Me,My Blades, & My Darned Machanical Brakes

[seanchan00]

Hi Guys,

Time to share my exasperation/experience with my wind generator. It started with a dual rotor 24 mags 9 coil alternator similar to Tim's 10 footer only I mismatched it with a set of 8.5 footer TSR 5.5 blades to begin with. That started my quest for enough power from the windgen in my area with marginal wind speed. This first set of blades was up a year ago with my added mechanical brakes activated by the tail if the wind is strong enough to furl.

The Mechanical Brake at the back of the alternator.

Here the blade is actually spinning.

So while I started making a new 11 feet blades I had a bright idea to extend the 8.5 footer to 10.5 feet.





Of course the extension with the same TSR of 5.5 resulted in too slow a TSR and I got even less power. Starts spinning at lower winds but take a very strong gust to hit cut in and only for a brief period.

Finally finished the 11 footer and raised it with renewed hope for sufficient power. However this set was too heavy at 4.5 kg each blade and although it turns easily in lower winds it seldom reach cut in.

It is spinning slowly here in fair wind.

Back to the drawing board and I decided to go all the way. Used light wt pine strips laminated to make blanks of 6 feet by 12 inches by 2.75 inch thick. I decided to make this at TSR 8.3 after feedback from Flux. Here look at it, beautiful I dare say. Notice I enlarged the tail to track the wind better.

Raised this set with great expectations in strong winds only to be stumped because it won't budge. No reason I could think of because it was spinning at ground level while we were balancing the blades. Actually had to wait for pauses in wind gusts to balance.

I just had to lower the tower to find the Bug. The CULPRIT was my mechanical brake system. The spring which normally opens it when the tail unfurls was jammed and the brake was engaged. Oiling it and several attempts failed as each time I tried to raise the tower the damn brake just stubbornly remained on. I finally found a temporary solution by inserting a small piece of wood strip tied to a nylon string between the brake pad and the steel plate. I intended to pull the wood strip loose once the tower is raised so the brake can remain open. Disaster struck on my last attempt to raise the tower. I somehow lost control and the tower came crashing down.





Sad day for me. My new set smashed to pieces.

After a week without wind power I had to reinstall my first set now shortened to 9.5 feet. Thought of a good solution for my brakes by adding a long spring to pull the brake open when the tail unfurls. Seems to work at ground level.

Of course it didn't work. The damn machine just won't budge again. After watching for a few days of good wind but motionless blades I realized the pulling force of the spring must have pulled the stator into contact with the magnets. So down the tower comes and that was the problem. Removed the new spring and decided to tie the brake pad in the fixed open position and finally it works. I retained the broken new tail to remind me of my haste and actions without pre thinking of consequences. It works well being still bigger area than the last tail

Spinning even on the way up I had to short the leads to keep it still for fear of any thing else go wrong. Started generating sweetly the moment I opened the short, not much but the best I had for a year. I finished all these just in time to catch the inter-monsoon period of poor winds. I have been waiting for 2 weeks now and have not seen the machine turn yet. Just have to wait for the start of the northeast monsoon winds. For me back the making another set of 12 footer at TSR 8.3. Came too far to give up. Must get enough power one day.

SeanChan

a couple of your pictures are a little oversized try  to keep them under 150k next time OK
Kurt

[SparWeb]

Thank you for sharing this project with the forum.  I remember the photos you posted last year.  The progress and set-backs you have experienced since then are good lessons to us all.  The folks who share their mistakes teach me as much as those who succeed.  (I should have taken pictures of my wrecked wind VAWT last year.)

[willib]

It was a faulty mechanical brake the whole time!?

darn!

sorry to hear of your crash, it was painfull to see your new blades all busted up

best of luck , when you get the new ones built

[Flux]

Sorry to hear about the latest mishap.

Personally I think you would be well advised to throw that brake away, you don't have the wind to need it and I seriously doubt that it would work if you did.

Wait for the wind and see how the present blades work out. I am not too happy about the 12 ft blades with tsr 8.5. In theory it should work, but the lower the wind the less effective high tsr blades are.

In the long run I think you will need to wind a stator for lower cut in and use 12 ft at about tsr 6.

If you want to try the high tsr, then choose the angles for tsr 8.5 but use the chord values for tsr 7.

The blades that failed to cut in didn't fail because they were too heavy, there was another reason. Weight may stop them responding to light gusts but they will get there in the end.

It's a shame about those blades they looked really promising.

Flux

[Gary D]

Sorry to hear of your multiple missfortunes. Hopefully you made a new stator with more turns for the increased diameter blades, since they will be running at a reduced rpm at any given windspeed (even with the same tsr). Hope you get things running smothly as soon as possible. If you didn't rewind the stator, perhaps that could be the reason your heavier blades spun, but did not reach cut in speed? Gary D.

[Norm]

   Are you getting any kind of wind at all?

My anemometer doesn't register anything under

6 mph....I consider anything that registers here

in Northeast Ohio a wind that I can use...

            ( :>) Norm

[Ungrounded Lightning Rod]

I also sympathize with your problems.

Question:  Why not just dispense with the mechanical brakes?  You already have a furling tail, with what appears to be a good stop at 90 degrees - which should furl the rotor in any wind if properly adjusted.

You don't really need to STOP the blades, just keep them from running fast enough to overpower and fry the alternator and/or overspeed the blades.  So if you deliberately set the furling to happen too soon, then adjust it for more power after you've observed its behavior in high winds, you can approach the correct setting from the safe side.

You can always leave the brakes in place but only activate them manually - like when working on the mill or in case of a major storm before you're happy with the tail settings.  Meanwhile, getting them right seems to be holding up your project.

Given that mechnical brakes that activate automatically are going to wear out and malfunction after a while, you really don't want a design where they're necessary for safe operation, right?

