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BUILD YOURSELF A WINDMILL GENERATOR Part 2 - the alternator by Glenn Littleford* Have you ever wanted to build a decent-sized wind turbine to help charge those batteries? Are you handy with basic hand tools and a welder? Well, here’s Part 2 of our Windmill project, based on a motor from a washing machine, a few odd car parts, some timber for the blades and a kit “platform” to hold it all together. 12  Silicon Chip siliconchip.com.au Warning: please note the following! Inside the Fisher & Paykel Smartdrive washing machine motor – top left is the magnet hub, top right the stator, centre is the drive shaft, while at the bottom are the retaining plates and nut. We need all these parts for our windmill. I started this windmill project a couple of years ago as an experiment and it has since developed into not only a reliable wind generator but a rewarding hobby. Please note that what is described here is not a complete system but an ideas platform, to allow you to develop your own windmill. The results depend on your own abilities and the final location of the windmill. But with care in construction, especially the propeller blades and a position with 20km/h or higher wind speeds, you can expect to achieve output powers of 300W or better. Construction will be divided into three sections: alternator, platform, and blades. This month we will concentrate on the alternator. Next month will be for the platform to support the alternator, propeller and tail assembly and after that we will show you how to make a set of high-performance timber blades. But first up a reality check: are you sure you want to build a windmill of this scale? You’re going to need at leasT an acre of land – it’s not a good idea erecting a two-metre diameter windmill on *www.thebackshed.com siliconchip.com.au a six-metre mast in your suburban back yard, unless you get along VERY well with your neighbors! Some people consider windmills visual pollution and will complain. And you should get approval from the local authorities before putting up the mast. In addition, you will need good average winds and a location with a clear view (from the windmill’s perspective). This windmill won’t generate any useful power unless the wind speed is over 20km/h. Noise Despite what many think, windmills are not noisy. You will not normally hear any noise from a windmill unless you are almost standing next to it (or Windmills can be dangerous if not constructed carefully. While the windmill described here was designed to be strong, we have no control over the handyman capabilities of the builder or the effects of mother nature and therefore offer no guarantee of safely or durability. Also note that the alternator described here can produce dangerous voltages, even when spun at low speed. Treat all electrical terminals as dangerous at any time the alternator is rotating. We recommend the following: Obtain local government approval before erecting your windmill. Obtain an engineer’s approval for any windmill you build, especially the tower and footings. (Local government approval will probably require it anyway). Don’t scrimp on safety equipment (eg, guy wires) or on protection from the elements (especially rust and corrosion protection). Don’t place your windmill where a failure could cause injury, as towers can fall over and blades can break free. It is recommended that the ground around the windmill be clear of buildings, kid’s play areas, etc, to at least the height of the windmill (including the blades) and that it be placed at least that distance from your property boundary. A badly corroded drive shaft. This might be OK for bench testing but I wouldn’t stick a big propeller on it! January 2005  13 Exploded view of the motor from a F&P service manual. We need everything with the exception of item 2, a hall effect sensor used to detect the hub (item 5) position. unless the bearings are shot!). In high winds there is a distinctive “whooshing” noise but it’s not any louder than the wind blowing through the trees. There is, however, always some vibration produced by the alternator and this can travel down the mast. For this reason I recommend you don’t mount your windmill on the roof of your house – the drone could be unbearable. Sourcing the motor The heart of the windmill is the Fisher & Paykel Smartdrive motor, as used in Fisher & Paykel washing machines manufactured since the late The F&P Smartdrive stator before modification. 1990s. The Smartdrive is basically a huge stepper motor, wired in a 3-phase star configuration and consists of a fixed stator and a hub containing magnets that rotates around the stator. The stator consists of 42 poles constructed of steel laminations embedded in plastic. Stator diameter is 250mm. The hub has 36 magnets embedded in plastic, with hidden steel laminations to complete the magnet circuit. For our windmill we use the stator, hub, and also the stainless steel drive shaft, bearings and stator retainer plates from the washing machine. In this article the Fisher & Paykel motor will be referred to as the “Alternator” Use a screwdriver to lift up the interconnecting leads to make cutting easier. 