Dynomometer

[johnmessina]

Is there a way to construct a dyno (for a 5hp engine) using an A/C generator? Looking for a cheap way to construct.

 

[VEBill]

...and you'll end up with an emergency generator as a bonus.

 

[OperaHouse]

You have a couple of options. HP is speed times torque. Whatever motor you use, you can let it float just a little and measure the rotational force "torque" on a weight scale at the rpm. A big enough motor and you can apply a DC braking voltage to the AC coils. Or, you can fudge a little and just generate a voltage with it and measure the power generated. You will have to get rid of 4KW of heat.

 

[nbucska]

Measure the torque and RPM and calculate the HP.

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[VEBill]

Or, in accordance with commercial standards where 4 or 5 HP is available from a normal 120VAC outlet (~1.8kw), measure the peak stall torque and (separately) the maximum redline RPM, and use these two values to calculate mythical HP.

 

[eemotor]

VE1BLL, how is 4 or 5 HP equal to roughly 1.8kW, I thought 1 HP = 746W, so 4-5 HP would be ~ 2980 to 3730 Watts.

 

[itsmoked]

VE1BLL must have a reeeeeeeal special motor.

Yeah 2.5HP is even a stretch.

 

[VEBill]

Woosh... the sound of a too-subtle joke passing overhead.

 

[VEBill]

Haven't you guys seen the various consumer products that claim more HP than is available from the standard 120 VAC outlet that they plug into ? Things like exercise equipment, air compressors, etc.

"5 HP motor" (sic) running from a normal 120 VAC, 15 Amp outlet.

There are many examples on the market.

 

[eemotor]

Yes, I've seen some vacuum cleaner motors claiming 4 or 5 HP from a 120V 15Amp circuit. Is this a peak power representation or continuous duty. If continuous duty, how's that possible to produce 4 -5 HP from 120V @ 15A? It would seem to me that even with PF of 1 and eff of 100% the max you could get out of 120V @ 15A is (IxExPFxEFF)/746 => (120 x 15 x 1 x 1)/746 = 2.41 HP. Real world performance would be even lower because actual efficiency would not be 100% and PF would be less than 1.

 

[btrueblood]

Back to the thread, using an AC generator for a dyno -- the measurement of output power from the generator is the tricky part. "Normal" watt/amp meters can be fooled by the varying frequency output that you will be generating (unless you only plan to operate at the motor/generator synchronous speed -- 3600 rpm for most?). Not sure that the voltage won't vary with speed as well? You'll need to measure voltage/current with high speed o-scope or DAQ card. Putting a 1 to 4-kw variable load onto the generator should be fairly easy: go buy a bunch of lamp sockets at the hardware store, along with a supply of a range of bulbs of varying wattages. Wire all the sockets onto a board, and add/subtract load by screwing in or removing lamps. Remember, though, you may not be able to measure output power by summing the lamp wattages.

 

[itsmoked]

btrueblood: You should be able to use "true" RMS meters and multiply the readings, providing you keep the loads resistive. Don't know how resistive tungsten bulbs are.

And yes, I remember the first time I saw a SIX HORSEPOWER Sears air compressor. Noting the motor was about a third smaller than the 3HP on my home brew. Then I looked in the cooling ports to see that the motor actually filled only the front thrird of the the actual motor housing to boot!

 

[icrman]

You don't need to measure power out put from the alternator to measure the HP.
The tricky thing is to be able to apply a good load to the alternator. What you do is mount it just like a commerical dyno is mounted. And read the torque output. Either with a load cell or scale against a torque arm.