[richhagen]

I am sorry to hear of your blade and brake problems.  I thought that brake looked interesting when you first posted it.  I'm guessing you need a turn or two more in your coils because a heavier blade will still spin up, it may start a tiny amount later, and speed up and slow down more slowly, but in a sustained wind it should work fine.  If it spins up and you are not reaching cut in, then maybe the TSR and the cut in rpm are not well matched for lower wind speeds.  I wish you good luck with the repair of your turbine.  Rich Hagen

[dexxy]

I do believe that Sean deserves a 'Press On Regardless' award!  Good work Sean to not give up on your dream of home-made wind power!  You are an inspiration to us all!

[seanchan00]

Thanks Gary,

I have been thinking about winding a new stator for lower cut in. That's what I will have to do if the new 12 feet blades becomes too slow even with TSR 8.5. My coils now has 34 turns using dual strand AWG 15 wire. The stator is a little on the thick side being almost 6/8 inch. Shall I go to double the turns? I am also thinking of winding coils with flatter thickness so I can have a thinner stator using single strand AWG 13 wire. Am I on the right track? Is it worth the trouble trying to rewire and alter the present dual strand coil to single strand thus doubling the no of turns? I will have to chip off some fibreglass to get at the coil joints at the inner circle. The problem here will be the first & third coils of each phase which has a pair emerging at the outer circle. The starts and the ends of each phase.

I am still thinking through the rationale of Flux's suggestion of TSR 8.5 angle and TSR 7 chord for my new blades. It will add power and catch more wind but it may become even slower. My main reason to go for TSR 8.5 is I can cut down the diameter of the blades in small steps to the right diameter for my wind conditions. As I cut down the diameter I seem to always end up with the recommended TSR. Example just cutting off 1 foot will give me a 11 footer at TSR 7.5. Even cutting down to 8.5 feet I end up with almost the identical blades of my first set now in use TSR 5.5. I have kept in mind Dan's advise that a 9 to 10 footer is more suitable for this alternator.

SeanChan

[Flux]

I have had a look back at previous discussion and it seems as though the original intention was for about 8.5ft.

With your exceptionally low wind the power is too low. It seems as though you need at least 12ft and fairly well matched. Normally you would need more magnet but in your very low wind you can just about manage 12 ft with those magnets and limit things to about 300W.

I can't establish a cut in speed, if you can remember it would help.

With your thick stator and only 34 turns I think it is very fast for 12 ft. Trying to correct this with a high tsr prop will probably fail. you will end up cutting the prop down and that will throw away the increased power gain from the larger rotor.

High tsr props produce very low torque and bearing losses and everything else detract from low wind performance, they work fairly well in higher wind if you can stand the noise.

The idea of using a wider chord was to try and reduce some of these losses. Tsr is mainly determined by angle, you need the maximum chord without serious loss from blade interference and you can often exceed the usual chord predicted by calculators in low wind without loss, these occur at the higher winds.

I really think that you need to wind the alternator for lower speed and avoid the high tsr. If you can reconnect the present winding in series it should make a reasonable match for a prop of Dan's type at 12 ft. It may be a bit slow but you can increase air gap.

If you can do this it would give a lot of useful information and from that we may be able to design a better winding with thinner stator.

If you can't reconnect this then I would go for 50 turns of #13 and get it in as thin a stator as possible with that size of wire. ( less than 5/8" should be possible).

You really are in a low wind area but fortunately you don't seem to have the problem of generally low wind but the odd occasion where things gust to 70 mph.

Flux

[seanchan00]

Thanks Flux,

I understand now & I am convinced your are right as usual and I shall take the new blades 12 feet at TSR 7. This will give me the same angle and chord values if it is 8.5 feet TSR 5.5. I never knew what my cut in speed was as I could not measure it. Visually it seems to be around 180 + -. Visually looked like a ceiling fan going at speed no 3 and above. Definitely faster than 2. As to rewiring the present stator I still have not figured out the best way to bring in one of the two wires at the starts and the ends. If I saw a drain on the surface of the stator will it make the whole stator weak and break up? I will of course recover the drain with resin.

Probably can't escape from making a new thinner stator in the end. I will also take down the brake. Could'nt do it the last time it was down because my allen key set was metric and none of them fitted. I have the right one now.  

SeanChan

[scoraigwind]

Windmills have a way of getting us to keep on going.  You will get it right in the end.

I agree with Flux that the key thing is to rewind the stator for lower cut in, and use a blade that will work well in low winds, which will probably have a tip speed ratio of 7 or less.  As you increase the diameter you will reduce the rpm with this tip speed ratio.

There is one misconception here that I must try to dispel.  If blades are designed for (say) tip speed ratio 7, then the tip is designed to run 7 times the windspeed.  But the part of the blade which is 6/7 out from the centre is travelling at speed ratio 6 and is designed for this.  If you shorten the blade to 6/7 then you will have a blade designed for tip speed ratio 6.  So you do not gain rpm speed but you lose diameter and power.

On the other hand extending the blades is a little different.  Then the tip is desigend to travel at tip speed ratio 7 but it is now at a greater radius and its chord is a smaller part of the circle so it may run faster.  The angle of the blade will still be set for 7, unless you make it flatter in which case it will become a slightly higher tip seed ratio blade.  All this will make only small differences to speed, and will gain a bit of power.  Of course everything needs to be a bit stronger for the larger diameter and the blade extensions need to be stiff and not bend or they will crack and the blades will fly off.

I liked you big blade - the one that broke.  What a shame.  If you can make another set like that and a new stator then the machine can be a big success.  So long as it is strong enough and you put a furling system on it so it will not overspeed in a gust.

Keep on rebuilding :-)

Hugh