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I assembled the new windmill and bolted on a 1.5 watt solar panel (or so it's rated) on top for a bit more power. I wired everything up with blocking diodes (independently for the solar panel and generator.) I wired it up modular and consider it done.
While I was taking pictures ...
I have been in the habit of going for a walk in the mornings to clear my head and this was no exception. The one exceptional event was it's trash day and I was out very early. I came upon one house with what appeared to be a paper feeder for a copier (or at least most of such a beast.) I walked past it but then went back and took a closer look at the motors (which appear to be pretty beefy) and that it had a bunch of smaller springs (that I can use as tensioners.) I walked it back home and then went on with other things
Later on, I got a chance to test the motors. Actually, I just drilled a hole in a piece of dowel to use as a roller and bolted the motor in place — I had drilled holes in the the motor holder for what appeared to be two "standard" sizes. Well, this one is as big a motor as will fit and I brought it to the big attic fan and gave it a whirl. It generated about 25 volts open at that wind speed (a lot) and output 7.5 volts into 51 ohms: about 0.15 amps or 1.1 watts. I installed a larger spindle and got 8.8 volts (0.17A) into it or 1.5 watts. I found that with just a diode, I could charge the battery at 0.12 amps out. That's not bad, but it could be better. I decided that if I also throw on the solar panel I have (supposedly 1.5 watts) and hook it all up, I might be able to get to a point where the whole system is pretty close to self-sufficiency.
If the draw during the day is 0.2A and the draw at night is 0.4A, I might assume an average of 0.3 amps all day. If the generator can average 0.1 amps (very optimistic) and the solar panel 75mA for half the day (35mA average, also pretty optimistic) that's 0.135A average in, reducing my overall average load to 0.165A: the 7 amp-hour battery would then last about 42 hours! That's way better than the 23 hours I can get at 0.3 amps.
I don't think I mentioned it (and am too lazy to scroll down to check) but a friend of mine stopped by the other day and I was showing her all the stuff I've built so far. I loaded the switching power supply with 3 ohms to demonstrate the noise I get, but later I realized the -5 volt output was no longer working ... odd. Tonight (Friday, by the way, and yes, I have had a few drinks — a chilled shot of Ouzo, a Saranac Pale Ale, and a Genesee can at home) I checked the power supply and inexplicably, the LM324 died — the op-amp that controlled the pulse-width modulation stayed at the positive rail for no reason. I pulled it and threw it away, even though it might have just as well been a loose connection. Replacing it worked just dandy. I tried connecting every LED — both strings, all three colors — and the input drew 0.53 amps for 0.76 amps out (in power, that's 6.36 watts in for 3.8 watts out for an efficiency of 59.7% — cool: almost 4 watts of output through LED's!) Anyway, I decided that the switching noise wasn't going to be much of a problem. Even with all three colors on one string lit, the noise is noticeable but ignorable ... it adds an element of irritation. If I go to just one color lit (which, technically, is the load under bit modulation) the noise becomes nearly inaudible except very close. I have my fingers crossed.
I decided that in this last week or so before I leave town, I'd pick up one more task: build a Savonius generator on the Bike With 2 Brains. So on Tuesday morning I got up and started thinking about designing it. I figured out that the bicycle seat posts are the right size to fit the "#608" size skate bearings — I had bought a pack of them because the 8mm hole is just a hair bigger than the 5/16" (7.99mm) threaded rod and bolts I planned to be using.
Wednesday I got up and started designing it in CAD. By 11 I came up with building a basic cube frame with a pair of centered cross-beams from side-to-side to hold the rotor. The key part is the detail below with the arm to hold the generator with a friction-coupling to the baby-stroller wheel (which is ultimately why I went with 5/16": it's the shaft diameter of the stroller wheel.) The diagram of this detail is below:
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Basically, the rectangles on the left and right are the frame mounts and the center horizontal rectangle is the support bar. The small central circle is the bearing and the large circle is the baby-stroller wheel with the centered diagonal rectangle representing the 2x4 used for the rotor. The angled dimension lines surround the generator bar — the larger circle below the baby-stroller wheel is the motor housing and the smaller is the motor spindle (a wood dowel.) The line connecting the bolt (it's supposed to be a bolt and looks better in CAD zoomed in) is linked to the center frame by a spring.
