A DIY Dynamometer...

[Johansson]

Later this year I intend to build a small bench dynamometer for engines up to, lets say, 50hp so I can brake my pocketbike when it is done along with future projects. I have not yet decided what kind of dynamometer that would be best/easiest to build, but from what I know there are 3 kinds:

x Prony Brake , a rotating drum with brake pads applying pressure until the engine output shaft settles at the wanted rpm. The torque is measured by a spring scale connected to the brake by an arm. This version is easy to build but could be hard to use on my own since I have to both control the throttle, the pressure on the brake and monitor several gauges at the same time. It also produces lots of friction heat, so a cooling system will be necessary.

x Water Brake, a water pump is driven by the engine pumping water through a nozzle, and from the water pressure the engine power can be calculated. I don´t know everything about this kind of dynamometer, but it seems like a good choice to me.

x Electric Generator, by running a generator with the engine the power can be calculated from what the generator produces. I will not use this kind because of the huge generator needed and because I dislike electric stuff.

Suggestions, comments and snyde remarks are welcome! ;-)

//Anders

[Al Belli]

Hi,

I would use the water pump dyno. and connect the reaction arm
( mount ) to a scale for torque readings.

Al Belli

[Johansson]

Ahh, I got the water brake thing wrong. My bad.

Couldn´t a cars automatic turbine be used as such a dynamometer?

//Anders

[Al Belli]

Hi Anders,

You can use the torque converter from an automatic transmission by pumping water with it, and restricting the output flow.
The dyno. I used worked that way, using the water flowing through the system for cooling the converter.

Al Belli

[Johansson]

That would be a great way to build one, a torque converter from a small car should be able to handle at least 80hp. How was the water restriction on your dyno made? It has to be easy to change the water level in it in order to quickly balance the load.

//Anders

[Bruno Ogorelec]

My daughter made a Prony brake as a school science project when she was 13. It was so neat it propelled her into local, then regional and finally state science competition. She ultimately won the national silver medal with it. But, she used small electric motors as examples, not big fire-breathing stuff.

[Al Belli]

Hi Anders,

A ball valve was used to vary the load.

Al Belli

[Johansson]

Ok, do I need a ball valve both on the inlet and the outlet to get a stable water level or is it enough with just one?

//Anders

[El-Kablooey]

Hey, I ran across this and thought you might find it interesting.

http://www.kartingtechinfo.com/tech/dyno.htm

[Johansson]

Thanks for the link, that was a relly nice dyno! It seems better than the water pump kind since it is easier to use on your own. The cost is higher though so I will have to find out how much a good hydraulic pump cost around here before I decide which one to build.

//Anders

[Jim Berquist]

BIG , DC Motor. A magnet type dc motor becomes a generator when rotated. By placing a Load on the generator you incur resistance on the shaft. You should be able to calculate your out put via RPM verses lbs of torque.

Load could be light bulbs. Resistors. With a rectifier set up you could charge your car battery with it. Need more? A DC refrigerator keeping your beer cold....Ha.....

No fluids to mess with. No leaky valves. No leaky pumps!

Only a few switches . A tachometer. And some way to measure torque placed on the motor....

Don't fear electronics! Your talking 2 wires from the generator to the load and Not much more...........!

Out put from a generator is not linear! That's why torque measure would be more accurate. You could measure voltage out put, again not linear.
You would end up dealing with some logarithmic mess!

You do not need a big DC motor! You can gear it to the ballance! If motor , generator can produce X lb of resistance you can gear in the required limits. 5/1 ...10/1....20/1.....

Brain Fart!!!!!!! A starter motor would most likly work!!!!!!!


Just a thought!!!!!