Lenz2 Turbine

A few details for building the 3ft diameter x 4ft tall Lenz2 turbine...

Below is a drawing for the wing ribs cut from 3/4" plywood.

NOTE: The above drawing shows that only 6 ribs are required, that should actually be 9 ribs required.  I originally designed it with only the end ribs in place with a stiffener bracket in the center.  The 3rd rib actually makes them much stronger.

Wings...

The wings are basically built from 3/4" plywood for the ribs and the stringers were cut from treated 2x4's.  The stringers are glued into the slots and later drilled for wood screws.  Simply clamp the stringers into the slots and allow the glue to set. Once the glue has set you can cover the wings with aluminum sheet.  I've also used PVC sheet in 1/8" thickness which might be cheaper than the aluminum.  The aluminum sheet was .025 thickness and is actually lighter than the PVC sheet.   Other light weight weather proof materials will work as well.

Above is another shot of the wing frame

The rivets are aluminum 1/8" and are 3/4 to 1 inch long.

I start by bending a 90 degree angle on the leading edge of the aluminum and rivet it to the top outer leading edge of the wing frame.   Flip the wing over and roll the frame over the aluminum.   Clamp it to the trailing edge.   Start putting rivets evenly spaced around the nose through the aluminum into the wood ribs making sure the aluminum is pulled tight to the rib as you go.

When the aluminum is riveted to the frame bend the trailing edge to form a seal of sorts to the rear stringer.

The alternator for the roof top model is simply a modified version of my 500 watt kit.   The pdf instructions can be Downloaded Here .   The differences are... the coils have 55 turns of #18 magnet wire and the stator is 1/4" thick instead of 1/2".

NOTE: A more efficient stator can be made using 2 strands of 18 awg wire ( 15 awg equivalent ) , winding them for the 1/2" stator thickness.   Follow the instructions for the 500 watt kit  with the exception of the turns per coil.   2 strands of 18awg with 65 turns per coil ( or 15 awg single strand ).   This will make the alternator more efficient in lower winds and add a better load to the turbine in higher winds and ultimately extract more power.

Below is a picture of the alternator end of the turbine mounted to the 1 inch square tube frame...

The magnets for the project can be purchased from my product page as well as the steel discs.  The bearings used are standard 1 inch pillow block bearings purchase from Northern Tool ( best price I've found on them so far ).

The frame for the turbine was made from standard 1x1 square steel tubing welded together to form a "box" shape with plenty of clearance on the sides.  In the above picture you can see the two steel plates just above the bearing that is welded to the frame to hold the stator in place.  The top and bottom magnet disc rotate and the stator simply sits centered in the air gap between them.

Although it's shown in August 2007 Popular science on my roof, I don't recommend roof mounted turbines.  I used this setting because it's very turbulent and it seemed like a good place to test it for this type of wind.  It was also quick and easy as I was rushed while installing it in the late fall.  The turbine will perform much better on a taller platform in clean un-turbulent air.  It works very well where it's placed but it would perform much better and provide a higher more continuous output in a better location.

Scaling the turbine and setting the wing angle is shown in the diagram below...

Below are some formula's to help find the rpm it might run in a given wind as well as how much power you might expect from the unit....

Watts output = .00508 x Area x windspeed^3 x efficiency

Area in square feet ( height x width )

Windspeed in mph

Example:  the 3 x 4 described above in a 15 mph wind and an alternator of around 75% efficient would have a power output of ;

.00508 x ( 3x4 ) x 15^3 x ( .41 x.75 ) = 63.26 watts

Efficiency would vary depending on the alternator and building techniques.  The turbine as tested will function at 41% efficiency at the shaft.  The alternators efficiency will vary depending on the load.   If you have an alternator performing at 90% and a turbine at 40% then the overall efficiency of the machine would be .9 x .4 = .36 or 36% efficient.   If the alternator is only 50% efficient then the overall efficiency would be .5 x .4 = 20% .   As you can see the alternator efficiency plays a big part in the overall efficiency or what you would see for charging.

