid of my knowledge on the subject is starting to run out of juice quickly... Can anyone advise a good book, website, other information on this subject? I understand wiring diagrams, Y and Delta hook up, voltage selection, and how to rip one down to the individual parts and reassemble. The actual engineering involved with winding/rewinding, math, overdriving (higher current/voltage) are a little over my head. I know a motor can be run beyond the specs but how much-how long-how hard and if it can be done safely for extended periods and how I'm dying to learn.

cts_casemod> I'm a colonial, didnt know if you noticed that I'm working in HP instead of KW. A 25hp domestic industrial motor weighs 350lbs or better. In fact, SEW Eurodrive was the smallest/lightest one I could find, and the weight of their 40hp motor is only 20-30lbs heavier than the 25hp model. Seems the difference is they infuse copper into the rotor somehow (can't find much information on it). I used to work with their motors an an auto manufacturing plant, and I must say they're a piece of art in comparison to what we build stateside.

Sewasteja> You have brought up a few points I'm not clear on. Going back to Google to find more info. What I was referring to with the standards... since EV's are using DC voltage from a battery (even if it is being converted to AC) we are not locked to the standards offered by utility companies (single or 3 phase power @ 120, 208, 240, 480, etc etc) so it seems we'd have the world at our fingertips when it comes to motor design. Complying to standards/offerings is not an issue except for charger input voltage.


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## PStechPaul (May 1, 2012)

The only major limitation of utility power is the frequency of 50 or 60 Hz, which was chosen over 100 years ago because of certain limitations of the equipment at that time. It resulted in electrical equipment being very heavy and bulky. There is an entire class of equipment, mostly for aircraft, using 400 Hz, and this results in much smaller and lighter transformers and motors. But it does require a higher grade of steel and thinner laminations for best efficiency.

Now that solid state components are inexpensive and ubiquitous, it is easy to generate just about any frequency (up to about 1000 Hz) for motors. The motors that are made for 50/60 Hz are optimized for that frequency, but generally can be run at 2-3 times that without too much problem with magnetic losses. Motors and transformers use what is known as V/F which means that you can double the voltage at twice the frequency to get the same current. So you can get 2.5 times the rated 60 Hz power using 150 Hz, and 575 VAC on windings rated for 230 VAC. You are limited to about 600V because of the insulation class of the motor, and also you need to use medium voltage (601-5000V) protection and control equipment over 600V.

Sometimes you can just rewire (not rewind) a motor for nominal 120-140 VAC instead of 208-240 VAC so you might be able to get 3-4 times the output power by "overclocking". However you also need to consider the maximum speed of the motor. A four pole motor nominally 1800 RPM can safely run at 4500 RPM (2.5x) but perhaps not at 7200 RPM (4x). So you might be able to use a 6 pole (1200 RPM) or 8 pole (900 RPM) motor for higher overclocking, but they tend to be larger for the same HP rating so the benefits are not as good.

If you are adventurous you can try your hand at rewinding a small motor that you might get cheap or free. I rewound a freebie single phase motor for three phase and a much lower voltage, so that might be a worthwhile project to get started. I would suggest a 24 or 36 slot stator which are common for fractional HP motors. Larger motors may have many more slots and thus may be wound for a higher number of poles. You can also rewind for more phases but that gets very complicated and you will not be able to use standard drives. Three phase motors over 10 HP are usually 85-95% efficient and you won't do much better with more phases.

It may be wise to consider premium efficiency motors for EV use, even though they are usually larger and heavier than standard motors. They have more copper and iron with lower losses, and thus may be overdriven further and will run cooler and more efficiently at normal levels of power. You may be surprised to learn that it takes only 15-20 HP for most driving needs with a small vehicle.


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## kennybobby (Aug 10, 2012)

bhamguyspecv said:


> ... Seems the difference is they infuse copper into the rotor somehow ...
> 
> and ... since EV's are using DC voltage from a battery (even if it is being converted to AC) we are not locked to the standards offered by utility companies (single or 3 phase power @ 120, 208, 240, 480, etc etc) so it seems we'd have the world at our fingertips when it comes to motor design. Complying to standards/offerings is not an issue except for charger input voltage.


i really like the way you are thinking here--that's how progress is made. Tesla puts copper in the slots of their squirrel cage rotor also, it weighs more than aluminum but is such a better conductor with less resistance for the induced currents.


