What air gap to use between mag plate and stator

[scallywagard]

I am wondering what is the recommended air gap between the magnet plates and the stator. I live in a high wind area. fifteen mph average, During the winter we have weekly storms that blow thirty to forty five mph for days. Every couple of months it will blow forty five to seventy five mph and some times up to one hundred and fifty mph. Things can get hot, lots of power, I am using seventy wraps of sixteen gage wire. When things get hot, is it just the coils that get hot? or the magnets also? How much will the copper coils expand in the fiberglass resin. Does any one have this problem.

[Flux]

From a mechanical point of view you need enough gap for the magnet rotor not to touch the stator. That depends on many things including the type of bearings and the rigidity of the whole generator assembly. I have got away with 1mm but with other forms of construction you may need larger,

In a very high wind area it may be wise to have 2 or even 3 mm if you overhang things on allthread with the gyroscopic forces.

For a high wind area if you are following a common design you may not be advised to use too much clearance unless you use a higher magnet grade or bigger magnets . Large gaps mean running at higher speeds away from stall and you will have to be careful to get it to furl early enough.

You say things will get hot, yes that is true but you must make sure they don't get too hot, if you can't make it furl at a safe power level it will die. It's up to you to make sure you can control it and for your wind area I personally would use far more magnet than normal, thicker wire and make sure it doesn't get too hot. If you want to use a brake switch to stop it during the worst storms then you will need lots of magnet. I wouldn't attempt anything for your extreme winds without having a reliable independent shut down mechanism but that is just my personal view. You are likely in an area beyond survival for many commercial units. If a self build machine is to stand any chance of survival you need to give it every possible chance.

I don't know how much coils expand, I have never run anything hot enough for it to be an issue but I think burn out will be more of an issue than expansion and loosing the air gap. Once the thing gets too hot and the wire deteriorates and the resin gets soft the coils will deform and that is not the same issue as expansion. Things will not run for very long at the temperatures where deformation and wire damage takes place. I know some are pushing these things to near class H temperatures ( and likely beyond at the centre of the coils). I see no prosp[ect of any reasonable life if you do this.

I personally don't think the common resins are suited to working over 100C but many are doubling it so it depends on what you consider a reasonable life. On the average site the duty cycle is probably not much over 50% but if you have winds over 100 mph it may reach 100% and that is a challenging condition.

Flux

[scallywagard]

Thank You Flux; I am in the prosses of rebuilding 2 of Eds turbines. I had about 1 mm of air gap on the first go around, and I thought I did the furling the way it was described in the directions. They didn't start to furl untill it gusts over 45 mph. I am determined to get it right this time. I am NOT trying to squeez as much power out of them as possable. I would rather have them last.

I am wraping 1, 16 awg wire, 69 times, for 24 volt. Would it be better to wrap 2, wires 34 times, This is all for the 8 inch discs. 1/2 inch stator. 3/16 pie magnets.

Is there a better way to make this work? 1/4 inch magnets, thicker wire? I ma allready going to make them furl in the lightest of wind and work up to a good weight.

                   Thank You

                    Greg

[scallywagard]

Thank You Flux; I am in the prosses of rebuilding 2 of Eds turbines. I had about 1 mm of air gap on the first go around, and I thought I did the furling the way it was described in the directions. They didn't start to furl untill it gusts over 45 mph. I am determined to get it right this time. I am NOT trying to squeez as much power out of them as possable. I would rather have them last.

I am wraping 1, 16 awg wire, 69 times, for 24 volt. Would it be better to wrap 2, wires 34 times, This is all for the 8 inch discs. 1/2 inch stator. 3/16 pie magnets.

Is there a better way to make this work? 1/4 inch magnets, thicker wire? I ma allready going to make them furl in the lightest of wind and work up to a good weight.

                   Thank You

                    Greg

[Flux]

I think Ed's little alternator is quite small and I seem to remember it is intended for about a 6ft prop. The magnets are quite thin and big increases in gap will raise the speed a great deal.

If your bearings are good then for such small discs 1mm clearance each side should be enough. I have no experience with those magnets so I can give little winding details.

Probably for a high wind area you can most likely use less turns of thicker wire and not bother about output below 10 mph, this will make it more robust in higher winds.

I would have expected you to need to start furling in the 25mph region to keep the output under control. I seem to remember Ed has a formula to calculate furling based purely on thrust. My own experience is that the prop wind seeking force introduces a big error and  reduces the effective thrust significantly. I would expect you to have to reduce the tail moment very considerably. In most low wind areas the things never furl anyway so errors pass unnoticed.

You may need increased alternator offset or reduced tail hinge angle to get it to furl safely with a reasonably robust tail.

Concentrate on furling and keeping output under control. I wouldn't expect much over 300W from a small alternator in a high wind area where the duty cycle may approach 100%

Flux

[scallywagard]

Thank You so much Flux;.....In the future I want to build a larger one that is built for The Aleutians. For now I think these will do. They were puting out 15 to 25 amps at 26+ volts in a 20-25 mph breeze with no problem. Its just the bigger stormes.

   It seems the more I learn about turbines, I find the less I know.

I will keep on learning and testing in this enviroment, I will try to keep all posted.

              Thank You to all

                Greg