I built a rotor that afternoon. The original one I designed had two problems: first, the shaft holes weren't well centered, and second, the top and bottom plates were not exactly parallel. I paid more attention to those two problems and things came out much better. I also used whatever remained of the vent pipe I had bought — it's just like the original prototype except that it's about 14" long. I even got the bearings mounted on the end and thought, "gee, that's it?" expecting it to be harder to make.
Thursday I got up and started working on the frame. I welded together a basic frame and rethought the cube shape: instead I went with a wide bracket for the rotor bearings and put the vertical members on either side of that. By that evening I had finish-welded the frame and tack-welded the brackets to mount the generator. It was almost hard to assemble it in the very light breeze because the rotor would spin so easily.
Friday I built the rest of the motor mount, mounted the preferred motor, and tested it against the fan in the attic — essentially the blower from a furnace. I was able to get about 4.5 volts open-circuit, 2 volts into 5 ohms (0.8 watts) and 1.5 volts into 3 ohms (0.75 watts.) I had to use a weaker spring than I started with because the friction of the stoller wheel against the dowel was too much when it was pulled tight. I don't know the wind speed nor the rotation speed, but it was pretty dangerous looking. I finished up the brackets and threw on some paint in the evening.
I put the power supply on a board and wired it all up. I figure I'm getting around 60-65% efficiency — far better than the 42% efficiency of using a linear regulator. In other words, if my lighting stuff (the motivation for the 5-volt supply in the first place) outputs 1 watt, the battery will be hit with 1.5 watts whereas if I had used a linear regulator, it'd see 2.4 watts — the 84 watt-hour battery could run for 56 hours instead of 35 hours. Heck, it's almost half as much time as I put into making the fucking thing!
I got around to the basics of the circuit below. I set up the MOSFET in the configuration below and drove it from the op-amp. I added the PNP in a similar configuration to ensure that maximum current would get to the gate — I need to get that gate to 12 volts, and the 20 mA output on the op-amp wouldn't cut it. I got nice square square-waves but, using a simple pulse-width modulation to the capacitive output, I was getting the same problem of current-in equals current-out. I set up the buck configuration again and finally got some success: 6.6 watts in and 4.2 watts out for an efficiency of 63%.
At this point I realized the output-as-driven would end up as 5-volts from the positive battery rail. I remembered having 7905 negative-rail 5-volt regulators around (and always thinking, "what the hell will I ever use these for?") I switched to the terminology where the positive battery terminal was ground (calling it 0-volts) and the negative rail was -12 volts. I spent some time diagramming the circuit (using CADintosh from Lemke Software, GMBH.) I went back and set things up like I had drawn, made a few changes, and did some final tests on the breadboard. By varying resistors, and using the 51-ohm load I got 97mA out (4.95 volts at 470 mW) with 52 mA at the input (624 mW) for an efficiency of 75%. I tried the 8-ohm load and got 620mA out (4.96 volts at 3.08 watts) with an input current of 419 mA (5.03 watts) which gave me an efficiency of 61%. I think this looks pretty good.
So, after three days of slaving for a total of 20 hours or so, here's the circuit ...
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You can look up explanations for a twin-T oscillator and a buck converter for the oscillator and the inductor on the Internet, but one thing that I don't think is too obvious is that the diode after the op-amp is there so the base of the PNP transistor can actually go to the rail — the op-amp may not reach it, but the diode will be shut off so the 470-ohm resistor will shut the transistor down. The other thing is that the inductor has no value. I don't know what it is: it's a yellow torroid with red magnet wire that I pulled out of a dead computer UPS, so I don't know its value, but of the ones I had lying around, it worked best. I guess I should put parallel lines below it because it's iron-core ... oh well.
First, the "10-potentiometer method" is when you have the basic idea for a circuit but tune it by varying values until it works the way you want. That's basically where I started.
The general idea is that I wanted to make a high-current source for the 5-volts I'll need to run the logic circuits and LED's (I wired the LED's to expect 5-volts on the input resistor) that's pretty clean, but it doesn't have to be perfect. I knew I didn't want to start with a linear supply: if I went from 12 volts to 5 volts, the power efficiency is 42% (i.e. at 1 amp it's 12 watts in for 5 watts out and 5 watts / 12 watts = 42%.) However, I also didn't want to go with an off-the-shelf solution — mostly because I thought my requirements were really easy.
I got up on Monday, August 1 really early and got started. I dug through my transistor bin to find an NPN that could handle around 3 amps. When I started I figured I could go from 12 volts to half that (6-volts) and then drop the rest through a 7805 regulator to give a nicely cleaned-up output.
