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Sure you’ve seen LED torches. But not like these! Our Fantastic HUMAN-POWERED LED TORCHES! by Julian Edgar Drum-roll, please! We’d like to introduce our new DIY humanpowered electric torches. Using a deceptively simple design, a slow turn the handle is enough to give a quite amazing output. D EPENDING ON how you choose to build the torch, you can have anything from a pencil beam with a range of at least 50 metres (and incredibly, it will light reflectors at well over five times that distance!) to a broad and diffuse light source perfect as a general purpose torch. Plus, you don’t need to turn the handle continuously; the light itself is ultra-white; and we would expect such a torch to last for, well, nearly ever. And, to top it all off, if you play your cards right, the torch can also cost you very, very little to put together… The Design Basics So what’s inside these humanpowered torches? Just four basic components: a stepper motor, which generates the power to run the thing; a rectifier, which converts the AC (alternating current) from the stepper 56  Silicon Chip motor into DC (direct current), which the LED needs; capacitors, which store the power; and finally the LED itself, which produces the light. Stepper Motor The driving force in any of the designs is a stepper motor, driven as an alternator. Stepper motors are used in electric typewriters, printers, photocopiers, faxes – a whole range of goods. They are most easily identified as a stepper because of the large number of wires that come out of the motor – usually six leads. When you turn the shaft, you’ll also feel a ‘cogging’ motion. The huge benefit of using a stepper motor to produce the power (rather than the conventional brushed DC generator) is that the rotational speed needed is much, much slower. In fact, a stepper motor can be turned 10-15 times slower than a conventional motor-turned-generator. So using a stepper motor in this application means that you can completely dispense with the gearbox – not only does that reduce noise and cost, it also decreases effort, as even a good gearbox has noticeable frictional losses. Longevity is also greatly enhanced. And you shouldn’t have to pay much for the stepper motor – not if you get it from inside a discarded printer, electric typewriter, fax, photocopier or similar. Scrounging the steppers The stepper motors used here came from laser printers and fax machines (each around $5 at jumble sales), while an old electric typewriter (for example, a daisy wheel design) can yield three or four suitable steppers. Steppers are available in many different sizes www.siliconchip.com.au – smaller motors will generally yield less power than larger motors. Rectification Either four diodes or two bridge rectifiers are used to turn the AC output of the stepper motor into the DC that the LED and storage capacitor pack need. Pretty well any small diodes can be used – they can be salvaged from equipment (the PC board from the aforementioned discarded electric typewriter had no less than 16 suitable diodes!) or they can be bought new for nearly nothing. The wiring approach that you use depends on the stepper motor that you have at hand – more on this below. Capacitor Storage The low current draw of the LED makes something else possible – shortterm energy storage. Using capacitors within the torch serves two functions: 1: it smoothes out the pulsing coming from the alternator, which otherwise causes the LED to flicker; and 2: it allows the LED to stay on for a short time after you stop cranking How long the LED stays on for depends on how much capacitance you can squeeze inside the box. For example, using four 4700µF 16V electrolytic caps (ie 18,800µF total), typically gives a usable beam for about three seconds after you stop cranking – and the LED beam will stay dimly glowing for much longer. The latter means that it’s easy to find the torch in the dark if you put it down. The heart of the hand-cranked LED torch is a stepper motor. Several different types are shown here – these can typically be obtained from discarded electric typewriters and printers, amongst other goods. However, if you decide to invest a little more money and use a supercapacitor (eg, the RS Components’ 339-6843 1 Farad designs), the torch will produce a dim beam all night without any further cranking! LEDs The torches use white LEDs rather than conventional bulbs. LEDs are starting to replace incandescent bulbs in many applications. Until very recently, even highintensity LEDs were really marginal in high-output torches – the amount of light produced was simply not great enough for any distant viewing. However, that limitation can now be Using Stepper Motors To Generate DC Stepper motors use a multi-pole alternator design with four phases. When used as a motor, the computer puts a pulse of current into each phase coil in turn, moving the shaft on one step. As with a DC permanent magnet motor, driving the