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Forum Index : Windmills : Ideas on how to speed up a motor?
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mahela007 Newbie  Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
Hello.. i finally built a windmill. (its just a small proect, nothing too serious). The blades catch plenty of wind. The problem is I have hooked the blade up to a relatively small motor. ( a stepper motor from a printer). The blade radius is about 1 foot and 4 inches. As you can imagine the blades kind of limit the RPM of the motor. What can i do to speed up the rpm? I was thinking of gearing but I'm still not sure. If anyone else has any suggestion your help will be greatly appreciated. how come its not very windy where i live??? |
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| adric22 Regular Member  Joined: 06/08/2008 Location: United StatesPosts: 47 |
Just out of curiosity.. What kind of voltage are you getting from that setup? |
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hmmm... maybe flatten the pitch of the blades. I am not enthused about gearing up the motor in any way as the mechanical losses are too much of a challenge. If your quest for more speed is really a quest for higher voltage there may be ways of changing the connection on the stepper to get higher voltages. |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
yes I do want higher voltage. as it is I am only getting 0.7 volts. I only want to power a single LED so i need to get it upto about 1.7. how come its not very windy where i live??? |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
do you know how I could change the connection? I have the same kind of motor that had been used on the minimill. It has four wires comming out of it how come its not very windy where i live??? |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
0.7 volts is very low, do you get the same voltage from both pairs? |
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| Dinges Senior Member  Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
A stepper motor should have absolutely no problem lighting up a LED. Just *looking* at the shaft (let alone turning it) should be enough to light it. If you get only 0.7V out I suspect there's something wrong with your wiring, the stepper is defect, or you have the DMM set to the DC-range instead of AC, or... A picture of your setup and a detailed photo of the stepper and its nameplate and a scribbled schematic would be useful. Edit: are you sure you've connected the right wires of the stepper ? There are 2 coils in there, if you take a wire from one coil and one from another coil it won't work; both wires need to be of the same coil. |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
I dont think the motor is broken. However i did find out that the votage is 1.2v I had connected a rectifier diode and that reduced the voltage be 0.5 volts. Is that still low for a stepper motor? how come its not very windy where i live??? |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
sorry for my late repies guys... hear are some picures of my motor .. I got it out of a cannon BJC-256sp printer which broke down. 
for more photos please go to the link at the bottom of this post(they were too large to post in this forum). I captured all the labelling and text on the outside of the motor in these photos. dinges: "are you sure you've connected the right wires of the stepper?". yes i think so. One way of connecting them didnt work at all so I tried the other way and I got the tiniest amount of light out of the LED. I think the motor should give me more energy than this. The RPM is approximately 252.http://flickr.com/photos/9937638@N02/ how come its not very windy where i live??? |
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piercy007 Newbie Joined: 27/06/2008 Location: United KingdomPosts: 28 |
Just for referance this is a great article on hoe to identify the correct wires from a stepper motor Stepper Motor. I have tried a couple like this - 2 have had all the cables snappped and the third (the one I bought fom ebay) does not produce a single item of voltage!  My middle name is luck mind you my first is bad! |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
so what did you do in the end? did you buy a new motor? how come its not very windy where i live??? |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Ok, those pictures help some (mostly to verify that what you have is *really* a stepper in the first place). Run these tests: 1) short all the wires of the stepper motor together; does it become harder to spin ? (it should, as the generator now becomes loaded) 2) remove the rectifier bridge; measure with a digitial multimeter (DMM) set to AC-range (20-200V) what the output voltage is when you give it a spin. 3) wire a LED straight to the output wires of the stepper motor and give it a spin. First use a slow spin, progressively faster if the LED doesn't light up. If you're using all your might turning the shaft and it still doesn't light... then either the LED is broken, the stepper motor is or it's simply not useful for this application. The steppers I've played with put out plenty of volts (but only at very limited current, hence limited power). The first time I found this out was before I found these online websites on windgennies and was messing around by myself. Was testing a lot of motors using the tongue-test (didn't have a DMM within reach). Most DC motors needed a lot of RPM to barely make you feel a tingle on the tongue. So when I tested the first stepper this way I had a slight surprize, to the point I nearly bit off my tongue due to the high voltage. Just the other day I had 2 more steppers from an old printer; one put out 7.5V @ 300 RPM. It had no trouble lighting up a white LED (at approx. 3.5V) No worries, we'll get your problem sorted out. Run the above 3 tests and we'll know a lot more. |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