14  Silicon Chip As the Smartdrive has been around for several years now, they are starting to show up in recycling yards and dumps and can often be picked up for a few dollars. If you can get hold of a complete washing machine, all the better, as there is a collection of springs and bits that could come in handy for future projects. Removing the motor is a relatively simple task, requiring no special tools. And the motor controller has some fancy electronics, including a pressure sensor and power mosfets which could come in handy. Electrical repair shops are another source for Fisher & Paykel parts: find your local repair agent Lay down the first bus lead and solder the first coil lead from each group. siliconchip.com.au First cut and strip 6 lengths of 20A insulated wire as shown. These will form our new bus bars. The original stator had 3 sections, each with 14 poles. The modified stator will be divided into 7 sections, each with 6 poles. The windings are cut as shown above and reconnected to the six bus bars as shown below. Use different colour wires for the buses to make life easier! and offer them universal currency (a carton of beer) in exchange for a couple of used Smartdrive motors from their scrap bin. You might get lucky! Or you can buy the motor parts new from Fisher & Paykel agents at a reasonable cost. What to avoid There are a couple of things to look out for when sourcing your motor parts. Shorted Windings: Water ingress into the windings causes copper corrosion and shorting between the coils, or to the steel laminations, making the stator worthless. Corroded Shaft: The shaft needs to support the weight and thrust of the propeller, so make sure there is no serious corrosion or pitting. Another concern is cracking in the plastic hub or stator. If not too severe, a few small cracks can be fixed with epoxy adhesive. Once all bus wires are connected, you can use cable ties to secure it all together. siliconchip.com.au Fit a terminal strip to the finished stator. This makes it easier to change from star to delta configuration. January 2005  15 01-A DELTA CONFIGURATION 02-A 03-A 01-B 02-B 03-B 01-A STAR CONFIGURATION 02-A 03-A 01-B 02-B 03-B The difference between delta and star configurations. How you connect them is up to you – basically, you get more current but lower voltage with a delta configuration and more voltage but less current with a star configuration. Some windmills are arranged to switch from one to the other on demand. Warning: do not place the stator in the hub! The hub has a plastic spline and retaining nut designed to slowly feed the hub over the stator while it is still attached to the washing machine (or windmill!). There is a strong magnetic attraction between the two and its easy to get your fingers jammed. And if you do end up with a stator and hub stuck together, it’s quite difficult to separate them. Rewiring the stator In factory form, the stator is wound as a 3-phase star winding, each leg consisting of 14 poles wired in series to give 42 poles total. There are currently three basic types of Fisher & Paykel stators available. The early models were wound with 1mm wire and are not recommended 16  Silicon Chip for this project. Next, Fisher & Paykel released a 0.8mm wire version and the latest model is wound with 0.6mm wire. These are the most common and both versions are ideal for our wind generator. When spun by hand the alternator can produce over 100VAC. Even at this low speed the voltage is too high for charging a battery bank, not to mention dangerous. We need to make a few changes to get this voltage down to a useful level and, at the same time, increase output current. This is done by cutting the interconnecting wires between the stator poles and reconnecting them into a new configuration. By doing this the alternator can be wired for charging 12V, 24V or 48V battery banks. We will look at a configuration for charging 12V batteries, this being the most common. Once again, remember this series of articles is designed to let you experiment with windmill generators, so the following is a suggestion only. For our 12V setup we need to rewire the stator into seven pole groups, each with six poles. Each group generates 3-phase power and by connecting the groups in parallel, we can increase the output current seven times. We also have the option of connecting the 3-phase groups as either a star or delta configuration. Put simply, star produces more voltage, less current and delta produces less voltage and more current. It is possible to automatically switch from star to delta as the windmill speeds up but we will leave this for another day. Starting from the factory-fitted spade connectors, cut the stator windings as shown. You might find it helpful to use a small screwdriver to lift the interconnecting wires for easier access. You should end up with 42 wire ends, each about 20mm long. Strip 5mm of the enamel coating from each wire with a sharp