Author Topic: update on 17' turbine modifications (Read 2502 times)

dlenox · « **on:** November 22, 2009, 02:35:56 PM »

All,

Recently I have been able to bring down my 17' wind turbine from the tower.

Currently I have about 9.5" offset (center to center) of the yaw bearing, and my turbine unfurls itself as it appears to become wind seeking when the wind speed hits about 36mph. So I am looking to add more offset to see if I can cure this issue. From what I have gathered somewhere between 12" to 12.5" seems to be appropriate.

Previously I lightened the tail vane from 30lbs to 10lbs in an effort to help furling, but did not.

So looking for opinions - what do you think of 12.5" offset?

Below are a couple of pictures of the burnt stator, looks to have gotten fairly hot as bubbles of 'gunk' coming from beneath the glass cloth appears to be melted zip ties and vinyl tape...

Today I took my plasma torch and sliced off the mounting to the yaw bearing and got everything ground down nicely.

I have a new stator in the works with 50 turns, three in hand, #14 wire, previous stator was about 58 turns, two in hand #14 wire. The new coils just barely fit and should be an improvement in output as well as attempting to reduce my stall condition.

Here is a picture of the newest stator, like I said the coils just fit!

Lots of shrink wrap and vinyl tape to reduce any chance of developing a short between phases.

Finally between each of the coil is a short length of 1/8" thick masonite to insulate between each of the coils. This time I am not planning on bringing out the center star connection, I did not end up using it on the previous stator so not doing it this time. It will lessen any chance on creating a short this way as well.

I have yet to solder the output wires from each phase to a phosphor bronze bolts.

Dan Lenox

Flux · « **Reply #1 on:** November 22, 2009, 03:24:54 PM »

Dan

I think the 12.5 " offset should be ok. I agree you had a case of wind seeking and no messing with the tail weight will cure it.

Please done be offended but I see no place for pvc tape or cable ties in any form of machine winding, not even class A. As you are running on the edge of class H such things are nothing more than contamination.

The only thing to hold coils together with is glass tape. You could use glass sleeving for the connecting leads. The heat shrink tape is probably ok, I am not really sure what heat class it is but it probably works at class F.

If you can get Nomex that is excellent for insulating things, tough and capable of the temperatures you have but it won't impregnate as easily as glass tape.If you wet wind it with your potting resin it will be fine.

Your Pvc tape will impede impregnation and will melt and be totally mechanically useless to separate anything. I similarly regard superglue as a contaminant but it may not be too bad if use sparingly to tack coils together but again I hate it.

The nylon cable ties are not too bad for temperature but they are going to give up before the wire.

At this late stage you will have a lot of trouble removing that pvc tape and perhaps you may have to go ahead with it but try to get some glass or something over the places where contact between wires can take place when the stuff melts.Strips of Nomex or similar slipped between them would possibly be easier if you can get some.

You are wise to realise that some form of insulation is desirable in these areas where others chance the magnet wire alone and you can be forgiven for not knowing about the materials used in high temperature windings, it is a bit of a specialised field that few have experience in.

Pvc is the worst offender in your choice of materials, it is about useless at 60 deg C.

If you have heat shrink sleeve under it it might be ok, the pvc will just cause a mess.

Flux

fabricator · « **Reply #2 on:** November 22, 2009, 05:36:43 PM »

Damn, now ya tell me, my already cast stator for my seventeen footer has even more scotch 35 in it than Dans does

jlt · « **Reply #3 on:** November 22, 2009, 07:02:37 PM »

ON machines that i have built i always try to keep the prop offset small and the forward placement rather large . IT seems to help drop output in strong winds.

ibeweagle · « **Reply #4 on:** November 22, 2009, 07:13:58 PM »

look under ibeweagle for new designs for 17 footer in you tube search for ibeweagle look at videos cheers Mike Johnson

Flux · « **Reply #5 on:** November 23, 2009, 12:44:32 AM »

Bringing the prop forward does seem to alter the characteristics. If you can get it to start furling then having the prop well forward does seem to drive it into furl harder. The operation tends to be more bistable and the power drops rapidly once you get it to furl.

Even so there are factors that I have never sorted out. I am inclined to think that with the 9.5" offset it may have furled with more prop overhang, but I know from experience that there is still a minimum offset below which it won't work. What I don't know is how the minimum offset is related to the prop overhang. I have not done enough tests to prove the issue.

I built a machine with a considerable prop overhang and the offset was too small.This one refused to furl under any circumstance. When I increased the offset to get it to work it showed the tendency to drop to very low power during hard furling ( safe but wasting lots of available power).

Having a large offset does cause other nuisances such as poor tracking to the wind in normal operation without having to offset the tail away from furling to the point where it looks stupid but it is at least safe.

All the machines I have built have worked with the 1/2" per foot rule of thumb except one and that one had very little prop overhang and worked in stall mode. Some others also have very little prop overhang but don't run stalled.

All those that furl drop power in high winds, some more so than others because I have other control means than the inclined hinge and can alter it to some extent.

The one that doesn't work with the normal rule of thumb offset has a simple inclined hinge and worked perfectly with the intended prop. I modified the alternator from single rotor to accept a blank spinning disc and increased blade size, it now refuses to furl at all but is in a poor wind site and survives all the wind that comes its way.

I have never built anything that is a direct copy of the Otherpower designs so I really can't offer detailed information about the furling but all evidence I see from here indicates that the offset is marginal. Maybe that bringing the prop forward a bit may be all that is needed but it is something that I can only guess. Certainly the increase in offset will do the job.

