Radical micro wind generator

Difficult as we can't even tell from your profile what continent you are on!

Sorry about that - new to CR4. I'm in England and am exploring the potential for efficient, safe and quiet generation for urban and semi urban locations.

I'm into tinkering with stuff and have been toying with the idea of a small wind generator just for fun...I got as far a dissmantling an old washing machine motor and hacking the armature of the shaft with an angle grinder...I think the field coils are too big to allow many magnets (probably 4 max) I havn't got any machining facilities (I don't think a pillar drill and angle grinder count lol!)...so it's degenerated into an armchair project....

England 'eh?...getting closer...I'll pop next door and see if it's you living there....care to home in a bit.....?

There are a bunch of us living just north of London (we don't need an exact location...I'm amazed at the level of paranoia about personal details out there....oooh let's all have ID cards (not).....whoops in danger of getting political...[knock on door stage left]...)

KBO

Del

I'm in Wild Windy Cornwall!

I need to understand more about sizes and numbers of magnets and windings.

e.g. can an arrangement of many many small but powerful magnets moving very rapidly (say equivalent to 1000rpm) against coils compete with a conventionally designed alternator arrangement of few large and powerful magnets/coils? turning at the usual 200-600 rpm.

How's your knowledge in this area?

How's your knowledge in this area?

Pretty fuzzy...it's about getting a decent magnetic flux, and rate of change of the flux. There's loads of good stuff on the net, on every aspect of the topic.

It's that trade of between converting some existing motor/generator, scratch building or buying.

Del

HI !

There are a few vertical windmills out there that could be redesigned to give you the power you are looking for maybe you should investigate them first before starting from scratch.

see you later

goldrushnugget999

Though not an expert, my understanding is that you can either have slow moving large machine or a small fast machine to generate the same power. This is true for almost all machines. A small high rev engine can have the same power as a big chugger. In generators the EMF generated in each conductor is proportional to the air gap flux density, the length of conductor in the gap and the speed at which the conductors are moving. That is the basic theory. In a wind generator a big generator would block the wind over a large area; but the wind turbine speed would have to be stepped up if it is to drive a small machine. Gear reducers are easy. Gear amplifiers of speed are more difficult. So you need to think where to go to get the best fix.

Thanks Yanthram, your comments were very helpful.

I have always been fascinated by the idea.

Most "Home grown" units I have read about appear to work in gail force winds sufficient to trickle charge a D size battery. Ok for the flashlight at night.

The blade design is out of my ken, but have you calculated the potential power from a small windmill? This will determine the size of the generator, and you need to keep the losses to an absolute minimum, so PM is the only way to go as far as I can see.

Rotor gaps will need to be kept small, and friction and windage in the generator at an absolute minimum. Magnets from hard drives are incredibly strong, so could be a possible source.

Thanks GW - I have always wondered whether the common three blade rotor with standard design permanent magnet alternator has the best potential for micro generation.....

You might find this site helpful: http://zebu.uoregon.edu/1998/ph162/l11.html

Alternately, Google for "windmill calculations".

Thanks DVader1000 that link was very useful!

You might look at Popular Science or Popular Mechanics in the last couple of months. They are using a spiral unidirectional plastic blade and an alternator to charge home batteries. I am sorry I do not remember which magazine, but it should be easy to look in their archives for the story. I am a retired electrician and I have wired in both photo-voltaic slate roof tiles for a remote water dam site and a wind generator in our high desert area of Oregon.
Good luck in your interesting project.

See Masu's post CRIMINAL

Permanent Magnet came about 20th (after other possible choices, and, on the second page) on the first web acronym finder I got to.

OK: people who don't know are unlikely to be able to help, but, lots of people learn a lot by reading these threads and not having that vital bit of information makes it much more difficult to start picking up the meaning. Sorry just a common whinge.

On another point I've always wondered why modern wind generators nearly all seem to have 2 or 3 blades: traditional windmills had loads of sails. The three blade version must let a lot of wind through the "gaps".

Sorry Randall! I will try harder in future!

Meanwhile, TTFN!

Surely the gaps are to allow the machine gun to fire though?

The windmill is desined to function as a propeller (rotating airfoil) in a flowing current of air. Without the gaps, you have a brick wall with no flow through the rotor. Withput the gaps, the lateral forces from the wind are substantially greater, requiring a much stiffer tower, shaft, whatever.

RichH

HI NoScifi !

WHY don't you try an vertical windmill sense you want a radical design and power generator that would be a novel idea & it just may be a higher power producer.

Thanks

goldrushnugget999

I was thinking of playing with a Savonius type as I have a natural 'wind funnel' between my house and next door's. I was rather surprised by their relatively poor efficiency when I read up on them....still it would be fun, and they do have good start up torque I believe ...

Now if only I had an application ....

Hey hook it up to a giant bubble blower?

Perfect only works when it's windy...mmmm streams of pretty bubbles....drifts off into fantasy world...

You are mad; that's good.

Just like any engine, theoretical efficiency is something that is designed for, and as long as you aren't using a carbon fuel source, is not a concern, except that greater efficiency permits smaller designs. For home use, radius' of 5 to 10 ft would be the practical maximum, and a vertical shaft would be far less obtrusive and draw fewer complaints from the neighborhood watchdog. That would leave you with a squirrel cage about 5 feet high, or a anemometer type rotor, with perhaps collapsible cups on the return side, mechanical cam/vane directed, similar to a helicopter rotor. That takes the airfoil out that would be more "efficient", but the extended vertical shaft below the vane, could be cable stayed, reducing the rigidity required in the generator.

