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Live off the grid and need to generate your own power? Or maybe you have lots of space and you’d just like to take advantage of that old adage, “the wind is free . . .” BUILD YOURSELF A WINDMILL GENERATOR Part 1 - Looking at Options by Glenn Littleford 10  Silicon Chip siliconchip.com.au This windmill uses a small stepper motor from a computer floppy drive to charge nicad batteries. A lternative energy generation for the home is on the increase, with many domestic installation options on the market, including solar, water and wind generators. But the initial cost of a “free” power supply is considerable and it can take many years, if ever, to pay for such an installation. In this article. we look at a new trend in home-made windmills – and next month show you how you can build your own 300W windmill. Home-made wind generators have been around for decades, with designs as varied as the people who build them. But why would you build your own windmill? Why not buy a ready-made one, or use solar cells. After all, solar cells are reliable and virtually maintenance free. The answer is simple: cost! You can’t make your own solar cells at home; they need specialised equipment and clean rooms. But you can build your own wind generator for a fraction of the cost of a similar power sized solar array or commercial wind generator. Opposite: a motor from a Fisher & Paykel washing machine provides up to 300W in this 2-metre diameter windmill. siliconchip.com.au Another advantage of a wind generator is it will generate power whenever there is a breeze, night or day! There are downfalls to wind generation. The wind is not as reliable as solar energy; windmills need occasional maintenance; and location can be a problem. (A 10m high tower with a 2m diameter windmill in your typical suburban backyard might be frowned on by your neighbors and local authorities). The best option for the serious home power generation installation is a combination of solar and wind. There will be days of full sunshine and not the slightest hint of a breeze, or days with heavy rain clouds and strong winds. If you have the space and a location with good year-round winds, then a home-made windmill could be a viable alternative to solar cells. Building your own windmill requires no special abilities or equipment. All you need are some basic handyman skills, a few tools and the time to assemble and experiment. Using the wind There is a lot of energy in the wind. Power is proportional to the square of speed, so a 40km/h wind has four times the power of a 20km/h breeze. As an example, a theoretical perfect- ly efficient windmill which produces 200W in a 20km/h breeze would rise to 800W in a 40km/h wind and a massive 6400W in a 80km/h storm gust (if it survives!). But what sort of windmills are we talking about? First up, a few simple rules about windmills: they behave in a very similar way to your typical car engine with a power and torque curve and different speeds for maximum power or torque. Ideally, you need to operate your windmill at its peak power output. The number of blades and their size also affects the speed, torque and power for a given wind velocity: MORE BLADES = less speed, less power but more torque, perfect for pumping water. LESS BLADES = more speed. LARGER PROPELLOR DIAMETER = less speed but more power. Two other factors to consider are turbulence and wind-shadow. Turbulence can be caused by the disrupted wind from one blade to the next, or anything up-wind of the windmill – and will have a big effect on efficiency. Wind shadow is the effect the windmill mast has on the propeller as each blade passes the mast. This shadow causes a sudden pressure change beDecember 2004  11 Windmills need to be clear of any turbulence to run effectively. hind the propeller blade and results in vibration. As a rule, a 3-bladed propeller is the best compromise between power, torque and speed. A 2-blade propeller will run faster but there are dramatic vibration problems with 2-blade windmills during wind direction changes and they are therefore not recommended. A typical home-made wind generator with a 3-blade propeller diameter of 2m will spin from 100 to 600rpm and is capable of generating over 500W. Windmill blades can be made from just about anything – wood, steel, fiberglass, carbon fibre, etc . . . I’ve even seen a windmill using eight wheelbarrows! Wood is the most common material for the DIY handyman, its cheap, easily formed, strong and flexible (remember, trees are very good at bending in the wind without breaking). The profile of a well-designed windmill blade resembles an aircraft wing, giving lift on the trailing edge. There also needs to be a slight twist along the length of the blade. The blade tip is traveling much faster than the part of the blade closest to the centre of the propeller, so needs to have less angle of attack. You also need to consider tip speed. A 2-meter diameter propeller spinning at 500rpm has a tip speed of 188kmh. Any airborne dust or unfortunate insects will be very abrasive at this speed. For windmill blades made from a soft material, such as timber, a layer of wear-resistant material – eg, aluminum tape or fibreglass – should be applied to the leading edge. There are several options but a common car alternator is not one of them, at least not without modificiation (most beginners to home-made wind generation try to use a surplus car