Author Topic: Can our motors generate current as wind turbine? (Read 2533 times)

Mike Scholtes · « **on:** January 07, 2012, 02:37:19 PM »

A little off topic, but still in the neighborhood ...

I need to help my daughter with a 6th grade science project. She wants to build a model wind turbine to generate electricity. Can an outrunner DC motor like we use (say a Turnigy 42-50) generate current if fitted with windmill-type blades and exposed to wind? My understanding is "yes" but I am fuzzy on how to make it work. And, assuming the theory is valid, how many rpm would it have to turn in order to generate enough current to do some work, like light up a flashlight bulb?

How would one measure the amount of current produced, or estimate it in advance to get an idea if the project will work in the first place?

If anyone has a suggestion for a better source of a generator, I would love to hear it. This is probably pretty elementary to the electronics wizards we have on this forum but I'm not one of them so need some basic help.

Igor Burger · « **Reply #1 on:** January 07, 2012, 02:45:36 PM »

yes ... 3 phase alternating :- ))))

and the no-load voltage is = motor rpm / kv

the kv is rpm/volt motor constant :- ))))

Howard Rush · « **Reply #2 on:** January 07, 2012, 03:24:47 PM »

You could probably go to Radio Shack and get a two-wire motor cheap, but if you have a three-wire motor on hand, you might as well use it. I doubt if this application would hurt it. You could use three flashlight bulbs, one for each pair of wires. I'd get a three-blade model airplane prop and mount it with the flat side of the blades upwind.

Howard Rush · « **Reply #3 on:** January 07, 2012, 04:35:07 PM »

It works a treat. I used a Plettenberg Orbit 20-16 and an APC 13-4.5, because that was what was handy. I just used one pair of wires. After spending some time wondering why the shaft wouldn't turn while I held the body of the motor, I figured it out and proceeded with the experiment. First I tried to light up a 6V string of little Christmas lights. No joy. Then I measured the voltage across a pair of wires. 2.0V at whatever RPM it was turning while holding the turbine in front of the fan. I found a little flashlight bulb, which lit. I don't know the RPM, because the only nonflickering light source at hand for the tach was outdoors, where it is cold.

Tim Wescott · « **Reply #4 on:** January 07, 2012, 04:48:30 PM »

Quote from: Mike Scholtes on January 07, 2012, 02:37:19 PM

A little off topic, but still in the neighborhood ...

I need to help my daughter with a 6th grade science project. She wants to build a model wind turbine to generate electricity. Can an outrunner DC motor like we use (say a Turnigy 42-50) generate current if fitted with windmill-type blades and exposed to wind? My understanding is "yes" but I am fuzzy on how to make it work. And, assuming the theory is valid, how many rpm would it have to turn in order to generate enough current to do some work, like light up a flashlight bulb?

How would one measure the amount of current produced, or estimate it in advance to get an idea if the project will work in the first place?

Apparently, by posting your question on a forum frequented by Howard Rush!!

Quote

If anyone has a suggestion for a better source of a generator, I would love to hear it. This is probably pretty elementary to the electronics wizards we have on this forum but I'm not one of them so need some basic help.

The only problem real problem you're going to have is that for the power levels involved you need a big, high pitch prop that turns slowly, and a little high-speed motor. For 6th-grade level stuff, just do as Howard did and put it in front of a fan.

The smallest, highest-voltage motor that you can get, with a park flyer prop adapter and prop from your LHS, will probably give you the most useful 'lectricity while staying within your capabilities. I'd try motors I had on hand, but I'd also consider getting a '12V' motor from the Rat Shack. Get a few different props and experiment with pitch and diameter.

As Howard found out, a honkin' big motor still doesn't generate much voltage at the prop speeds you can get from direct drive -- if you wanted to do this "for real" (and one of our motors would probably be good for this sort of service) you'd probably want a two or three-foot diameter turbine, turning a few hundred RPM and geared up substantially. But even doing that with duct tape and baling wire is going to be beyond the capabilities of your average 11-year old.

John Rist · « **Reply #5 on:** January 07, 2012, 09:38:39 PM »

I looked and radio shack does have small dc motors. Cost is very low. I would look into using LED light bulbs. The operate on very low voltage and current. I also agree a large diameter high pitch park flyer prop would be best. I probbaly have enough junk laying to do the project. Email me and I will see what I can come up with.

Mike Scholtes · « **Reply #6 on:** January 08, 2012, 06:31:57 PM »

Many thanks guys!

I explained to Elizabeth that people as far away as Ukraine (Igor, if I am wrong about your homeland I apologize) and as exotic as Seattle had taken an interest in her project, and she is most gratified. She chided me however for thinking of using store-bought parts so we are winding our own coils and using rare earth magnets to build our own generator. I told her we could also put current into it and make it spin. I will post a photo of the completed project.

Howard, do the German engineers at Pletty know about your misuse of their products?

Tim Wescott · « **Reply #7 on:** January 08, 2012, 07:54:36 PM »

Well, obviously she's read the Builder of the Model rule.

If she bogs down in details, tell her that a real live systems engineer (that's me) has told you (right now, in fact) that it's pretty common for companies who make wind turbines to buy components like the actual generator, and build the rest.

Of course, its also pretty common that they'll do so in close consultation with the generator company, so what they'll end up with will be more or less customized just for them.

Mike Scholtes · « **Reply #8 on:** January 08, 2012, 08:17:07 PM »

Thanks Tim, I will pass your insight along.

