It seems like the standard for brushless motor stators is Silicon Steel, while doing some research I came across a reference to Supermalloy and how it amplifies a magnetic field 25x better/stronger than Silicon Steel. If this is correct, can I assume Supermalloy would make a better brushless motor stator and if so what are the tradeoffs, example is Supermalloy considerably more expensive, harder to work with, etc.

If Supermalloy is expensive what are the alternatives, e.g. different/better variations of Silicon Steel?

Supermalloy and nickel-heavy alloys (for example Carpenter 49) certainly offer higher permeability, but these would mostly be of use in inductor and transformer designs that operate nowhere near saturation.

In motors, you're generally more concerned with saturation and operating at high flux densities. Also, a significant portion of the magnetic circuit is air (that exists between the rotor and stator). Because of this, you could never take advantage (if there was an advantage in the first place) of a high permeability material. In fact, we've done designs that operate silicon steel at permeabilities as low as 25 (in regions near tooth tips).

Highest flux density capacity comes from iron. As you add anything (other than cobalt) to the iron, you'll reduce flux density capacity. Adding nickel significantly reduces flux density capacity. Adding 1% silicon reduces it somewhat, and 2% reduces it even more. BUT adding silicon also reduces electrical conductivity and core losses.

Engineering is an art of tradeoffs. You'll need to consider all factors in your design -- flux density, core losses, operating frequency and waveform, etc. to come up with an optimal choice.

James,

The size of an electric motor is a direct function of the saturation flux density of the steel used in the motor. Silicon steels have a saturation flux density of about 1.5T. Supermalloy has a saturation flux density of about 0.7T. So, if you used Supermalloy, the motor would have to be significantly larger to have the equivalent performance of a motor made with silicon steel. There are other materials that have saturation flux densities higher than silicon steel such as Hiperco which saturates >2T. Of course, there are many other materials that fall inbetween these.

But, saturation flux density is not the whole story. The 2nd most important performance parameter of an electrical steel material is the core loss. Supermalloy would have lower core losses as compared to Silicon steel at similar flux density/frequency. Hiperco has even higher core losses (much higher).

Of course, cost is also a consideration. Hiperco is more expensive than Supermalloy and Supermalloy is more expensive than silicon steel. Hiperco and Supermalloy are also both more rare and harder to get.

So the best choice of material depends on the motor operating conditions and costs/schedule considerations. If you are looking for the absolute lowest core losses at the expense of everything else, you may well want to choose Supermalloy. If you are looking for the absolute highest torque at low speeds (frequencies) and smallest size, you might well choose Hiperco. For most applications, a silicon steel material is the correct choice for losses, size and cost.

Hi all,

I think another best supportive material for PMSM motors is soft magnetic composite like Somally..
And where we have control with electronics to drive these motors....
As william expressed Engineering is an art of tradeoffs, that to when redefining the system with new materials.

FYI - there are some new Hiperco materials out now called Hiperco 15 & 27 that are lower cost and fill the void between silicon steels and Hiperco50 in terms of price vs. permeability. I have not gotten pricing yet but I understand it will be significantly less than Hiperco 50. My company produces motor laminations for prototype and motor development work and we commonly utilize all of aerospace electrical steels.

James,

It looks like your motor is a 16 pole motor (the best I can tell from the web site). At 10k rpm, the electrical frequency would be about 1300 Hz. Hiperco (50) would not be a good choice at this high frequency. Core losses would be extremely high and would probably create enough parasitic torque to offset any benefit of using Hiperco in the first place.

1300 Hz is a pretty high electrical frequency in general for any electrical steel. It should be ok, but in general losses in any steel material will be relatively high.

JFE steel has some good materials for high frequency. JNEX, JNEH.