knife, sandpaper, or you can do what I do and use a small blow torch to carefully burn off the enamel and then sandpaper to finish. Next you need six lengths of wire, about 700mm long. Use wire capable of 20A (a length of 7-core trailer wire is perfect). Use different coloured wires if possible as it will make identification of the phases a lot easier. Each wire needs to be stripped in seven places at 70mm intervals – these will be our bus wires. Now lay down the first bus wire and solder the first lead of each pole group. Repeat the process for the remaining 5 wires. After you have soldered all the groups to the bus wires, use some cable ties to secure the bus wires together. Finally, add a terminal block to the end of the bus wires. Once the stator has been re-configured, you need to protect it from the weather with a couple of coats of paint. The plastic used in the F&P motors is subject to UV damage. That’s not much of a problem when hidden under a washing machine but it’s a real concern on a windmill. So paint the stator and hub with a UV resistant exterior paint. Make sure the siliconchip.com.au + “DC” OUTPUT 3-PHASE AC INPUT – 6 AUTO K DIODES (EG FROM CAR ALTERNATOR) A Above: two 35A bridge rectifiers, mounted on suitable heatsinks, can be connected to rectify the 3-phase output of the alternator. Note that two of the diodes in the second bridge are unused but this is a cheap way to go! Delta vs Star configurations There are two possible ways to connect the six output leads. From the factory, the F&P motor is configured as a star winding, so I would leave it in this configuration and use it as a starting point. Once you have completed and tested your windmill, you can try changing the connection to a delta to see how it affects performance. Rectifying the output Now that we have our 3-phase AC alternator, we need to convert this to DC for charging batteries. If you have a old car alternator sitting in the junk pile, then pull it K A A 3-PHASE AC INPUT 2 BRIDGE RECTIFIERS poles ends are properly sealed against water ingress, as the laminations can easily rust. K + “DC” OUTPUT K K K A A A apart and use the diode pack as your rectifier. These diode packs are built very tough (they need to be to survive in an engine bay) and can handle 50A or more. Another option is to use two heavy duty bridge rectifiers (such as a 3504), or you could just buy six single automotive diodes and wire them together. Either way, the rectifier needs to be able to handle 30A or more. And remember, all diodes will need a heatsink. Next month we will look at the construction of the windmill platform and tail. The platform is supplied as laser cut steel components and requires some welding. Once assembled, it provides a strong mounting frame between the alternator, propeller and mast and includes – Left: use this configuration if you have a rectifier assembly from an old car alternator or wish to use individual highpower rectifier diodes. The diodes need a rating of at least 35-40A or more. a self-furling tail to safely turn the windmill out of the wind during strong gusts or storms. SC NEXT MONTH: The windmill platform Another commercial wind turbine alternative: Airmarine Australia In amongst scads of really neat alternative energy gear on their website (www.airaus.com) Aimarine Australia have a number of wind turbine alternators ranging from the 300W Ampair Pacific, through the 1.6kW Bergey XL.1 (pictured right) and right up to 3, 5, 10 and 20kW Westwind Wind Turbines. The Bergey model shown has a rotor diameter of 2.5m and is intended for the off-grid home market. Rated power is 1kW, or 1.6kW peak, with an output of 24V DC. The XL.1 combines a number of advanced technical features, including a completely new airfoil, to provide the highest efficiency yet achieved in a small wind turbine. The XL.1 is an up-wind, horizontal-axis, three-bladed turbine. The blades are pultruded fibreglass, a material that is over ten times stronger than the injection-molded plastic used on most small wind turbines. In fact, pultrusions have a breaking strength exceeding 100,000 psi, which is twice as strong as normal steel. The blades attach directly to a specially-designed verylow-speed permanent magnet alternator which uses stateof-the-art neodymium super-magnets. Low wind speed per-formance is greatly enhanced by a low-end-boost circuit that optimally loads the wind tursiliconchip.com.au bine down to wind speeds as low as 2.5m/s. Combined with the new blade system, this circuitry allows the XL.1 to produce useful power more than 6000 hours a year at a typical site. For reference, a typical solar system produces power 3500 hours a year at a typical site. The XL.1 is priced at around $3500 (various options are available) and is offered with an easy-toinstall tubular tilt-up tower kit in heights from 9m to 32m, offering a complete “ready to install” kit. Price of a 10m tower, engineer-certified to withstand howling gales, is about $1800 Contact Airmarine Australia on (03) 9459 2888, website www.airaus.com, or email grd<at>hotkey.net.au January 2005  17