Help wanted for designing a rotor for 5KW Generator

[Usman]

I have got a hold of a PM alternator that outputs 5KW at 115 rpm, originally designed for VAWT, I need help to design a suitable HAWT rotor that is effecient at that low speed.

Any input would be appreciated.

Thanks.

[Stonebrain]

ok 5kw at 115rpm,a good start.

guess you want it at windspeed v

Power is: efficiency times constant times A times third power of windspeed (P=eff*c*A*v^3)

constant depends on the unities you use.

A is the swept area of your rotor.

Now you guess the efficiency,say 0.2,you know you want 5kw at a given windspeed,so you can calculate the swept area.The swept area is a circle so you know the radius.

You want it for 115 rpm.For a known radius and a known rpm you can calculate the tipspeed(if you're clever).

Now you can compare the tipspeed to the windspeed,so you have the tsr(if you don't know what it is,do a search for it.

If you're happy with it,design a rotor for this radius and tsr.

Just put the ciphers and you're ready

Good luck

cheers,

Jaap

[vawtman]

Hi Stone

 I think the first thing that needs to be determined is if the alt is real.I'm a bit surprised that there are no pics of it.

 Mark

[Usman]

Thanks Jaap,

Great explanation. But the rotor diameter still comes out at 4.5 meters for 11m/s, as most other turbines.

The difficulty here is to imagine a rotor turning that slow, as have never seen that before. Techncially, we know that the rotor on the other 5-KW turbines are designed to cut-in (with the battery-volatge) at around 50-80 rpm, so they have enough momentum built up to prevent stalling.

In this case, I would presume that the cut-in rpm would be around 20. So, wouldn't that stall the rotor in low-moderate wind speeds?

Or am I making a mistake somewhere?

Then, if such low-rpm design was effeciently-achieveable, why no manufacturer has done it, given that such a turbine would have litterally no noise-issues, making it a perfect fit for the urban environment, for a nominal increase in the price?

Thanks.

[Usman]

Yes, you are right? I haven't got it yet, but will attempt to take a picture and post it sometime this week. But check my other posts, and investigate if there is any controversy in my comments and the pictures posted.

My entire quest on this board circles around a 5-KW battery charger. I have attempted to accomplish that in a DAWT design, VAWT design as well as conventional HAWT.

Thanks.

[dnix71]

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

here is a video of a 5KW VAWT. The presenter is cute, too. It has a monster sail, but no noise, because it turns so slow. There may be (probably are) gears in the base.

Here is a home brew with a modded car alternator:

http://www.youtube.com/watch?v=a_-nu4vm-Pg&NR=1

[Flux]

Stop dreaming, let's have some real data on this alternator. What does 5kW at 115 rpm tell us - virtually nothing.

We need to know cut in speed, resistance, efficiency or something to get an idea of its curve and it might help to know for how many seconds it will hold its 5kW rating.

"Great explanation. But the rotor diameter still comes out at 4.5 meters for 11m/s, as most other turbines.

The difficulty here is to imagine a rotor turning that slow, as have never seen that before. Technicaly, we know that the rotor on the other 5-KW turbines are designed to cut-in (with the battery-volatge) at around 50-80 rpm, so they have enough momentum built up to prevent stalling. "

You are probably not far off this sort of figure if the thing is near 50% efficient at 5kW.

At 50% efficiency you would expect a doubling in speed for threefold increase in wind speed so that would put you very close to the cut in at 50 - 80 rpm that you consider normal.

You can't hope to design anything without alternator details.

Flux

[vawtman]

How much will it cost you?

 Just because you post a story here is not considered an attempt in my opinion.All the designs could do it but no one here would have a cookie cutter recipe for you.