Playing with wind power
 

So it's always windy here in Tomball at my house and I have been playing with the idea of a small wind generator. The type I have been looking at are the ones that look like a cylinder cut in half and then set up so it looks like an "S" so it picks up wind in any direction. I was thinking of something small scale just tinkering. But the ones on the Net the guys are assembling the stator and magnets separately which seems like a huge waste of time to me for efficiency that probably isn't that good.

So my idea is to use a brushless motor as the power device, my question is, what Kv? I have noticed that if I short the windings together that the back emf increases the amount of torque required to turn the shaft (obviously). I have also noticed that the lower the Kv the harder it is to turn, Which makes since because there are more windings turns in a lower Kv motor allowing for a higher voltage to be generated for a given RPM. So the motor would need to have enough voltage to be able to charge the battery (probably a 12V for now), but not stall the windmill. I know that my 7700 is super easy to turn with the leads shorted. I also notice that the braking is less as my overall gear ratio decreases, so I have to up the braking force, (I understand why).

I guess first I need to figure out what RPM the thing will spin and the voltage produced at that speed. I already have a 3phase bridge rectifier from another project (Alternator welder). So what do you guys see as a problem or suggestion?

Jeff

The only problem with using RC motors is that, since they have a small diameter rotor, you need to spin them up pretty fast to get usable power from them. This could be solved easily by using a planetary GB on the motor and attaching the windmill to that shaft. Maybe even two PGB in series if possible... I would guess that you would want 8-10K rpm on the motor to produce a decent current. Good luck with your project. I want to do something like that too since there is a lot of wind in my neighborhood but town laws are very prohibitive.

A higher kv will generate more voltage for a given rpm, so I would go with that. And, I wouldn't worry about stalling the motor because charging a battery is not nearly as much load as shorting the motor leads. The battery charge current is "regulated" by the current battery voltage and any inline resistance or circuitry. And, you might have to gear up the motor because a windmill does not spin very fast and these motors will have more output at higher rpms. Maybe an outrunner would work better in direct drive?

Wasn't really thinking direct drive I was thinking 4:1 to the motor. I have a bunch of prototype parts from when I was developing a small coonveyor for our company so I have a bunch of .080" pitch belts and some 60 tooth 1/4" sheaves and belts and 15 tooth sheaves that are bored to 5mm (our motor uses a 5mm shaft too). I think the gearboxes would have too much drag, and the only ones I have are about 30:1 and another that's about 100:1.

I swear that at the same RPM the lower KV motor had a higher voltage out.

This is going to be a pretty small unit about 16" tall and about 12" in diameter. Just for testing too see what I can do just with what I have laying around.

Jeff

Keep the ideas going!

It may be easier to use an automotive alternator or generator. Just an idea.

Ya that's been done and works, you can get about 500W out of one, but since you either have to drive the field coil (the magnet in an alternator) or make a new rotor with permanent magnets it’s a little more of a pain to do (Although I have been toying with making an alternator into a brushless motor). I want to keep this small since I have deed restrictions. I get enough crap about an oil spot on my driveway.

Jeff

I'm really curious about the small sheaves and belts you speak of. I've been toying with the idea of a belt drive rather than a traditional spur/pinion. Have any links or pics?

Stock Drive is a place that carries them. They are called Timing pulleys, I guess I just use sheave for anything that uses a belt. http://www.sdp-si.com/web/html/drivesystems.htm

I can’t pull up anything on their site right now but I use a 3/8” wide .080” pitch Kevlar reinforced belt. A 15 tooth drive pulley that we bore to 5mm and a 30 tooth that comes ¼” bore and, is just under 1” in diameter we bore it to 3/8”. The belts are strong but would probably wear out fast in a RC think belts run about $6 the larger pulley runs about $15 and the smaller ones about $9. Of course that’s just a 2:1 ratio they also have plastic pulleys and ones with larger teeth (that’s usually the first thing to go). There are some others but I’ll have to check at the office.

Jeff

I thought some companies found the motors kv by finding the rpm needed for the motor to put out 1 volt. I don't remember who said that, but it was on rcm. Could take a while to find in a search, so I can't be bothered looking :whistle:

Hmm, I am sure it's the other way around a motor will spin X rpm per given volt. Generating power and producing power seems to be 2 totally different results. I'll give it another try later tonight.

Jeff

I think you got it backwards there Brian...

Oops, yeah, I may have. :oops:

Not much info here but I used amy drill to spin the motors and took the voltage of of 2 leads. I used my Fluke 112 and set it to record ACV. They are all Delta winds but I spun them both ways to make sure and this is what I got.

