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Physics Project - Wind Turbine

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danny_galaga:
Nice project (",)

It's a pity you couldn't get a DC motor since at this sort of size, it would probably produce a lot more power. DC motor= almost exactly a DC generator. But an AC motor is not much like an alternator unfortunately. Then again, you aren't trying to power a house, just prove the concept so top marks!

@ Kevin. I think a car alternator would need much larger blades to drive at any sort of speed (we're talking over 1200W potential easy), so at that size you would definitely be better off using a basic dc motor as a generator. For instance, just spinning the shaft of a 540 motor with your fingers (the motors used in radio controlled cars) would produce more than .16W. I would predict something between the 540 and a car blower motor would work well with this sized turbine.

Flip_Willie:
@ Shardian
Thank you, I appreciate it. I have certainly felt challenged by both courses at my college. Although I have been able to maintain an A so far, a lot of people struggle with both courses.

@ Keven
I was very surprised myself with the performance of the blades. I certainly did not expect some simple PVC blades to perform as well as they did. One thing to keep in mind though is that the turbine appears to be rotating faster than it is in the video because of the frame rate on the camera. Even considering this, they are moving quickly. You feel very uncomfortable if you stand close to the blades while they are rotating. It takes a while to gain momentum, but once it gets going it maintains its speed pretty well. It was also shockingly well balanced. While going, you can feel it shaking if you place your hand on it, but otherwise it is unnoticeable.

We took it outside one particularly windy day and it really got going. With the Floor fan, we were getting about 25 AC volts. During one particular gust outside, we reached around 50+ Volts.

Actually, several people suggested using an alternator. The reason why I initially avoided it is because this guy suggested not too use one. His reasoning is that is most car alternators work at much greater RPM than what the turbine would produce (as Danny has mentioned).

@ Danny
Yeah, I am certain that a DC motor would produced much more exciting results. I initially anticipated purchasing a motor off of Ebay, but in the end I decided to save money and shipping time and just take the freebie. The generator I used was rated for 230 AC V for 850 RPM. Which was much higher RPM than I had originally wanted, but it worked sufficiently for the demonstration.

I feel certain that with a little more work, the unit would have been much more practical.

Flip_Willie

Ed_McCarron:

--- Quote from: Kevin Mullins on November 14, 2009, 10:25:14 am ---I was rather impressed that the floor standing fan was able to push the turbine so well.
I know those fans have a fair amount of force at that range, but still, when you throw in there the design of the blades, balance, pitch and tuning , etc, etc.....work out quite nicely.

If you ever go looking for a readily available small DC "generator" again, just grab an automotive alternator. Just about any these days are already internally rectified to output DC. (a single wire GM version would be a good choice)


--- End quote ---

Car alternators need to spin rather fast - in this application, not so good.  Ideally, you want a DC motor that will produce the voltage you want at much lower RPMs than its designed for.

IE, you want 12v at 200rpm, you need a motor thats spec'd at 120v, 2000rpm.  When it spins at 1/10 of its rated speed, you get 1/10 of the rated voltage.  Its not exact science, but this'll get you in the ballpark.

Motor, generator, who cares?  My question is what does a 'AC to DC transformer' do? ;)

Flip_Willie:

--- Quote from: Ed_McCarron on November 14, 2009, 05:31:53 pm ---Motor, generator, who cares?  My question is what does a 'AC to DC transformer' do? ;)

--- End quote ---

Ah, I was referring to a Wall Wart. In this case, it was one of those with the brick inline. We included it simply to run the DC LEDs.

Flip_Willie

danny_galaga:

--- Quote from: Ed_McCarron on November 14, 2009, 05:31:53 pm ---
--- Quote from: Kevin Mullins on November 14, 2009, 10:25:14 am ---I was rather impressed that the floor standing fan was able to push the turbine so well.
I know those fans have a fair amount of force at that range, but still, when you throw in there the design of the blades, balance, pitch and tuning , etc, etc.....work out quite nicely.

If you ever go looking for a readily available small DC "generator" again, just grab an automotive alternator. Just about any these days are already internally rectified to output DC. (a single wire GM version would be a good choice)


--- End quote ---

Car alternators need to spin rather fast - in this application, not so good.  Ideally, you want a DC motor that will produce the voltage you want at much lower RPMs than its designed for.

IE, you want 12v at 200rpm, you need a motor thats spec'd at 120v, 2000rpm.  When it spins at 1/10 of its rated speed, you get 1/10 of the rated voltage.  Its not exact science, but this'll get you in the ballpark.

Motor, generator, who cares?  My question is what does a 'AC to DC transformer' do? ;)

--- End quote ---

Generators like to spin fast too, more so than alternators. In fact, that's one of the reasons (as well as efficiency and cost) that they went to alternators in cars, trucks planes etc. At idle, most generators produce virtually no charge, aircraft were the worst- the battery would be slowly going flat when taxiing. Alternators are charging from the get-go and are up to full voltage at fairly low revs. Even though in general alternators are more efficient than generators, for something small like this  a generator would be the better choice, since you would be hard pressed to find an alternator small enough. Since DC motors are so similar to generators (there are subtle differences in design detail to optimise charging) you have a huge spectrum of choices, from slot car motors up. Most choices up to car blower motors will be dirt cheap too.

To get better efficiency out of either, you need to gear 'em up, like these bad boys. The blades spin at about 19 RPM. I don't have more specs, but i would guess the alternator would be spinning somewhere between 10-100 times the blade speed. Standing near them, you can hear the gearbox whining, even though it's 50 meters up!

It's all irrelevant now, since the project is done. Hindsight is always 20/20. Still fun to talk about though. Dragging up memories of things i learnt in trade school all those years ago  :)

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