test one: It didn't become A LOT harder to spin but there was definitely increased rersistance. The best way to describe it is that the notches felt much more distinct.I know I didn't imagine it(lol) because I also asked my father to test it and he also said the same. test two.. Unfortunately I dont have a digital multimeter. I broke mine a couple of years back. :-) and i didnt want one uptill now. I also didnt yet make a rectifier bridge. Just a single rectifier diode of model 1N4001. test 3 The LED definitely ligts up ,quite brightly infact but it takes one heck of a spin. I'd say at about 2-3 revolutions per second. (which translates to 120-180 RPM) how come its not very windy where i live??? |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
1) very well observed, I considered editing my reply to say that sometimes the difference between loaded and unloaded torque in steppers can be pretty small. And that actually tells you quite a bit about the suitability of a motor as a genny: if the generator turns very easily with open outputs, but becomes hard to turn with shorted outputs, then that's good. It means the generator has a low resistance, which makes it better than one with a high resistance. 2)If you don't own a multimeter, then how do you know your voltages, e.g. the 0.7V you've stated earlier in your post ? 3) Good, the LED lights up. I consider 120-180 RPM not to be a very high, I expect the PVC blades should easily spin it at 120-180 RPM. Did you have a look at Gizmo's project story ? Probably your stepper isn't very well suited for this application. If it came out of a printer, there should be a 2nd stepper in there. Maybe give that one a test as well, with a bit of luck it's better. If not, there are ways to wire it up without the external rectifier that would still make it work. The external rectifier in this case drops quite a bit of voltage (~1.5V). Normally this isn't much of a problem but in your case, with such low output voltages, there's nearly nothing left at the output of the rectifier (or diode, in your case). So we'll have to try to get rid of the rectifier. I'd say, give the other stepper a test. If it doesn't perform better we'll have to make do with what you have now. 180 RPM should be an achievable goal with those PVC blades, and I'm sure we can get a few LEDs to light even without a rectifier  .
Edit: Are you sure the diodes were installed correctly, i.e. correct polarity ? Try swapping the LED leads and see if that works better. If the LED was wired incorrectly (50% chance) it couldn't work. |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Dinges and Mahela007, blades of about .8m should be doing 5-600rpm at 10mph.(10watts) If they are not getting up there, the blades may be running in stall, and not getting going. I can't help with how a PVC blade behaves (because I have not used them), but it is a possibility, as I find it hard to think you can hand spin at maybe 300 rpm and it works, and the blade should be doing a lot more and it doesn't work as well. perhaps the blades look faster than they are running (in stall). ..............oztules Village idiot...or... just another hack out of his depth |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
I cant spin the thing with the blades attached. What i meant was that I spun the motor after disconnecting the blades. My blades are about 0.4m long. However what you (OZTULES) say might be correct. I didnt know the exact dimenstion for blades of this length. If anyone knows how to calculate the dimensions pls post them. I read somewhere that the tip width should be about 20% of the width of the base. Thats how I made my blades. But for now I would like to concentrate on the motor how come its not very windy where i live??? |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Blade calculator you will find here: blade calculator If it is not doing 4-600 rpm in a 10mph wind, then the motor is stalling your blades. If it is doing 4-600 rpm, and your voltage is no good, then you have problems with the genny. ...........oztules Village idiot...or... just another hack out of his depth |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
I had a voltmeter I got for a science project. I used that to measure the voltage. Of course I had to use the rectifier diode so I added the 0.5 volts dropped by the diode to the final output. I also checked that the LED is wire correctly. Thanks for the blade calculator OZTULES how come its not very windy where i live??? |
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| mahela007 Newbie Joined: 06/07/2008 Location: Sri LankaPosts: 29 |
What kind of motors would you guys use if you were to make a windmill? (assuming you made something about the same size as mine) how come its not very windy where i live??? |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
In any toy project where no energy storage was involved, I would only use a DC brush motor as a generator. There are plenty in the 1-5W power range. These could come from junked video or tape plyers. Just connect up the led with a series resistor and place across the motor. The direction of blade rotation determins which way to connect the led. At the low power and voltage levels, it is pointless to add diodes and have to spin faster than needed. In an AC output machine, I would use 2 LED's back to back and a resistor across only 1 winding. No need to complicate with more phases. try the tape load motor on a VCR. Gordon. become more energy aware |
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