motor’s shaft makes it work as a generator – in this case causing pulses of current to come out of the windings. The developed current is AC, going positive as a magnet pole approaches a coil and then negative as it goes away again. Usually there are four phases at 90-degree intervals so when one comes down to zero, the next one has reached maximum. This is a benefit as it means the output can be rectified to produce much smoother DC with hardly any gaps, but it means these www.siliconchip.com.au motors have a scarily large number of wires coming out. Luckily, it’s quite easy to figure out which way around they are by using a resistance meter (preferably digital), and getting them the wrong way around won’t do any damage. The most common type of stepper has six wires coming out. The six wire stepper is actually two motors on one shaft, so the six wires can immediately be separated into two groups of three. Each group will have some connection to each other, but no connection to any of the other group. In each group, one wire is the common and the other two are the opposite ends of a winding which will give out oppositely-phased AC. In terms of resistance, the reading from the common to either end will be half the reading across the two ends. Having found the common on one set, you can use the same process to find the common in the other one. All four windings will have almost exactly the same resistance. The majority of steppers are six wire, but there are other varieties. Five wire ones are easy; the two commons on the six wire have already been connected together for you, which makes things easier. Eight wire ones are just like a six wire but with all the windings separate, and four wire ones are half of an eight wire one (or half a six wire one with the two windings separate). Courtesy of www.c-realevents.demon.co.uk/steppers/stepmotor.htm - used with permission February 2004  57 Fig.1: most stepper motors that can be salvaged from old equipment use this type of wiring configuration. Finding out which wire is which can be done with a multimeter. overcome by (a) using very bright white LEDs, and (b) using first-class coated optics to develop a very well focused beam. The great advantage of using a LED is that its current draw is so low. The disadvantages (and of course, there are also disadvantages…) is that the LED costs more than an incandescent bulb, and in the final analysis, doesn’t produce as much light as a hard-driven filament lamp. However, we’re immensely pleased with how strong the beams of these torches are, especially considering that the effort put into turning the handle is really quite low. Focusing Lens A key ingredient in getting a good beam is the use of a focusing lens. High intensity LEDs are already very directional – some light comes out of the side of the LED but the vast majority is aimed straight out of the front. So while a reflector is good to channel the minor amounts of light scattering out the sides, it’s much more important to focus the beam that’s already being formed. The best lens that we have found is formed from some of the glass elements from an old standard 35mm SLR camera lens. These days, with the advent of digital cameras and with pretty well all SLR cameras being sold with zoom lenses, the standard lens is unloved and unwanted. In short, you can buy them secondhand for nearly nothing. For example, one of these torch designs uses a lens formed from the reversed rear section of a 50mm f2 Ricoh lens. (Note that the ‘speed’ of the lens – ie in this case a maximum aperture of f2 – is important as the ‘faster’ the lens, the larger will be its glass bits.) Using what was once a very good quality lens (ie, much better than a cheap plastic magnifying glass or 58  Silicon Chip Fig.2: the simplest way of getting DC out of a stepper motor is to link the two commons to the ‘minus’ terminal and then connect the four live phases through small diodes to provide the positive output. similar) gives plenty of light transmission and also allows for the focusing of a tight beam. After all, how many commercial torches use high quality, low dispersion, coated glass optics! Organising the Bits 1. Finding the Stepper The first step is to find a suitable stepper motor that can be used to generate the power the LED needs. Digging through discarded equipment, it’s not hard to come up with four or five steppers of different sizes and outputs. A quick way of sorting out the better ones for the torch application is to firstly go for the larger motors (but which are still small enough to fit in your designated box), and then select those which most easily light a white LED wired directly to two of the output wires. (Despite the stepper producing AC when wired like this, the LED will still light when the stepper is turned – it will just flicker a lot). You will need to find a stepper where even when the shaft is turned quite slowly (eg, 1-2 turns a second), the LED shines brightly. The experimentation