Author Topic: Small Wind Generator/Motor (Read 6450 times)

SparWeb · « **Reply #33 on:** December 29, 2020, 02:05:14 AM »

Hi SR71P38,
You've struck on the need to match up the blades and the generator.

For each part, you can make a chart to visualize what they do in different wind.

Starting with the generator, plot the point where you have the rated power and speed on a chart. The chart has speed (RPM) on the bottom, power (Watts) on the vertical side. From that point draw a straight line to the 0,0 if you are using a DC motor to be a generator and a battery as the load. That line is the generator's output power line but you need the generator's input power line. Any generator needs more power to make it turn than you can get out of it. For the sake of simplicity (a bit too much) assume the generator is 50% efficient so then draw a line that takes 2x as much power as the line you first drew. That's the input power line for your generator.

Now you need a power curve for the wind. There's a common equation for working that out, so no point in my trying to write all the greek letters and exponents here. To put that on a chart you'll want to have wind speed on the horizontal axis of the curve. The wind power curve is not a straight line, it's a "cubic curve". When you get that, you have to account for the efficiency of the rotor blades. Here, you use 50% (optimistic) and in this case you get to capture only 50% of the energy in the wind.

Now you have 2 graphs that aren't quite the same. To match them up, you can use the design TSR of the blades you've made. The red ones have a TSR of about 5, the grey ones are about TSR=2. When you look up the equation for TSR, you can take points from the generator curve and work out the wind speed that corresponds to the RPM at any point you pick. That allows you to plot the generator curve on the wind power chart.

Once you have a wind power curve and generator power curve on the same chart, you can tell if they match or not. If you do the plot for both your sets of blades, you can see which ones match better. What you have described all along is a combination of rotor that does not have enough power to drive the generator at any wind speed, except at some very strong wind speed where the two lines cross and finally the rotor can spin up the generator adequately.

sr71p38 · « **Reply #34 on:** December 30, 2020, 09:42:48 AM »

SpaWeb,

Thanks for the input. I actually did this and this is one of the reasons I am really confused. With a blade length of 16" and a wind speed of 15mph I get a TPS of 1259 RPM, using a 4TSR. The graph for this motor, using the 13.8VDC curve, has a 16W (1 amp) at 1000rpm. Would be more than happy with those results!!!!

This lead to this maybe being the blades so I redesigned them and that seemed to not do anything at all. I thought it might be the way I am testing so I attached it to the car and that seemed to give me a more accurate reading, which was at 15mph I get 1.53W at 122mA. This would mean that my system is only 10% efficient. Could this be true? I know when I put it at 24V battery packs I do get more power output. It is a very simple circuit, but I get more RPM when it is wired this way.

Are there other suggested motors I can buy that folks are using that they have seen higher Watts? That is relatively small? Could it be a battery connection issue.

MattM · « **Reply #35 on:** December 30, 2020, 09:48:26 PM »

Extended blades and your gearing might make the current generator work well enough. Wider diameter increases net power. Wide roots help you start up. Wide blade roots are likewise under-appreciated as your RPMs increase.

I've only seen two of each blade in your pictures. Are you populating blades at all six positions or some subdivision of six?

MagnetJuice · « **Reply #36 on:** December 31, 2020, 12:12:19 AM »

David, I saw this little windmill on Amazon. It sells for $250.

What I noticed is that each blade is 24 inches long, the same length as what you printed.

Notice how wide the root of the blade is, that helps it to start spinning at a lower wind speed.

Maybe you can imitate that blade profile. Why re-invent the wheel.

Also, I think that I found the power curves for the genny that you are using. Is this the one?

Others can help you to figure out if that genny is a good match for your current blades.

Ed

sr71p38 · « **Reply #37 on:** December 31, 2020, 12:12:03 PM »

Yes, I am populating all 6 blades into the system and yes you found the generator I am using and the curves. I have seen the Pikasola and others like it but the one thing I haven't been able to find out is what generator they are using. I picked the windpower generator because that is what fit and I had no idea what I was doing. So open to changing the design, now.

