On Thu, Oct 15, 2009 at 11:31 PM, NOPE9 <yes@nope9.com> wrote:

> =A0 =A0 =A0SP says power would be a function of Ampere turns. =A0 This is
> what I thought as well. =A0 SP also says Neodymium permanent magnets are
> used in high performance motors for model aircraft. =A0This is my belief
> as well.
>

Gus, I would say that to a first order approximation, the power
ability of the motor is independent of the number of turns, as long as
you fill the entire available space with turns. In other words, the
power handling ability of the motor depends on these things:

motor thermal capacity
motor max temperature
motor cooling
motor efficiency
magnetic saturation (limits max magnetic field)
winding inductance (limits rotational speed and causes phase shifts
between current and magnet positions)
bearing and rotor speed limits

In turn, motor efficiency depends on:

rotational speed (faster increases most forms of loss)
eddy current losses in iron
hysteresis loss in iron
winding resistance (at the AC commutation frequency)
motor current
bearing drag
air drag inside motor

You care about power out, which is the product of the speed times the
torque (or current, since they are directly related unless the motor
goes into magnetic saturation or has a significant phase shift in the
current with respect to the voltage). Reducing current reduces several
of these loss terms, but it also would reduce torque unless you added
more turns. Adding more turns increases resistance. In the end, my
understanding is that there is a theoretical limit on the max output
power (both instantaneous and sustained) for a given motor size and
materials, materials being the conductor used in the winding, the core
material (usually laminated iron or steel), and the type of magnets
used.

Sean

-- =

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