that you do should be with a LED similar to that which you intend using in your final design – LEDs vary in their current requirements. For example, the Luxeon Star 1-watt models (available in Australia from Prime Electronics (www.primelectronics.com.au) or the Alternative Technology Association (www.ata.org.au/leds.htm) certainly can’t be brought to full illuminance by a small stepper but that same stepper can work quite well with a conventional white LED. The Jaycar ZD1780 6000mcd LED is suitable for use with many small steppers, for example. The physically larger the stepper, the more Fig.3: if you want to generate a higher voltage for the same cranking speed, you’re usually better off using this circuit which uses two bridge rectifiers. likely that you will be able to drive a high-current LED. 2. Wiring Approaches There are two wiring approaches that can be taken when building the torch – these are shown in Figs. 2&3 in the “Using Stepper Motors to Generate DC” breakout box. Fig.2 is the most common approach but Fig.3 has a distinct advantage in some applications – often it will increase the voltage available from the stepper. Deciding which approach is better for your application requires some further experimentation. First, use a multimeter to find out which wire is which, then wire the stepper to the LED as is shown in Fig.2. The next step is to turn the stepper as fast as you will ever be able to (you can use a bulldog clip to make a temporary clamp around the shaft of the motor to act as the attachment for a test handle) and measure the voltage being developed as the LED is powered up. In addition, turn the shaft more slowly (that is, at a comfortable speed) and view the LED brightness. The ideal www.siliconchip.com.au Step by Step: Making a Narrow Beam Torch We selected a rigid plastic box as Using a holesaw, a hole was then 1Electronics the enclosure for the design – Jaycar 11 cut in one end of the box. The two Cat. HB-6122 at $7.25. It halves of the box were then separated, is made from high impact ABS, uses a tongue-and-groove seal around the lid, and is dust and hoseproof. Importantly to hand-holding comfort, it has rounded edges and corners. first step was to mount the 2usingThe stepper motor in the lid of the box, the two screws that originally held the stepper in place inside the laser printer. Next, the lens/reflector package needed to 3disassembled be organised. This Ricoh camera lens was and it was found that the rear lens elements (mounted in a sub-assembly) gave good results when placed about 20mm from the LED. The assembly is reversed in orientation to that used in the original camera lens. torch was then disassembled, 4Athesmall reflector removed… …and the reflector 5 opening for the bulb carefully drilled out (jn small steps) until the LED was a tightish push-fit. (The reflector isn’t critical but it adds a ring of light around the main beam.) The pump-lid of a plastic 6having container of skin cream was then selected as a hole in one end about right for the reflector and a length about right for the LED-to-lens distance. The lid was disassembled 7opened-up and the hole in the cap a little with a round file so that the reflector sat nicely in it. 8 The threaded top of the skin-cream container was then cut off, cleaned-up and then screwed back down inside the lid, holding the reflector firmly and securely in place. The holder from the 9 camera lens was filed from its original semi-circular shape until it was about the same diameter as the reflector holder (that’s the former skin cream cap, remember!). Good quality elec10 trical tape was then wrapped around the lens/reflector assembly, holding the two pieces together. Large diameter heatshrink could also have been used for this purpose. www.siliconchip.com.au the lens/reflector assembly inserted, and the box temporarily re-assembled to check that the lens/reflector assembly was held firmly in place. It was. The capacitors were placed into 12 position next, being held in place inside the lid with double-sided tape. The diodes were soldered to the four 13 stepper motor outputs, making sure that all their bands were furthest from the stepper motor, then the wiring was completed. Note that the capacitors are polarised – their negative terminal is shown by a line of negative (-) symbols down the side of each of their bodies and they must be connected around the right way. The final design is quite a 14 tight fit – as you can see here, there’s only just enough room for all of the bits. The hand crank was made from 15 a piece of polypropylene plastic kitchen chopping board. This material has a distinct advantage in this application: if a carefully-sized hole is drilled in the material, it can then be forced over the stepper motor shaft giving a good non-slip fit. In the case of the stepper motor shown here, a small diameter cog was already in place on the shaft and so the push-fit of the crank is even more secure. At the other end of the crank, a 17 