17' wind turbine failure

[DanB]

In mid sept we left for 3 days to give a work shop in town and I left my 17' wind turbine on to help keep the batteries up while we were gone (I shut down the 20' machine).  During that time we had pretty incredible winds and I came home to find that the stator had burned out.  Last week we finished a new stator for it and installed it.  The machine seemed to work brilliantly afterwards, producing 10 amps in seemingly no wind at all and it worked fine for a few days.  Last Friday morning I woke up and my 20' machine was running well - but the 17' machine was turning very slowly (as if it was shorted).  It had been a breezy night - but not that windy (not enough for a burnout).  Then - about 1 hour later it started running again all by itself and ran for a couple hours and stopped again.  This made me pretty certain there was a short in the line - the line is over 3 years old and it's been  pretty twisted up before, I figured it was an intermittant short.

Monday we took it down.  I pulled the line out of the tower and untwisted it carefully and inspected the most stressed spots, it seemed fine.  We put it back up -same thing, it was seemingly shorted.

By sending 12V up into it (from a makita drill battery) all 3 phases would 'motor' it a bit - but, when checking the current into each phase while doing that, 2 of the phases were drawing about 14 amps, one was drawing about 20.  So I figure our new stator has an 'intermittant' short inside it across a couple coils.  Probably when we clamped the lid on the mold somehow we damaged some insulation somewhere.

My first thing will be to try to fix it (the stator is fairly time consuming and expensive to make).  I'm hopeful that by sending current into it while its on the bench we can figure out which coils are shorted (there should be a lack of magnetic field and a lack of heat) and maybe we can find a 'hot spot' (if were lucky) and go in with a dremel tool and repair it.  'I figure the odds be fifty fifty'

[DaveW]

  DanB - I had much the same problem on one of the first 8 footers I built, I feel your pain.  Made up some shims and just made the stator thicker so there was no chance of "squishing" the coils.  Makes for more gap and some loss, but I haven't lost a stator since out of five in the air.  I'd rather go with a little less power and more reliability on run time.

[electrondady1]

danb,

that 17' unit is deffinetly cursed.

i think the best thing to do is dismantle it and ship it up here to me in ontario.

[DanB]

I'm not sure what to think on this one...  we've made over 50 stators w/o this problem ever coming up.  I think I have to attribute this to lack of attention when we were casting.  I wind the coils on a form that is thinner than the final stator - so we're not realy smashing things that hard. Hopefully we can repair it.

[DanB]

Cursed... maybe.  I won't give up though... it's been a pretty good machine overall, it's made a lot of energy!  When it warms up (is about 5 deg F now with 4" of snow on the ground) we'll try again.  Funny thing is - if it's breezy at all I really don't need it, the 20' machine is plenty - but I like the idea of having a redundant machine in case one breaks down - and - hopefully, Ill get some good heat off them this winter.

So - Im not ready to ship it off to you just yet ;-)

[Flux]

I am fairly certain that you should be able to find the fault. I suspect the most likely place is where the inner end comes out.

I tend to treat everything as though it was a 1000v machine. Use pieces of nomex or your equivalent slot insulation where every connection crosses and anywhere coils of different phases touch. Use sleeving on all interconnecting leads where they have even a remote chance of touching.

There are likely to be significant forces with resin contraction and also whenever you use the brake switch. Failure between turns of a coil is unlikely. Failure is likely to be between ends of a coil or between phases.

I think your idea of applying a limited current dc and looking for field on each coil with a magnet should find it. You may have to apply a bit of pressure if the fault is intermittent.

An ac voltage applied and a search coil connected to a meter is more sensitive but you may not have such things at hand.

Knowing your resourcefulness I put your chances nearer 90%.

Flux

[JW]

Could be a open, versa a short.

 In theory, if there were 3 wire in hand and 1 or 2 leads, open/connection from where they parallel, it could cause just as much head as a shorted winding, but have higher dynamic impeadence(in ohm's) when at speed. Makeing it harder to test when its cool. I would suspect less on the actual insulation on the magnet wire, but more on any soldered junctions within the stator assy. Just a thought.  

