# Building an AC Motor



## brian_ (Feb 7, 2017)

It's certainly possible to build one. It's certainly not practical to build one as good as a common production unit. Would a 'good enough' motor be any cheaper to build than the cheapest used motor of about the right size that you could buy? That seems unlikely to me, but it depends heavily on your knowledge, skills, available equipment, and sources of materials.

Would anyone really build a motor, or is the plan to rewind an existing motor to different specs? It seems unlikely that most people would want to stamp out and assemble iron plates for the laminated stator and rotor, or cast or machine end frames or a shaft.

I do understand a desire to make something for an EV conversion which is lighter than a typical industrial motor.


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## resspt (Mar 18, 2019)

Hmmm okok. But i was looking through ebay and i only saw second-hand motors at more than 2 grand. Is that the normal price or was i not looking correctly??


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## brian_ (Feb 7, 2017)

resspt said:


> But i was looking through ebay and i only saw second-hand motors at more than 2 grand. Is that the normal price or was i not looking correctly??


I don't really know whether that is normal or not - for one thing, it really depends on what type and size of motors you're looking at. But if you value your time at more than nothing, and have to pay for materials, do you think you can build a motor from scratch for even $2000?

I realize that the build-your-own idea was from a conversation, not some published information, but is there some online source of a description of how you would plan to build a motor?


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## resspt (Mar 18, 2019)

About the time, I'm an Eletrical Engineering student, so I was actually doing this to gain some experience and learn some things as well. About the materials and any other additional cost, that's why I came here and to know if this could be done for a reasonable price!


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## brian_ (Feb 7, 2017)

As a learning exercise, it might make sense to try a much smaller motor, if you have a project (not a car) that needs one. It would take less time, cost less in materials, and matter less if it turned out to be marginal in performance.


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## resspt (Mar 18, 2019)

Ok! Thank you so much for your advice!


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## Duncan (Dec 8, 2008)

resspt said:


> I've been wanting to do my own EV conversion with my 2001 VW Golf for a while and i've been researching for a while now, but a few days ago I talked with someone that was also intending to build his own AC Induction Motor.
> Do you think it's possible to build one (not expecting to be the best motor, but one that can have a nice performance)?


Building from scratch is going to be difficult and expensive however you could look at rewinding and rebuilding an existing motor

Alter the magnetic design to suit the needs of a car motor


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## Ivansgarage (Sep 3, 2011)

Winding 3 phase motors for high amps electric car

https://www.youtube.com/user/Ivansgarage/videos

https://www.youtube.com/watch?v=QqeuxGBFHas

https://www.youtube.com/watch?v=dLE-JLQ36IQ&t=815s


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## henrykeultjes (Apr 13, 2017)

resspt said:


> I've been wanting to do my own EV conversion with my 2001 VW Golf for a while and i've been researching for a while now, but a few days ago I talked with someone that was also intending to build his own AC Induction Motor.
> Do you think it's possible to build one (not expecting to be the best motor, but one that can have a nice performance)?


There is all kinds of information on the web about building your own Switched Reluctance motor - much simpler and does not require an inverter since those type of motors are inherently DC.


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## brian_ (Feb 7, 2017)

henrykeultjes said:


> There is all kinds of information on the web about building your own Switched Reluctance motor - much simpler...


There is nothing simpler about the stator of a switched reluctance motor compared to any form of motor with a similar pole count. The SR rotor is just as complex in the construction of the laminations, so the only simplicity advantage compared to an induction motor is the lack of the induction motor's "squirrel cage" of conductors.

While there may be lots of information, it would be interesting to hear from someone who has actually built a successful motor from scratch... of any kind. And I mean a car-worthy motor - I built a simple brushed DC motor long ago, along with everyone else in my grade 10 electrical shop class, but it wasn't good for anything except a (valuable) learning experience.



henrykeultjes said:


> ... does not require an inverter since those type of motors are inherently DC.


A switched-reluctance motor requires a switching controller with the same fundamental complexity as a sine-wave AC inverter, except for the pulse-width modulation used to form the sinusoidal waveform. The switched reluctance controller still has two IGBT's (or equivalent) per phase, switched in synch with rotor position; it is only the low-current controller section of the SR controller which is somewhat simpler.


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## bga (May 25, 2009)

resspt said:


> Do you think it's possible to build one (not expecting to be the best motor, but one that can have a nice performance)?