MattM · « **Reply #38 on:** December 31, 2020, 12:44:55 PM »

If I'm understanding correctly then you have an effective 36" diameter. (And the charts are for a 48" diameter.) If your 3D printer could make you three 6" extension plugs for your blades then your available power grows considerably and closer to your expectations IMHO. With the gearing your drop in RPM is less of a concern. Even with plugs your diameter is low enough that you could easily reach 1,000 RPM without 100 MPH windspeeds. You don't really need to extend all six unless you want them to be uniform.

Then again, maybe I'm wrong about what I'm interpreting from your previous posts.

sr71p38 · « **Reply #39 on:** December 31, 2020, 02:55:15 PM »

Matt, 36" pretty darn big, my diameter from tip to tip is 16", the blades are just over 6". I was trying to get to the 1000rpm with a smaller blade and what I thought was an efficient motor since when I did the TPS for 15mph I was pretty darn close. I did a third blade design which looked just like the gray ones just with thicker root. Wasn't seeing any difference so have been just using the uniform blades. I tried to research small blades to see if others had done it but hadn't seen much on this except for folks doing a classroom experiment, which is where I might be falling down. Maybe I need to go with bigger blades and a more commonly used generator if such a thing exist.

MattM · « **Reply #40 on:** January 02, 2021, 11:46:28 PM »

Pretty tough to squeeze much out of a 16" diameter. You're already over the expectations I'd had for such a small project. Without a bigger diameter there's not much to improve.

SparWeb · « **Reply #41 on:** January 03, 2021, 12:43:21 PM »

Just use a smaller motor if you want to keep trying things with the blades you have. They look fine, but they can't really start turning against the resistance in the motor/generator you're using.

sr71p38 · « **Reply #42 on:** January 07, 2021, 02:23:16 PM »

Thanks to you both. I agree this is a very small diameter, I even added 2 inches to the blades to increase this. I guess do either of you know of a smaller motor/generator that might work? I am not looking for a lot of power output, just looking to see if I can get 1 amp on a 12-volt battery or 24-volt.

Bruce S · « **Reply #43 on:** January 07, 2021, 05:05:56 PM »

sr71p38;
look around for ECM motors ,if you know someone who has a HVAC biz, they should be able to hook you up with one.
There's are gems, small 3phase and easy to work with. All you need to do is cut the controller away , throw it in a refuse bin. It'll be the thingy with the black rubberized embedded electronics .

I had a couple still laying around, GHURD lent me one and I got hooked on playing around with them, If I find the others I'll let you know and possibly get it posted to you. BUT your best bet is a HVAC biz that'll give you a couple to work with.

Otherwise the older 9 & 18 pin impact printers have motors on them you can use as well.

hope this helps
Bruce S

MagnetJuice · « **Reply #44 on:** January 11, 2021, 12:50:59 AM »

David,

I think that this little motor could work with your small set of blades.

https://www.mpja.com/24VDC-1050-RPM-Gearhead-Motor/productinfo/32684+MD

It is a geared motor, but the RPM is high so it probably does not have too much friction starting to spin. And because the voltage is 24 volts, it would be easy to get 12 volts out of it.

Ed

SparWeb · « **Reply #45 on:** January 11, 2021, 01:41:41 AM »

The static torque of a gearmotor may be too high for this.
It's hard to tell how stiff the gearbox is to start turning.
The max torque output rating is no guide to judge it - so maybe not actually an issue.
For the cost of the motor, it's probably worth taking a chance that it won't be a problem.

sr71p38 · « **Reply #46 on:** January 12, 2021, 04:27:29 PM »

Thanks! I am going to look at these motors. I guess the thing that keeps sticking in the back of my mind is the overcoming of the motor forces when a voltage is applied. The reason is that when I apply a 24 volt vs a 12 volt I get a much higher RPM. Of course when no load has been applied the thing spins well into the 1000rpm. The 12volt requires so much more force to overcome than the 24volt yet the curve seems to imply it would be the other way to me. Could something be wrong with the batteries I am using? Or something else in the electrical.

SparWeb · « **Reply #47 on:** January 13, 2021, 12:25:14 AM »

Got a diode in there?

sr71p38 · « **Reply #48 on:** January 15, 2021, 02:59:19 PM »

Not anymore. I had 10W 10 Ohm resistor during generator testing. Right now I have the generator wired to a bridge Rectifier Diode,35A 1000V Single Phase,Full Wave 35 Amp 1000 Volt Electronic Silicon Diodes,4-Pin, from there it is direct to the battery pack, with a Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt also attached. I tried to keep it simple but I am thinking maybe to simple.

