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Forum Index : Windmills : Can I rewind this one?
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| adric22 Regular Member  Joined: 06/08/2008 Location: United StatesPosts: 47 |
This motor came from a 24V electric scooter. I took it apart to see what was inside. 
If I spin the motor at approx 200 rpm, I get about 2V out of it. If I use the chain-drive mechanism that comes with it at the same speed I can get about 5 volts out of it. So it definitely needs something to get the voltage up higher. Any suggestions? I only want to generate maybe 10 watts of power. |
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martinjsto Senior Member  Joined: 09/10/2007 Location: AustraliaPosts: 149 |
probably could rewire it as it looks like a 3 phase star. maybe just changing the magnets to neo's will be enough for 10 watts, there is a lot of posts about these type of motors or similar ones. the bushes can be quite troublesome as they create drag/resistance can you get a hold of an F&P motor? there a lot easier and you will get better results with them. martin free power for all McAlinden WA |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
I've opened up my MY1018 motor (24V scooter motor, 250W, 2750 RPM, 14A) a few days ago after your previous question. Turned out mine has a burned winding, after a magnet came off. I reglued the magnet about 2 years ago but the motor *needs* a rewind to be usable again. I've considered doing something else to it, turning it into an 'outrunner', where the rotor (the part you're holding in your hand) would become stationary and a new permanent-magnet (PM) rotor with neos would rotate. However, I've decided not to: the rotor has 16 teeth, so it 's practically impossible to rewind to 3-phase. But I digress. Back to your question: Yes, you can rewind. 10W is a very reasonable amount of power, considering that your motor was originally rated at 250-300 W. First, you have to decide on a cut-in speed; the speed (RPM) at which your generator should start charging the battery. You don't want it too high (as you don't want your genny to only work in a hurricane) and you don't want the cut-in speed to be too low, as that may 'stall' the blades. To muddle the waters a bit more, cut-in RPM is also related to windspeed, blade diameter and TSR (tip-speed ratio). Let's assume you will build a blade with about 0.7-1 m diameter, that you want to charge a 12V battery and that you want cut-in to happen at 300 RPM (somebody, if my figures are off please correct me.) The motor as-is now yields 2V at 200 RPM. We want 12.5V (the voltage at which the genny should 'cut-in', i.e. start charging) at 300 RPM. Current volts/RPM is 2/200=0.01 V/RPM Desired volts/RPM is 12.5/300 = 0.042 V/RPM So in the new situation your rotor will need 0.042/0.01 = 4.2 times as many turns than it has now. Next thing to do: unwind the rotor, carefully making notes of which coil is connected to which commutator bar. Make as many notes of every detail as you can, with drawings/sketches. Make some pictures too, you'll thank yourself later when you want to check your work. Unwind the rotor and count the amount of turns per slot. Save the epoxy 'strips' that close off the rotorslots, you will need to install them again after the rewind is finished. Then, measure wire diameter (in my motor it was 0.6 mm, including enamel); yours may be slightly different. You will be putting 4.2 times as many turns in there, so to make all that extra wire fit you will need to use thinner wire. The diameter should be roughly half (square-root of 4.2 =~2), so about 0.3 mm (including enamel), perhaps 0.25 mm even to make sure it all fits. Then, rewind, using the notes you've made. I've never actually done this myself to such a motor. Definitely read the links to Fungus' rewind attempt I gave in a previous reply. After the rewinding the rotor will need to be 'varnished' in motor varnish or epoxy, to make sure the wires won't vibrate and damage their insulation during use. This step is as important as the actual rewinding. This video gives an idea as to how much movement there can be on those windings: http://www.youtube.com/watch?v=lPNU2vniUIc&feature=related Rewinding isn't rocket science, it's not hard to do, just a lot of work. Pay attention to detail, don't rush it, and after a few hours you should end up with a rotor with the desired voltage/RPM characteristics. As stated in your previous thread, the issue with the brushes and the small bearings (I re-checked, definitely 608 ones in mine) remains. However, that has nothing to do with the technical feasability of rewinding. I'd give it a go if I were you. In fact, I may just rewind my motor myself when I'm bored enough someday. 