I got a buck-style converter set up. It was similar to the circuit above — using the twin-T oscillator as a source for pulse-width modulation on an op-amp — but I didn't use the 7905 and just had a couple 100K resistors on the input pin of the feedback op-amp to approximate 6 volts, I didn't have a high-pass filter on the feedback circuit, the oscillator was running from +12 volts to 0 (or 0 to -12 volts as I've got it diagrammed) and the output was just a current follower where I had an NPN set up with the base tied to the output of the PWM op-amp (top right) with its collector tied to battery-positive, and the emitter driving the diode/inductor/capacitor buck setup.
I ran 127mA through 51 ohms to get 6.7 volts (850 mW) and I was able to source 5 volts at 1 amp into 5 ohms (25 watts) although it seems to go linear. I suspect the transformer I'm was using as an inductor doesn't have enough current capacity. I tried 8 ohms and managed to source 800mA at 6 volts (2.4 watts) and that seemed to be the limit of the power source before going linear (the transistor was on at over a 90% duty cycle.) With that output current, I checked the input and it was drawing around 650mA at 12 volts or 7.8 watts — hardly efficient at all at 33%. With the 51-ohm load, it uses 130mA just like the output ... then again, maybe my meter just isn't very good at measuring transient currents like the circuit is drawing from the battery. I used the oscilloscope instead so I could estimate the waveform (and actually calculate RMS voltages) with an 0.1 ohm resistor — a handy value for converting to current (volts times ten.)
I tried some differnet chokes and found one that would cause the circuit to input 700mA RMS (2A peak-to-peak) at 12 volts (8.4 watts) for an output of 1 amp into 8 ohms (8 watts) so that's pretty good (although for some reason it decides to output 8 volts instead of 6 volts.) I tried switching to another op-amp (now the LM324 which is what I stuck with throughout) figuring that it could get its output closer to the rails — that got me to around 65% at 8 ohms but only 24% at 51 ohms, but running that inefficiently, I would expect 2 watts dissipated on the bare transistor to get hot really fast ... hmm ... I'm concerned about my measuring efficiency. I tried estimating the waveform power levels with some calculations and got to a 45% efficient — worse than the 50% efficiency of just dropping half the voltage as a resistive load.
I kept switching coils, transistors, and resistors. Man am I sick of staring at breadboards and oscilloscopes. I got varying figures and even created perpetual motion machines: I had a 115% efficiency at one point. I was certain it was measurement error.
Up until now, I was using a linear power supply for the 12-volt input. When I switched to the battery, everything stopped working. I had to start all over again — I tried varying the frequency of the PWM oscillator then I tried removing the feedback loop to see if I could get something out unregulated and met with some success. I also floated the PWM oscillator (oh yeah: originally I had the emitter tied to ground, so the oscillator was running very close to the rails.) I added a filter capacitor at the input. All this helped but didn't get me any closer to something that could significantly beat a linear supply.
I decided to check my 0.1 ohm resistor to make sure it's good. Using the meter, I measured a 203 ohm resistor in series with the 0.1 ohm and measured 12.67 volts across it (when I hooked the two series resistors across the battery) for a current of 62.41mA. The 0.1 ohm resistor dropped 0.0123 V so the resistance is actually 0.197 ohms. Once I figured that out, all my efficiencies were twice as good. I took a break and enjoyed the catharsis, but I really didn't believe my measurements so I went back and did them again. Using a 303 ohm resistor, I get 12.74 volts across it which is 42mA and I measured 4.0 mV across the 0.1 ohm resistor, making it 0.095 ohms. Darn. I tried the other resistor: it now reads 205 ohms and dropped 12.70 volts or 61.95 mA. Given the 5.9mV drop on the test resistor, I get 0.095 ohms again.
I tried making a PNP current source to drive the NPN current follower off the op-amp ... somewhat similar to what I've got above, but the PNP output goes to an NPN current follower. That gave me an efficiency of 42%. I stripped the circuit back to the point that the transistor is switching a full 12 volts on-and-off at a 50% duty cycle, and still it has a 50% efficiency. The collector-emitter voltage switches between 12-volts and 1.5 volts, but that only accounts for some of the inefficiency. I decided to try a MOSFET in the same configuration but got the same result.
Tuesday I got up early again and I figured the feedback loop was giving me trouble by switching off the resistors too soon regardless of the high-pass filter I added yesterday. I thought about using a sample-hold circuit on each pulse, but then thought that was stupid and would be a waste of time. Instead I figured that the output transistor can't get fully on or fully off based on the op-amp. I couldn't figure out what to do about it. I tried using a buck-boost configuration where the inductor is in parallel to the output but that didn't work. Heck, the inductors had no appreciable effect at all.
