I'm with Norm for the first guess, something kind of wide at the root.
The 20" fan blades I have do pretty well for torque compared to many others.
Been thinking about buying a new one, rewind with microwave wire, but all the rest the same, with 4 magnets, and 3 coil pairs.
G-[ Parent ]
Now if I could just get "a bit" more oomph out of the rotor I think I'd have this problem of mine solved. Do three blade rotors provide more "oomph" in the startup department?
And BTW.......I did get just a mite scarey holding the genny in my hand with the blades spinning fast enough that they looked like a blurr........
Later today I'm going to build a cap with a bolt welded on the end for a piece of one inch thin wall electrical conduit so the bottom point on the arc of the blade is a few feet over my head for further testing.
Hopefully some pics will show up below......
[ Parent ]
If I can get either this prop or a three blade of similiar design to work to my satisfaction, I'm planning on finishing the blades with "monocote" which folks use to skin balsa airplanes......[ Parent ]
Yes. 3 or 4 blades start easier. I think I would go with 4 blades but not that long. A steeper angle starts easier too. More blades or a steeper angle will reduce the RPM or TSR. I don't know much about blades :/
I wouldn't trust 1" thin wall very long or very high for something that big around.
Don't forget to put 3 or 4 drops of light oil in the bushing pads.
What angle are the blades mounted?
I used an extremely scientific method to design the angle.....using two one by twos for a hub, I cut an angle on each that was just less than a quarter inch deep on both two create an angled slot just less than a quarter inch deep when sandwiched together.....whatever that angle is....it's one quarter inch of drop over a two inch span.
With the "hub" the rotor measures about 4 feet 6 inches, and once started the thing will continue to spin with just a breathe of breeze, and so far off my multimeter I've gotten readings of 15.6 volts on the DC side of my bridge rectifier.
And if thing'll go a "lot, LOT" faster I'm thinking I better use more than thin wire nails to hold it all together.....oh well....I bought a bandful of 10-24 bolts and nuts for the rotor anyways...and I better put in a setscrew or two rather than just a "poosh" fit to hold the rotor on the shaft..... [ Parent ]
Rather than what I expected, when I stood my ten foot thinwall conduit tower/pole up with the genny on it, the thing turned into the wind and the rotor started turning. All I could do was grin like an idiot*L* Probably had 15 mile an hour gusts today and I was getting readings 15.4-15.6 volts DC.
After that I tore it apart and painted everything, tomorrow, if it's windy enough I'll put it back together and see if I can get "she who thinks I'm crazy for building a windmill" to snap a pic or two....
Yup....today was a VERY good day grin[ Parent ]
How easy did it start? If it started very or quite easy, you may want to take off a couple more inches to get some more RPMs. (its not like me to tell someone to cut up something that all ready works) Maybe 2" at a time if there is no apparent difference in the diffuculty in start-up, then stop at the first sign it starts harder.
But the low voltage reading could say it needs more RPMs. You were getting 32VAC spinning the 20" fan blade by hand, so it should be getting 40 or 50VDC open circuit without much trouble in the wind. It sounds like the blade is too slow. (I'll point out again that I'm not the guy to ask about blades)
My belief, which may not be based on fact. On a day with some wind power, a gust should get it started turning, then it will keep turning a lot easier. And the faster blades will get more power at a lower wind speed after the gust gets it turning past the cogging of course. I never flew anything that cogs magneticly like I'm sure that does.
""the thing turned into the wind"". Did you get a tail on it?
With single phase, does it vibrate like a cat with its tounge in a 220 socket? It might when a battery is connected.
The bridges are high voltage I hope. Like 100 or 200V. If the thing gets turning fast, without a charging battery to take the power, the volts can rise very fast and maybe pop the bridges. I mean, when the blades are right and it really gets spinning, it can just take off spinning much faster than you imagined, the volts can go up a lot faster than many people expect. And it can shock the s*^t out of you too, which only seems to happen when my neighbors are watching. ("Hey everybody! Come watch! That goofy guy with the fan shocked himself again!")
How much pressure did it put on the mast? However you can explain it.
And yes I did put a tail on it....I C-clamped a 2x2 foot piece of 1/4 birch plywood to the angle iron that I'm using for a "body". Tomorrow the new "tail" cut from the old one(just trimmed some off to give it a better shape) gets bolted on....But it gets bolted on about 8 inches further back to give a tail a bit more leverage for steering As of right now the alternator is offset 4 inches from the center of the tail so I can add a side furling tail later.
