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I promised a few pics...
By monte350c, Section Homebrewed Electricity Posted on Thu Oct 2nd, 2003 at 05:15:21 PM MST
Here are a few pics of my home made electricity adventure so far...

Hi all,
Thanks for the replies about the stall question I posted last night. I'm trying to find out if stall regulation of speed is worthwhile considering or not.
I built a 15.25" diameter alt. with 18 coils - 18 AWG, 70 turns ea. with 24 neo mags 1" x 1/8" round on each rotor. The rotors I had made at a local machine shop for about $75 total. They are made out of 3/8" steel plate. I had 4 cutouts put in each one to cut down the weight a bit. The rotors ride on a 4 bolt trailer hub/axle, which is welded to an X-shaped frame made out of 2" box tube, 1/4" wall.

I wound the coils using the usual sort of former - 2 pieces of 3/8" plywood, but I used a 1/4" dowel in each of the 4 corners of the coils, with a spacer in between of about 1/4" thickness. I cast the rotor with 2 layers of fibreglass cloth on both sides for strength. The overall thickness of the rotor is 3/8". The airgap on each side between the stator and magnets is a little under 1 mm (sorry about the mixed units!).
The first place this alt. ended up was on the bottom of a Savonius rotor assembly:

One day last week when the wind was at around 16 mph, this thing was turning at 125 RPM. The load was one 25 watt light bulb on each phase (48 ohms ea.) I measured the voltage on one of the phases by taking out the light bulb. The Fluke reported a peak of 34.5 VAC/50hz.
I hate to say it but I am undecided what will be flying on this alternator - Darrieus wings, or a conventional prop! Now that I've tried a small Savonius, I kind of get the idea that a big one would work - but there are problems with scaling these up. So now I'm making some foam core/fibreglass covered Darrieus wings to try on it. BTW it's EPOXY resin - not the normal styrene based stuff you get at the Auto Zone. I tried that and it melts the foam quite effectively!
I cut out some NACA0015 profiles using a home-made hot wire setup, and profiles from the excellent X-Foil program which you can download for free at http://raphael.mit.edu/xfoil/ With a little prodding the program will create a ps file, which can be opened in Acrobat, then scaled as desired. It's pretty easy to make a vacuum bagging setup:

That's an old frig compressor - and the switch is from a water pressure pump - with a vacuum advance unit from a GM HEI distributor pulling on it...

Here's a pic of the first wing in the vac bag:

I'm aiming for 200 RPM or so with this test setup. It will be mounted to horizontal struts on the same frame where the Savonius now resides. About those wings - they do have to be strong, and light, due to centrifugal forces. At 200 RPM, and a 54" diameter on this test unit, the force involved will be about 30G! So if the wing weighs in at 2 lb. it will weigh 60 lb at speed. There's a nice mechanical brake on the top rotor with a long piece of rope attached if things don't work out!

Sorry for being so long winded! I'll post results of the Darrieus wings as soon as they are mounted. Again my sincere thanks to all you guys - I've learned a lot in a short period of time. And got a new hobby/obsession!

I promised a few pics... | 5 comments (5 topical, 0 editorial)

Re: I promised a few pics... (none / 0) (#1)
by RobC on Thu Oct 2nd, 2003 at 08:28:18 PM MST
(User Info)

What a nice looking alternator. I can't wait to see your
next project. Keep up the good work.
RobC

Re: I promised a few pics... (none / 0) (#2)
by sean on Fri Oct 3rd, 2003 at 01:32:28 PM MST
(User Info) http://homepage.ntlworld.com/s.amesbury/homepage.htm

Fantastic stuff i gotta hand it to you, like the blades in fact i like the whole thing. have tested to see what wind speed the drag blades start up and when the alternator hits charging voltage? Something i havent tried on a large scale yet and thats a drag type vawt so im courious as to any data you may have on it.........sean

Re: I promised a few pics... (none / 0) (#3)
by monte350c on Fri Oct 3rd, 2003 at 02:22:05 PM MST
(User Info)

Hi Sean,

The unloaded blades will start to rotate in about 7 mph worth of breeze. The alternator hits 12 volts AC at 40 RPM. The fastest I have seen this particular unit spin was at 125 RPM in a really stiff breeze of 16-20 MPH. The output at that point was around 35 volts AC. That day it had a load of one 25 watt/120 volt bulb on each phase. To measure the voltage I unscrewed one of the bulbs - this was at night, and I would say the bulbs were at about 1/3 to 1/2 their rated brightness. If it was more highly loaded, of course it would slow down. The blades are 18" wide and the stack of 4 is 56" high. For the next couple of days I'll be continuing to work on the foam core Darrieus blades. I'll mount them, probably removing a few of the Savonius sections and see what happens!

