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Wind turbine for your garden by Julian Edgar Relatively low in cost and well-made, this turbine is ideal for experimenting with wind power. W ind turbines now produce a major proportion of the world’s renewable energy. Great strides have been made in their design, especially in the sheer scale of the turbines now used. However, for people wanting a small wind turbine for home use, the story’s not been so good. Small scale wind turbines have remained expensive, typically costing around £300. However, things are changing – as this story shows. The wind turbine pictured here cost only a little over £100, including delivery. In addition to its low cost, it’s surprisingly well made and has a useful output. Will it work for you? Wind turbines are not for everyone, so it’s important before buying one to think carefully about your situation. First, you need a place that has lots of wind. And that means not only strong winds, but winds that blow hard all year around. It all sounds obvious but it’s easy to overlook these vital points. For example, the turbine shown here, as with many similar turbines, has a claimed ‘start-up’ wind speed of 2m/s (metres per second) – that’s just over 7km/h. However, I found that to get a useful output, the wind speed needs to be more like 20km/h. Depending on your location, 20km/h might be regarded as a windy day – or just a gentle breeze! Where I live, we tend to get afternoon and evening gully winds. That is, they blow quite strongly, but only for a few hours a day. (Some coastal areas have a similar wind pattern, with sea and land breezes.) So I am likely to get a useful output from the wind generator for less than one-tenth of the day. Without getting too far ahead of myself, that makes the turbine ideal for charging a battery that runs a low-current alarm, or lights 54 that can be manually operated – for example, in an outhouse or shed. But in my situation, there would not be enough harvested energy to run a powerful light that is switched on all night, for example. Second, wind speeds increase dramatically with height above the ground. The wind speed at the top of an 8m-high tower can be twice that measured at 1.5m elevation. So, for best results, you will need to mount the turbine on a tower or pole. Again, for some people that will be a minor issue, but for others it might be a deal-breaker. Finally, if you live in a sunny environment, it will likely be more cost-effective to use PV solar panels than a wind turbine. Even if you need a larger battery, so allowing for (say) a week without sunshine, you are still likely to be finically ahead of buying a wind turbine. So, all doom and gloom? Not at all. If you live in a windy location that doesn’t get a lot of sunshine, you have space to put up a tower and want to power something that has a low average current draw, this wind turbine will work well. So, let’s take a look at it. The wind turbine The turbines (plural – because I liked the product so much, I ended up buying three) were purchased from Banggood. There is a wide variety of wind turbines available, all with different descriptions and claiming different power outputs. However, the one I bought can be recognised by these characteristics:  Downturned tail with a distinctive patterned cut-out  Forward part of the housing has heatsink fins  Five blades with a 1200mm diameter  Cast flange to which the blades bolt  Cast alloy mast clamp  Electronic controller Practical Electronics | May | 2022 Fig.1. The disassembled wind turbine. The quality is very good, but the nylon blades and plated mild steel fasteners should be protected with a coat of paint. (Pic: Banggood) The design uses a three-phase AC alternator, and the body is cast alloy. Claimed output is 300W – but more on this in a moment. Two versions are available: 12V and 24V. I used the 12V unit. Just a note about pricing. I paid about £100 each, but at times the same turbine is listed at anywhere up to double that. The trick is to keep a good watch on prices, both on Banggood and eBay. Wind turbine prices seem to fluctuate a great deal. (Plus, new models are introduced, changed and updated at quite a rate. Don’t be put off if you can’t find exactly the same model shown here, or the most similar looking one is now rated, at say, ‘400W’.) As stated, the unit I bought is really well made. The alternator turns on a generous bearing that can be replaced after removing a circlip. To allow the turbine to face into the wind, the whole assembly rotates on another vertical bearing. Power output is via three slip rings that use large carbon brushes. Some assembly is required – the blades need to be bolted to the cast hub with the provided bolts and nyloc nuts. A small socket tool is provided to do this. Ensure you mount the blades in the correct orientation – recesses in the blades match the shape of the hub. The blade assembly is then attached to the alternator shaft with a large nut – again of nyloc design. The shaft nut fits within a shaped recess in the hub, so the nut is actually screwed onto the shaft by rotating the blades. To prevent the shaft from turning while doing this, the provided Allen key fits into a recess within the shaft. Note that this nut screws on a long way – ensure that Practical Electronics | May | 2022 Fig.2. The assembled wind turbine mounted on a mast. Note the well-designed mast clamp that requires a 54mm diameter pipe. it is fully home and that plenty of shaft thread is showing. The mast mount is a well-made cast alloy design that clamps around a mast that’s 54mm in diameter. This is an odd size, but if you are using 50mm pipe, some curved shims can be cut from an offcut of pipe. There are only two question marks about the wind turbine’s durability. First, the nylon blades may degrade when subjected to full sunlight, and second, while some of the fasteners are stainless steel, others are not – they’re just plated mild steel. To protect these non-stainless-steel fasteners and the nylon blades, I painted them with a good quality outdoor paint. The three-phase output needs rectification to allow battery charging. This rectification is one of the functions achieved by the electronic module that is provided with the turbine. Called the ‘wind turbine controller’, the module has five connections and three monitoring LEDs. The connections are the three phases from the turbine and the two to the 12V battery terminals: positive and negative. The LEDs show battery, charging and braking. Braking needs some explanation. When charge voltage exceeds a designated level, the controller slows the turbine, presumably by introducing a load across the windings. Fig.5. Inside the wind turbine – the alternator windings can be seen around the periphery, with the brass sliprings visible through the opening. The sliprings work with carbon brushes and allow the wind turbine to always swivel into the wind without winding up a connecting cable. 