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Forum Index : Windmills : Finding the right generator, help!?
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mystiquesbs Newbie  Joined: 09/08/2008 Location: New ZealandPosts: 10 |
Hi, We are currently undertaking a project at university. The project entails finding a suitable generator that will run off a spinning sculpture and run LED lighting within the sculpture to illuminate it. The power being drawn by the LED's is very low, less than 10W. So far I have looked around and see that there are only 2 real options that we could use. Either a PMDC motor or some sort of PMA that we would build ourselves (see F&P smart drives thoroughly recommended on this site but think it may be too hard to source 15?). The PMDC motor appeals as there will be a total of 15 sculptures and we need to be able to source readily available parts. I have learned that for a PMDC motor to work properly as a generator the RPM's must be low and the voltage high. e.g 300RPM @ 30V. However I am struggling to find any motors locally that even come close to these ratings. The best I could find for an option under $100NZD is a motor that has a speed of 3500RPM @ 24V. However These are the only ratings I could find on the motor as it did not specify power or current so am unsure if this could actually work. There were a few other motors with ratings around the 3000RPM mark and 24V-48V however most of these are around $150 - $270NZD and we have a budget of $200-$250 for all components (generator, lighting, regulator circuitry, mounting for generator and lighting.) So Basically I am wondering if these type of motors could work for low power generation? The other option is to build a PMA around the rotating shaft that is attached to the prop, it is 100mm. However I am not sure on the cost of the magnets as yet and am struggling to find helpful instructions on the net. Any help on this problem would be so greatly appreciated. Regards, Brent Wilson |
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oztules Guru  Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Try looking around Ed's site such as this little one for lighting leds. windstuffnow radial alternator ........oztules Village idiot...or... just another hack out of his depth |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
10Watts is actually quite a bit to get from a sub $100NZD generator you can buy. Most bicycle generators/alternators were about 6W and depending on where you live in NZ (Christchurch maybe?) an old Sturmy Archer hub dyno might suit your needs perfectly. But I have another idea, it just so happens that I have 9 30V tape recorder motors, about 6mm in diameter which will light 12v globes from a car tail light when turned by hand with a geared hand drill, 100rpm or so I guess. I am in beautiful sunny Wellington. (Actually, I have a lot of stuff in my garage!) |
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| mystiquesbs Newbie Joined: 09/08/2008 Location: New ZealandPosts: 10 |
Sounds interesting, I am in Auckland and the sculptures will eventually go in Wellington by the airport. Is there anyway we could possibly acquire one of those tape motors from you for testing purposes? Also where would I find a Sturmy Archer hub dynamo? Cheers for your help guys Brent |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Brent. You can find everything you need to know about the hub dynomos at this site note there is a link there to another page which has information on more modern equivalents. Old bike shops in Christchurch and Palmerston North would be the places to look for them in NZ, or anywhere you can find an old English bike. One of these tape drive motors, incidently about 60mm not 6mm diameter  , might find it way to your place if you PM me your address.
Cheers |
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| mystiquesbs Newbie Joined: 09/08/2008 Location: New ZealandPosts: 10 |
Have just PM'd you john, via email through your profile. Don't know if that's the same thing? Incidently I just wired up a 22 x 4 (22 parralels of 4 led's in series)string of ultrabright LED's they were operating at 14V and only pulling 200mA so the power was only 2.8W and there was more than enough light to illuminate the sculpture. So the bike generator may be an idea if I can find one. Also where do you find tape recorder motors? Are they out of VCR's or old floppy drives? Cheers |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
I think these tape motors came from old reel to reel tape recorders use in telephone exchanges or some such. The motors in 3.5" floppy drives are maybe good enough but if you can find a few old 5.25" drives they had bigger motors. The disk motors were (at least in the ones I have ratted) a magnetic disk spinning against a printed circuit board which carried a number of coils. You can find the ends of the coils easy enough on the PCB and even turning at finger speed I get a high intensity LED to light with just one coil in the circuit. I think the problem you will have with the bike generators will be finding enough for your project. They would be a few hundred times overkill but if you are building something substantial to spin in the Wellington breezes maybe you could use the Fisher and Paykel washing machine motors? They have a really heavy stainless steel shaft and two ball bearings and this site has all the expertise you could ever need describing how to rip a washing machine apart and make something useful (or at least interesting!). Maybe the floppy drives are best especially as there will be plenty of them around for a while yet but not forever so grab some while you can and put them under your bed, or wherever. |