How large will it need to be to make a specific power output in a given wind...

Watts / ( .00508 x windspeed^3 x efficiency) = total square feet of area

Example:  Lets say we want 63 watts in a 15 mph wind using the number from above;

63 watts / ( .00508 x 15^3 x (.75x.41)) = 11.94 sq ft ( or a 3ft diameter x 4 ft tall )

How fast will it run in a given wind speed...

Windspeed x 88 / ( diameter x 3.14 ) x TSR

Windspeed in mph

diameter in feet

the "88" is simply to convert the mph to feet per minute

The TSR ( tip speed ratio ) for this machine for peak power is 0.8.  Because it is a hybrid lift/drag machine in order for it to extract energy from both the upwind and downwind wings it needs to run slightly slower that the wind.  0.8 seems to be optimum while loaded although it will run at 1.6 unloaded.

Example:  The same turbine in a 15mph wind loaded to 0.8 TSR...

15mph x 88 / ( 3 x 3.14 ) x .8 = 112 rpm

or unloaded -  15 x 88 / ( 3 x 3.14 ) x 1.6 = 224



Some things to consider when designing... if the alternator is weak the turbine will "run away" or overspeed in higher winds.  It needs to be well balanced to handle these conditions or it could vibrate and cause something to break as well as burn up the alternator.  It's better to overbuild the alternator slightly.  You should incorporate a way to control the speed such as a shorting switch or break to slow it down and even stop it in high winds.  The shorting switch is simply wired to your output wires from the alternator and shorts the alternator.  This loads the turbine considerably, it won't stop it from turning but it will turn very slowly with that high load - here again this depends on the alternator in use.  Since VAWT's can't be "furled" out of the wind they do need to be controlled.

I've designed the turbine to work very well in low winds, and operate at much safer speed than some of it's counterparts.   This wing design is very dirty in winds above 20mph and the efficiency drops off considerably in higher winds although it will continue to produce higher outputs as the wind speed increases.

You are responsible for building and controlling the turbine, as with any wind machine mother nature can be cruel so build it strong and mount it well and you'll get years of use out of it...

Have Fun! Play safe!

If you'd rather buy this in kit form...

www.WindGenKits.com is making a very nice Lenz2 Kit available with all the goodies available for building it from start to finish.  They have also produced some very nice videos for building the stator and finishing it up.  Everything you need for getting it up and running in short order... check them out !


REFERENCE: http://windstuffnow.com/main/lenz2_turbine.htm

Vertical Axis Wind Turbine

I've always had sort of a soft spot for the Vertical Axis Wind Turbines because of the advantages they offer.  Unfortunately, most of them such as the Savonius aren't very efficient but do offer low wind characteristics.  About a year ago I was emailed a patent of a VAWT that was a bit different.  This one used the "Venturi effect" to duct air around the wings.  After reading through the patent I decided to build one and see if It was any better or worse than some of the others out there.  As it worked out it did outperform the Savonius but still seemed a bit low on the overall efficiency.  I started searching for any others that used this principal and found one other like it.  I ended up building this one also and found similar characteristics but this one also seemed a bit low on the efficiency return, still it did outperform the Savinous again.

I started playing around with small units and built a coffee can model which ended up running at 700 rpm and was named the "700 RPM Coffee can".  It really didn't make much power being as small as it was and was basically cut and duct taped together. Below shows a picture of the original coffee can experiment... If you decide to try this be advised the metal is very sharp and you should wear gloves as well as observing all safety precautions...

Basically I divided it up into 4 sections, cut two out and taped them back into the can on the two remaining sections.  It ran at 700 rpm in a 12.5 mph wind.

I decided to build a larger one using a plastic 5 gal bucket and similar techniques were used in the construction.   This was a real dud!   It didn't work at all.  After some thought as to why it wouldn't work I decided to try a round drum in the center.  I stacked a couple large coffee cans inside and taped them in.  By changing the airflow through the unit it worked although not very well.