7700Kv .045V
6000Kv? .059V
5300Kv 30mm can .062V
4436Kv .068V

This is only about 600rpm but I don't have anything faster at the moment. I am going to start gathering parts. I think I am going to make the blades out of fiberglass for weight savings. It's called a Savonius type.

This is a pic of the type I want to make:

Based on that geometry you could just get a thin tube (in the metarial of choice) and cut it down the middle for use as the vanes.

Thats what I had planned but the closest thing I have available (and light enough) is 2.5" X .0625 wall aluminum tube. I think I need something with a diameter of around 6" a Coffee can size would be perfect but it's too short. I'll look into some of that thin wall PVC. Any other suggestions?

Jeff

Ever seen those spinning signs they have outside some shops powered by the wind, they have one word on the back (top) and another on the front (bottom); when the sign spins you see both words together.. (like 'fish & chips') etc. Stick a shaft down the middle and mate that to your motor via the belt drive or whatever you plan to use...

http://www.youtube.com/watch?v=V-PiJrD4P4M

They are shaped basically the same as the turbine you want to use, only in a single molded piece.

ametek 12v motor

this is the motor you want to try and find and use. If you really want to do it right, I mean.

You are talking about those brushed reel to reel motors they used to use back in the dawn of computers? What makes it better than a brushless motor with more powerful magnets and better winding tech? Those are usually used for larger scale windmills aren't they?

Jeff

Well direct useable 12v power that's not 3 phase like a brushless


very low rpm to achieve 12v.

expect to get between 300-700 watts depending on swept area and wind velocity.

3rd link is a diy thing

http://www.seco.cpa.state.tx.us/re_wind_maps.htm

http://www.wind-sun.com/ForumVB/forumdisplay.php?f=13

http://www.mdpub.com/Wind_Turbine/

Creating DC from 3 phase power is easy and I don't have to add anymore diodes (to keep from backfeeding the motor) because a 3 phase bridge rectifier already has them built in. I am only looking for about 100-150W this is just testing an idea. I am only dealing with something that is going to be about 16" tall and 12" in diameter. As I recall those Amteks (they have them at the old school electronics parts store around the street) and they are about 6" in diameter and about 10" long. They have a few other sizes as well.

I am looking to produce about 16V and around 8 amps to which would give me about 115W to start off with, and I shouldn't need a regulator to keep the voltage down.

That Last site I have seen before and read with great interest, low tech is good but No body is dealing with these brushless motors. I may pick up an outrunner once I see what kind of V/rpm I can get out of those.

Jeff

Good luck, keep the thread running.


Can you post the part and data sheet of the bridge rectifier you are using.

The bridge rectifier I thought I might use may be overkill for this application but I had 2 of them. :rofl: One is on the Weldernator and the other is setting in a junk box. Actually at this power level I will just use 6-10 amp diodes or maybe one of the rectifier modules I took out of the Alternators I modified (that’s what they are after all).

If you look at the schem you will see how it's done. Basically you have 6 diodes they are all facing the same direction and are paired so that the anode and cathode are connected together. Then all the anodes (this is your negative terminal) that are left are connected together and all the remaining cathodes (this is your Positive terminal) are connected together. Each winding of the motor goes to the anode/cathode junction. And there you have it presto change-O, DC from 3phase AC. Real easy like.

Just as I am sitting here I remembered we have a sheet metal brake and bender at work I think I can make some nice blades out of 1/16” aluminum. Hmmm.

Jeff

Well I scrounged aup a few parts. I had an old motor laying around, it's a NEMA 17 that the control baord went out the gear on the back is actually the incoder gear (it basically has a tape head as the pickup), and a bunch of prototype parts when we originally developed our small conveyor. The SST thing with the pulley was a jackshaft for the first system I have 2 of these and they each have 2 1.4" ID 3/4" Od bearings in them I may use them as the top and bottom of the assembly. The motor will generate about 12.5V at about 600 RPM on 2 of the phases I need to do a little more reasearch on the way it's wound. I had 2 wires that I could get 12.5V and only about 2.3 on another pair. like I said i'll check into it, (its a stepper motor). I am going to remove the 3.. screws and add longer 4-40 screws all the way through so that I have 1/2" long 4-40 screws. (we do a lot of mods to these motors to make them water resistant. The other gears I can get anywhere from 1:1 to 4:1 in a single overdrive. I'll show the guts later when I take more pics.

I also bought 6" diameter stove pipe that I will cut in half it's perfect at 24" tall and I think will work fine, I may need to add some support since it's only .030" thick.

Jeff
Jeff