HeLP with COP of motor

[gyulasun]

Ein= (254x2x0.0004)+(262x9x0.0012) = 3.03 Joules (per cycle)

Eout= 0.31*2*pi=1.95 Joules (per cycle)

COP = Eout/Ein = 1.95/3.03 = 0.64

I agree with your input energy calculations.

You may wish to rethink your output energy calculations.

Once the RPM is given, you have to consider it.

See this link, out of many : http://www.engineeringtoolbox.com/electrical-motors-torques-d_651.html

rgds,
Gyula

[terry1094]

Okay, I'll rethink it.  Done.  Nope, it doesn't matter how fast the motor is spinning as long as your energy calculations are done per unit.  In this case the per unit calc is one revolution.

Think of it this way, work is force times distance.  With the newton-meter, you are applying one newton of force to a wheel with a radius of one meter.  The distance over which the force acts in a single cycle is the circumference of the wheel, pi x dia, or 2 x pi x the radius.

Hence, the mechanical energy expended in rotating the wheel one complete revolution is Newton x 2 x pi x radius.  It makes no difference in the ENERGY calculation whether the wheel turns its cycle in one second or one year.  The same amount of energy is expended.

The RPM does come into play when using POWER to calculate COP (a far more difficult calculation).  Then you would take the Joules (which is a Watt-second) times the revolutions per second to get average power.  But the Ein calculation becomes a bear since you have to average the pulses over the time for a cycle to get input power.

Nope, stick with the energy calculation.  Far simplier.

Terry

[Honk]

I understand want you mean.

But if the input pulses becomes shorter at higher RPM and average power stays the same while the output
increases as the RPM increases at the same accessible torque it should theoretically increase COP.
But then again, the average input pulse power will most likely increase as the RPM increases due to the
affect of the electromagnet inductance. It takes more power to run the EM faster. Right or wrong?

[terry1094]

Try a couple of COP calculations using power.  You'll find that RPM is in both the numerator and denominator and thusly cancels.

As far as what happens to available torque in reality as you increase RPM, it must surely decrease as you reach the mechanical limits of the bearings and windage.

I have never built one; so, I do not know.  But, yes, it should take more input power to run faster.

Terry