And yes it did push against my "tower/pole" but it wasn't hard to hold or anything. Needless to say I duct taped my multimeter to my pole so I could use two hands to hold the pole
And after building my new swastika hub, I think I might have done something good rather than bad as the something seems to have either added a flywheel effect of sorts or lowered wind drag caused by the old 2 inch thick wooden hub (X shaped) and it seemed to start easilly, and it keeps spinning at a lower windspeed than before. Whatever I did it starts a lot easier....it still cogs though
The one thing I did do wrong was I gave no thought to the balance of the entire unit and it's tail heavy. Maybe phase two, the furling mechanism will use a piece of square aluminum tubing to lower the weight on the tail
The bridge is rated at 200 volts......I used heat sink paste and drilled and tapped a CPU heat sink and mounted it to that...
And I've never seen a cat with it's tongue in a 220 socket*L*[ Parent ]
Please.....I'm not very knowledgable in this field,.....don't tell me it'll stall or some other technical term that I don't know about yet. Tell me what the physical manifestation will be and what sort behaviour it'll display, so that I can "see" it going on if the blade isn't very well behaved....[ Parent ]
They have to be just long enogh, but not too long!
Seriously, you are surely asking the wrong guy. I think I can tell you some physical manifestations, but I have very little understanding of how some guys can say "Use a 4.3' dia with a TSR of 6.2" and be right on. It just never works out for me.
OK. The blind leading the blind. Here goes.
With the same TSR (Tip Speed Ratio) A long blade will start easier than a short blade. The trade off is the long blade turns at a slower RPM than the short blade.
Real example... I have a stepper motor I had high hopes for. Put on a longer set of Zub-Woofer PVC blades, because they happened to be on the hub that fit the shaft. Startup was no problem, but even in a good wind the RPMs were not fast enough to get up to charging voltage. So I put on a shorter set and they worked great. So I put on an even shorter set, but they were to short to get really started, because of the cogging.
And when they did get started, the RPMs were high enough to reach cut-in BEFORE there was enough power in the wind to make what the generator wanted to make. So they wanted to turn faster, but the power to the battery was more than the power in the wind, so it almost acts like electric brakes. That is my understanding of one kind of stalling.
The other kind of stalling is when the first blade to pass a spot leaves a large wake of turblence behind it, and it interferes with the next blade. At a certain RPM, the thing just can't go any faster because the air is swirling every which way, one blade to the next, keeping the blades from working like they were designed. High TSR and lots of blades do this kind.
The standard 6 magnet 6 coil box fan conversion's BIG problem is the cogging is huge. To overcome the cogging, it takes a big slow blade, but then the big blade has a low RPM, so it takes a LOT of wind to reach RPMs for charging voltage. So it ends up being a blade that should make 1000 watts (and tower and related strong enough to handle 1000W of wind) all for a generator that only can make 50 watts. Jerry's garbo-gen with 4'dia "Jerry Blades" makes what, like 1000 or 2000 watts?
I'm sure most people feel, by the time you have the big blades, strong tower, etc, needed to overcome the cogging, you may as well have something that makes some 'real' power.
That's why I thought I'd try it this way. Keeps everything small, cheap or even free, and easy. It just worked much better than I expected !
(I have 20 failures for every success. No kidding. But I always do stuff that is kind of strange, and always small. Bigger is easier. Proven designs are easier. I wonder if this is a proven design? But I find this strange stuff much more gooder funnlier, and fun is the only reason I do it anyway. Hardly a place for a 20" windmill where I live anyway.)
I'll post a bad news (rust) here too. G-[ Parent ]
A little diameter counts for a lot of power. If I recall corectly, the center 1/3 is only 10% of the power.
Laser Cut? I have a hacksaw. And it is not even a good one! The factory put the teeth on the blade facing the wrong way. G-[ Parent ]
Oh and by the way.....did you notice how nicely these motors fit inside a 3 pound coffee can?........you know.....the kind with the resealable plastic lid*grin*[ Parent ]
Ya they sell anything these days. I was putting in a new floor and the store sold me ceiling nails instead of flooring nails. Both boxes had the points on top and heads down :)
Have fun on the trip if you read this before you go, OR, I hope you had fun on the trip if you read this after you get back :). nothing to lose
Spelin and tpying are my strong points, not electronics.[ Parent ]
