My no frills home made Dyno.

[oldbikerarlo]

As anybody who keeps up with this forum knows, I'm designing and starting to build a simple, no computor, no frills, basic dyno. This dyno will give an accurat HP, and torque value, at desired RPM's, for the conditions that your engine is at the time. So far I have rounded up a base plate, steel stock, some bearings, and shafting. I have located a tach, and a scale, I'm still on the fence on a mechanial brake or useing a high output altenator as brake. No photo's yet as it's just a pile of hardware on the bench. Ideas are wecome.

 

[sexyvicta]

I like this.

Once you get it sorted. Do a whole lot of runs at different density altitudes and record carb settings etc, which make max power, in a note book. Then when you goto the race track be like a pro: calculate the density altitude on the day and then look in your notebook for the most ideal set up. Fine tune as necessary. Choice.

 

[oldbikerarlo]

I raced electric, RC asphalt oval for years. Had a little dyno, and a notebook, for my race moters. All i had to do was open up my book and start messing with a moter on the dyno and I'd have guys all over me looking at what I was doing. They would run back to their pit table and do the same thing to their moter. The fact is I very seldom raced the moter I had on the dyno, it was just a psyhc out thing I did between races.

I have no intentions of raceing, I just rip up the desert, but I do like to tinker with my engine.

 

[Clayton]

Could you please take pictures? i would really like to build my own dyno too. I saw a pic that Eric Rickmann shot of a couple guys from HMR testing a west bend kart motor on a really small, bare bones dyno. The picture was from the 1960's, but ever since the I wanted to build one to have to tinker on.

 

[Doc Sprocket]

Go Arlo, GO! I can't wait to see how this turns out. I got faith in ya, man!

 

[oldbikerarlo]

Little update. I have located a 360 amp altenator, I think it should provide the load I need. Any suggestions on how to apply load to the alt, with adjustability?

 

[Orange Krate]

A rheostat wired in series with a resistance heater(stove burner?). Multiply the reading of a digital volt meter across the entire circuit by a digital ammeter. Convert Watts to Horsepower and Viola! Low buck dyno!

Go a step farther and lay out varying results against your digital tachometer on graph paper for a low buck power curve.

You’ll have to work some Ohms law figures first to size the load correctly.

Rheostat

Here, the component would be the heater and the voltmeter should be across the power source(entire circuit) for total load.

Again, swap light for heater.

Someone please chime in if I'm wrong.

I LOVE this idea!

 

[anderkart]

We should probably start by finding out if that alternator uses an internal or external voltage regulator?

 

[oldbikerarlo]

A rheostat wired in series with a resistance heater(stove burner?). Multiply the reading of a digital volt meter across the entire circuit by a digital ammeter. Convert Watts to Horsepower and Viola! Low buck dyno!

Go a step farther and lay out varying results against your digital tachometer on graph paper for a low buck power curve.

You’ll have to work some Ohms law figures first to size the load correctly.

Rheostat

Here, the component would be the heater and the voltmeter should be across the power source(entire circuit) for total load.

Again, swap light for heater.

Someone please chime in if I'm wrong.

I LOVE this idea!

This is a good idea, I could use a couple burners and rheistats. to get all the load I need.

Would I need a voltage and amp reading to get watts?

 

[oldbikerarlo]

We should probably start by finding out if that alternator uses an internal or external voltage regulator?

What is the voltage output of an altenator that is unregulated? does rise and fall with RPM?

 

[oldbikerarlo]

My Idea is to use the torque value, and engine RPM to calculate the HP.
I want to mount the altenator so it will rotate on the same axis as the armiture, then use a 1 ft arm attached to a digital scale. As the load is applied the body of the altenator will try to rotate aginst the lever and scale giving me ft lbs of toruqe. then with a tach reading from the engine, its simple math RPMxTorque/5252 = HP.

But I like the convet watts to HP cause with just a tach, plotting a curve would be very easy.

 

[anderkart]

What is the voltage output of an altenator that is unregulated? does rise and fall with RPM?

An unregulated alternator charging wide open into a 12 volt battery can easily reach 20+ volts until the battery exploded. I've never experimented with an alternator charging into any type of resistive load, but I'm guessing its a good possibility that the diodes in the rectifier would quickly overheat/blow causing the alternator to stop working.

Yeah most alternators would vary in output from around a 1000rpm on up to 3000rpm where they should be producing their max output.


I understand what your trying to do here. I spent 20 years rebuilding/diagnosing alternators at a rebuild shop. I'd suggest you choose an alternator with only around a 100 amp output. Those take between 3 and 5hp to spin up to full power and It'd probably be a more realistic choice for your dyno.

Whether the alternator had a built in regulator or not, you could rig any alternator to change its max output. All you'd need to do is ground one of its brushes and feed the other brush 12-v DC. Any Alternator would charge wide open that way. You could even conect either one of the brushes through a rheostat to control the alternators output-level with a twist of the knob.

 

[devino246]

What is the voltage output of an altenator that is unregulated? does rise and fall with RPM?

An alternator without a regulator wont produce any power. The regulator varies the voltage supplied to the alternator to adjust the power output.

 

[oldbikerarlo]

I just did another search. I find that useing the electricle output is not as easy to convert to HP as the moment lever.

The reason for the 360 amp alt. would be to over power any toruqe the engine could produce, With a rheostate I should be able to control the load applied by the alt. right?

 

[Orange Krate]

This is a good idea, I could use a couple burners and rheistats. to get all the load I need.

Would I need a voltage and amp reading to get watts?

Yes. I edited my post because one of the pics quit showing.

Volts x Amps = Watts

Watts x 0.00134 = HP


again, the voltage must be taken across the entire circuit, not just the component to calulate the total load.

 

[Orange Krate]

Lets just say you get 5 hp at 2000 rpm.(thin air guess)

1hp = 550 ft-lbs/sec and of course there's 60 sec in 1 min.

5 hp x 550 ft-lbs x 60 sec x 1 min
---------------------------------- =
1 hp x 1 sec x 1 min x 2000 rev

165,000 ft-lbs
--------------
2,000 rev

= 82.5 ft-lbs/rev

 

[anderkart]

The reason for the 360 amp alt. would be to over power any toruqe the engine could produce, With a rheostate I should be able to control the load applied by the alt. right?

Yeah good point. I'm just not sure if any alternator will survive charging into any type of resistor-load, and I was thinking with a 100 amp alternator you could just charge into a car battery, but if you push much more amperage than that your battery probably wont survive for long.

Maybe a hydraulic pump and reading a pressure gauge would be a better method to consider...

 

[Doc Sprocket]

Maybe a hydraulic pump and reading a pressure gauge would be a better method to consider...

Wouldn't that require a "load", too? I don't think you can just thread a pressure gauge onto the outlet of a pump, and let 'er rip. Maybe you could put a hydraulic motor on the other end of the circuit?

 

[Orange Krate]

= 82.5 ft-lbs/rev

Oops! Can't have that /rev haning out there. I think I gotta convert to radians. Of course this doesn't account for heat or friction loss in the alternator. Also, I didn't think about it "releasing the blue smoke."

If you were to do a hydraulic pump, pressure and flow are equated to volts and amps respectively. Same circuit...different calulations.

 

[wingnut]

How about coupling the output of the motor through a simple mechanical brake?