55 Fig.3. The controller that is provided with the wind turbine. It doesn’t control charge voltage very well and has no ‘boost’ function, so resulting in a low output at speeds below 25km/h. Performance in standard form So, and I know everyone’s been waiting for this with bated breath, how much power can this turbine develop? The approach that seems to best reflect reality is to connect the turbine, via its controller, to a 12V battery and monitor the charging current and voltage. To make it as fair as possible, a dead flat battery wasn’t used – instead, it had a voltage of about 12.4V. The turbine was placed on a short pole that was attached to the back of a vehicle that was then driven down the road – a closed road, of course! The following data was measured: Wind speed (km/h) 40 50 60 Current Voltage (A) (V) 1.2 12.5 4.6 16.2 4.6 16.6 Fig.4. The upgrade controller incorporates an effective boost function, giving useable 12V battery charging output from about 20km/h. The device also better brakes the turbine, limiting charge voltage to about 13.9V (not the 14.4V written on the box). to make one of this size yourself), and I wasn’t even much fussed by its relatively low output in strong winds. But to make it viable for me, it needed to have a better output at wind speeds around 20km/h. So, what about adding an auto-regulating step-up converter? Braking could then be controlled by a voltage-sensing device that switched in a large resistor. By good fortune, Banggood had beaten me to it and has available the ‘12/24V MPPT Dual USB Wind Power Controller Auto Work Wind Generator Voltage Booster Controller Wind Controller PWM’. It’s rated for 500W (easily enough) and so I bought the 12V version (£24) and did some testing. (Incidentally, the device has no USB functions at all, so I am not sure how that crept into the description.) The good news is that, at low wind speeds, the new control module effectively doubles the output of the wind turbine! For example, at around 20km/h wind speed, and charging the 12V battery, the output had previously been about 0.5A. With the new boost converter, this rose to about 1A. Furthermore, the new module is much more effective at regulating turbine speed (and so voltage output), fiercely braking the turbine at 13.9V (not the 14.5V written on the box) and so preventing any higher charge voltage. Final set-up My final set-up is this. The turbine is mounted on a 6-metre pole that is bolted to a well-seated fence post. At the base of the pole is located a 12V, 26Ah sealed lead acid battery. (I have ended up with a number of these batteries, but if I didn’t have them, I would use a discarded car battery. Many car batteries are thrown away when they still have plenty of life left in them for an application like this.) Power (W) 15 75 76 A final run was then done at 80km/h, which gave a power output of 90W. These figures are way below the claimed 300W, but I wasn’t much surprised – always apply a large discount to stated wind turbine power outputs! But two things did concern me. The first was that at 20km/h there was very little power available to charge a 12V battery. And my second concern? As the table above shows, the turbine braking seemed completely ineffective at regulating charge voltage for the 12V battery. I then mounted the turbine on a 3-metre pole, wiring-in an LED floodlight that was able to operate on 12-24V (and so catering for the – at times – very high charge voltage). But while this worked in strong winds, in my average wind conditions, the light mostly stayed off. Boost converter Hmmm. I was impressed by the engineering and construction of the wind turbine (it’s certainly much cheaper than trying 56 Fig.6. Charging a 12V SLA battery in a 15km/h wind. Charge current is just over 0.5A – more than enough to keep the battery charged for its occasional use in powering LED floodlights. Note the fuse at left – this should be placed in circuit between the battery and the controller / load. Practical Electronics | May | 2022 site. The lights are seldom used for more than an hour at a time and so the battery has plenty of capacity, even if the wind doesn’t blow for a while. And the other wind turbines I have bought? One will power a battery backup shed alarm, and the other – well, to be honest, I haven’t yet quite decided. Conclusion It’s not going to power your house but if you’re after a relatively low-cost wind turbine that – especially when equipped with the boost module – has a useable output, this is one to go for. Fig.7. What can’t be shown in the pics is the graceful elegance of the whirling blades. The turbine is quiet, developing only a faint whhhsssssh noise at speeds over 30km/h. Unlike huge ones used for grid generation, this turbine is a highspeed device. Adjacent to the battery is the boost controller module. Mounted on the pole are two 10W LED floodlights (also, of course, from Banggood). These lights are powerful, well-sealed and use stainless steel fittings. A manual weatherproof light switch is mounted on the pole. The floodlights illuminate a vegetable garden that is on land where we are building a new house, but there’s not yet mains power on- Fig.11. 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