Yea, I know, another stator failure

[Seekscore]

We are having high winds today with one of those spring blizzards. I got up this morning before daylight and looked at the turbine. It was dark and appeared to be furled out of the wind. When it got light, I noticed that it wasn't spinning and not furled. Uh oh! I went out to get a closer look and saw that I must have let the smoke out of the stator and the wires followed. I know my dump load wasn't big enough and was one of those things that I was going to get around to fix. It was on my list anyway.

Could the dump load be the cause of the failure? It was about 8 ohms and was a heating element from an electric heater. The stator was wound for 24V using the directions in the Homebrew book. I figured having a too small dump load would cause the turbine to possibly over speed, but would it effect furling by having less of a load on the blades?

What are the effects of having a too small dump load?

[Flux]

No,  the dump load only looks after the battery.

Without any dump load the battery will still provide load to the mill even when fully charged. If charging continues for many hours it would eventually electrolyse all the water and make the battery go open circuit but if your battery is still intact and still working ( and I bet it is) then I am sorry to say that this is not the cause of your failure.

The dump load only limits battery volts to a fully charged value, without it you may have seen something like 35v if fully charged but this would load the mill well enough.

Flux

[Seekscore]

Thanks Flux.

I guess it's going to take a little more research and checking why this happened. I braved the 40mph winds and took a couple of pictures.

[TomW]

Hopefully your magnets did not overheat and hit their Currie temperature.

Seems those sprung coils work pretty well to brake the prop so the whole unit doesn't overspeed to destruction.

Sad to see hard work gone up in smoke!

Good Luck fixing her up.

Tom

[KEG]

Have you got some info on how you made the stator. size of wire and number of turns.

[tecker]

Double nut that Stator . Use a jam nut On both sides , the jam nut deforms a little when you torque it down .

[tecker]

Air gap maybe also .

[tecker]

There is some stability advantage to mounting the inner rotor on the back on the flange if it's true you may need to turn it true .Doing so would give a shorter stator mount stud .

[halfcrazy]

my guess is looking at the pics the stator went off center and rubbed the magnet rotor. it is quite clear in the pic the nuts are all loose on the stator. so i suspect the rotor rubbed the stator in a particular spot and wore into the coil shorting it and pulling it apart

[Dave B]

 Thanks for posting. It looks like your upper stator bracket nut has come loose, if so it could be the start of the destruction.

 Several things come to mind but my intial thought is to get the stator mounted with much shorter bolts (and several more in my opinion) The amount of torque on the stator is incredible and this will bend and twist the bolts and obviously could have caused the nut to loosen etc. etc.

 Many arguments about gyroscopic forces but looking at the front, counter clockwise rotation with the offset to the right and vice versa I have proven can help assist the furling. I can't really tell what you have there.

 Assumptions are being made about your system. Your dump load and other details about your complete system can certainly have something to do with your failure.

 Keep us posted, thank you for showing us this.   Dave B.

 

[Volvo farmer]

Hey, them are big clear photos. Where's the police?

[Seekscore]

Oh, I didn't see that nut loose. That probably explains it. I put locktite threadlocker on all the nuts. One thing about making your own is that you live and learn even with all the great advice available. Of course, I should have known better. I'll add that to my list of things to not do again.

Mike

[Seekscore]

I built it with the instructions contained in the book Homebrew Wind Power that you can buy on this site. Very good instructions and a good source for all kinds of info. It may be on the web pages as well.

[Seekscore]

That is one of those hindsight things. I know that would have moved the stator closer to the hub and allowed some shorter bolts which would have stiffened it up some. When I had the hubs machined, I didn't take the back side of the hub into consideration. I would have had another one machined if I had known this before I mounted the magnets, shrunk the bands on it and poured the fiberglass resin.

[tecker]

I don't think about the failure either  I miss the power when it's down /

[ghurd]

They are a little long and wide,

but a good example of how clear a <50K pic can be!

Firefox sizes them to fit usually, so I don't often notice the height / width issues.

G-

[kurt]

max photo size on this board is limited to 640 x 480 pixels and less than 150k or they are subject to removal. 2 of yours are 800 x 600 pixels which is not super bad so i am gonna leave them but keep the rules in mind for next time. thank you.

Kurt (editor)

[Seekscore]

Sorry about the width. I didn't even look at that, I just checked the file size.

[ADMIN]

Seekscore --

The loose stator mount nut is likely the problem. Due to forces from eddy currents and power generation itself, the stator when loose actually tends to "float" and "track" itself without rubbing on the magnet rotors in normal operation. But when the turbine yaws......it will rub the magnet rotors.

ADMIN

[Flux]

Excellent pictures.

If this happened at night and you have no idea what it was producing it will be difficult to come to a conclusion on what happened.