alternator, without much success). While cheap, readily available and capable of producing over 600W, a car alternator needs to be spun at over 2000rpm before it will generate any useful power. A windmill large enough to drive an alternator to its full power capacity would not spin fast enough (the larger and more powerful the windmill, the slower it will spin), so you would need a mechanism to step up the windmill speed to over 2000rpm. You could use a gear set, chain or belt drive but these have disadvantages, including noise, unreliability, poor starting and reduced efficiency. You need a generator that will produce power at low speed, which is why most successful home-made windmills use permanent magnet alternators. Large Permanent Magnet DC Motors, like those used in electric wheel chairs and golf buggies are one option. Unfortunately, these are expensive, have relatively low output when used as a generator and need to have the brushes replaced from time to time. Modified Car Alternators: some success can be achieved by replacing the standard armature with a new machined armature containing perma- Generator So much for the propeller. What can we use for a generator on a windmill? 12  Silicon Chip The iconic Aussie outback windmill: big and lots of blades for lots of torque. It’s great for pumping water but not much use when it comes to generating power! siliconchip.com.au nent magnets. While results are better at low speed than a standard alternator, output is still not good. Modified Induction Motors: single or 3-phase induction motors can be modified by fitting permanent magnets to the armature. This is done by machining the armature (in a lathe), down to a size that will allow you to glue magnets to the armature. By using strong Neodymium magnets, a typical 1HP induction motor can supply over 10A. The available current is limited by the gauge of the copper wire in the windings, so some hobbyists rewind the motor with heavier wire with good results – in excess of 30A. A disadvantage of modified induction motors is the power curve. Peak power will be reached at a low RPM, any faster and the power drops off dramatically. This is due to the high number of laminations in the stator, giving a poor high-frequency response. Switched DC motors: ie Stepper Motors, such as used in most computer equipment, can make fantastic generators! They have good frequency response over a wide operating speed, are readily available and cheap. Larger motors can be sourced from industrial equipment, motion systems and some domestic appliances, including washing machines (more on this later). One disadvantage of these motors is the cogging effect. Cogging is the vibration you can feel when you try to rotate a stepper motor and is caused by the interaction of the magnets and laminations/poles. In a windmill applications this can make the windmill hard to start in light winds, as it needs to overcome the first “cog” to get going. Once motion has started, the cogging effect has little impact on performance, other than a slight vibration and whirring noise. While most motors can be modified to reduce cogging, it’s reasonable to suggest that if the wind isn’t strong enough to start the windmill, then it’s not really windy enough to generate any useful power anyway. Air Core Generators: one way to reduce the cogging effect is to remove any magnetic material – ie, laminations – from within the coils of your generator. Of course this will reduce the overall efficiency of the generator as the magnetic path isn’t concentrated around the coils. siliconchip.com.au Don’t want to do it yourself? Oatley’s “off-the-shelf” alternative As this article was being prepared for publication, we became aware of this alternative wind generator kit from Oatley Electronics in Sydney. If you’re not into rewinding or otherwise modifying motors – or want it NOW! – this “ready to rock and roll” kit could be just what you are looking for – especially as everything you need comes in the kit! The completed generator, mounted on its mast, is shown above. What you see (in pic below) is what you get – three-phase alternator, mount- ing plate, three blades, tailfin, nosecone, three-section mast, heavy duty cable, even the stainless steel guy wires, turnbuckles, ground anchors, nuts and bolts . . . in fact, all the hardware you’ll need. Also included is a rectifier with voltage and amperage metering. The generator is capable of 200W output at 12V (or 24V) and the kit sells for $699. Freight must be added and be warned: it’s pretty heavy! For more information, visit the Oatley website, www.oatleye.com. December 2004  13 in a violent storm . . . and nothing more rewarding than having it survive with no damage! Using the power Regulating windmill power is a little more tricky than for solar cells. Solar cells can be open circuited when the storage battery has reached full charge. This is not a good idea for windmills. Say your windmill is spinning at about 400 RPM in a strong wind, pumping out 20A into a 12V battery. If your regulator suddenly open-circuits the windmill, it has no load and will speed up to, say, 600 RPM. At this high speed the unloaded windmill output could reach over 50V. If your regulator suddenly reconnects the battery, the windmill output Yes, that’s a ceiling fan! Modified by rewinding and fitting permanent magnets, output is up to 3A at 12V. There have been some clever ways to overcome this problem. One common design is to embed the