Sounds great.

If I ever decided to build such a contraption, I'd simply dump the raw unprocessed power into a heater in my basement. For the non-heating season (~July 15th to ~August 15th, LOL) I might rig up a simple water pre-heater using a $200 water tank. There'd probably have to be a third power-sink for rare occasions when the other two are not required.

For parts, I'd be tempted to purchase an inexpensive ($200) gasoline power generator in the 1.2kw class and scavenge the generator from it. There'd be the obvious issue of gearing up the windmill speed to something close to 3600 rpm.

Even with this simple approach, and electricity rates of more than $0.13/kWh, the payback period is likely to exceed the lifetime of the Universe. So I probably won't bother.

Yes if you get hung up on a "pay back" then it's pointless. If you build it for pleasure, then it's fun, multidisciplinary, and satisfying. I don't know why so many people bring up the subject when they certainly wouldn't expect to save money by building their own cars, airplanes, or furniture, yet millions of people do that in their garages.

STF

For just heating consider one or more automotive alternators from the auto-wreckers. They are capable of over 100 Volts (But if running at higher voltages you may want to avoid load dumps.) Flat micro vee belt drives are fairly efficient. The speed will vary so that the voltage and power dissipated will match the power into the turbine.
Much more forgiving of a wide range of speed than most 60 Hz alternators.

Bill
--------------------
"Why not the best?"
Jimmy Carter

If you try the auto alternator, you'll need 2000 RPM or more to get any useful power out of it. Mate that up to a wind turbine that only wants to turn 500 RPM and you'll be gearing up a lot before the speeds match. Talk all you want about vee-belts, you'll be fussing with it forever before it works. The bearings will wear out before then. Auto alt bearings are only sized for a few 1000 hours of operation before they quit (boy, do I know about that) but a wind turbine turns almost constantly for years before you should be taking it down for new bearings.

STF

I'm at around 10,000 hours on my old truck at a 2:1 ratio. My car gets about 1000 hours on an alternator, but that's load dump issues taking out the diodes. Never lost a bearing.

Bill
--------------------
"Why not the best?"
Jimmy Carter

SparWeb - interesting unit. Did you build the permanent magnet rotor by machining the magnets into the existing rotor? Ever consider building your own generator? The disk or pancake generators seem to work really well. I'll have to dig up a picture of the unit I was involved with building a number of years ago.

No-one building a serious wind turbine would use an auto alternator. The generator from a little 3600rpm gas generator really wouldn't be very suitable either.

Auto alternators are only around 60-70% efficient typically (it varies a lot), in that case at 13.5V, 4000 rpm, 60A.

A cynic might decide that it is easier to fit 50% bigger blades or watercooling than sort out a more efficient generator I suppose.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

Waross: I still think it's a bad idea, but if you want to prove me wrong, fill your boots. I warn you that I have already read of the frustrations of 3 people who have tried what you suggest.

Lionel: Yes, and your question is answered in the photos I posted on my journal webpages. Rather than force you to go look it up though, since I've done a number of these projects, and only one is on that tower now, I'll tell you some more about the current one. At the time I was able to use the machine shop at work for personal hobby projects (alas, I cannot any more). I started by taking an old Baldor induction motor apart. I have no idea why these things get junked when the wires are clean and the shaft is true. I pushed the induction rotor off of the shaft, and press-fit a bored steel cylinder in its place. More iron means a better circuit for magnetic flux. The cylinder was machined with flats on it for the magnets to rest on. These I attached with brass screws and adhesives. I won't try to explain the pattern of magnets, but if you're curious go see the pictures. The diameter of the magnets just fit inside the stator. Turns out I left about 1/8" clearance when I was aiming for 1/16". Impossible to say how much that affects performance, but it's plenty good for me so I don't worry about it. As for wires, the Baldor was already wired for dual voltages and 9 wires were in the connection box. That wasn't enough so I cut the star point and brought the remaining 3 for a total of 12 wires. I now have it wired with coil pairs in parallel, and rather than star or delta, I rectify the phases independently to get 28VDC. Batteries and diodes don't care about, or see much of, the harmonics that causes.

I did build a "pancake" alternator once. It fried in its very first storm. The blades survived. I replaced it with a converted motor (the first one I tried). The successive generators have all been homing in on the "sweet spot" of electrical performance matching aerodynamic performance.