The bottom coil that has exploded doesn't seem too burnt but there is severe blistering round the top coils. When you get it down you will have a better idea if it is completely burnt from overload or whether it is local burning from a rub between rotor and stator.

It is difficult to know whether the loose nuts are cause or effect but certainly it looks as though the loctite has not worked on one nut at least, it should never have moved that far.

I agree with the others about the stator mounting bolts but as you have not tried braking the thing I doubt that those bolts would have caused failure although it is a weak point.

When you get it down a few pictures of the stator may give more clues.

Flux

[Seekscore]

I don't know what kind of power it was producing when it failed, but I just looked at my Doc Watson meter and it has 66.28Ap displayed for max current. It looks like the machine has done close to 2000 watts at least once. Last I checked peak it was around 55 Amps. I am sure that was in some gusting winds though. Normally at around 25mph winds it was between 700-800 watts with sometimes getting to around 1100 for a few seconds/minutes at a time. I have seen the voltage as high as 32. It does look burnt from what I can see although it isn't clear in the pictures. When the wind dies down, I'll take it down and apart to see what other carnage I have.

[Dave B]

 With only 3 stator mounts and the long bolts this thing will twist it's self crazy, especially when cranking out the power and yawing besides. That's if everything is tight, now loosen one bolt as is indicated and wham-o. I will say it again, the torque on that stator and mount is huge, those bolts and bracket need to take care of much more than just holding the stator. The force of the magnets crossing those coils is trying to rip that stator off of there constantly when under load.

 There are limitations to the book design and this is no fault of the design, every design has limitations. In my opinion you are starting to furl at or above the continuous rated output of the machine, this is too late. The continous winds at this speed and the gusts above will burn it up.

 Just my opinion but as a suggestion to if or when you re-build it .. Most definetly shorten the stator bolts substantially and if possible add more around the perimeter. Add large washers between the nuts against the stator itself to help even more with the support. Properly add locktite to all nuts, (clean the threads of oil and grease) Finally, lighten the tail and or lessen the tail mount angle so the furling flops around like a fish out of water to start. Then over time tweak it SLOWLY so that it FULLY furls BELOW it's continuous rated output.

 I know this is a lot of work but I would hate to see you rewind a stator and maybe just double nut the stator and call it good. The continuous high winds will come again, Mother Nature wants to rip our machines apart and with time will win everytime.

 Thank you again for posting and the great photos.  Dave B.

[Flux]

Yes , I also think that you were way above the rating it can stand, peaks of about 700W with a few second peaks to 1kW or slightly more should be ok. If it holds 1100W for minutes rather than seconds I think you are pushing things very hard. If these are gusts that happen occasionally as may be the case at 25mph then it may have a low enough power duty cycle to handle it.

In high winds the cooling intervals are much reduced and I think if you are near the thermal limit a minute or so at 1100w will get those coils very hot.

If it is not furling then these may not be occasional peaks and your 55A peaks may be on top of something well beyond its capability.

To be safe I would want to see it starting to furl at perhaps 700W with short peaks not exceeding 1kW. In higher winds if the power rises rather than drops I seriously doubt that it is furling, if you are stall regulating and it pulls through it the power will go way up and it will fry in minutes.

Flux

[fabricator]

I don't think I'd ever dare to fly a mill with only three stator stand off bolts that long, if you were to hit the short switch while the blades were turning it would be the beginning of the end.

[halfcrazy]

I completely missed the fact the back magnet rotor was on the front of the hub not the back so I agree there will be some issues with the stator and the mounts for sure.

[cdog]

My nuts backed off too, thats what wrecked my stator!!!

The glass must squish over time and let the lockwashers back off, I used locktite and nylock nuts this time, also peened the threads!

Cdog.

[bob golding]

an idea i had,but haven't done it yet,is to have bushings in the stator so the nuts are not tightening on the fibreglass. i am planning to do this on my stator next time i have to get it down to change the bearings. i use 2 nuts on either side but i am not happy about locking them up to tight against the stator. if you made the bushings just the right thickness you could use big washers on each side and secure them with loctite to the stator. that would stop them moving if the glass shrinks with movement.

[Dave B]

 Cause and effect. If the bolts are long and few supports the stator will rotate causing the bolts in effect to shorten. The small area of support being just the face of the nuts will flex into the stator and loosen. The constant vibration under load finishes the job.

 More supports and shorter lever arms (support bolts) along with a larger surface contact area (big washers) on both sides of the stator will help. Before snugging down the stator bolts properly apply lock tight to the threads.

 Back it up one step further. Do not run your machine beyond it's rated outut. Do not run your machine beyond it's rated output. Do not ......

 Dave B.