coils in an epoxy disc which is held stationary, with magnets rotating on each side of the disc. Good results have been achieved but there are disadvantages. Winding and gluing your own coils into a non-metallic core stator is very time consuming. And as the coils are embedded in epoxy, heat dissipation is poor, making it very easy to cook a set of coils. Location, location, location As they say in real estate, it’s all about location. An effective windmill needs clean air – that is, a breeze with no obstacles. Obstacles can include trees, buildings and even the contour of the land. As a rule, the higher the better – but be practical. While a 20m mast might be ideal, you need to get the windmill up there and may need to bring it down for maintenance. Five metres above the nearest obstacle is a good start. Do not mount the windmill on the roof of your house! All windmills produce some vibration and while this is almost inaudible on a mast, mounted on a roof the vibration could be VERY audible, especially if it finds some resonances. Also consider safety – things can go wrong. Blades can come off, towers can fall down. So please locate the windmill in a people-free area. My personal preference is a 7-metre tall folding tower made from 75mm OD, 6mm-wall galvanised pipe. The tower is supported by three 5mm stainless steel guy wires, each connected to a steel post embedded in a 700mm deep hole filled with concrete. You may need to talk to your local council before erecting a tower and they may require a structural engineer’s plan before giving approval. There is nothing more worrying than watching your windmill buck around Left: this strangelooking contraption is my first-ever VAWT (Vertical Axis Wind Turbine) windmill, with its offset bearing shown close-up at right. They have lots of torque and will start in a light breeze. Worth looking into further! 14  Silicon Chip About the author... Glenn Littleford started in electronics at age 10, as a teenager assembled many electronic kits, and was often called on to fix electronic gadgets for friends and family. The interest in computers started at school with a crash course in programming TRS80’s (remember them?) At 17, he started an apprenticeship with Telecom as a technician and bought his first computer, a Microbee. His Telecom training included radio transmission, power supply systems and computer programming. At age 25, Glenn was made redundant as part of the downsizing of Telstra. After trying his hand in a range or jobs, including a car mechanic and repairing video arcade machines, he started his own computer repair business. The introduction of the GST in 2000 convinced Glenn it was easier to be an employee and let someone else worry about tax forms, so he started working as a software developer for an e-commerce business. In 2002, a new career direction was offered as a laser operator. The use of an industrial laser cutter opened a whole new world to Glenn. Laser cutting gives you the ability to design a part on a computer and five minutes later hold the finished part in your hand. The laser was used to design and build the first of many windmills. A new job offer to manage a laser cutting department and IT department for a local engineering firm was too good to resist, so Glenn made the move and now works for Swift Engineering in Mackay, Queensland. siliconchip.com.au A 7-metre tall folding tower made from 75mm OD, 6mm-wall galvanized pipe. The tower is supported by three 5mm stainless steel guy wires, each connected to a steel post embedded in a 700mm deep hole filled with concrete. current will be excessive and can cause damage. Remember, the windmill is acting like a big flywheel and will take some time to slow down to a safe speed. Excessive speed can also increase the wear and tear on the windmill, especially bearings and blade tips. So a suitable regulator will need to switch the windmill output from the battery bank to a dummy load, therefore keeping the windmill RPM down to a reasonable speed. I use four 100W 12V spotlamps, wired in parallel – but you could also use several electric heater elements. I have heard of installations where heating elements are mounted into the hot water system, so once the batteries are charged the windmill is helping to provide hot water. Building your own windmill can be a very satisfying experience. I have built several over the last few years, learning from the failures and improving with each new design. Next month, we will describe how you can build your own 300W windmill using car and washing machine parts, based on an Australian-made short form windmill kit. SC Superbright Lumileds - Indoor & Outdoor LED light fitting range D HIGH BRIGHTNESS D LONG LIFE D FULLY DIMMABLE D ENERGY EFFICIENT The range of LUMILED downlight fittings shown here have been designed for domestic, display, marine, mobile home and caravan applications. 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The OPLLGG series Brushed Gold Finish This series is a ceiling type gimballed fitting and require a 57mm diameter cutout (MR11 size). Email us: sales<at>prime-electronics.com.au BRISBANE SHOWROOM 22 Campbell Street Bowen Hills QLD 4006 Telephone: (07) 3252 3762 Facsimile: (07) 3252 5778 SOUTHPORT SHOWROOM 11 Brickworks Cntr, Warehouse Rd Southport QLD 4215 Telephone: (07) 5531 2599 Facsimile: (07) 5571 0543 SYDNEY 185 Parramatta Road Homebush NSW 2140 Telephone: (02) 9704 9000 Facsimile: (02) 9746 1197 December 2004  15