# which motor is better?



## amir.pe (Jun 9, 2012)

hi
we are a group and want to build a electric car(or convert usual car to ev).
and i have some questions:
if you know or have an article that help us in these questions field please refer. 
1.which motor is better?(AC or DC and that's type)
2.some information or article that help in power electronics of ev?
3.I am power engineer student but in outset and want to know challenges in the motor type that selected for EVs to research more?
thank...


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## major (Apr 4, 2008)

amir.pe said:


> 1.which motor is better?(AC or DC and that's type)


The pros and cons are discussed here often. Unfortunately you cannot search on this site for "AC vs DC" so those threads are hard to find. Nose around the motors forum here and stay for a while and the subject will come up again.....it always does 

In the meantime, don't dwell on it. Use the best package available for your design with the constraints you have to deal with.


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## Ziggythewiz (May 16, 2010)

major said:


> The pros and cons are discussed here often. Unfortunately you cannot search on this site for "AC vs DC" so those threads are hard to find.


Yes, but you can google anything. I see about 9 decent threads here:
https://www.google.com/search?q=site:diyelectriccar.com+ac+vs+dc


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## major (Apr 4, 2008)

Ziggythewiz said:


> Yes, but you can google anything. I see about 9 decent threads here:
> https://www.google.com/search?q=site:diyelectriccar.com+ac+vs+dc


O.K. smartypants, which wins?


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## Ziggythewiz (May 16, 2010)

For me?, DC of course. 

That really doesn't help a noob at all though, they should read enough to understand each side and make their own conclusions.


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## EVSource Mikey (Apr 24, 2012)

n00b help is my specialty!

Amir:
DC motors and compatible parts are less expensive, and have a stronger community support. For these reasons I would recommend a DC motor & system for your school project.
If your school has a large budget, and your class wants to brave the less popular world of AC systems, then please do.


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## Ivansgarage (Sep 3, 2011)

Ziggythewiz said:


> For me?, DC of course.
> 
> That really doesn't help a noob at all though, they should read enough to understand each side and make their own conclusions.


Ziggy, you are way wrong, ac is the only way. dc, old old technology.


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## PStechPaul (May 1, 2012)

For an engineering student my suggestion is to purchase some good books on magnetics and motor design and control. Irving Gottlieb's book is excellent. Look up articles on various types of motors and try to understand as much of the theory as possible. Also read as much as possible about the prevailing battery chemistries, Lead-acid, NiCd, NiMH, LiPo, and LiFePO4. Follow some of the threads comparing the performance and cost factors. I don't know what is being taught in schools these days. When I went to Johns Hopkins University 1966-1970 it was a much different world. But basic motor theory has not changed much since then regarding brushed DC motors and induction motors.

Most important for me has been actually building things and testing them. I was always much better with lab stuff than theory. Math is not my strong point. I think it would be very useful (and fun) to build some simple motors as can be seen on youtube. There are some far out free energy demos as well as some well done tutorials and several interesting examples. Try to analyze what is being shown and use analytical thinking to do a "reality check" to identify false claims.

I happen to prefer three phase induction motors. They are inexpensive, rugged, powerful, efficient, and fairly easy to control. They do require a rather complex VFD but they are available cheap as used and surplus, or you can make your own.

DC motors, particularly series wound traction motors as used in fork lifts and golf carts, run at lower voltages and have high starting torque and can be controlled with a rather simple PWM circuit. But they require maintenance of brushes and can easily overspeed without an RPM sensor and protection circuit.

I suggest that you try building an electric bike or go gart or tractor, using whatever motor and controller and battery technology appeals to you. It will only cost a few hundred dollars and you should learn a lot and you'll have a useful vehicle as a result. Based on your experiences you may gain a better appreciation of the technology you choose and you will be able to select the "best" for your full-size EV project.

If you plan to pursue a career in EVs it may be better to concentrate more on AC induction motors or BLDCs, and maybe switched reluctance and other emerging types. I think brushed motor technology is a dead end for commercial applications, although it is perfectly appropriate for DIY and small motors such as fans and accessories.

Most important, perhaps, is to maintain contact with other EV people and actively discuss your projects and theirs.


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## Roy Von Rogers (Mar 21, 2009)

Why would one have to buy a book to learn about motors, all the info you ever want to know is in here, especially since we have a Major contributor and expert in here..... 


