# Motor casing material discussion



## Tesseract (Sep 27, 2008)

I defer to major in all things motor, but here's my take (which is colored by my tending to view motors as a particularly ornery form of a transformer)...

The motor housing in all motors - AC and DC - is a critical part of the magnetic circuit between rotor and stator. If too little "iron" is present then efficiency and torque production suffers.

In DC motors the housing is usually made of solid steel with a cross-sectional area at least equal to the sum of the pole roots (or is it half the pole roots... can never remember that). In AC motors the housing is typically made from thin silicon steel laminations as this results in lower AC losses (eddy and hysteresis, mainly); the downside is a lower saturation flux density (less "torque per amp-turn of excitation").

And just in case it isn't clear, it does not matter whether the motor is AC or DC as in both types a rotating/alternating magnetic field exists, it's just created by semiconductor switches for the AC motor and by the commutator/brushes for the DC motor.


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## major (Apr 4, 2008)

mizlplix said:


> Has anyone ever custom made an aluminum or titanium motor housing?


You need the steel or iron magnetic yoke. You can put anything you like around the outside of that, aluminum, titanium or a coat of paint


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## z_power (Dec 17, 2011)

How about endplates (where bearings are); does it matter if I change iron to aluminium?


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## major (Apr 4, 2008)

z_power said:


> How about endplates (where bearings are); does it matter if I change iron to aluminium?


Endplates or end bells or end heads (DEH & CEH) are often made from aluminum. That is not part of the magnetic circuit. Most of the DC motors used for conversions have aluminum ends.


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## z_power (Dec 17, 2011)

Thank you for prompt answer, major.


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## mizlplix (May 1, 2011)

> You need the steel or iron magnetic yoke. You can put anything you like around the outside of that, aluminum, titanium or a coat of paint


Ah....now that makes more sense than "no it can't be done".

This question was the product of wondering about building a custom AC motor in a size not currently available for less than my yearly salary.

Thx, Miz


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## lazzer408 (May 18, 2008)

If a motor has a lamination, like the one shown, the housing can be anything you want. Some motors, including some series-wound DC motors, don't have a housing at all (second pic). Most of the DC motors you'll see around here have bolt in stator poles and the housing is the "magnetic connection" between the poles.


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## mizlplix (May 1, 2011)

In the case of a motor with a thick ferric metal housing...

If I were to switch everything into a thin metal shell,pressed into a thick aluminum shell (for lighter weight but good strength), then the motor would most probably suffer from lesser torque because of the reduced magnetic efflux caused by the thinner magnetic shell.
(I hope I made sense)

? Miz


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## lazzer408 (May 18, 2008)

mizlplix said:


> In the case of a motor with a thick ferric metal housing...
> 
> If I were to switch everything into a thin metal shell,pressed into a thick aluminum shell (for lighter weight but good strength), then the motor would most probably suffer from lesser torque because of the reduced magnetic efflux caused by the thinner magnetic shell.
> (I hope I made sense)
> ...


You are correct.


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## Tesseract (Sep 27, 2008)

miz - major made a subtle yet important distinction that I did not: the "yoke" completes the magnetic circuit for the stator/field and may or may not also be the housing. The "housing" is the outside case of the motor and may or may not also be the yoke.

You need a certain amount of cross-sectional area for the yoke (/housing) if you want to get the most torque per amp (AC or DC, remember) so reducing the thickness/weight/saturation flux density of the yoke (/housing) just to save a few pounds is never a good tradeoff, IMO.

The yoke (/housing) just needs to be thick enough to not saturate before the poles, and that thickness is, unsurprisingly, calculable (off the top of my head I don't remember the equation - not a motor design engineer...  )


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## mizlplix (May 1, 2011)

Thanks guys: I have this idea about a large sized but weight reasonable motor. 

I also have access to a motor graveyard.

The idea is to try and plug the gap between a $3000 and a $14000 AC motor by hybridizing an existing unit to be more suitable to EV use. 

I have spoken to the three motor rebuilders here in my area and they are interested in the idea and offered help. They all rebuild motors, none actually have experience or data for modifications or EV requirements. (just guesses)

Miz


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## JRP3 (Mar 7, 2008)

The cost in the AC motor system is usually in the inverter, not the motor. The AC50 you already have is limited by the Curtis inverter.


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## mizlplix (May 1, 2011)

I am just dreaming a magnitude above my current system, using a converted stationary use inverter/controller. (like from a large materials conveyor system) as I have had some experience with those.

Yah, For my current car, I would have rather had an equivalent to a Soliton 1 but for an AC system. Oh, well''.

Miz


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## JRP3 (Mar 7, 2008)

I think that's basically what our HPEV's motors are, rewound Leeson industrial motors with different ends.


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