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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!

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jeff-o

9 years ago

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.

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lemonie

9 years ago

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

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NachoMahmalemonie

Reply 9 years ago

. 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.

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moistureNachoMahma

Reply 9 years ago

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.

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NachoMahmamoisture

Reply 9 years ago

. 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.

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moisturelemonie

Reply 9 years ago

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!

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moistureTool Using Animal

Reply 9 years ago

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.

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11010010110moisture

Reply 9 years ago

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

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11010010110

9 years ago

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

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moisture11010010110

Reply 9 years ago

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?

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NachoMahma

9 years ago

. 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.

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caitlinsdad

9 years ago

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.