high quality knob was made by using two ball-bearing pulleys, previ- ously found inside an electric typewriter. Sandwiched together and with a couple of washers under them, they give an easily-grasped knob which has excellent quality bearings built right in. Note that the distance 18 centre-to-centre between the knob and the motor shaft (ie the working length of the crank) is very important to the ‘feel’ of the device: you should experiment with this distance until the leverage suits your preferences. February 2004  59 La Crème de la Crème – the big-buck design This torch is the big buck design – it uses an expensive 1-watt(!) Luxeon Star/O LED and super capacitor energy storage. As you’d expect, in operation it’s also the most impressive of the designs, able to light a room or create a swathe of light outside that – for example – is ideal for walking. Despite the fact that extra focusing optics would have given this torch an incredible beam reach, it was decided to use only the Luxeon built-in lens and reflector, resulting in a very even 20° beam. When held close to a digital light meter, a reading of over 34,000 lux can be recorded! In practice, when walking down a road at night, the full width of the road is illuminated with a range of six metres or so. The torch uses for its body a plastic housing that was originally one of the satellite speaker enclosures in a PC sound system. The knob is a ball-bearing equipped cog (with the teeth mostly sanded away) that was salvaged from an old fax machine. Both wiring approaches were tried and the simple diode rectification gave the best output for the least The output of a focused cranking effort. Inside, a 0.47µF beam or Luxeon Star electrolytic capacitor and a 1 farad LED torch is sufficient to super capacitor are used for energy storage. cause eye discomfort and This is an enormously impressive possibly eye damage. torch. In fact, the only downside Do not look directly into is that generating a full watt by a the torch, and don’t shine Warning! the beam into anyone else’s eyes at a close distance. hand-cranked mechanism is hard to do quietly – despite the direct drive, the stepper motor makes a whirring noise when being turned. The size of the required stepper also makes this torch the heaviest of the designs – it weighs 600 grams – but the sheer light output is just staggering. Very few people can believe that a simple turn of the handle can produce this much light – especially from a LED! If you want the best, you have to be prepared to pay for it. This torch uses the VERY bright LUXEON Star/O LED and a supercapacitor. But its performance is exceptional! 60  Silicon Chip www.siliconchip.com.au A Broad Beam Torch After my partner saw the results of the narrow beam torch, She-Who-Must-Be-Obeyed decided that when out walking she wanted a torch that would light up the area immediately in front of her – that is, producing a very broad, diffuse beam. This meant that a focusing lens was not required, so creating more room inside the box for storage capacitors – nine 4700µF capacitors were installed, giving a total capacitance of 42,300µF. Secondly, it was preferred that the torch weigh less than the first design, so in this model a smaller stepper motor was used. It was also decided to fit two of the high intensity LEDs, rather than just one. The stepper motor is easily able to drive two LEDs (and probably more as well), and without the dramas of trying to integrate multiple LEDs into a reflector-and-lens system, it was easy enough to use two. However, when wired with separate rectifying diodes, the smaller stepper proved to have a lower voltage output than the larger stepper used in the focus-beam torch. This meant that the crank had to be wound very fast to get a good light output, so a revision was made to the wiring. Two bridge rectifiers were then used (ie, Fig.3’s wiring approach). In practice this resulted in the voltage rising to 3.2V at an easy cranking speed – and peaking at 3.4V when the short handle was being turned as quickly as possible. While the effort in turning the handle rose when this alternative wiring configuration was adopted, it is still quite easy to turn. In some respects, the handle is actually easier to use when working against the slight resistance – before, it was almost free-wheeling. A very short handle was fitted (about 10mm centre-to-centre), with its knob formed by three sealed ball bearings from discarded video cassette recorder video heads. In a small room with a white ceiling and walls, the twoLED torch will dimly illuminate the whole room. Following outcome is a peak voltage of around 3.5V – that’s what is needed by the LED – and a ‘slow turn’ voltage as close to this as possible. (In fact, of course, it’s the peak current – rather than the voltage – that should be limited, but if the stepper being turned flat-out develops only around 3.5V, in real use the LED will be well within its ratings.) Matching the stepper motor to the LED in this