Loading a small motor - Simple solution available?

[higherflyer]

Good Morning

I have a requirement to run a test on a few small motors, 28V DC, with an applied load of 0.3Nm at a speed of 2750rpm. The test success criteria is that at the load of 0.3Nm the current draw is below a certain limit.

I am looking for a simple solution to this requirement if possible, as the cost of purchasing a dyno or shipping the work to an outside test house may be prohibitive.

Any help you could offer would be much appreciated.

Regards

higherflyer

 

[aolalde]

Since the power you are handling is around 90 watts dissipate the energy by friction.

Attach to the motor shaft a pulley with a diameter around 100 mm; Get a rope string around 3 mm diameter and fix a spring scale to one end of the rope. Wind two or tree turns loose of the string around the pulley.
Onece the motor starts running if you apply light tension to the loose end of the cord the friction will increase the torque demanded to the motor. Measure the tension of the string attached to the scale.

Multiply the radius of the friction surface by the scale lecture and you will have the torque. The energy generated will warm the pulley but the windage will cool it down.

The string should be perpendicular to the scale hook (hanging scale).

 

[tinfoil]

I remember a demo in class where the prof used an electric kitchen mixer. He started 'mixing' water, and then gradually added molasses to increase the viscosity of the mix to slowly increase the load on the beaters. He also raised and lowered the beaters so that more or less mixture was being mixed. An ammeter showed a corresponding change in input current.

If you have a 'known' or 'standard' motor, you might be able to 'calibrate' a setup, and then use it to test the rest.