Once I did some measurements, I figured out the big problem. The MOSFET output was swinging from 0 volts to 8.1 volts when using the 8-ohm load. That 4 volts at 670 mA (6 ohms) with 50% duty cycle accounts for 1.3 watts of power loss (out of a total input of around 8 watts and an output of 3.5 watts, so there's still some 3.2 watts going somewhere I haven't found yet.) I tried the 51 ohm load and the peak is around 9.1 volts with a current of 120mA but with about a 30% duty cycle — 75 ohms this time accounting for 360 mW out of a total loss of 710 mW. I checked, and if I supply a full 12 volts to the gate of the MOSFET, the maximum output is only 9.1 volts into 51 ohms. Harumph.
I switched to some 2N277 PNP transistors I had lying around in the switch-configuration I have on the first stage of the output in the circuit above. However, that didn't work. I tried the more reliable small-signal PNP's but that didn't work either.
I went back to using bipolar transistors and managed to make a circuit that could get up to 12 volts. I changed the output circuit to a darlington network to get more gain (hopefully.) The circuit was operating at an input voltage of 2.7 volts.
I tried switching to the 5-volt supply and I could comfortably get 12 volts into 220 ohms — 54 mA for a total power of 0.65 watts; with 51 ohms, I could get 8 volts or 1.3 watts. I'm pretty sure I'm up against the output capacity of the transistor at this point, so I tried a heat sink but it didn't help.
Anyway, in the process of digging around, I found this high-power NPN transistor. I hooked it up on the DC-DC converter and managed to drop 15 volts across a 51-ohm load with 5 volts in — a total of 4.4 watts. That's getting there.
I found a website that described DC-DC converter basics. I took a crack at building a "boost" style step-up DC-DC converter (where an inductor is placed in series with a power source and the output side is switched to ground.) I managed to step 5 volts to 24 volts across a 1.2K load (using low-power components) for a current of 20mA or almost 0.5 watts.
I found that transformers work particularly well in the circuit — plus, the secondaries offer useful voltages as well. By switching to better transistors (i.e. 2N2222 instead of 2N4123) I achieved 38V out into 1.2K: 32mA or 1.2W. This looks very promising ... now if only I could get it to work from 1 volt.
I measured across 51 ohms and got up to 9.3 volts out. The input current is about 0.46A at 5.7V, so that's 2.62 watts and the output into 51 ohms is 0.18A or 1.70 watts out, so it's about 65% efficient. Using a smaller torroidal inductor, I got 8.62V into 51 ohms or 1.47W with 5.82V at 0.40A in or 2.34 watts for 62% efficiency.
I started building one to work off 1.5 volts or so. At first I didn't get it to work. I rebuilt the whole circuit and got exactly the same bizarre result: a short-cycle square wave that seems to ring down. I couldn't get the thing to work. The capacitor on the NPN transistor seems to be running into negative voltage territory somehow ... it actually oscillates, but the final output is a stilted square wave. I switched to a (possibly more stable) twin-T design which I managed to get to work with as little as 3 volts.
I thought that I could try using MOSFETs but I couldn't figure out how to get them to work.
I found a circuit at a website called the Joule Thief. It's a nifty LED driver circuit that can allow an LED to be driven from a nearly dead battery. I figured it would work to boost the voltage from the generators I had but I couldn't get it to work with my limited knowledge (and lack of caring to figure out how the circuit really worked.) I suspect it relies on the nature of LED's to oscillate properly.
I got a couple bigger 12-volt motors from the electric cars for kids to drive around in — all from the trash. The smaller one can source 8A at 0.5V or 4 watts, and the larger can source 9A at 0.6V or 5.4 watts ... both at 3,100 RPM.
I drilled shallow holes and glued the rare earth magnets to a wood dowel to try them out as a generator rotor. They really are strong and tended to pop out of the glue to stick together. I managed to get it built with two poles but it didn't make an appreciable difference in the performance of the generator.
I glued a couple magnets onto a wooden dowel with a screw through it to make a permanent magnet rotor. The magnets aren't particularly strong, and my first attempt had the poles opposite one another: that is, the north on one magnet mated with the south on the other, so the field was even weaker. (This all fit into the field coil from the Dirt Devil motor.) At 3,100 rpm, I could output 53 Hz AC at 2.7 volts open, 2.1 volts into 51 ohms (0.086 watts) and 0.7 volts into 3 ohms (0.16 watts).