way removes the need for a dropping resistor, saving valuable energy – energy, remember, that’s being put in by you! If the voltage that you see during the test is well below 3.5V, try the wiring approach shown in Fig.3. Often (but not always!), this will increase the www.siliconchip.com.au an outside path at night, the torch casts a soft white glow that extends about five metres ahead and a metre or so either side of the path. In fact, the light output is similar to a small fluorescent lantern. Interestingly, with the LEDs sticking out of the front of the torch, any light being produced by them is more easily seen than in the focusing torch design (where the LED is buried from view behind a lens). In fact, the LEDs in this torch stay faintly glowing for a very long time after the handle has stopped turning – in pitch darkness, they can be seen for over six hours – and that’s without using any expensive super capacitors! This characteristic, and the diffuse spread of light that it develops, makes this an ideal torch for moving around a house at night when the lights are off, walking down a dark footpath, or for use as an emergency torch during blackouts. voltage output of the stepper motor. If neither approach yields a high enough voltage when powering the LED of your choice, select another stepper and try again. In our testing of more than 50 stepper motors salvaged from used con- sumer goods, we’ve not seen a stepper motor that, when cranked in this way, produced well in excess of 3.5V – so your chances of overpowering the LED are slim. On the other hand, probably half of these motors had enough ‘oomph’ to drive a conventional white Emergency? These human-powered LED torches have some really good emergency applications. The light is visible from a very long distance (especially if you build it to have a narrow, focussed spot beam) and the torch will never get a flat battery. Because of the direct-drive system, the quality bearings used in stepper motors, and the LED light source, the torches should also have an almost unlimited life. February 2004  61 If the LED torch is constructed with precision focusing optics, a very intense, narrow beam is formed. This lens assembly uses elements from a discarded 50mm SLR camera lens and gives excellent long-range performance. LED to a high brightness. In short, a great many small salvageable steppers are ideal for white LED torches. 3. Optics Once you have found the right combination of LED and stepper, you will need to make some decisions about the optics. There are three basic choices: • A narrow, intense beam – this requires a series of lenses, preferably an optical assembly from a 35mm camera lens as described above. • A broad, bright beam – usually, a single lens can be used to achieve this – eg, a single element from a 35mm camera lens or a good standalone glass lens; eg, a quality magnifying glass. Alternatively, a very 62  Silicon Chip high quality LED lens-and-reflector combination (such as the Luxeon Star/O 1W white LED) can be used. • A diffused, relatively dim beam – in this case, one or two LEDs can be mounted ‘bare’; ie, without any optics at all. Think through the choice carefully – the utility of the final torch for the application that you have in mind is dramatically affected by the decision on optics. 4. Storage Capacitors The type and number of storage capacitors that you use depends on how much room you’ve got inside your box – and how much you want to pay. Electrolytic capacitors are the ones to go for and if you select those with a lower working voltage, the size of the capacitor becomes smaller for a given capacitance. In other words, a 1000µF 16V capacitor is physically much smaller than a 1000µF 63V capacitor. Since we’re working with only 3-4V, the lower voltage capacitor is fine. Basically, the more capacitance that you can squeeze in, the better – which brings us to super capacitors. While these mighty marvels are available from a variety of sources, extensive testing showed that the cheaper super caps give poor results – we recommend the RS Components 339-6843 1 Farad component. Note also that a super cap used on its own won’t work very well –you should always have a conventional electrolytic capacitor as well, of as high a capacitance as will fit in the box. You might be wondering how all these capacitors are connected – again it’s very easy, with the capacitors wired in parallel to both each other and the LED. No current limiting resistors, no zenor diodes, nothing. It works extremely well and wastes no energy. Conclusion Despite being very simple in design and construction, these torches really cut it. They’re effective and cheap, working well in both general-purpose and specialised applications. Not one of the many people who have seen the prototypes was unimpressed – in fact most people had to have the torch removed from them by force, so intent were they on winding the handle and shining the torch into SC dark places! www.siliconchip.com.au