Motors are full of big, precise pieces of metal, so this is one thing I would definitely buy, but there are possiibilities to re-purporpose something industrial:
Some years back, a number of us did some research for using industrial 3-phase AC motors in EVs. One of our members went as far as cobbling some industrial gear together:
http://www.evalbum.com/1149
This was very successful and cheap to do. It used SLA batteries and an off the shelf industrial controller because it was an experiment.
A relatively small industrial induction motor can be used (11kw ~15hp) and still deliver lots of power and torque. The motor in question was a 4-pole type and has a free running speed of 1500RPM (1800 at 60Hz). Also, these idustrial motors have big (and heavy) output shafts, about 40mm on the unit used. with robust bearings designed for pulleys and belt loads. They are designed to operate on hot, dirty industrial environments and endure frequent serere overloads.


The over-torque capability on 2-pole motors is a lot lower than the 4-pole types, making the 4-pole types far better cadidates for EVs.

If you're looking at motors, the 4-pole type can deliver 3 to 4 times their rated torque for short periods of time (about a minute), making the 11kw a 40+kw motor.
Also, they can be run at frequecies considerably higher than the normal line frequency. The makes the motor turn faster, producing more power at a particularl torque. That 11kw motor could deliver up to 120kw peak for a minute or two by doing both. The 30kW VSD used in the Red Suzi project is capable of somewhere around 150hz.

One issue with 'overclocking' a motor like this is that the required terminal voltage goes up linearly with the speed, so 2-3x the orginal line voltage. This can be overcome by rewinding the motor for lower voltage, but this increases the running current (at that lower voltage) and also decreases the inductance, which can cause the controller problems.

Later, the red Suzi motor got rewound by bringing out a pair of terminals in the middle of each winding, allowing them to be connected in either series (same as the original) or parallel (1/2 the voltage of the original) This decreassed the peak torque some (controller limit), but allowed considerably higher road speeds in excess of the approx 80kph safe speed limit on the Suzuki.


I've had trouble giving one of these motors away recently.


Good luck & happy motor hunting.


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## brian_ (Feb 7, 2017)

bga said:


> Some years back, a number of us did some research for using industrial 3-phase AC motors in EVs.


Great description of this approach, and that Suzuki is a tidy conversion. 



bga said:


> One issue with 'overclocking' a motor like this is that the required terminal voltage goes up linearly with the speed, so 2-3x the orginal line voltage. This can be overcome by rewinding the motor for lower voltage, but this increases the running current (at that lower voltage) and also decreases the inductance, which can cause the controller problems.


For those that don't already realize this, the Azure Dynamics motors were regular induction motors - although liquid-cooled - from Siemens, which Azure Dynamics ordered wound to suit their needs. Azure Dynamics went broke long ago, but some of their stock (which was auctioned off) still seems to be kicking around from multiple retail suppliers, even in a tandem configuration.


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## el_gallo_azul (Nov 22, 2015)

I imagine that the most cost-effective option, *by far*, would be to buy a used AC induction motor (SCIM) from some industrial site, like a mine or a processing plant. They'd be as common as anything, available in a range of sizes, capacities and speeds (numbers of poles), and you'd find one that could be used to power an EV. I'm pretty sure you'd get one for less than $2,000.


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## Duncan (Dec 8, 2008)

el_gallo_azul said:


> I imagine that the most cost-effective option, *by far*, would be to buy a used AC induction motor (SCIM) from some industrial site, like a mine or a processing plant. They'd be as common as anything, available in a range of sizes, capacities and speeds (numbers of poles), and you'd find one that could be used to power an EV. I'm pretty sure you'd get one for less than $2,000.


 $2000? - then you would need to re-wire it THEN find/make a controller

That does NOT sound as "cost effective" as buying a crashed Leaf or a $200 DC forklift motor


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## el_gallo_azul (Nov 22, 2015)

True. I don't know what (if any) controllers would be readily available for a SCIM.

You're right about DC forklift motors, of course, but it seems to me that the main advantage of DC motors (ie. lower purchase price) is gradually being whittled away, but for getting mobile quickly, easily, and "cheaply", it would be hard to beat a used forklift motor with its controller, if AC motor advantages aren't a significant concern.


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## MattsAwesomeStuff (Aug 10, 2017)

> $2000? - then you would need to re-wire it THEN find/make a controller
> 
> That does NOT sound as "cost effective" as buying a crashed Leaf or a $200 DC forklift motor


Or an AC forklift motor. I grabbed one from a forklift wrecker.

I think you would have trouble buying the *wire* to rewind a motor for less than you can buy a forklift motor.

Building a motor as a learning experience is a learning experience about machining, not electrical engineer. You can design a motor on paper, you won't learn anything about actually building it except perhaps how reality does or doesn't match the book values.

In short, if your eye is on frugality, know that a huge portion of the DIY EV community is in the community because they're cheap and thrifty and want to save money (the others being performance oriented). If it was cheaper to build your own motor, 80% of us would be doing that. I can't think of anyone who ever has, so, that indicates it's not cheaper.


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