 

[imsmooth]

I have nylon lock nuts on the back of the stator plate holding the bolts.  I use lock washers and nuts to hold the stator in place.  I don't use any nylock, or anything else for that matter. Nothing has moved yet in over two years.

[cdog]

I had mine the same way, lasted 2 years, I would keep an eye on it.

[DanB]

Here's a few thoughts based on your posting and some of the comments so far.

These machines depending how you build them really need to furl such

that sustained output is not more than 600-900 Watts (at 24V, 600

Watts is about the limit if you used rectangular 1" x 2" magnets and

wound the stator with AWG 14 wire).  By sustained output I mean

steady/constant output - on gusty sites I would still expect to see

peaks of twice that.

Presumably your dump load is tied directly to the battery and it

shouldn't be an issue.  It might be an issue if your battery is very

very small and voltage was allowed to rise way too high... I doubt

that's the case though.  In any even...  an 8ohm dump load at 24 Volts

can only dump about 3 amps (75 Watts) so it is very much too small for

the job.

Stator bolts - It doesn't look like you have any lock washers on the

machine at all - I wonder if you've used locktight?  One or the other,

there are pros and cons to both and lots of opinions, but with neither

used I would expect things to fall apart.  I've made lots of these

machines and only twice had an issue with stator hardware coming loose

- once, was on a machine we built years ago and it had no lock washers

or locktight.  The other time was on my own machine when it ran single

phase for a while and vibrated intensely - and some stator hardware

came a bit loose.  I do think that on these smaller 10' turbines,

supporting the stator at 3 points is fine - that's based on quite a

few machines that have not had problems, some of which are quite older

and had much weaker stator brackets and the studs between the brackets

and the stator were about twice as long.  Those didn't have problems,

your's should be much much stronger than them.  The torque  on the

stator, and the stator hardware is significant - but it's nothing on

these 10' turbines compared to some of the larger ones we and other

folks have built - that are perhaps supported at 5 or 6 points.  (the

torque on the stator for a 17 or a 20 foot turbine is much much

greater - perhaps 4 times greater and the torque on the stator

hardware is even more because of the greater stator diameter)  Once

you fix it - I think you're OK to go with what you have, make sure the

bolts are tight and make sure to either use lockwashers, locktight...

or nylocks.

Furling: - again, you need to limit the sustained output.  I'm not

sure how exactly you followed the book, I wonder what your tail vane

is made of.  That could be one factor.  Another factor maybe... it appears from the picture that your tail bracket is almost set straight at the back of the yaw bearing (it's hard to tell for sure)  -  and maybe not at 45 deg like we normally do.  In other words - looking straight down at the machine from the top of the yaw bearing, if the wind is coming from 12:00, the tail bracket (the piece that attaches the tail pivot to the yaw bearing) ought to be at 4:30 (I think Hugh would have it at about 4:00).      (that is if you build the way you did - we have things turned around 180 deg but that shouldn't matter).  If you get that wrong though it will affect furling.

DaveB - I can't get my head around the idea that the direction of blade rotation affects furling much - in my mind it's really just an issue of blade/tower clearance but perhaps I'm missing something there.  His appears to be backwards from ours, the alternator is on the opposite side and the blades turn the opposite way (CC) - which means that during furling or during gusts from such a direction that the tail will not be raised, the blade tips get pulled towards the tower ~ which I think is fine so long as there's enough clearance built in.  Ideally though - it probably ought to be the other way 'round.

[ChrisOlson]

I can't get my head around the idea that the direction of blade rotation affects furling much

I can't either.  I've built machines both ways and have never seen where it makes one bit of difference.  I've burned up a couple of them that were set up right, according to popular consensus, and have three flying right now that are built "wrong" - and they furl just fine.

It doesn't look to me like this one was as much of a furling issue as (probably) wobbly magnet rotors that hit the stator and shorted out come coils.  Those bolts can be tight but when the magnets hit the stator and start tearing it up they'll come loose no matter what you use on them.

--

Chris

[DanB]

My guess is it did just burn up - and that lead to hardware coming loose (hard to say for sure!).  The 10' turbine, wound with AWG 14 wire for 24V is on precarious ground with sustained outputs of 700 Watts or more in my experience.  They need to furl properly and folks who have them should really watch sustained output - if it's too much some adjustments should be made.

In the book we called for offsetting teh alternator 5", I think 5.5 or 6 is probably wise - and I do see folks all the time fitting tails that weigh too much.  I guess in the book, we build it to be pretty light weight.

Keeping the airgap pretty tight is also necessary when folks build with N40 or 42 grade magnets on that machine, otherwise they run too fast (which delays furling).

There are a lot of variables...  usually when a burnout happens I find that something was changed, or there was a problem with the system.  That said - there have been a couple times with these machines where they burned out and best I could tell, there was  nothing 'wrong'.