Wind Turbine

This blog has been put together to cover the trials and tribulations of building your own "home" wind turbine.
In fact it is more an exercise in demonstrating what not to do and then learning from those experiences.
I am reminded of Thomas Edison and his inventing the light bulb. He failed hundreds of times trying different techniques until finally hitting on the right one.

Picture: Wind Turbine MK1

on my garage roof

Hopefully you will read this blog and learn from my (many) mistakes.

The Project

My initial intention was to build a small, quiet, low cost wind turbine that would generate about 500W and simply drive my refrigerator via some old batteries and an inverter. I did not expect it to drive the fridge all of the time so when the batteries were low it would simply revert to normal AC grid power via a simple relay circuit.

So basically a project that was not too ambitious. How wrong I was.

I didn't want to go to the hassle of building my own blades to I found some suitable ones on the web http://www.survivalunlimited.com/windpower/turbineblades.htm

I then found on ebay some 25mm x 5mm Neodymium magnets, and as metal rotors decided on circular saw blades as they were cheap and balanced. I got the steel for the support frame from a machine shop cut to size, drilled the holes and had it welded together. Then some bearings and a shaft were added and it was set to go.

The coil assembly was put together (see seperate post on how this is done) and then it was put up on the garage roof (see photo above) and then waited for some wind. 4 x 50watt 12V downlights in a series parallel configeration were attached to the rectifier as a load.

The unit. 16 25mm x 5mm Neo magnets 8 on each side. 10 coils in 5 phase config with two coils per phase.

RESULTS Mk1: The unit did make the 4 x 50w globes glow very brightly but only at VERY high rotational speed ie 20 + KPH wind. This was probably the max output this unit could produce and at the wind speed required was totally unsuitable.

Back to the drawing board.

To make a long story short, there was a MK2 version that was also a dud. With MK2 I went totally overboard. Much bigger magnets, more coils in fact more everything.

DESIGN TIP: The blades can only deliver so much torque. Design your turbine with this in mind as the blades will not even rotate if you over engineer the turbine.

The main problem with MK2 was that with the bigger magnets and the same diameter coils it contravened Flemings Left Hand rule. Yes, we all did it at school, trying to contort our fingers to understand current (electric) direction in a coil when exposed to a magnetic field. Suffice it to say that if the magnets diameter is larger than the hole in the coil, the the currents oppose each other and your turbine will not rotate.

DESIGN TIP: Always make the hole in the centre of the coils the same size or slightly larger then the diameter of the magnet. This applies to square/rectangle magnets also.

MK3

It was put together using the magnetic assemblies of MK2 and a new stator design that obeyed Flemings left hand rule.

Overview.

Parts used:

Hub from the rear of a Toyota Corolla $10.00

Two laser cut circular discs to carry the magnets. 242mm x 5mm $95.00

DESIGN TIP: Don't skimp on the thickness of the rotors. The magnets use this thickness in a feedback loop increasing the effective magnetic strength.

16 Neodymium magnets on each disk. 30mm x 10mm. Total 32 magnets $150.00

8 Plastic Composite blades $200.00 from:

http://www.survivalunlimited.com/windpower/turbineblades.htm

Mounting bracket custom designed from a local machine shop. 1 slab (beer)

SOME PHOTO's

THE COILS. The coils on the left were those used in the final design. Five coils was not the ideal number (more would be better) but as I had put together the magnet assembly for MK2 and it was too hard to remove the magnets without damaging them a compromise of less coils was used. This compromise was reached after extensive testing on a bench jig driven by an electric drill. A better design would be less magnets and more coils.

MK2 COIL ASSEMBLY. This was the failed MK2 design. You can see it has 12 coils. Unfortunately the internal diameter of the coils was 25mm and the magnets had a 30mm diameter causing problems with Flemings left hand rule.

Even if the coils had had the correct (wider) inside diameter it would have required much larger blades to provide the torque that this deisign would need to obtain the optimum power output. Note the wiring. Three phase with 3 coils per phase.

OUTER ROTOR WITH MAGNETS. The outer rotor was designed to support the magnets AND the blades. The tabs protruding are there for the blades to attach to. The inner rotor is identical but without the tabs. The large centre hole is there to fit onto the Toyota Corolla hub. The magnets were were initailly attached with super glue to give a quick bond and then Araldite was used to lock them in. Note: A later change made it clear that Arildite alone will do the job. The attraction of the magnets to the metal rotor will keep them in place ie they will not be sucked off when placed close to the other rotor. The Arildite simply holds them in place.

The magnet spacing is crucial here. In this constuction each coil is 50mm outside diameter, 30mm centre with 10mm for each coil half. The gap between the magnets MUST be 10mm. Any less (or more) and you will have one magnet entering the coil before the other magnet has left. They would then fight each other. One pushing current clockwise while the other counterclockwise. See coil construction in next post.

THE TOYOTA COROLLA REAR HUB. This was used as it was found cheap at a wreckers. The bearings were removed using a press, the assembly cleaned and reassembled with low friction grease and not fully tightened to give it a freer rotation. Undercoat and powder blue paint finished it off.

This line added to sort photo spacing out.

And another.

SUPPORT ASSEMBLY. This was welded together by a machine shop for a slab (beer). It has a pipe that will slide onto the mast of the turbine, a stopper ring welded internally at the top, a plate at the front to support the turbine assembly and two small brackets at the rear to support the tail assembly.

Note the hole at the top. This is to allow the positive cable to go down the centre of the pole.

PARTIAL ASSEMBLY. A circular piece of marine ply (to keep the weight down) was bolted to the support assembly. The bolts basically wedged the ply in place as a sort of a spacer by bolting the plate on the support assembly to the Carrola hub. Hidden from view is the inner magnet rotor. On the outer edge, stainless steel (not normal steal as they would be magnetic) rods connect the coil assembly to the ply. In this way the the magnet rotors can rotate and the coils (now embedded in resin) remain stationary.

A BETTER PICTURE OF ASSEMBLY. Here you can clearly see the support assembly at the top, the marine ply, the Carolla hub and the inner rotor with magents. The coil assembly is also shown connected to the ply by 5 stainless steel rods. These rods need to be securely attached to the ply as they will have to provide the rotational resistance to the rotating magnets. Note also at the top, attached to the support assembly, the bridge rectifiers. The blue coil wires will connect to these to convert AC to DC current. A star wiring of the coils was used. This means all the centres of the coils are connected together (within the resin) and each outside connection of each coil goes to the bridge rectifiers. 3 rectifiers are required with one spare input.

OUTER ROTOR WITH BLADES. This is the outer rotor. Eight blades have been used. It could be excessive but will give it a try. This bolts onto the Corolla hub. The magnets are arranged so that a north polarty faces a south ie attracting. Times this by 16 and you have a very strong attraction. CAUTION 1. Be VERY careful when getting these magnets close together. It can cause serious injury. These Neodymium magnets are EXTREMELY powerful