Home Made Dyno

[HeadSmess]

i have an excercise bike here i grabbed off the cleanups for just this reason...it has an alternator with a regulator and load resistor for the pedalling pressure. im sure the controllers fried but its a start.

im more leant towards making a stand so the motor is bolted to that instead, with just a simple chain drive to the alternator. i hate installing and removing from the pushy frame when i do something! i want to do everything on the bench. and i hate having something go wrong and push home...

an alternator with no regulator can produce very high voltages. not only is output voltage proportional to speed, but also to the current through the field windings. the regulator controls the voltage to the field windings, to keep the output constant at various rpm.

this is why they work better at low speeds than simple "generators"

anyway. the actual load part is quite simple, just a matter of measuring what current/voltage is present across the load resistance, and doing the maths. use a tacho to load down to a certain speed, measure output, graph results.

it does make for more definitive tuning than just "yeah that pulled ok".

it maynt be industry standard but there arent many standards in the industry either!

 

[Fabian]

Headsmess, if you can make a relatively inexpensive dyno that has a PC based plug and play system, i will have interest in purchasing such a system.

 

[HeadSmess]

i dont think the PC part is entirely necessary. this isnt EFI or anything.

just a simple readout of estimated power to compare outputs. someone that knows programming a bit better than me could easily set up a pic chip to read rpm, read current through load, read voltage across load, calculate and display as a simple HP or Kw reading... hp being a rpm rating. should be able to calculate BMEP as well. on one of them cute lil lcd bar displays.

this could then be fairly easy to feed into a usb port somehow if needed. software to compile results into a neat-o graph for visual reference.

(in fact, theres funky little displays that could do the graph as well...all stand alone?)

i think a lot of people would have interest in such a system. cost a bit to develop but! the problem is software, in my mind.

when it gets into programming, im stuffed. my electronics stops at the old thermionic valve


ill stick to the mechanical side of things. (unless anyones a programming genius?)

 

[Barnfresh]

I've always liked the simplicity of a hydraulic pump, needle valve and pressure gauge. http://www.bergfeltracing.com/powerwagon.html

 

[HeadSmess]

yep, simple alright. been the basis of many dynanometers since the very beginning.

one or two issues...the oil gets HOT, really hot. theres also water pump types, exactly the same thing. even better, really, as the amount of energy requires to heat a volume of water is a well documented fact. with oil, finding specific information can be a challenge.

oil viscosity changes with temperature, so when cold, you will get different readings that change as the oil heats up. this means the valve will require closing etc to remain, well..."calibrated".

oil being viscose, means you have no ability to run completely unloaded. the pump also adds a load that may or may not be calculable.

i did make a rudimentary dyno using permanent magnets and a brass disc (really wanted copper but took what i found at the scrapyard) and it did work quite well for the initial test.

that was ages ago! its been two years(or is it 3?!) now since the MB was banned where i live. that is, any IC engine powered MB. electric is still legal.

so my dyno sort of sits on a shelf, gathering dust.

try google,"permanent magnet eddy current dyno", rough vid on youtube.

using an alternator doesnt work, because of HEAT. they will work, at low powers, but once you try to push them, the windings in the alternator simply overheat.

my system replaced the wires of an alternator with a solid disc, that could easily have been made from aluminium, copper (given enough money to buy the damn stuff!) etc...can easily be water cooled, aircooled, etc...and readings stay consistent despite the heat. (within a percent or two, i guess, as conductivity also varies with temperature)

most commercial dynos use exactly the same concept but with electromagnets rather than permanents. simply vary the current, therefore the magnetism. i chose to have my magnets mounted on a steel disc, and simply opened or closed the gap to vary the load the engine saw.

whatever, it worked really well, i planned on getting a piece of aluminium bar and machining it to make something more permanent, but yeah... legislation changed. seemed pointless?


can easily be made as a roller type dyno, or as i did it, driven from the crankshaft. the higher speed at the crankshaft requires far less magnetic field for the same effect. (lenzes law i believe, moving magnetic fields create currents in conductors, that then create their own magnetic field that opposes the original magnetic field)

heat is the killer. power is watts. watts is energy. all that energy has to be disposed of somehow! fans, blowers, pumps, etc, all add to losses that have to be catered for, calibrated for, etc etc etc.