After trying a bunch of different drums and shapes I decided to get a bit more scientific in my testing instead of my hit 'n miss style up to this point.  I was intrigued as to exactly what was going on.  I started doing some static tests of the air flow through the machine while in different positions but not spinning.  Using a hand held wind speed meter I checked the wind speed in front and behind the unit as well as inside.  The air flowing through the can was actually faster than the air entering the can.  I found some Venturi formula's and started testing shapes and wings.  I figured I had enough information to design something a bit larger, and get some better test results.  Using a combination of Savinous design ideas along with the venturi theory I came up with a design that is a bit different than the normal.  Although similar to the Darrieus, wings similar to the Savonius, and a triangular drum in the middle to guide the flow of air the design was set.  I built a few smaller versions for testing and the results looked promising and showed that I seemed on the right track.  A larger one needed to be built.  Below is the last one built to this point...  Simple construction using plywood and aluminum flashing the machine is a bit under built but all the components are in place for the testing...

The alternator is a homebuilt single phase axial design and the first test run showed 17 watts in a 12.5 mph wind. The alternator serves as a pony brake, the stator has bearings and is allowed to rotate, has an arm attached with a spring scale for taking torque readings.  From there the output is calculated.   The unit stands 2ft tall and 2ft in diameter.  I would say it would come close to competing with the Horizontals.  It will start turning in a 3mph wind although the alternator doesn't start charging until about 5-6 mph.   The turbine ran 240 rpm while driving the 17 watt load which comes out to a TSR of about 1.3.   Static testing with my wind meter and unit not turning, 12.5 mph in front of the machine about 3mph 1 ft behind the machine but 17 mph going through the wing.   I think there is still a considerable amount of work in improvements to be done and testing will continue.  I'm calling it the "Lenz Turbine" and giving credit to all those before me for their unique and innovative work in this field.  Also, to Hugh Piggott for helping me with the formula's for working out the wing angles based on the Darrieus type.

Below is a diagram representing the dimensions for the machine above based on percentages of the overall size for those who would like to build one for their own personal use and/or for testing purposes.

Lenz v2 ... update 8/28/05



Another update to the fascinating worl

Below shows the beginning of the second version.  Using parts from the first one and some quickie fabrication for the wings I began testing the unit.  The alternator is a 12 pole 3phase machine I made up just for this project.

It took some tinkering to get it where I thought it should be with good and not so good results.

Since the unit was slightly different than the original my wing angles didn't work out real well.  I played with one wing on the machine to find out where the torque was as it progressed around the 360 measuring every 10 degrees.  I realized at that point the torque wasn't where I had thought and started playing with wing angles again.  Finally it was dialed in at 9 degrees and worked like a dream!

It was time to take it outside for some real world testing.  I mounted it on the front loader of my tractor and out in the wind it went.

The wind was dying down by the time I got it in position so I really didn't get a chance to give it a work out.  Below are some output readings...

5.5 mph starts charging

7.1 mph 3.32 watts

8.5 mph 5.12 watts

9 mph 5.63 watts

9.5 mph 6.78 watts

Not to bad for a small 2ft by 2ft machine.

It was time to build a larger one to see if it could be scaled up and still maintain its efficient run.

I built up a larger one 3ft dia x 4 ft tall unit shown below..

I'm not going to get into a lot of details but it does 52 watts in a 12.5 mph wind.  I'm not one to be impressed easily, this machine has definitely impressed me.  Now,  Its time to take it to another level....

Page on building the wings can be found here... Lenz2 wings

www.WindGenKits.com is making a very nice Lenz2 Kit available with all the goodies available for building it from start to finish.  They have also produced some very nice videos for building the stator and finishing it up.  Everything you need for getting it up and running in short order... check them out !


REFERENCE : http://windstuffnow.com/main/vawt.htm