14 inch Rotors

[leesafur]

Hi,

I was wondering if 14" rotors would be better than the 12" rotors for the 2"x.5" round N45 magnets?

I made some drawing with Google sketch Up and posted them here

http://cid-4138295650274151.skydrive.live.com/browse.aspx/windmill

One of the pictures has the magnet rotor and the stator on top of each other.

I was just playing around with Google Sketch Up and thought that this setup might be better. Any thoughts on this design would great.

Thanks

Lee

[hapuna beach]

Lee,

Oztules did exactly that (14" rotors/2" round magnets), and with great results. I was impressed with the low resistance of his coils. I beleive his blades were 12' diamater, but it appears that for a small additional cost, he had superior results as compared to the "normal" 10' design. Perhaps he can chime in, but his article is here: http://www.fieldlines.com/story/2008/8/18/83321/8140

Hapuna

[hapuna beach]

Lee,

Here's a link with alot more info on it:  

http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1194&PN=6

Hapuna

[Flux]

"I was wondering if 14" rotors would be better than the 12" rotors for the 2"x.5" round N45 magnets?"

Better for what? Yes I am quite sure that 14" discs would make better use of the magnets but where you go from there is another issue.

If this is the Otherpower 10ft machine then it was designed to be a good compromise with the 12" discs. If you change to larger discs and don't change anything else the as always when you change a proven design you mess up and it will probably stall and perform badly.

If you know what you are doing and compensate for your changes with larger blades, higher cut in speed or with line resistance added you may be able to get higher power out safely. Unless you make changes to compensate you will most likely increase the wind speed needed for the same output and if you keep the same wire size you will get more stator heat for the same output.

I would expect that with the correct changes you could probably go up to a 12ft prop with better low wind capture and probably some increase in full power output for the same stator heating. If you keep to 10 ft then you should be able to get a higher safe output but not with the same windings.

Flux

[oztules]

I think there is much benefit to be gained by adding the extra steel.

This is a personal view only, but I think the original 10' design is elegant, but living too close to the edge. The number of machines that have failed because of poor furling on the 12" disks with the rectangular magnets, leads me to think it is too iffy to be reliable in the hands of novice flyers.

Much has been written about how to stop the overheating in the stators. It is simple... get the furling correct.

This stops the problem, but most seem to be keen to get those few extra elusive watts, and so err on the side of later furling, ignoring the fact that strong winds will catch them out sooner or later.

The move later to the 2" disks was a huge improvement, and I can't recall seeing a tale of woe on 10 foot machines using these magnets and the upgraded stator. I feel sure the same proportion of people are getting the furling wrong, but the bigger magnets seem to have made the 10' design far more bullet proof.

If you move the disk size to 14" and use the n45 2" disks, then 10' will have a tough time cooking it. The amount of extra real estate released to the designer is marvelous.

Suddenly you have much more room for much thicker wire, and a few less turns. I found that you could get #13 into it where the Dans were restricted to #15... a big change in current carrying capability.... a huge safety margin.

I used a 4m prop, which pulled the safety margin back considerably, but still the resistance is so low that the stator calls the shots (or my blades are crappy), and can stop it cold in all the winds I have seen. (I'm on the 40th parallel known as the roaring forties... the bent over trees tell the story).

If your not comfortable testing coils and making decisions on cut-in, tsr, loading and prop sizing, then follow the Dan's 10 footer with the 2" disks. If your prepared to fiddle a bit, the rewards are considerable with the extra 2" of steel disk... best money you will ever spend for the returns.

Thats how I see it anyway.

............oztules

[Dave B]

 

Oztules,

  Right on the money, especially stating that there is no problem with stator burn out if the machine is set to furl properly. The design has it's limits for any size that is built. In my opinion the machine should start to furl no later than it's highest rated safe CONTINUOS output. If it only fully furls at it's highest rated safe output then it will burn up when the continuos winds blow at speeds just before furling starts. If the machine is set up for fully furling like this then it isn't "if" it will burn up but "when" ?

  It's a hard pill to swallow, we all want to believe our machines can do more than what they actually can and intermittently we get away with it. This makes it even harder to believe as for possibly long periods of time we may never know just how close burn out it has been, it only takes once.

  Too bad so many have put so much time into convincing themselves that it must be a stator design issue. Cooling holes, exposing coils, replaceable coils, different casting material and fillers etc. for the same size stator and wire may possibly help cool the stator but the real solution is either setting the furling properly to stay safely below the Max. rated output of the machine or doing as stated : have a more powerful alternator than the size of the blades could ever over power. Dave B.