Lower cost design for a water brake for a dyno.

[TSutrina]

I worked with electrical engineers designing 400 Hz 3 phase induction motors for pumps in aircraft. They had to meet a tight performance curve. They had the simplest dyno for short runs to collect data points. A pulley for a flat belt which was nylon flat strap. (what you see on a exercise spin bike of a exercise skiing machine with a spring on one end and a knob to set the tension on the strap going to the pulley. A fish scale was our spring so that you could read force when the person on the other end got the tension sufficient for the belt to grab. Cooling was required and accomplished since the pulley was machined "J" shape. The top of the "J" is the center and under side of the "J" is the OD surface for the flat belt or strap to rub against with lips to keep in on the pulley. The "J" cup inside, water was poured to evaporate and cool the pulley. So it took multiple people to take a data point. Water poured, strap tensioner, and motor operator. Read the tension on the fish scale, RMS, current, and voltage for each point. If needed wave shape a oscilloscope was added. Could take a data point in less then 30 seconds. Didn't take long to fill out a data sheet. They wanted the relationship of motor slip to torque, rpm, and voltage. Motor would heat up to operating temperature quickly so that could be done with the set up in a few minutes and it would stay hot between data points.

 

[TSutrina]

Also used a water brake for testing a 270 hp high speed induction motor driven by an inverter that could output 3 phase about 1000 Hz. The amount of water in the dyno was controlled to very the relationship of speed to torque.