efficiency - output / input

[willib]

when calculating the efficiency of an Alt

should i subtract the power going to the motor when the stator/coils/coil are not connected? ie not drawing power from the motor

when i do this i get an effiency of .32 for one coil ( i hav'nt finished the stator yet)

otherwise it is .111

the setup is--

one coil rectified charging a NiMH battery

i turn on the motor to some RPM , measure the power going to the motor

then i insert the coil measure the power going to the battery and the power going to the motor.

and subtract the initial power from the input power?

[Flux]

You need the OUTPUT power of the motor, you will be measuring the combined motor and alternator efficiency otherwise.

It will be incredibly difficult to calibrate a small inefficient motor as a dynamometer. The armature current should be fairly directly related to torque so if you check a few points with a prony brake you can plot a graph.

You had better measure speed direct, it will be related to armature volts but very load dependent.

For the alternator efficiency you need power out over power in. You include all losses. With stator coils not connected efficiency will be zero. When on load the no load losses reduce the efficiency.

Flux