Hmmm... I still have a reel of 0.25 mm wire.... and it would also make a nice genny for an exercise bike, now I come to think of it... Shame on you for giving me these ideas that lead to new projects! |
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| adric22 Regular Member Joined: 06/08/2008 Location: United StatesPosts: 47 |
Funny you should mention it. I was sort of thinking along those lines. If I couldn't make this motor work for a wind generator, then I bet it would work for an exercise bike because I could gear it to the desired RPM. I'm thinking if I use the original chain-drive that came with this thing, and put the turbines on the larger gear, then the bearings in this motor would not endure any more punishment than they were designed to take in the scooter itself. Plus the chain would give me even more RPMs. So I'm thinking I could rewind this thing in a way that would still be spun around 1,000 RPM but give me 12.5 volts. |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
LOL. Yep, great minds think alike. Except I don't have need for yet another bicycle genny...  http://www.anotherpower.com/gallery/exercise-bike-generator. This one's now gathering dust in the attic.
Most people resort to gearing their windturbines due to lack of a generator with suitable characteristics for a windturbine. Gearing up is fraught with all kinds of difficulties in building it and maintaining it. There's wear (did you know a bicycle chain doesn't last much more than 2000-3000 km ? And the chains on those scooters are even smaller than plain dérailleur chains for bicycles...). Since you will be doing a rewind anyway, why not rewind it in such a way that you don't need any gearing at all? (ok Oztules, I know, I know... if he geared up he could use less turns of thicker wire so less copper losses.  ). Personally I wouldn't use gearing for the above reasons. But if the downsides are acceptable to you...
Edit: a bit of back-of-the-enveloppe calculations. Assume the chain will last 20.000 km (as it's not as heavily loaded in a windturbine as a cyclist does). My 27" wheels have a circumference of 2,15 m.; 20.000.000m/2,15 m = 9.3 mln revolutions before the chain is worn out. Now, if your genny turns at, say, 400 RPM, it would last 9.3 mln/400 = 23.000 minutes = 388 hours = 16.1 days. The chain would last 16.1 days of continuous use at 400 RPM, under the given assumptions. That's also assuming you keep the chain squeeky clean and greased . |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Just an idea... If you decide to go for an exercise bike generator instead, you may have a look at a 'roller track', a training tool for bicyclists. Could install your motor/genny to one of the rolls. You could probably use the motor as is: http://www.off-duty.be/item.php?id=3&itemid=213 at 25 km/hr (cruising bike speed) and 2.15 m wheel circumference, there are 11.628 revolutions per hour; that's 194 RPM. The rolls have a diameter of 0.11 m, i.e. a circumference of 0.35 m; my 27" wheel is 2.15 m circumference, so for every revolution of the rear wheel the roll would turn 2.15/0.35 = 6 turns. So, 194 * 6 = 1200 RPM. That's pretty close to your 12V cut-in speed (2V @ 200 RPM; 12V @ 1200 RPM). No need for rewinding. Build a little stand to mount the bike on with suitably sized rolls and you'd be ready to go. Can even use your normal everyday bicycle that way, and use its gearing to shift to a comfortable speed/load. |
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| adric22 Regular Member Joined: 06/08/2008 Location: United StatesPosts: 47 |
There is just no way to win on this wind turbine stuff, is there? Everything costs a fortune one way or another. Oh.. for whoever asked about why I don't use an F&P. I live in the USA and have no idea where to get one. |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
This is a DC brush motor. Each winding appears to span 3 pole fingers. There are 16 commutator segments. This has no relationship to an Alternator. As dinges has said, this could be remade to an outrunner. I see no problems with a multi phase unit. 4phase works really well on my windmill. Gordon. become more energy aware |
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