With the net force related to the radius, the buckets would only be of value at the outer 1/3 of the arms.

The gear required to sell surplus to the grid is not very cost-effective. PM is nice, but requires fairly constant loads and speed to function, whereas variable voltage field allows full voltage at slower speeds if load can be limited, and can vary your power output at high wind speeds, leaving less energy to "dump".

Winter dump can be water heating, but summer would have to be a heat coil to atmosphere. ( Or Coleman liquification of air for later thermal/pressure recovery). High winds last for several hours or days, meaning a lot to dump. Cost/size of battery storage and inverter, along with a switchable load based on available power, capable of phase balance because of the occasional 220 volt load, and the existing neutrals, and the project becomes a nightmare. For the DIY.

Redesign appliances , switches and controls, for DC, and convert your AC supply for use as DC, (shades of Thomas Edison) replace motors with universals, with sc regulators rather than resistance control, install LED lighting, and double all neutrals currently in networks, perhaps a separate 240v AC panel for larger loads, and you might have a future.

RichH

Thanks for all that - very illuminating!

This is a web site that discusses windmills with 2 blades or multible blades. It seems that with small wind multiple blades are better.

http://nov55.com/wdm.html

Thanks Stan, that article was most encouraging!

With respect to blade nos. Its a matter of wind shear. Wind travels more slowly the closer to the ground it is.

This presents a real problem for a 2 bladed turbine design, even though it suffers from less overall drag (=wind force against the tower) as the rotating turbine is in the horizontal position, each blade is subjected to equal force from the prevailing wind, but as it rotates towards the vertical position , the wind shear effect means that the top blade is experiencing greater drag and the lower blade reduced drag and the turbine begins to oscillate about its axis. In strong wind conditions, these oscillations become destructive leading to structural fatigue, bearing failure and collapse.

Apparently, a 3 bladed design offers an efficient counterbalance to the wind shear effect. More than 3 blades and the coefficient of drag begins to work against the design (loosely speaking).

Thanks for that

The "gaps" do not constitute a loss. It is possible to have a single thin blade going fast and extracting all the available energy going through the swept area-- in fact it has been done! You can have a lot of blades going slow or a few going fast to intercept the same power. Old wind mills were connected to slow reciprocating pumps or grain grinding wheels and so they had to be slow. Modern wind turbines can go fast because they ultimately drive electric generators with shaft speeds of the order of a thousand RPM. But of course it is not possible to go that fast even with one blade. The inertial forces on the blade would be prohibitive for big machines. And power is of course proportional to the swept area (and cube of the wind speed).

'power is proportional to the swept area'.......

Surely, whilst the swept area governs the maximum power available, the power converted from any given swept area is governed by how efficiently that area is swept?

It can be proportional to swept area...and proportional to efficiency,

and maybe lots of other things too...colour? Wire gauge, shoe size?

I only meant that for a given efficiency the power will be approximately proportional to the area or square of the rotor diameter. Like the Carnot efficiency limit for heat engines, there is a Betz limit to the theoretical efficience of wind turbines, which is just under 60%. I believe real life turbine efficiencies are about 40% or less.

Sure. Efficiency comes into it. But for a given efficiency, power is proportional to swept area. How can it be otherwise? While on the subject of efficiency, I believe currently operating turbines achieve something like 40% efficiency.

Thanks Yanthram

The number of blades is not as important as the availble area in contact with the fluid. Try an equal ratio of .81 at the hub and the tip then start with too much pitch and decrease that till you find the best power output (rpm and torque) from your design. Once you have your optimum power and useful rpm range you can design the generator.

The best alternator designs and efficiencies are from Rasor Tech. You are going to need to match whatever the power is from the wind-turbine. The best would involve a variable field alternator the will allow max power to develope from the turbine.

Otherwise just make a spiffy looking thing that does a mediocre job just like the commercial fecal combinations currently available.

....an equal ratio of .81 at the hub.....I don't understand. Please explain.

I agree, current (ouch!) offerings of small generators offer very small returns, but maybe their makers know something I don't......!

Try googling " piggot wind " for UK; Hugh has travelled internationally with a working windmill design to teach the entire process of workshop to hillside. He makes his own(open source) generators from copper wire magnets, epoxy resin and marine ply; together with accessible blade design calculations and guides and a scrap van wheel bearing!

Concepts (from the downloadable workshop manual) include lift and drag of the turbine blades, why 3 blades and not 2 etc., etc.

Well worth a look. An alternate design (google again) of a louvred tower (4 faces) that directionally vented wind through a split level chamber -through a horizontal turbine.

A perfect archtectural solution for higher buildings ......? Retrospective conversion or pre-emptive inclusion.

Hello Blob,

I have been throwing around the idea of a windmill. I have found the Danish Wind Institute http://www.windpower.org/ to be a wealth of general information. Additionally, you might find this site http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html good for reviewing some e&m theory and equations. The latter site is also fantastic for just about any kind of physics knowledge. I use it all of the time with my students. Through some really serious internet searching I found a site that details the design process for wind turbine airfoils, but I can't find the link. If I find it, I will post again.

Thanks DAG. I will follow those up.

.81

(pi x dia x .81) / number of vanes = vane length measured around the circumference at the tip and at the hub of the turbine vane. I would make the hub .2 x the periphial diameter. You are not making a propeller to push something plain flat vane vectors will work well.

The airfoil can double the efficiency of flats. Power in or out improves. Even jet engine turbine buckets are airfoiled, whether power, bypass, or compressive rotors.

RichH

I have developed a really efficient PM alternator...

If only I could get it to work in the morning as well!

Silly sob

Willy Nilly lob