While this isn't particularly promising, I purchased a pack of 50 0.25" diameter neodymium rare-earth magnets from K&J Magnetics. They're supposedly rated at N45 which I guess is almost as strong as you can get.
2005-Apr-2: Generators #4: A New Hope — AC generatorsI figure I can easily convert a DC motor to an AC motor by tying one side of the rotor windings to both sides of the brush assembly rotor thing, and the other side to the shaft. That way I can step up the output voltage to a useable level. I went to the basement and grabbed all the motors. I decided to try converting the drill motor since it generated the highest current (next to the original) and it's the largest. I decided against the air pump motor because, although it can source a lot of current, the output voltage is so low it's almost not worth it ... then again, that's based on running it up to 3,100 RPM on the drill press, not the huge speeds from spinning on the rubber wheel. Anyway, I took apart the gold-colored motor and rewired it. I started by cutting a groove around the commutator and soldering the original poles together so I ended up with a 2-pole slip-ring instead of a 3-pole commutator. I ground down the brushes so each would contact one pole of the slip-ring. I disconnected the three poles, undid the connection that tied the windings in a loop and connected each end to the slip-ring contacts. When I reassembled it and tested it, I roughly zero volts out. I had successfully demonstrated that the motor was wired efficiently and Kirchoff's laws still apply: of course there was no current flowing at that point — otherwise, when run as a motor, it would short-out. Dummy. I took it apart again and wired it for 3-phase. Two phases were wired to the brush output, and the third was soldered to the shaft bushing so I could use the case as the third phase. It sort-of worked, but then the wire I was using to tie the third leg to the shaft came loose and wedged between the rotor and the magnets. I reassembled the motor with a stiffer wire. I found that the brushes would bounce on the imperfect rings I had so they wouldn't transfer the power. I could get up to about 1 amp of output on any one coil and up to 1.5 volts or so. I cleaned up the rings and such but couldn't get them round enough with the tools I had so I gave up on it. However, I also had an AC brush motor from a Dirt Devil hand-held vacuum and figured I could make a rotor with permanent magnets to induce current in the outer coil. Finally a break in all this: the rotor shaft was 5/8" which is the same size (well, 8mm) as the the bearings I bought for the Savonius rotor. Even better, the magnets in the gold-colored permanent magnet motor are very close to the right size. 2005-Apr-1: Generators #3: ExperimentationI tested some of the motors at high-speed to see how much they'd generate and to see if any would be suitable. Note that the motor speed was dictated by the shaft diameter; the drill motor, 6V motor, and original motor had larger shafts and ran slower.
For the stepper motor, at 1,100 rpm, using both phases through a bridge rectifier, it would source 0.63V into 3 ohms or 0.13 watts. One phase through a 5:1 step-up transformer frustratingly yielded the same results: 0.6V. Both phases in series yielded 0.67 volts, and at 1,720 RPM, 0.8 volts. The open voltage on the transformer secondary was 11.75 volts. I also took apart one of the pumps that I used to use for the air horns in the car and got its motor separated. It could source 3 volts into 3 ohms and had a short-circuit current of 5 amps at 3,100 RPM. 2005-Mar-31: Generators #2: Stepper motors suck as generatorsI decided to go buy a motor so I went to Glenwood Sales (549 Hague St.) and browsed for a while before eventually settled on a 30 V stepper motor with a 48 ohm coil. It apparently has 4 phases, and each phase would ordinarily consume 0.625 A or 18.75 watts. The stepper motor could generate as much as 50 volts open-circuit (it's wired with two coils center-tapped.) Through a 51-ohm load I found it could get as high as 5 volts, and through a 280-ohm load, 20 volts. The good news is it's pretty linear from about 1,000 RPM through 3,000. The bad news is those two ratings yield only 0.5 watts and 1.4 watts respectively. Using a full-wave bridge on each side and tying the outputs together and running at 3,100 RPM, I could get 9 volts into 51 ohms and 34 volts into 280 ohms: 1.6 watts and 4.1 watts respectively. Open, it would generate 90 volts. Indeed, none of the motors would source more than a half a volt at 3,100 RPM; one that I hadn't tested would generate 0.5 V and 1.5 amps, so at least that's promising. |
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I found that I have some 1" thin-walled tubing from an exercise machine that has a nearly 22mm diameter — the outside diameter of the bearings I bought. I figure I can weld a piece of tubing to the ends of the windmill frame then cut a slot and use a seat-post clamp to grip the bearing.