JW

[JW]

"could cause just as much head as a shorted winding"

That's oppsta be-

'could cause just as much heat as a shorted winding"

why is it easier to see these type of typo's after you post... Oh well

JW

[keith o]

i don't believe a open would cause the jenny to slow down like a short would

i'd think it would overspeed instead  fwiw

if it were me?  doing it ghetto?

i'd freeze the stator and spritz some water out of a spray bottle on it while frozen

to build up a thin ice layer

then i'd connect the offending coils in series between a battery and a headlight

seems the first area that melted may be whereabouts the short is at

and thats a big "maybe"

fwiw

[vawtman]

Dan this might be irrevalant but the 17 rotors seem to have the mags pretty tight on the inner diameter of the coils compared to the 20.

Just went back in time to study airgaps for these.

[picmacmillan]

very good thread here dan and fellas...i built the  same machine(or close), but havent had time to put it up yet...really appreciate the comments here nice to see everyone putting there heads together to figure out, and hopefully make our gennies better(as they always do become)....this is what makes this site as good as it is...its the people here ..havent been able to be on much, and miss it take care all, and i will be reading to see what happens on this post

......take care all..pickster

[JW]

Hmmmmmm,

"if it were me?  doing it ghetto?"

Now let's all take a moment here, Step-Back and reflect...

IN theory- if 3 wires in hand were used to wind each coil, what would be the possible ramifications.

YES-

 air-gap is a serious consideration. If a technition was trying to reduce stator overheating this would be the obvious coarse of action. Regardless of the state of the stator...

NOW-

 if the coil had 2/3rds the amount of copper in place acting as a 'inductive-load' and one third of the coil acting as a generator, what exactly would happen. dynamic braking could occur at rotation band-width speed range. Would this slow the prop? The only way to be sure would be to gauge acceleration thru 360* average mean speed. nevertheless the prop could slow under this rare condition. Considering Dan wires all his stators in star could lead to a clue. But i was watching the weather channel today,and its snow in Fort Collins Co. today. Perhaps at some point in the future, dan will actually share what he has learned from this project. At this point, Im just a spectator. Best to all. It will be neat to here Dan's conclusions to this puzzle...

JW

[WXYZCIENCE]

Dan, I use a mylar tape to protect the coil lead wire. Also I have found a wire called ultra double coating. It has a higher temperature rating than standard double enamel wire. They use it in power inverters that run hot.


Joseph.

[GeorgeT]

Hi DanB,

  Have you considered multiple thin layers of clear polyurethane varnish or Spar Varnish on the coils prior to casting? I've used it many times on electrical solenoids on shrimp boats with a good deal of success. Let it dry naturally for best results. If you are in a hurry be careful not to apply too much heat since the varnish will bubble. You could spring for "Marine Varnish" if you want, but I haven't found a difference. While I don't "squash" my solenoids like you do the coils I believe that the coating would provide a better insulation barrier for you to put the squeeze on.

BTW, dunking them in the varnish doesn't help. Seems to leave voids in the coating.

Cheers!

George Taylor

[DanB]

Hi Joe -

I've used tape before to protect the inner lead coming out - somehow I got out of the habit.  I don't believe that's the problem here though - I think the coils themselves are fine, its the connections between the coils that somehow failed (Which is odd, because things are not that tightly packed in there).  My guess is that the copper tubing I cut up so that I could crimp the leads together were sharp and one of them cut into another wire.

Yes, the double insulated inverter grade wire is what I always use as well.  It takes much higher temps and the insulation is very tough.

[bj]

   DanB---first of all THANKS for all of the posts.  Makes my day worth

starting.  

   For what it is worth,  I have have found that 600 volt copper is a

lot more forgiving.  I use a plastic hammer to seat windings, which is

bad, but have not had an insulation failure ever. I have a sympathic

motor winder, that has clined payment.  So cost is not a factor.

   I am luckier than most.

   But, my point is, IF you start with better wire, can some of this

R&D be put to better use?  

   Insulation failures seem to be prevalant.  If the upgrade is worth,

it, TRY

   bj

[bj]

    Dan:  just a comment, or If you will, a question.  I use 600 volt

rated wire, as it has been free.  (sympathetic friend).

    Since I started using this wire, I have had no failures.

    Didn't put it together, until I re-read your last post.  I went out

to the shop, and tried a "scratch" test on some of the new(600V) wire

and some of the old (automotive) wire.

    Big difference.  I had noticed before that soldering was a bit

more of a headache, but hadn't made the connection (no pun intended)

    I do not know, for sure, but is this of help?

    bj