# about 3-phase motors



## NintendoKD (Apr 29, 2012)

Ok, we are not talking ICE here, so shouldn't a motor turn less rpm's and produce more torque relatively than at higher rpm's. I imagine that there is an efficiency range of a motor right? like, I toss a ball in the air, there is a point at which it appears to hover seemingly defying gravity. The motor should also have a point like this right? I am looking for formulas, and information on how induction motors are made. I want to do this right and just need more information. I want the most "efficient" motor. I need low weight, good, electromagnetic efficiency, low friction bearings, high input voltage and low input current with the capability to quadruple the output temporarily. I want to understand these things better here. wouldn't it just take too much power to make the motor spin at higher rpm's? wouldn't the motor be more efficient while inside a vacuum? I was also thinking of using something unique in the construction of a "new" design of motor. I understand electromagnetism, magnetics, and electricity, fairly well and have a very interesting theory. Before anyone gets too excited, I want to debunk any free lunch ideas, no free lunch, just more efficiency, via lower losses overall. I need to find a custom motor shop, or perhaps someone who can help me work out some intricacies of the three phase motors. I need someone in the know to guide me before I get too carried away.


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## subcooledheatpump (Mar 5, 2012)

Are you thinking 3 phase induction motors or 3 phase brushless DC? (I know you said induction in your post, but if you're looking for the most efficient then....)

Technically speaking a 3 phase brushless DC motor is the most efficient. 

There is an efficiency curve for every motor, yes, but for an AC motor that happens at it's rated frequency and about 80% rated load (give or take) If the frequency is increased, increased electromagnetic losses in the steel stator cause heat (think induction heater) At low frequencies, the motors' impedance drops and thus disrupts the power factor, so full current will happen without full voltage, therefore less actual power. The copper windings though, are the main source of losses at the rated frequency and load. 

Induction motors benefit from more conductive rotors, IE copper rotors increase efficiency. 

Brushless DC motors are more efficient because it's not necessary to magnetize the rotor, since it's always magnetized. Though they aren't as flexable as induction motors in terms of making torque at low speeds and they can be demagnetized at high temperatures, resulting in less torque.

As far as overloading, that is very limited due to the magnetic abilities of the stator steel. At a certain point, the steel won't be any more magnetic regardless of the magnetizing current. I find that induction motors can usually overload to 4X rated current, but only at low frequencies.

Also because of that, larger motors are usually more efficient, at rated frequency and load

Some info 

http://www.transtutors.com/Uploadfile/CMS_Images/8775_Power%20Factor%20Characteristics.JPG

http://www.reliance.com/prodserv/motgen/b7097_2.htm

www.esat.kuleuven.be/electa/publications/fulltexts/pub_1485.pdf


www1.eere.energy.gov/industry/bestpractices/pdfs/10097517.pdf


www.geindustrial.com.br/download/artigos/asdi.pdf


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## NintendoKD (Apr 29, 2012)

That makes sense as the applied electromagnetic field need be much less to perform the same work on the rotor. Who makes em? Does anyone have one installed in their ride? Realistically, I do not need many rpm's, the motor will be coupled to a transmission, but the low end torque production may be an issue. I want it to drive like a normal car, to some extent. Higher efficiency is a must because of sheer distance, so it looks like 3-phase brushless dc is the way to go.


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## subcooledheatpump (Mar 5, 2012)

Induction motors are industrial standard, and many, even here have induction motors installed in their cars. 

I'm one of them. 

Right now, I'm in the process of replacing the 15 Hp 6 pole induction motor in my van with a 30 HP 4 pole. 

The old 15 HP motor could run the van and make it feel pretty normal up to about 40 MPH. I want a little more speed, thus the upgrade. No transmission in the van 

Etischer here on the forums has a specialized induction motor that was made for the ford ranger ev in his car, he's got a transmission and some pretty impressive results. His top speed is over 100 mph.


Brushless DC motors are also industrial standard, alot of professionally developed cars use them (nissan leaf, chevy volt, a few more I can't think of at the moment.....) They are a little bigger and heavier though.

Making a car feel "normal" is pretty easy though, you just need a VFD with variable torque. low torque and low speed when the throttle is minimum, and then high torque and high speed when the throttle is maximum. Couple that to a transmission and you're set


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## NintendoKD (Apr 29, 2012)

well, I thought I was confused before, now I know that I really know nothing.


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## PStechPaul (May 1, 2012)

I have pretty much concluded that the ultimate motor, in terms of cost, efficiency, ruggedness, low maintenance, and ease of control, is the three phase motor (or perhaps six or more if you are going custom). There are some novel ideas that may challenge the usual choice of BLDC, especially if EVs become more than a niche and the market "explodes". Buy stock in rare earths!

What you might want to do is start with a small conversion project, such as a riding mower, tractor, or go-cart. I'm doing that now, and the only thing that you may need to build is a DC-DC converter to get the high DC link voltage for a VFD. But you can also use something like a 2000 watt or higher inverter to get 120 or 240 VAC and rectify that with some diodes and filter capacitors to get 300-360 VDC.

You can get a small 3 phase motor very cheaply. I bought a 5 HP motor for $100, and my 2 HP motor was less than $50. Then I bought a 2 HP VFD on eBay for about $50. I got a riding mower/go cart for $40, and I was able to (just barely) go for a ride using a 17 A-H SLA battery. Here's a link to the last video of my project:
http://www.youtube.com/watch?v=y0qWY4bVnEA

So with a couple hundred dollars of parts you can have a working and possibly useful vehicle, and you can gain valuable experience with three phase motors. Also take the time to watch some of the many presentations on youtube about three phase motors, and also basic tutorials. But for myself, I find there is nothing like crafting something with my own hands and mind. And I even wound an 8 V 3 phase motor using a junk single phase motor. Materials: almost nothing. Time: several weeks. The value in experience and AHA value when it finally worked: _*priceless*_!

I am also interested in exploring the design of the VFD itself, and I made a crude version quite a few years ago which used a step approximation of a three phase power source and I ran my custom motor directly on a 12 V battery. It finally died with an impressive puff of magic smoke, but that was because of improper choice of components and some design flaws. But I only blew up a few dollars worth of MOSFETs.

I cannot say that I am an expert in the "field" of motors and drives, and certainly not in EVs, but I enjoy my experience and education as I explore this means of reducing our use of fossil fuels and achieving high efficiency transportation. After quite a lot of research, I think three phase motors are the way to go. And they CAN be made much more efficient and with enormous power-to-weight by using high frequency drives and higher grade magnetic materials, WITHOUT the gotchas of rare earth magnets.


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