Cheap Torque Measurement?

[Mike Betts]

Originally Posted by DeepWater

...Why is it important to use to of the same type motor instead of an "unkonwn" motor as the test and a known motor (one you have power curves for) for the load motor/generator?...

As I noted in my first post, we are sacrificing some accuracy for expediency here... The efficiency of a motor as a motor may not be exactly equal to a motor as a generator. However, for the purposes of this experiment we can assume that a motor is a perfect bidirectional conversion device.

As Al Skierkiewicz stated, your measuremnts will not be as accurate as a manufacturer's lab. By using two identical motors, you are signifigantly reducing errors caused by your instrumentation being exactly the same as a lab's equipment.

Using the same motor for both motor and generator makes the math a lot easier... You will find that losses in a motor are not linear and are dependent on speed, torque, voltage and current.

Lastly, by using the same motor, you are assured that you are using the generator within it's operating range (the max speed of a CIM is not the same as a FP, for example).

Originally Posted by DeepWater

...What it the power resistor used for? Is this so that the generator now acts like a brake?...

Exactly. You need both voltage and current to have power (P=V*I). Without a resistor, your output power is zero therefore your mechanical power is only the losses in the generator (fairly small in a good motor).

Mike