Roy


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## otp57 (Feb 7, 2012)

Ivansgarage said:


> Ziggy, you are way wrong, ac is the only way. dc, old old technology.


AC or DC the key is to build a EV
I feel that both motors are good dc motor ar not as complex as ac motors.
A first time builder should start with a dc systen and after learning go for the better AC system. DC may be called old school but it works.


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## Hollie Maea (Dec 9, 2009)

amir.pe said:


> hi
> we are a group and want to build a electric car(or convert usual car to ev).
> and i have some questions:
> if you know or have an article that help us in these questions field please refer.
> ...


If this is for school, you should go AC. DC is cheap and easy but if this is supposed to be a learning experience, better to learn the future rather than the past.


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## otp57 (Feb 7, 2012)

Hollie Maea said:


> If this is for school, you should go AC. DC is cheap and easy but if this is supposed to be a learning experience, better to learn the future rather than the past.


 
DC is still the future and so is AC each has it place.
Learn both system the cost of a ac sysem is much higher I would like to do a AC system at 144v or more.


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## Ivansgarage (Sep 3, 2011)

otp57 said:


> AC or DC the key is to build a EV
> I feel that both motors are good dc motor ar not as complex as ac motors.
> A first time builder should start with a dc systen and after learning go for the better AC system. DC may be called old school but it works.


DC motors are much more complex.
dc motors can self destruct, over rev and other problems, here is two examples. 

Hear is a thread on brush failure
http://www.diyelectriccar.com/forums/showthread.php?t=73628&highlight=putty


Here is a over speed problem
http://www.diyelectriccar.com/forums/showthread.php?t=73286&highlight=putty


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## amir.pe (Jun 9, 2012)

thank for your attention but:


Ziggythewiz said:


> Yes, but you can google anything. I see about 9 decent threads here:
> https://www.google.com/search?q=site:diyelectriccar.com+ac+vs+dc


I read almost all of these articles and have a collection but i couldnt achieve a exact consequence 



major said:


> The pros and cons are discussed here often. Unfortunately you cannot search on this site for "AC vs DC" so those threads are hard to find. Nose around the motors forum here and stay for a while and the subject will come up again.....it always does
> 
> In the meantime, don't dwell on it. Use the best package available for your design with the constraints you have to deal with.


we dont have Circumstance for buy a package because of university rules and we are researching and want to assemble a car exactly and my field is motor and control unit.then I want a list of motor and control unit parts and some primary information that I can continue these information to achieve conclusion?



EVSource Mikey said:


> n00b help is my specialty!
> 
> Amir:
> DC motors and compatible parts are less expensive, and have a stronger community support. For these reasons I would recommend a DC motor & system for your school project.
> If your school has a large budget, and your class wants to brave the less popular world of AC systems, then please do.





otp57 said:


> AC or DC the key is to build a EV
> I feel that both motors are good dc motor ar not as complex as ac motors.
> A first time builder should start with a dc systen and after learning go for the better AC system. DC may be called old school but it works.


we dont have budget problem and we are not limited for that but in this case why major companies use AC motors for their products like Tesla?



PStechPaul said:


> For an engineering student my suggestion is to purchase some good books on magnetics and motor design and control. Irving Gottlieb's book is excellent. Look up articles on various types of motors and try to understand as much of the theory as possible. Also read as much as possible about the prevailing battery chemistries, Lead-acid, NiCd, NiMH, LiPo, and LiFePO4. Follow some of the threads comparing the performance and cost factors. I don't know what is being taught in schools these days. When I went to Johns Hopkins University 1966-1970 it was a much different world. But basic motor theory has not changed much since then regarding brushed DC motors and induction motors.
> 
> Most important for me has been actually building things and testing them. I was always much better with lab stuff than theory. Math is not my strong point. I think it would be very useful (and fun) to build some simple motors as can be seen on youtube. There are some far out free energy demos as well as some well done tutorials and several interesting examples. Try to analyze what is being shown and use analytical thinking to do a "reality check" to identify false claims.
> 
> ...