We have settled on a Savonius vertical axis drum type rather than the horizontal axis prop driven (or driven prop) type. We have a wealth of the real deal in our area in the windy Livermore Pass, thousands of them in many types including what looks like a vertical eggbeater. We also have a huge solo installation near Vacaville with a prop that appears about 200' in diameter. I could be wrong on the size since have only seen it in the distance. They have some truly monstrous ones in Holland facing the North Sea, one I think with a counterbalanced single blade several hundred feet long. Our goal is a little more modest: light up a 5mm red LED.

Failing that I have that unused Turnigy and a lot of 3-blade props.

dave siegler · « **Reply #9 on:** January 08, 2012, 08:51:23 PM »

P = 1/2 rho S v^3.

Highest efficiency is about 59%.

http://en.wikipedia.org/wiki/Betz_limit

That does not take in account of generator losses.

Vertical axis machines are even less efficient mostly due that 1/2 the time the blades are in dirty air.

also the blade pitch is all wrong

http://www.gregorie.org/freeflight/wind_turbine/

Igor Burger · « **Reply #10 on:** January 09, 2012, 01:41:02 PM »

Quote from: Mike Scholtes on January 08, 2012, 06:31:57 PM

people as far away as Ukraine (Igor, if I am wrong about your homeland I apologize)

not so far, little bit closer ... 500 km ... I live in that small town called Bratislava with 500 000 people which is capital of that small country with 5 000 000 people ... that is why we understand such small wind turbines so well :- ))))))

... and only 5 of them fly c/l stunt :-)))))))

Tim Wescott · « **Reply #11 on:** January 09, 2012, 02:22:12 PM »

For those of us who are still not clued in (as I was, until I went to the Font of All Knowledge that Fits):

http://en.wikipedia.org/wiki/Bratislava

Igor Burger · « **Reply #12 on:** January 09, 2012, 02:41:47 PM »

for better reading :- ))))

http://sk.wikipedia.org/wiki/Bratislava

Larry Renger · « **Reply #13 on:** January 09, 2012, 06:05:29 PM »

My expertise in electronics extends as far as never having installed a resistor with reversed polarity. However, would it be possible to create a diode network that would make the Outrunner output a pulsed DC? Or is it already?

Tim Wescott · « **Reply #14 on:** January 09, 2012, 06:33:07 PM »

Quote from: Larry Renger on January 09, 2012, 06:05:29 PM

My expertise in electronics extends as far as never having installed a resistor with reversed polarity. However, would it be possible to create a diode network that would make the Outrunner output a pulsed DC? Or is it already?

Our brushless motors put out distorted three-phase AC (carefully distorted three-phase AC -- it's designed to make the ESC design simpler).

Search on "three-phase bridge rectifier". Or look here, where it says "three-phase":
http://en.wikipedia.org/wiki/Rectifier#Full-wave_rectification

dirty dan · « **Reply #15 on:** January 13, 2012, 01:25:21 PM »

I would like to point out that for the best grading possible it would be nice to not only have the generator work properly it would add an element of real-world effects to toss a few baby chicks into the spinning blades of the turbine.

Dan

Mark Scarborough · « **Reply #16 on:** January 13, 2012, 01:41:04 PM »

Dan,,
good to see you are back on your meds,,

I wonder if baby chicks may be a bit out of proper scale proportion ,, though I am at a loss as to what WOULD be in scale proportion,,
on a related note, you are quickly stacking up post counts,, it wont be long and you will be an admiral,,
keep up the good work mate,,

Tim Wescott · « **Reply #17 on:** January 13, 2012, 01:53:51 PM »

Newly hatched hummingbirds?

Or maybe some little moths, individually painted up to look like songbirds.

Or, since this is a sixth grade science project, perhaps it would be adequate to make some little bird silhouette cutouts, and wrap them around the leading edges of the blades.

Mike Scholtes · « **Reply #18 on:** January 13, 2012, 09:29:44 PM »

Being the environmentally sensitive Californians that we are, this is a vertical-axis device that uses half-drums for power. No spinning propeller. The chicks that wandered in would get dizzy but not diced and sliced. The thousands of full-size propeller-driven wind turbines in the Altamont Pass (yes THAT "Altamont" for you Stones fans) do a nice job of slicing the hawks and occasional eagle that hunt in the same currents that drive the turbines. It is a legitimate problem that is getting lots of attention.

We are almost ready for testing. I will post pics tomorrow or as soon as my 6th grader can explain to me how to get them out of the devil-box where they reside. "Digital Camera" I think she calls it. I can't figure out how to open it to get the film out.

REX1945 · « **Reply #19 on:** January 25, 2012, 10:43:12 AM »

Mike,

What you really need is a Lego DC motor (9V).

They can light lamps and you can plug one into the other as a motor-generator pair and turn the shaft
on one (slowly by hand. even) and watch the other one rotate. Works forwards and backwards.

The props to use are made from formed from balsa wood and will rotate when you blow on them
from your mouth.

http://www.philohome.com/motors/motorcomp.htm

I had some kids make a wind turbine with it for science fair and the won a trip to NASA Ames.

Tim Wescott · « **Reply #20 on:** January 25, 2012, 10:50:24 AM »

Quote from: Mike Scholtes on January 13, 2012, 09:29:44 PM

The thousands of full-size propeller-driven wind turbines in the Altamont Pass (yes THAT "Altamont" for you Stones fans) do a nice job of slicing the hawks and occasional eagle that hunt in the same currents that drive the turbines. It is a legitimate problem that is getting lots of attention.

Oh, you mean those are wind turbines? I thought someone was doing testing in preparation of making some really big Piper Cub models, or something.

I mean, you know how crazy these RC guys are getting.

Howard Rush · « **Reply #21 on:** January 25, 2012, 04:06:12 PM »

Haven't they replaced the ones at Altamont with slower ones that don't bother birds?