Flux

Roger Stafford · « **Reply #6 on:** November 23, 2009, 05:29:35 AM »

Hi Dan 3m makes high temp tape www.Shop3M.com, Have not tryed this but keeping it in mind for next time. 30 years ago when I worked at a motor rewind shop we used string and insulation varnish. Didn't think about heat on my first stator 8 months ago.

dlenox · « **Reply #7 on:** November 23, 2009, 05:31:59 AM »

Flux,

I seem to remember now that you mentioned glass tape and Nomex before...

It certainly is not too late and I can look into it at my electrical store and see what they have available.

Now that I think about it, by using three in hand (rather than two) not only will it have more current capacity, it may also run hotter? Assuming that more amps equate to more heat.

Since I have already cut off the 4 x 6 x 3/16 tubing that connects the turbine to the yaw bearing I may be able to bring the turbine forward an inch or so as well.

Thanks Flux, will try to listen harder in the future...

Dan Lenox

bob golding · « **Reply #8 on:** November 23, 2009, 08:08:42 AM »

hi dan,

i dont think you will find nomex tape at the local electrical wholesaler. try a motor rewind shop or a transformer manufacturer. they will be bound to have some.

cheers

bob

SparWeb · « **Reply #9 on:** November 23, 2009, 10:06:44 AM »

As a theory to start with, the offset starts pushing the rotor around when it's facing the wind, and the overhang keeps the rotor fuled when it is facing away from the wind. The thrust on the rotor times the offset is a moment starting the furl. When furled the blades "slice" at the wind. A small profile for sure, but the drag force in that situation is not zero. Drag times overhang would equal a moment that keeps it in furl.

Plausible?

Flux · « **Reply #10 on:** November 23, 2009, 10:57:34 AM »

Yes I think you are right, it must be drag as the thrust component is still along the alternator axis so overhang wouldn't affect that.

Flux

Ungrounded Lightning Rod · « **Reply #11 on:** November 23, 2009, 05:08:45 PM »

You might want to look at a tail stop for the extended position.

If the tail is over too far and the turbine is facing a little away from the wind in the anti-furling direction you can end up with your center of effort on the wrong side of the yaw axis. Then you get an UNfurling force. Or it can just put the center of effort closer to the yaw axis than you expected from the offset. The more overhang, the less wrong-way turn it takes to lose your furling force, and thus the more bi-stable the behavior.

An extended-position tail stop can help limit the prop's tendency to face in the "wrong" direction and thus guarantee at least some "starter" furling force.

willib · « **Reply #12 on:** November 24, 2009, 06:01:44 AM »

Dan Lenox,

Adding a third wire will increase the current capacity AND it will run cooler.

Because by using three in hand you have decreased the resistance and kept the number of turns almost the same.

IMO it will barely get warm , were before it was hot.

libra · « **Reply #13 on:** November 24, 2009, 09:09:02 AM »

For your consideration. In order to allow more heat dissipation I left the inside ends of my coils open to the air. Where you have the tape, is exposed with no epoxy and just super glue to keep coils together.

I have gone through a wild ride where my wind genny ran away, and I pinned the amp meter at 90- 100 amps for 15 seconds. 30v and there was no damage or burn to the coils.

Hope this helps

Libra

dlenox · « **Reply #14 on:** November 24, 2009, 04:02:43 PM »

Flux/Bob,

Went to local electrical store and they had some Scotch #69 glass cloth electrical tape, the box says that it is class 'H' insulation and good up to 356 F degrees (180 C). Got two rolls - they are about $20/ea!

I plan on dipping the coils in resin - before I pot them into the stator with epoxy.

Would you recommend that once the coils are impregnated with resin (and hardened) that I should totally wrap the coils with this tape to act as a barrier between the epoxy and hot coils? I assume that this may be a good idea to act as a bit of a barrier between hot coils and epoxy?

They did not have nomex for no contact barrier between coils, would this tape be sufficient electrical insulation?

Dan Lenox

Boss · « **Reply #15 on:** November 25, 2009, 09:03:00 AM »

Great discussions of furling, just what I needed thanks

Adding a little to the tail stop tab seems like a simple test to see if my blade/tail orientation issue can be simply fixed. Antifurling position" I love that

Ungrounded Lightning Rod · « **Reply #16 on:** November 25, 2009, 02:19:59 PM »

By the way: It doesn't hurt much to have the stop set so the mill is turned a bit away from the wind in the furling direction even when you're on the stop. (Effective wind speed and swept area fall off with a cosine law, and cosine is really close to flat for small deviations from zero degrees.)

That might help overcome seeking-force if your offset is too small.

bob golding · « **Reply #17 on:** November 25, 2009, 03:35:54 PM »

hi dan,

it think it will depend a lot on the resin. what you could try is to heat some resin up to the same temperature as the insulation on the wire and see what happens to it. the easiest way would be to use a laser thermometer if you have one. as regards wrapping the whole coils in tape i would say if the resin will work at high temperatures it probably isnt worth the effort. more important to keep the connections from rubbing together. it would definitely be worth protecting the edges of the coils as well. if you can get hold of it the varnish used for motor rewinds would work best. but you have to bake it. most people seem to get away without it, but if you wanted to go to the trouble it is well worth doing. furling early is the safest way, but it is nice to have the extra capacity for emergencies.

good luck with it

bob

dlenox · « **Reply #18 on:** November 27, 2009, 07:06:44 AM »

Bob,

I am using West Systems epoxy and pretty sure that it is good to 240 F degrees, will have to confirm with them. Nothing around me as far as motor rewinding - I'm pretty much country.

So I will probably go with removing all vinyl tape, dipping and wrapping the coils using the Scotch #69 before potting in the stator mold. It's about the best that I can do.

I used good grade shrink wrap on all phase connections but will go back over them with this high temp glass tape and be sure to keep them well physically separated when potting in the mold.

thanks,

Dan Lenox

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Author Topic: update on 17' turbine modifications (Read 2502 times)