• Free as the wind: homebuilt wind turbine

    • Becker made a number of templates to simplify the building process.
    • The turbine's four blades were made from 1 mm-thick balsa because of its impressive strength-to-weight ratio. The hub (connecting the blades to the turbine) comprises two discs of 5 mm marine ply (chosen for the same reason).
    • Four 12 mm stainless steel bolts connecting the rotors distribute the torque and take the pressure off the stationary central axle, while two sturdy automotive bearings keep everything running with minimal friction.
    • The completed coils are held securely in place before being encased in epoxy.
    • The completed stator
    • Large rubber mounts prevent any vibrations from finding their way down the pole to Becker's home.
    • The 6 m-long pole is relatively simple to lower, allowing him uncomplicated access to his turbine.
    • The turbine's hub is fixed to the turbine via the four bolts that connect the two rotors.
    • The free-swinging wind vane acts like a shock absorber, preventing the turbine from snapping around in strong gusts.
    • A lot of thought went into the mounting bracket and connection points because of the powerful forces that come into play when the turbine is spinning under load.
    • The secret to an efficient design is to get the magnets on both rotors as close to the coils as possible without touching the stator.
    Date:30 September 2007 Author: Sean Woods Tags:, , , , ,

    Back-to-basics householder solves his power-outage woes with a homebuilt wind turbine

    It’s become fashionable (and perfectly reasonable, in most cases) to castigate Eskom for the occasional failure of our creaky national grid. Buckling under the ever-increasing demand for electricity, it periodically catapults us into the “dark ages”, prompting pessimists to stock up on canned beans and doomsayers to dust off their worst-case scenarios (the breakdown of society and rampant cannibalism come readily to mind).

    But, as Capetonian Peter Becker can attest, there’s a more pro-active option available for those willing to spend some time at their workbenches. It’s called DIY wind power, and although it’s unlikely to send shockwaves through the power-generating establishment, it could be one of the most satisfying projects you’ll ever tackle.

    Fed up with playing victim to the vagaries of grid power, Becker decided to build a modest wind turbine from scratch – and generate his own. His quest for DIY power began last year when a wayward bolt in the Koeberg nuclear powerplant prompted an emergency shutdown of the facility. The consequences were dramatic, to say the least, causing rolling blackouts throughout the Western Cape.

    A ‘light bulb’ moment
    It was also one of those “light bulb moments” for everyone concerned, showing how easily their lives could be upset – and in some cases, turned upside down – by the simple flick of a switch. While business leaders cried foul, commuters saw red and householders did their best to save frozen food from spoiling, Becker – along with friend Barry Stott – began searching for solutions to keep Stott’s business afloat (he manufactures customised flight cases for valuable items).

    Their first move was to couple an inverter to a car battery. As far as standby power went, it was adequate for Stott’s immediate needs, powering a band saw or drill for a short period – but it was far from perfect. For starters, the battery still required charging from the mains, and that seemed contrary to everything the two friends were trying to achieve.

    Says Becker: “We thought it would great to be completely independent of Eskom. This was an especially important goal because its power, derived mostly from coal, is extremely dirty and contributes significantly towards global warming.”

    As both live in Cape Town, one of the windiest regions of the country, locating a natural resource to charge Stott’s battery was a no-brainer. Solar power wasn’t even considered because of the prohibitive costs involved. Becker elaborates: “Solar panels are high-tech items priced for first world buyers, and the average guy like us cannot make or fix one. But wind turbines are easy to make from readily available components, and the best thing is, you can teach your buddy how to build one.”

    Becker went online in search of answers and was amazed by the size and co-operative nature of the virtual DIY wind turbine community. He also discovered that the science behind magnetism and the properties of electrons was intimidatingly complex, as were the principles determining the relationship between wind speed, turbine height, generator size and blade diameter (to mention but a few of the relevant issues). Fortunately, as he says, one doesn’t need an in-depth understanding of the principles involved to construct a perfectly respectable wind turbine. In fact, the strategy adopted by most backyard turbine builders is to aim for a particular output (anything from 250 watts to 500 watts), then rely on old-fashioned trial and error to tweak their designs and improve efficiencies as they go along.