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| Dinges Senior Member  Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Brent, Now that your power requirements are so much smaller than initially stated (2.8W vs. 20W) you may actually get by with a stepper motor (can be found in 5 1/4" floppy drives, old printers, scanners, etc.) These easily put out 40V+ just by handspinning them, but their current is very limited, maybe just 100mA or so. If they don't produce enough power you could even install 2 or more per turbine. The advantages: cheap(free if you know where to look), easy to acquire, easy to use (no DIY genny building needed). Power is very limited but 2-3 W may be doable. I've built a tiny genny too like that once (handcranked) and it lit up white LEDs just fine: 
Definitely have a look at this story by Gizmo too: http://www.thebackshed.com/Windmill/assemblyMini1.asp |
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| mystiquesbs Newbie Joined: 09/08/2008 Location: New ZealandPosts: 10 |
Sweet, inorganics is on at the moment and I just went and ravaged a few printers. I managed to score 3 stepper motors (look like yours dinges) and will definitely go back for more in the next couple of days. No one seems to want printers  not like they want washing machines 
I will test them out and let you guy's know how it turn's out. Thanks for your advice so far guy's it has been really appreciated. Cheers, Brent |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Heh. Just don't do as I did the first time and hold the wires to your tongue while you give the shaft a quick turn. Nearly bit my tongue off at the time... Didn't you see this page by Gizmo in the link I gave you ? http://www.thebackshed.com/windmill/assemblyMini3.asp A 4-leaded stepper is shown at the top of the page. Find out with a multimeter which wires belong together (are connected to eachother), then connect a DMM to them, set to measuring AC voltage and turn the shaft. Next, you could also try setting the DMM to AC current and measure short-circuit current. Build a simple rectifier as shown in Gizmo's article, measure output voltage at your desired RPM (depends on your actual windturbine) and wire it to a string of LEDs with series resistor to limit current through the LEDs. The number of LEDs you can put in series depends on the maximum voltage of the stepper under load at the desired RPM. You'd need to experiment a little and play around to find out what works best. |
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| mystiquesbs Newbie Joined: 09/08/2008 Location: New ZealandPosts: 10 |
Yeh i edited my post as soon as I wrote that as checked out that link you gave me and was very helpfull  .
Hooked up the multimeter last night and it overloaded the volt meter when I gave it a fast spin but was putting out around 6V easy. Looks hopefull, will get some rectifiers today and see what happens. - Just tested the circuit out, works a treat. I just did one handspin and the output was 14V. When I measured the current I could get around 100mA. - I spun it once and then hooked up an LED to the output after about 10 seconds and it blew the LED  .Now we will test the outputs at various RPM's and see what max power we can get.
Thanks for all your help guy's |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Ummm, are rectifiers needed for LEDs? |
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| Robb Senior Member Joined: 01/08/2007 Location: AustraliaPosts: 221 |
Depends on the peak reverse bias voltage applyed and the specs of the reverse bias voltage the LEDs can withstand. |
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| mystiquesbs Newbie Joined: 09/08/2008 Location: New ZealandPosts: 10 |
I think they flash without rectifiers as they are diodes and only allow current through one way. But by rectifying it I can also double the voltage which is handy although this decreases the current at higher speeds. |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
It may be worthwhile to study the characteristics of LEDs as I suspect they can be 'flashed' much brighter than with a steady current but persistence of vision would show a steady bright light at most frequencies. Of course you could have half the LEDs on one half of the cycle and half on the other. Voltage doubling at rectification requires the use of capacitors in your circuit, do you want minimal circuitry something more complex? |
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| mystiquesbs Newbie Joined: 09/08/2008 Location: New ZealandPosts: 10 |
That's a nice idea having half the LED's on one cycle and the other half on the other. I will definitly have to try that out and see what happens. Circuitry is not really a problem, have hooked up the diodes to make bridge rectifiers and 2 caps to create the voltage doubler, seems to work quite nicely. But now I'm really interested in trying your idea! Will give it a go tomorrow and see what results. |
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| mystiquesbs Newbie Joined: 09/08/2008 Location: New ZealandPosts: 10 |
Well I tried a few different things and it seems that the straight AC is the way to go! Gives off more than enough light to illuminate the sculpture. I am just wondering do bigger stepper motors give a higher current? As the current we are getting at the moment is a little low. |
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