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## bhamguyspecv (Sep 25, 2013)

I didn't even think about a copper cage... I can see how that'd perk a motor up a bit.

It is sad though, I just don't really see any of the big auto manufacturers pushing EV tech except for the startups. Old habits (and dirty money) die hard. I wish everyone and every company could think outside the box a little, especially the ones who have the resources to turn great thoughts into amazing realities. I can't believe a battery exchange station is just now a concept for EV's. They have been used for decades where battery electric equipment has to operate around the clock. Who's actually raving about it? The little EV company that could (Tesla) not Toyota, Nissan, GM, Ford, Chrysler.

Sorry for going off on a tangent, wanted to bump the question on reading material, I really am quite eager to learn about the winding and design aspects that I have the power to change to see where I can improve.


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## bhamguyspecv (Sep 25, 2013)

Holy wow, the controller for your A2 looks like a piece of art! GM put that hideous piece of plexiglass into the hood of the Vette to show of the supercharger... I'd GLADLY cover that with a piece of glass and show it off! KUDOS to the guy that designed and built it! My partner has very little knowledge of electricity, and he even complimented how cool it looks.

Speaking of the FI system you were talking about, it always boils down to absolute necessity. California's air quality had to turn so bad for you that it was almost better not to breathe before anybody did anything, and for a good while their emissions standards costed extra!

Then the auto manufacturers sued the pants off of them for the electric car mandate... I still refuse to buy GM products, being they were the biggest culprit AND the closest to being sucessful in the EV arena.


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## cts_casemod (Aug 23, 2012)

bhamguyspecv said:


> Holy wow, the controller for your A2 looks like a piece of art! GM put that hideous piece of plexiglass into the hood of the Vette to show of the supercharger... I'd GLADLY cover that with a piece of glass and show it off! KUDOS to the guy that designed and built it! My partner has very little knowledge of electricity, and he even complimented how cool it looks.
> 
> Speaking of the FI system you were talking about, it always boils down to absolute necessity. California's air quality had to turn so bad for you that it was almost better not to breathe before anybody did anything, and for a good while their emissions standards costed extra!
> 
> Then the auto manufacturers sued the pants off of them for the electric car mandate... I still refuse to buy GM products, being they were the biggest culprit AND the closest to being sucessful in the EV arena.


You are right. And I believe that such as we have electrics today as an option, one day they will be standard, with the remaining being plug in hybrids for those that travel a lot. A lot still needs to be done to the current charging infrastructure, Its quite a shame you cant stop in a petrol station to fast charge and pay the equivalent KW or so even if they would charge twice it would still be a deal. Certainly not a reality these days... If instead of rebates for the purchase of electric vehicles the ICE (Only) counterparts were made to pay a premium, not only the prices would be more close, but also an incentive for manufactures to start producing plug in hybrids, that could work most of the time as electric and provide long range on petrol. Just look at the first versions of the Toyota Prius - A wonderful example of great engineering, but needs to burn petrol to charge the tiny internal battery. Many people successfully converted them to great hybrids (that work most of the time in Battery mode, being charged at home, just like an ordinary electric), why couldn't Toyota do the same?

Makes me remind of incandescent bulbs... Today they cost nearly as much as the low energy equivalents, but I still see them everywhere. And that will continue until the phase out is complete. 

Regarding GM... I don't blame them. They were in fact pioneers and I think there was a lot more to what happened that the public never got to know about. As always many factors to put pressure over the manufactures...


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## Hollie Maea (Dec 9, 2009)

What would you guys say is a good source of winding wire?


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## Ivansgarage (Sep 3, 2011)

This is where I buy my mag wire.

!0lbs 18 gauge 102.00 wont find any cheaper that that.

http://www.temcoindustrialpower.com/products/Magnet_Wire/MW0154.html

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## Hollie Maea (Dec 9, 2009)

Thanks Ivan!


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