[ Parent ]

Re: Vawt's get a bad rap... (none / 0) (#4)
by windstuffnow (elenz(at)windstuffnow(dot)com) on Fri Oct 3rd, 2003 at 07:07:50 PM MST
(User Info) http://www.windstuffnow.com/main

You really have to load the Savinous to about 33% of free speed rpm to achieve full power out of them. So if it runs no load at say 100 rpm's in a given wind then the best power extraction will be at around 33 rpm for that wind speed.
I think the VAWT's get a bad rap because the blades really extract power quite efficiently. They simply have alot of built in design flaws. You figure at any given time only half of the machine is extracting power, the other half is simply robbing the power. You calculate the entire area of the machine when in reality your only collecting from 1/2. Then consider what the downwind blade is doing... its moving away from the wind. This means your really collecting 1/2 of the machine and from a slower windspeed. So if the wind is 12 mph and the blade is running at 4mph your collecting from an 8mph wind. This also means the upwind blade is being held back by a 16mph wind. If you calculate exactly what the downwind blade is doing you'll find its collecting at over 50% efficiency.
Analyzing a 2ft x 2ft unit (4 sq ft total) in a 12.5 mph wind. Free speed is 175 rpm so the optimum rotor speed would be around 58 rpm. The total watts available in that area would be around 39. The down wind blade makes about 3.23 watts but the up wind blades steals 1.12 watts leaving 2.1 watts harvested... pretty poor indeed. Lets say your only collecting from the downwind side and the upwind is blocked off. That leaves you with only 2sq ft of collection area but your getting the 3.23 watts well geeze thats much better. Total available watts in 2sq ft at 12.5 mph is around 19 that jumped the machine up to 17% efficiency. But wait !! The blade is moving away from the wind so in reality we're only collecting from a 8.5 mph wind. There's only 6.2 watts available in that wind and we are getting 3.2 of that.... ( 3.2/6.2 = .51) Yes thats 51% efficient on the downwind blade. Getting very close to the Betz theory. So basically the machine gets a bad rap but the blade is quite efficient, It simply needs a bit of redesigning... without all the flaws.

Have Fun
Ed
Have Fun! Windstuff Ed
[ Parent ]

Re: Vawt's get a bad rap... (none / 0) (#5)
by monte350c on Fri Oct 3rd, 2003 at 10:28:02 PM MST
(User Info)

Hi Ed,

Yep - I kinda favor verticals too - that's why the emphasis so far has been with this configuration. I think there will be a way to do this - so even if it's going over ground previously covered I feel sort of compelled to keep trying (and of course having fun at it!). I liked your venturi ideas and this may be a good way to combine D & S styles to produce something good.

The trailer axle & hub I used for this alternator I feel will be able to accept quite a bit of loading. I am considering using a schedule-40 pipe with a flange welded to it that bolts under the hub bolts, about 6' long, with no top bearing.

The alternator is a fairly large diameter so it can develop some power at lower RPM's. I think for these power levels a gearbox or rpm step-up devices are not going to be to efficient.

Current plans will see a couple of different things attached to this. The first will be an upscaled Darrieus with NACA0015 wings. Big. (inspiration: http://infoserve.library.sandia.gov/sand_doc/1977/771063.pdf) The wings will be 10' high, the dia. 17'. Perhaps by eliminating the smaller diameter regions of the trop. shape, and using struts instead, good things will happen. The wings for this will have an aircraft type stainless control cable in them, running back through the struts and bolted to the torque tube for containment just in case...

I am working out moveable aerodynamic devices for the struts, rather than the wings themselves. Downwind deployment for startup, and deployment on all three sides for speed control (with a mechanical governor friction brake as backup, and a hydraulic caliper with master cylinder a long way from the tower as a backup for that!). This I suppose could be called an H-Bar D. setup. I like the idea of large diameter, since that way rpm and therefore RCF can be held to a reasonable level. If things go well I will be winding a bigger alternator.

The experiments I have been working on with vac bagging foam core wings look very promising. The first one out of the bag is a NACA0015 with a 7" chord - 5' long. Last night I placed it on 2 chair backs and put a box of books in the middle that weighs about 60 lb. There was no deflection at all. These things are really strong, and very light. Boy am I long winded!

I'll post more as this develops!

[ Parent ]

I promised a few pics... | 5 comments (5 topical, 0 editorial)

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