Prony Brake Testing HP: Accuracy & Shaft Diameter

[jimmyz]

Is a prony brake a fairly accurate way to test HP. I built a prony brake just with wood to fit on a rotating shaft with a 1 foot arm. I get .75 of 1 HP if the shaft is rotating about 180 rpm and the arm lifts and holds 22 lbs. The diameter of the shaft is 2" - does that matter? And is a prony brake very accurate? thanks from a tinkerer.

 

[brewnog]

As long as all torque is counteracted by your weights/arm and nothing else, then yes a de Prony brake will give you the foundations of a good power measurement. Just make sure you can dissipate the heat well enough under steady conditions.

Let us know how you get on, this should be a nice little project.