I agree your opinion.our activity is often theoretical in university or if I say clearly we are in theoretical level now.
in the period that I research understood that the AC motor is better a little but not exactly for example the AC type use more power because of its stator winds but in DC type we can use magnet instead of stator wind and it can help us to drive more distance.in this case this difference in miles per one battery charge is much or little?
the car we want to assemble is a SD or family car and we dont need to more starting torque and our aim is more mile driven with least power.whats your opinion in this case?
at last I need some information in the control of AC motors field?like VFD(or PWM)(our lessons cover this field but I want to know something now in simple language) 
now we can see articles from electrostatic motors,are these motors useful for EVs industry?whats your opinion?
thank lot


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## aeroscott (Jan 5, 2008)

check the wheel motor discussion and link for switched reluctance motors . the biggest earth moving equipment uses them . max power at stall with out heating armature , switching is square wave 1/10 the switching speed of vfd's(AC) and no shoot-threw shorting in the controller . Much lighter motor because high speed possible and cooling . higher overall efficiency .


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## PStechPaul (May 1, 2012)

Seriously, read Gottlieb's book and then you will see why an electrostatic motor is not practical for an EV. Electric and magnetic fields are analogous and theoretically you can get just as much power from electrostatic as electromagnetic, but you need to consider the physics. 

For the same amount of energy, in Joules, 0.5*C*V^2 = 0.5*L*I^2. So, for a 1kW motor you need 1000 Joules/sec, and at 50Hz that's 20J/cycle. For a 1H inductor, 20J is 6.3A, and you need to get that current in 0.02 seconds, so that is 316 A/sec, which is about 316V for 1H. If you look at standard components you can probably find a 1H inductor good for 6 amps and it will be roughly the size and weight of a 1kW motor. the current and voltage are well within normal ranges of wire and insulation. 

I will let you perform an analogous computation for an equivalent electrostatic machine. But you will probably find that you need a 1F capacitor rated at 6.3V. This is easy to achieve in a much smaller size and weight. And you just need to achieve 316 V/second which is 316A.

But the problem is that magnetic energy is stored in the gap of an inductor, and you can make a motor with a gap of a few thousandths of an inch and a magnetic field does not break down air and as long as the magnetic components are strong enough the gap can be maintained and the motor will run. 

Electrostatic energy is also stored in a gap. For a given amount of energy, such as 20J, and a motor of practical size, you might be able to get a surface area of 10" x 10" or 100 square inches and maybe 100 plates with a spacing of 0.1", for a cube 10" on a side, similar to the 1.5 HP motor described above. Capacitance is determined by e*A/d, in meters, so in this case the capacitance would be about e*100*0.064/0.0025 = 2580*e. Now e is the permittivity of free space (or air) and is 8.854*10e-12 Farads per meter. So this capacitor would be about 0.228 uF. 

In order to store 20J of energy in this electrostatic motor you would need a voltage of sqrt(40/C) or 13,231 volts. But air breaks down at about 10,000 volts per inch so the 0.1" spacing would only support 1000V. Thus the electrostatic motor would need to at least 13 times bigger. This might be improved by adding insulation between the plates, which simultaneously increases the breakdown voltage and increases capacitance for the same spacing. 

Most plastics such as polypropylene have dielectric constants of 2-3 so you might be able to reduce the voltage by sqrt(3) to 7600V. But then it is a mechanical nightmare to maintain spacing between large metal plates containing opposite (attractive) electrical charge, without excessive friction (if the insulated plates touch). And then there is the problem of converting the compressive force to a more useful rotary force. 

It would be interesting to design a non-trivial electrostatic motor. An electrostatic voltmeter is an example of how an electrical charge can produce rotary motion. But it requires several thousand volts and creates only a tiny amount of torque and designing a 5000V commutator or solid state switching circuit is also a huge challenge. This would be a great science project or engineering project. It's certainly an area that has not received much attention!


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## amir.pe (Jun 9, 2012)

thank you for exact information 
then we can design an electrostatic motor that suitable for EV but we have some problems.and I think these problems are serious.ok?
can I find the principals of electrostatic motors in Gottlieb's book?
if that is possible to answer my other questions in post 14?
thank...


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## PStechPaul (May 1, 2012)

Google is your friend:
http://en.wikipedia.org/wiki/Electrostatic_motor
http://www.instructables.com/id/Be-a-Scientist:-Build-an-Electrostatic-Motor/
http://users.tm.net/lapointe/Electrostatic_Motor.html
http://www.aml.t.u-tokyo.ac.jp/research/es_motor/es_motor_e.html
http://www.webping.net/electroDynamic/electrostatic_motor.html


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