I also tested the motors I had selected as candidates for a 10-watt generator. None of them performed better than the motor I had originally selected.
Based on my former calculations, the rotors would only run at 300 RPM in a 10 MPH wind, so a 7x gear-up would only yield 2,100 RPM which wasn't enough to generate any appreciable power. To get any power out, I had to run the baby carriage wheel in the drill press at 620 RPM with a 0.33" gear, so the ratio to the 7 3/4" wheel (23.5x) means I ran the motor at 14,500 RPM. If this were 20 mile-per-hour wind, then a 70 mile-per-hour wind would overcrank the motor to over 50,000 RPM and probably blow it up. I'll have to see how slow I can get the motor to run and still get decent power. Well, I know that 3,100 RPM is not enough: the motor, when hitched directly to the drill press, would only generate about 3.4 volts open and 1.9 volts into 3 ohms (only about 1 watt.)
Ok, so let's say I limit the motor to 15,000 RPM at maximum wind speed of 70 MPH, or 2,100 RPM. The ratio, therefore, is 7:1 ... bummer. I think I'm going to need to get a different motor. If I use 21,000 RPM as the cap, I can get to a ratio of 10:1, so in a 10 MPH wind, the rotors would only run at 300 RPM driving the motor at 3,000 RPM which isn't enough.
I hunted around on the Internet for ball bearings to fit a 5/16" shaft but wasn't having any luck. When I switched to metric — realizing that 5/16" is just 0.8% shy of 8mm — I discovered that I should be looking into inline skate bearings. I bought a pack from Pleasure Tools.
I wondered what kind of forces the windmill will need to reckon with in strong winds. I found a g-force calculator on the Internet and determine that a 9.2-inch rotor (4.6-inch radius) running at 2,100 RPM (the speed I calculated for a 70 mph wind) will exert 578 g. Therefore, if there's one ounce of material at that radius — ergo an imbalance of one ounce — it will exert 36 pounds of force. Although I think 5/16" rod will easily handle 36 pounds of force, it's the 30 cycle-per-second vibration that might kill something.
I guess I have to be careful about balancing it.
I thought I bought 6" round duct pipe, but apparently it's actually 5" in diameter. Anyway, I played with it a bit and figured I could make a neat rotor using a 2x4. I put it in the CAD software to get the dimensions (note also that I'm using a 10% gap between blades at the axis which is recommended by most people.
Savonius rotor mounted on a 2x4 (which is the 3.5" dimension)
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The idea was to notch the ends of the pipe halves and bend them into tabs to screw onto 2x4's. I wanted to ensure that one tab extended to screw into the end of the 2x4 and that the arc of the pipe fell tangent to the edge of the 2x4 so I could put another screw in the side through a tab. What I found was to cut the 2x4 to 9.2 inches long. I learned that it was important to ensure the bent tabs form parallel planes. My first rotor came out crooked ... not by too much, but enough that it would vibrate like mad in even modest wind. (By the way, that's the axle from a baby stroller wheel that I used as a pivot point to test it.) That, and I should alternate my cut tabs inward and outward so they don't overlap on the inside of the curve. Oh, and that you can only screw into tabs that are on the outside of curve — I guess unless you've got a short screwdriver or make the pipe segments longer than I did. The best part, though, is that the rotor is very rigid. I'll be more diligent about the next design, and I sure hope it will survive strong winds. |
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I started with the spindle motor from an old hard drive. I figured it was a pretty nifty use: the permanent magnet 3-phase motor should make a cool generator, plus it will supply 3-phase power. Unfortunately, my hopes of hitting 20 watts with it are pretty much dashed.
I cut out a Compuserv CD into fan blades, heated it to bend them, and mounted it to the motor. With the air hose, I managed to get to 600 RPM (a far cry from the rated 5400 RPM) and dumped 30 volts into 1000 ohms for a power output of 0.9 watts. Indeed, the power rating on the drive indicated it was only supposed to draw about 6 watts total, so my chances of getting past 5 watts or so is not too likely. However, even 5 watts over 20 hours would provide me with enough power to run 10 watts of lighting and other stuff for 10 hours or so. At least the 100 watt-hours generated each day is far more than the 50 watt-hour capacity of the batteries I'm looking at. Oh, then I broke the blade.
All content copyright ©2005 Jason Olshefsky.