SparWeb · « **Reply #49 on:** January 15, 2021, 08:09:04 PM »

Uh, you're using what to make measurements?
Depending on how you hook up the ammeter, you could have a dead short there.

sr71p38 · « **Reply #50 on:** January 17, 2021, 02:47:54 PM »

A dead short? I am using a Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt also attached which is in the picture attached.

.

I am assuming the bridge Rectifier Diode counts as the diode and I don't need a resister or anything?

SparWeb · « **Reply #51 on:** January 19, 2021, 10:50:43 PM »

Yeah.
If you aren't passing the current through a resistor, and without the battery as the load, the shunt could be acting like a short-circuit, depending on how you connect it.

That looks like an E-bay gadget. It might not give you accurate information either. I actually have one, and I might use it someday, but I would carefully check all values with a separate meter before trusting it.

Do you have a multimeter? I can't say you absolutely have to get one, but I will say that you will make no better investment toward measuring information you can trust, if you get a quality multimeter. You can make do with cheap ones just fine, but there is added value in the better ones (eg. true RMS) that grows with you as you know more and try to do more.

I can recommend stuff if you want to do that, but don't know what to choose.

Scruff · « **Reply #52 on:** January 20, 2021, 02:14:31 AM »

Not all gearboxes are reverse drive compatible, turntable motors aren't, anything worm drive is auto-locking.

I tried small wind. Didn't do it for me. Swept area means increasing blade diameter gives exponential returns of power. I decided after the 7W peak in 7m/s Mk-3b I wouldn't do anything less than a 2.5m blade diameter after solar stopped being so much better at quiet and affordable portability.

Quote from: SparWeb on January 19, 2021, 10:50:43 PM

the shunt could be acting like a short-circuit, depending on how you connect it.

...can't everything?

Quote from: SparWeb on January 19, 2021, 10:50:43 PM

That looks like an E-bay gadget. It might not give you accurate information either. I actually have one, and I might use it someday, but I would carefully check all values with a separate meter before trusting it.

I have a box of them. It took me about 15 to believe they are nearly all bad. If it has an adjustable trimpot you usually have a hope, but I stopped buying cheapos. Not that the expensive ones aren't equally flawed in other ways. At least with the cheap ones there's no suspension of disbelief that it's a lemon.

I've a €300 meter only reads amps & amp hours, because watts & watt hours was too grown-up a concept for them to grasp. So I have to thick it up like the engineer who designed it to use it.

PS a shunt's ampacity is not a rating it's a reference. ie it's 75mV drop across the bridge at 100A load infering 150mV drop at 200A. You ought not be limited by that figure. Understanding that the author of the advertisment doesn't understand this speaks volumes to it's credibility.

sr71p38 · « **Reply #53 on:** January 20, 2021, 04:57:00 PM »

Yeah, that has been my worry about the gauge I am using, and yes I do have a multimeter. I haven't been able to get an accurate Amps reading with my multimeter, which is why I switched the gauge but I am not an EE by any sense of the word. As for the small generator, what is the MK-3b? I haven't heard of this one and didn't find it when I did a search. I am starting to believe that the generator/motors seem to be the weak link in the smaller wind generators.

SparWeb · « **Reply #54 on:** January 21, 2021, 08:31:32 PM »

They can be. You rely on their bearings for the stability of the big propeller disk, for instance. Many motors aren't actually designed to run constantly for a long time - just short bursts. Many motors are not sealed against the elements.

In your case, whatever motor you choose, a few simple measurements with a simple multimeter can define a lot before you start testing. For instance, what's the resistance between the two wires on your DC motor? That's important, it sets an upper limit that can flow for a given voltage, and that's easy to work out. You can also give it a spin and let it generate a voltage for you. Just open-circuit, not hooked up to anything. If you measure the speed and the voltage together you get a ratio of volts produced per RPM. Usually that's linear so you can extrapolate. Then go back to the resistance you measured and you can work out the maximum amps that can come out for a given speed. Voila you have a power curve, and you didn't even put the prop on it.

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Author Topic: Small Wind Generator/Motor (Read 6450 times)