3290Views14Replies

Author Options:

How to test the power output on a wind turbine? Answered

I'm on a team prototyping a water filtration system powered by a Savonius wind turbine; the energy from the spinning turbine is mechanically transferred to a reverse osmosis filter/pump setup. We're doing tests of various blade configurations and are trying to determine the power output by hooking up a small DC motor (1-3V, 5000+ RPM) to the shaft. We're seeing only mW outputs though and were expecting something significantly larger. How do we pick a motor for the job? Do we need to match the RPMs of the motor to the expected RPMs of the shaft (~150)? Any other ideas for testing power? Thanks for any help!

14 Replies

user
sam D (author)2009-08-02

Maybe overlap the two buckets for better efficiency?

Cheeck out my build's design at:
https://www.instructables.com/id/Build-your-own-Savonius-VAWT-Vertical-Axis-Wind-T/

When they are overlapped I think it helps the air moving in the 'pushed' bucket to exit the concave shape.

Cheers!

Select as Best AnswerUndo Best Answer

user
jeff-o (author)2009-02-24

Perhaps not so cheap to buy, but a bicycle hub motor is designed to operate at that rpm range. Get one that is brushed (instead of brushless) and you can use it as a generator. Make sure you give it a bit of a load or you won't be able to properly test its current output.

Select as Best AnswerUndo Best Answer

user
lemonie (author)2009-02-23

Like other comments you need more load on this. A 12v motor hooked-up to a suitable load might do better than what you've got at the moment. Perhaps you could get a car-cigarette-lighter and a radiator fan-motor for some heavy load? (I can't quite judge how big this is)
But that might be a bit much without strong wind, a large-ish RC car motor perhaps?

L

Select as Best AnswerUndo Best Answer

user
NachoMahma (author)lemonie2009-02-23

. An automotive alternator/generator would be an excellent choice. You can get them in sizes from ~50A (~600W) to >200A (>2400W). You will need to use a speed multiplier (pulleys?) to get the alternator speed above ~1500RPM.

Select as Best AnswerUndo Best Answer

user
moisture (author)NachoMahma2009-02-23

Speed-multiplier..yeah ok, that makes sense. Thanks. The automotive generators are going to be a bit too much for our tiny turbine, I believe. Something similar though may be possible.

Select as Best AnswerUndo Best Answer

user
NachoMahma (author)moisture2009-02-24

. How much mechanical load the generator puts on you turbine is dependent on the electrical load (resistor bank) on the generator . If the generator sees a very high resistance, it won't produce much mechanical load. Hook up several high-power resistors in parallel with switches in series with each resistor. No switches on (infinite resistance) = low mechanical load. The more switches you turn on, the greater the load.
. V-belts are usually pretty stiff and may present too much resistance. I'd try a more flexible serpentine belt.
. A clutch may help in getting the turbine up to speed before applying any load.

Select as Best AnswerUndo Best Answer

user
moisture (author)lemonie2009-02-23

The turbines we're testing are only about 1.5 feet tall. I have a PC fan that I may try; the RC motor's a good idea, thanks!

Select as Best AnswerUndo Best Answer

user
Tool Using Animal (author)2009-02-23

Yes, the motor speed has to be matched to the rotor speed, however low speed DC motors are uncommon.

Why not just rig couple of pulleys and have it lift a weight as it spins, and time how long it takes to lift the weight a distance. mgh/s (kg*m2/s3) is a watt.

and here's a power curve graph for various turbines
http://redjar.org/jared/projects/windmill/images/gallery/data_pictures/power_output.gif

Select as Best AnswerUndo Best Answer

user

The pulling-a-string approach was an idea our team tried. It's difficult to create something that engages the weight system when the turbine hits its stable rpm.

Select as Best AnswerUndo Best Answer

user
11010010110 (author)moisture2009-02-23

i think the overall time (including before it gets to full rpm) still roughly represents the full rpm

Select as Best AnswerUndo Best Answer

user
11010010110 (author)2009-02-23

connect a thin wire of khown length to the pivot and measure the time it takes to wind up for accurate results you should test under load (the actual filter or some friction load). one setupo may give more torque even though it has less rpm when free use appropriate gear (wheels with ratio + band between) to couple the energy. for example you may want the filter to spin slower and with higher torque whie the turbine spins easy and fast

Select as Best AnswerUndo Best Answer

user
moisture (author)110100101102009-02-23

Yes, I agree with this, thanks. I posted a comment about the wind-up idea under Tool's comment, what do you think about creating a weight-engaging system?

Select as Best AnswerUndo Best Answer

user
NachoMahma (author)2009-02-23

. Sounds to me as if your generator is not large enough. . You need to feed your generator output into a resistor bank to provide a load. Measure volts and amps, then compute power. . For most generators, speed is not critical.

Select as Best AnswerUndo Best Answer

user
caitlinsdad (author)2009-02-22

You can search on wind turbine instructables. Lots of discussion comments in figuring out the torque and rpms to see what kind of output you want to generate and then sizing up the appropriate generator. Good luck.

Select as Best AnswerUndo Best Answer