Large vs. Small Motors for Generating

[bwprototyping]

Hi All,

I'm new here, hoping to start getting my first project up here soon. What drove me to start investigating wind power was the vast amount of misinformation online about small scale wind, along with a lot of nay-sayers that claim it can't be feasible. Seems to remind me of something else that was once deemed impossible.... (*cough cough* Tesla). I think this technology is in need of some disruption so people stop wondering why their "1kW Generic Scamming Internet Company" Turbine is only reaches 150W

ANYWAYS, what I really wanted to bring up was the topic of motor size. Everything is sized based on these large winding, heavy, low KV generators with low operating speeds to match the capabilities of turbines at safe speeds. This is great and the direct coupling between the turbine and generator is wonderful for negating mechanical losses, but I would like to investigate small, high RPM motors with reductions.

In basically all EV applications (racing and otherwise), they use small high speed, high voltage motors with planetary reductions. These motors work over a large range (entire operating speed range of vehicle) and are very efficient. I think that this ideology could (or maybe should?) be adopted for wind turbine generators as well.

Thoughts?

[DamonHD]

Welcome to Fieldlines!

One big issue with small wind is that urban areas are bad places for wind power generally, whatever your technology selection, due to poor wind conditions.

But I'll shut up and let some people who know what they are talking about join in!

Rgds

Damon

[makenzie71]

Turbines can only produce so much power per copper coil and magnet...that's why the ones that go up are big and heavy for what they produce.  There are actually quite a few high rpm generators out there that are run with gearboxes...they're all giant megawatt machines, but it's added complexity for no gain.  You can make your generator capable of producing all the watts in the world but you're still only going to get what the wind gives you.

[Mary B]

There have been a few geared up designs here, Chris Olson(I think...) and his chain drive with oil bath case that took him 2 years to complete due to the machining needed. There have been others but that is the only one I can think of offhand. There are drive losses that add up fast, especially in low wind areas... I though about one and I have a very good wind location but the losses are just to high to get an extra 200-300 watts into the battery bank. Simpler and cheaper to go with an F&P motor that only needs the stator rewired to star then build the machine around it.

[DanG]

There is a leap in engineering between transportation/appliance devices and doing RE wind man'f specifications... its a rare over-the-counter device that can survive, a HD trailer stub axle & attached rotor plates etc. might seem "higher-tech" after 2000 hours in service compared to combating moisture intrusion in a conversion motor blah blah blah... Sure there are Stainless washdown motors but try finding one for less than $$$$'s...

With wind power maybe look at it as constant duty, a nearly infinite duty cycle - no 30 minutes on and 10 minutes off blah blah. And storms, gusts & turbulence will twerk even the stoutest of hardware. To find the planetary reduction set beefy enough, not purpose built for something more delicate, that is scaled to a hobbyist turbine output, umnn - well, it would take deep pockets.

Example - the car I have parked outside is ten years old and 69000 miles on it, the computer will tell you its been started 6100 times... at 45mph that 69000 miles is 1535 hours run time out of 88000 lifetime hours.  For a wind turbine that would be less than three months in service...

[bwprototyping]

Good point, getting something purpose built might be pretty cost prohibitive.. and finding a planetary that just happens to have the right sized gears would be quite a fluke

I'll be sure to check out the geared designs to see how they perform.

I've been looking into it a little more, and I noticed this relationship on engineering toolbox (love that site).



This curve would suggest that if your torque requirements aren't proportional to power, then higher speeds would give more bang for your buck. Although there weren't many extra details provided with it and having a curve like this for just 'Electric Motors' in general seems a bit iffy..

I think the key point that makes the smaller high speed motors seem favorable to me is that the torque required for generating power decreases as your operating speed increases. So lightweighting all of those rotating components with a really high speed, low torque motor should allow you to reach and maintain an optimum operating speed at a large range of wind speeds. I'd just have to think of a way to make it all absolutely bulletproof as DanG mentioned....

[makenzie71]

The wind can still only provide so much torque.  You can use a small, high rpm generator with a transmission and a big wheel and produce 500w, or you can use a big, low rpm generator with a big wheel to produce 500w.

[bwprototyping]

Yes, but if the small generator can start producing that 500W at a lower wind speed, that sounds like a pretty good advantage!

[makenzie71]

Unless you're using a larger wheel, no it really can't.  Energy doesn't let you get something for nothing...it's not really fond of letting you get a little more for a little less.  A given amount of wind can only give you so much power.  If you could get the same wattage per swept area at a lower wind speed this way everyone would be doing it.

[bwprototyping]

I'm talking about increasing efficiency, not breaking the laws of thermodynamics 

I may be way behind the wind power learning curve here... if there are any good threads comparing the motors, send them my way! I love experimenting though so I'll probably just give er a try once I have so more free time!

[bigrockcandymountain]

There was a 20' awhile ago, based on an induction motor i think 7.5hp with a 5:1 planetary reduction.  It was called prairie turbines inc.  They are gone now and their website is down. 

For small wind, i would say the bigger the better for a motor conversion.  I have a monster for what it produces and am very happy with the efficiency.  It is a 1200rpm 5hp 3 phase induction motor converted to permanent magnets.

It weighs about 150lbs and is swinging a 13' prop powering my house and computer to write this. 

I have no experience directly with gearing.  It works too, but the added complexity doesn't seem to pay back on small wind.

What scale are you thinking of building? What will you do with the power? We very much encourage building for experiments here.  So go ahead and try it, even if we say it is a bad idea

[kitestrings]

I think this is the Chris Olsen build that Mary described:
https://www.fieldlines.com/index.php/topic,146180.0.html

I believe one of the reasons he went in this direction was that he was using Ferrite magnets instead of NdFebs due to the corrosion issues with the latter.  The trade off I assume is that with the less powerful magnets, you have to spin them up faster to get the same result.

I also noted this discussion:
https://www.fieldlines.com/index.php/topic,147484.msg1020026.html#msg1020026

[bwprototyping]

Those are great links kite, there are a ton of cool builds on here!

Bigrock, I want to start small (very small - ~100-200W) to help me get a good understanding of it all first, and then look at scaling up. Current plans are just to look at battery charging, most likely with an mppt to help out with possible less-than-ideal generator choices at the start haha

[Mary B]

Email http://www.randysworkshop.net/products.html he has a sale on for the F&P(and that sire has some good info on using it!) another mention are the GE ECM DC motors form furnaces... they are a PM motor and produce a decent amount of power at lower RPM with some rewiring of the phases.

[Bruce S]

Those GE ECM motors are 3-phase and have a around a 54V out put while driving it with a DeWalt drill and max speed .
 No current (wattage) data at this time.
I now have a few I'm hoping to get ground level VAWT going. I know, I know ground level and VAWTs .
I'm in the city (have to be for job) and of course cannot put up a 'mill anywhere. VAWTs are considered "lawn art" .

Cheers
Bruce S