28VDC is a very very low voltage to be operating a motor (even after all the conversion work I've done) that was originally designed for 240/480 VAC. The performance as a generator suffers as a result, so I get no brownie points for efficiency. Someday I might change to a 48-volt system (which charges at 56 Volts) and it would have better performance if I did, to boot. The whole point is to "match" the operating speed of the generator to the operating speed of the blades. The generator reaches 28VDC at less than 200 RPM, also the speed the blades turn in a 8 mph wind. System in balance.

STF

Quote:

Impossible to say how much that affects performance

The air gap is significant. If you double the length of the magnetic circuit for a given magneto-motive force,the strength of the magnetic field is cut in half. (And the induced voltage will be cut in half). The lengths of the various components of the magnetic circuit are weighted according to magnetic permeability. Given that the ratio of the permeabilities of good magnetic iron versus air is in the order of over 10,000:1, you can often ignore the iron without serious errors. Just remember the saturation limit. Saturation of the steel is a limit but up to that limit the magnetic field strength and the open circuit voltage at a given speed are almost inversely proportional to the length of the air gap. What is next is some way to estimate the strength of the magnetic field relative to the saturation knee to determine whether it is worth while trying to shim the air gap. Possibly shims of magnetic material under the magnets.
If you are going to try to up the voltage the air gap is a good place to start.

Bill
--------------------
"Why not the best?"
Jimmy Carter

Here's a view of the magnetic circuit, modeled with a 0.06" gap. My memory was incorrect: the actual gap is about 0.09"-0.10". In the model
results I arranged the output windows so that you can read them all in the image. The average flux per pole is 0.71 Tesla, or 1.5 Tesla in the teeth themselves, and there are peaks up to 2.0T in some areas. The model was drawn in FEMM, and I selected standard electrical iron for the stator.

STF

Not sure what alternators you guys are using. The one in my Galant has minimum 2500 hours, assuming 100% the time the engine was running I was heading down the highway doing 75 or so.. I'll be turning over 200k miles in that car within a month or so. I have driven multiple vehicles with well over 100k miles and I have yet to replace an alternator in my memory.

-handleman, CSWP (The new, easy test)

I haven't replaced an alternator in ten years or so.
... but in the ten years before that, I was losing two a year or more.

It seems to be a cyclical 'fashion' sort of thing.
Every time the alternators get redesigned for 'higher efficiency' (read 'less copper'), the producers forget how to make them durable, and it takes a while to get the details right again.

There could be another cycle involved.
To use an example not specifically involving alternators, a certain large construction equipment manufacturer hires only the brightest engineers from the very best schools. They keep them about three years, then they dump most of them into the cold cruel overcrowded engineering job market. They keep just a few percent of them to follow what is alleged to be a technical ladder, and put them in leadership positions, where they are expected to pass on the knowledge passed on to them, as well as what's been learned the hard way during their tenure.

Sometimes they cut too deep or too soon, and _everything_ gets screwed up. It takes about ten years to recover from a disaster like that, if it can be done at all. A substantial portion of what should be retained corporate knowledge is just flat lost in every one of those bloodlettings.

Mike Halloran
Pembroke Pines, FL, USA

This thread got me to dig out an old book I purchased years ago titled 'Producing Your Own Power', edited by Carol Hupping Stoner (Copyright © 1974, Rodale Press). The first chapter covers Wind Power and in addition to ideas and plans for building your own wind turbines it also discussed some previously available commercial wind generators developed primarily for use on farms before the coming of rural electrification in this coutry. The two most commonly used and affordable models was the cheaper 'Stewart Warner Wind Charger':



http://www.vintagewindmillparts.com/phpBB3/viewtop...

and a more expensive and efficient unit, 'The Jacobs Windmill':



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

Anyway, I thought this would at least have some nostalgic value.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

Thanks for the pictures, John. There are some old Jake's still running out there, as long as they get enough TLC. People can still fix them because the Jacobs patents are so detailed that they read like overhaul manuals! A farmer down the road from he has what looks like a Parris-Dunn turbine that's been in the parked position for 10 years. When I drive by, I'm always tempted to turn in and ask him about it.

STF