    Becker concedes this approach doesn’t guarantee an efficient design, but points out that we’re talking DIY home power generation here, and not commercial installations. His view: “You’re producing power for your own needs, so as long as you have enough, does it really matter how many inefficiencies are built into your system? Anyway, you can always improve efficiencies over time as you understand more about the mechanics involved.”

    Because of the inter-relatedness of all the components involved, Becker recommends would-be wind turbine builders first tackle a small version. It’s all about learning curves, he explains. For example, the rotors (housing the magnets) can be placed too close to the stator (housing the wire coils) and rub the insulation off the wiring, causing the generator to short out. And the wiring can only take a certain amount of bending before it breaks, so one must have a clear idea of where to place the connection points. “For any number of reasons, the odds of your first turbine working properly are almost nil.”

    In pursuit of real performance
    In its simplest form, a wind turbine’s blade requires only a five-degree pitch down its entire length to perform adequately. But as soon as you give the blade some taper, and make its pitch greater at the root than at the tip, you start getting real performance. The length of the blades also determines performance levels: for example, if they are too short, they will be unable to turn the generator fast enough to produce efficient power. Conversely, if they are too long, they can overpower the generator, causing it to burn out.

    Blades are mostly carved out of wood, but some enterprising individuals have fashioned simple but effective blades from PVC piping. Becker chose balsa for his because he lives in suburbia and likes being polite. “Balsa is light and strong, and if a blade is going to fly off in high winds, I didn’t want it to break any windows or cause injury,” he explains.

    He began by carving the required profiles out of solid balsa, but once he started work on his present turbine, his curiosity got better of him. “When making these blades, I used 1 mm balsa sheets because I wanted to see how long they’d take to break… and they haven’t.”

    He uses wedges to set the blade’s pitch at an angle of about 30 degrees at the root and about 6 degrees at the tip. This gives the turbine an added boost during start-up as well as enhancing high-speed performance. The root area, where it’s fixed to the turbine’s hub, is reinforced with extra balsa and glass fibre, and a strip of pine adds rigidity to the leading edge.

    Finally, the entire blade gets a liberal coating of epoxy inside and out. They taper from 100 mm at the root down to 50 mm at the tip, and are 1 m in length (there is no arcane reason for this measurement; the length is limited solely by the availability of suitable balsa from Becker’s local hobby shop).

    He used 5 mm-thick mild steel for the two 250 mm-diameter rotor discs, explaining that these helped contain and intensify the magnetic field in the air gap between them. To ensure they mirrored each other perfectly, Becker had them precision-cut by experts. He also had a template made so that the rotors could be accurately drilled and aligned. Another template ensured the accurate positioning of the 16 magnets on each rotor.

    Since the strength of the magnets determines how much power your turbine can produce, Becker opted for the best – namely, rare earth (or Neodymium-Iron- Boron) magnets. Measuring just 20 mm x 50 mm x 8 mm, they seem rather benign when examined individually – but they can drive you crazy when assembled in a small space.

    Becker explains “When you put them down, they have to be at least 15 cm apart or they are forcefully attracted to each other, causing them to chip. By the time you’ve found a place for all 32, you have no space left in your workshop – and you’ve still got to find a safe place to put your screwdriver!”

    Becker coaxes the magnets into position by first attaching his template to the steel base and then gently sliding them into position from the open end. The magnets are placed with their poles alternating north and south to shunt the electrons in a steady stream along the coils on the stator. The faster the alternating north and south poles pass the coils, the more p
    ower is produced.

    Once the magnets are in position, the template can be safely removed. Epoxy is then poured between them to hold everything in place.

    According to Becker, making the stator is by far the most complicated part of the construction process. Fixed in position between the two rotors, it encapsulates nine coils (three coils per phase) to produce three-phase power. Says Becker: “I wanted three-phase power because it allows me to squeeze more power from the generator, and the current is more stable. In a single-phase design there are always periods were no power is produced.”

