# Motor laminations



## major (Apr 4, 2008)

abudabit said:


> I want to build a 10 hp (continuous) 3 phase induction motor. I've never sourced laminations before though. I had a few questions about them. Mostly sourcing questions.


Google "electric motor laminations"  There will be numerous sources. Ask them.


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## abudabit (Sep 18, 2008)

Thanks for the thorough help. 


I'll ask around tomorrow... something tells me most of the places won't do small quantities. I did find this place that had non custom: http://www.rbourgeois.com/induction_motors_laminations.a234.en.html

Wrong calc: Actually using those I determined the answer for one of my questions I think... ~0.16 lbs for an 8 inch diameter x 1 inch deep section... that depends on the pattern of course. That is for both rotor and stator. A lot lighter than I thought it would be. 

Updated: I really misunderstood the dimensions on that link, I was going by slot area when it should have been the opposite. Why is stator slot surface so much smaller than diameter? I guess estimating that 2/3 of the laminate is non slot / air the weight for 8 inch diameter x 1 depth would be about 10 lbs.


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## major (Apr 4, 2008)

abudabit said:


> Why is stator slot surface so much smaller than diameter?


Hi abud,

It's difficult to understand your question exactly because you don't use "motor" terminology. But I think the answer to your question would be:

1.) To provide structural support.

2.) To provide the required magnetic circuit, called the back iron or sometimes the yoke.

Regards,

major


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## samborambo (Aug 27, 2008)

abudabit said:


> I want to build a 10 hp (continuous) 3 phase induction motor. I've never sourced laminations before though. I had a few questions about them. Mostly sourcing questions.
> 
> 1) How much do laminations cost? I guess these would be made from maybe 8 x 8" sheets.


How long is a piece of string? Seriously, there are only two manufacturers in the world that produce electrical steel - both are in Japan. You're looking for electrical steel or silicon steel - same thing. Transformer manufacturers I've visited have said that the core material is by far the most expensive component.


abudabit said:


> 2) Are there any sold in smaller quantities. I'm not necessarily only purchasing enough for 1 motor, but it would still be limited quantity.


I think your best option is to source the steel through a local transformer manufacturer. The same grade of steel is used in line frequency transformers. 


abudabit said:


> 3) Are there standard / stock lams or do you need to buy custom made?


Bulk quantities of electrical steel are usually supplied as large sheet spools in a custom width for the particular transformer design for large power transformers (>100kVA). For smaller transformers, the sheet steel is stamped into specific shapes by the customer. 


abudabit said:


> 4) How much do they weigh? Just looking at cross sections of motors, is it safe to assume they are one of the heaviest components? Are there any tricks to reducing the weight of the core?


Electrical steel is typically around 92% steel and 6% silicon, by weight. From your calaculations you should be able to see where the flux density is low and could therefore remove some core material.


abudabit said:


> 5) Are iron powder or air cores realistic alternatives?


Iron powder for very high frequency motors due to its lower coercivity but also lower flux density. Even at high frequency/speed the rotor flux is still rotating relatively slowly so there's not much benefit changing the rotor material. Air core induction motor wouldn't have enough power to pull the skin off a rice pudding.


abudabit said:


> Thanks.


Steel has a very high permeability. Normal steel is fine in applications where the flux doesn't change direction, like in a permanent magnet circuit. The problem with steel in an AC magnetic circuit is that steel is conductive. If a transformer or motor core were made of solid steel, the alternating magnetic field would induce eddy currents perpendicular to the magnetic circuit. Insulating laminations reduce the size of the eddy current circuit and therefore reduce eddy losses. Silicon (and other trace elements) are added to the steel to increase it's resistance and therefore reduce eddy current. Silicon content in electrical steel is typically limited to 6% because of its effect of hardening the steel making the stamping process problematic.

Have you modelled your motor at all? Have you done any calculations on flux density or air gap, etc? It is not so simple as to slap together a stator and a squirrel cage rotor and say "that'll fly". The reason I'm suspicious is the mention of air cores. if you'd done even some rough calcs you'd know that the flux density in air is dismal. 

At a minimum you should be modelling the motor using a finite element analysis method, like FEMM: http://www.femm.info/ 

To give you an idea of the learning curve you are about to embark on, have a look at this guys blog: http://myownhybrid.wordpress.com/2007/12/07/electric-wheels/

That guy started from scratch learning about radial LRK (BLDC) motors and designed a hub motor in FEMM. Since there are too many parameters with non-linear effects on the motor performance, he built an automated script to try every possible combination of magnets, windings and dimensions. I think he was fairly successful. His LUA scripts for FEMM are available on sourceforge.

The main limitation of FEMM is that it only solves two dimensional problems. That's fine for simple designs like a radial BLDC motor but I don't think it can model induction motors properly, mainly because the the squirrel cage is skewed. The cage in an induction motor is skewed to reduce torque ripple. You could design the motor as a 2D problem with no skew and then add it later to the final design. It shouldn't have too much effect on the other parameters.

If you've got an electronics engineering background, you've got about a 6 month learning curve ahead of you and lots of money to blow on fabrication iterations. Or you could buy an Etek 10hp BLDC motor for $500.

I'm not trying to put you off designing you're own motor. I'm just being honest with you about what you're getting yourself in for. It would be an excellent achievement to design your own lightweight induction motor for traction applications.

Sam.


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## abudabit (Sep 18, 2008)

You're right, the cost benefits just don't justify the development trouble. 

I wish the mars wasn't so high speed.


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