    If all else fails, try meditation
    Enamelled copper winding wire was used for the coils because of its thin insulation and superior heat resistance. There are a number of factors to consider before winding the coils. For example, thinner wire allows for more windings per coil and delivers better performance at low speeds than a coil comprising fewer windings of thicker wire. But as soon as the wind speed increases, the thinner wire becomes less efficient.

    After much experimenting, Becker settled on wire with a diameter of 0,8 mm and 80 turns per coil for his latest design. Even with his specially devised coil winding jig, getting it right was an excruciating task. “You almost have to sit in a meditative state while counting out the turns, because it’s critical that you make them exactly the same length.” They also have to be wound tightly, and as flat as possible, to keep the air gap between the rotors as narrow as possible, and they must be exactly the same shape and size to ensure they are correctly aligned with the magnets.

    The completed coils are then placed in a mould and connected in threes to produce three-phase power. Finally, the coils are encapsulated in epoxy and the stator’s square corners are reinforced with glass fibre, giving it the strength to be securely attached to its mounting bracket by four long bolts.

    Connecting the components isn’t complicated, says Becker, but it does require a degree of finesse. When assembling the turbine, he treats the two rotors with great respect, and with good reason – their combined magnetism is sufficiently powerful to crush fingers if they snap together. Using wooden levers and spacers to keep them apart, he carefully tightens the four bolts until the two rotors are parallel.

    The secret lies in getting the magnets as close to the coils as possible without touching the stator. Once it’s fully assembled, the wires from the stator are fed into four diodes (each rated at 35 amps) to turn the three-phase power into direct current and feed the batteries. The diodes, in turn, are mounted directly on to the mounting bracket to dissipate heat.

    Becker put a lot of thought into the turbine’s mounting bracket and connection points, being aware that powerful forces come into play when the turbine is spinning under load. The four 12 mm stainless steel bolts connecting the rotors distribute the torque and take the pressure off the stationary and decidedly weaker central axle, while two sturdy automotive bearings keep everything running with minimal friction. The free-swinging windvane acts like a shock absorber, preventing the turbine from snapping around in strong gusts of wind and causing the blades to flex.

    ‘Hey, it works’
    Becker’s turbine is mounted on top of a 6 m-tall galvanised steel pole fixed to a one wall of his house, protruding just above the roof, and stabilised with stays similar to those found on yachts. Says Becker: “Granted, it falls short of the recommended minimum height of 10 m, and it definitely doesn’t clear many of the neighbourhood’s obstructions that influence air flow, but hey, it works.”

    Practical tweaks abound. Large rubber mounts prevent any vibrations from finding their way down the pole to his home. The electric cable connecting the turbine to the batteries runs through the centre of the pole, and is long enough to cope as the turbine swings on its horizontal axis. The turbine is blissfully quiet, the only evidence of its operation being a flickering shadow in the garden.

    Becker is still experimenting, conceding that his setup is basic and his battery bank still rather small. However, it works, and produces enough electricity to power the compact fluorescent bulbs in his home and workshop.

    As he tells it: “I get a huge kick out of using the light generated by wind power to build other wind turbines.”

    Becker’s battery bank comprises two 12-volt 7, 2 amp batteries connected in series to give him 24 volts. But he’d much rather have two 100-amp batteries to increase his storage capacity so that he can run his computers.

    He’s also heard of a 12-volt camping kettle that’s piqued his curiosity. Because he has not yet built a circuit to protect the batteries from overcharging, he can leave them unsupervised only when they’re very flat. In the interim, he has devised an alarm that screams a warning when the batteries reach their maximum capacity.

    He became aware of just how much power was consumed in an ordinary home only after building his wind turbine, Becker says. “When you can see your batteries being depleted, it makes you a lot more aware of your power usage – and that automatically makes you use less.”

    Becker believes if everyone with a modicum of DIY skills took the trouble to build and install wind turbines at their homes, the cumulative power savings would be astronomical. In the meantime, he’s actually looking forward to the next opportunity to switch on all his lights while the rest of his suburb is swathed in darkness.

    * Peter Becker’s turbine cost about R3 500 to build. For more information, visit his Web site at www.windpower.org.za

     

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