7.6 puts out 2 kW

[ChrisOlson]

I was in my shop office watching the gauges for my 7.6 footer and it hit 33.5 volts and 61 amps.  I had already manually disconnected it from the batteries so it wouldn't cook the batteries, and was running an engine block heater in a N14 Cummins with it to keep a load on it.  So I ran outside to take a picture of it.  According to my AC frequency meter it was putting out 88 Hz current (880 rpm) when I took the photo.

Needless to say, that's approaching Orbital Escape Velocity for a 7.6 footer.

It was supposed to furl at 28 mph but it didn't.  Although you really can't see it in the photo, the tail was just starting to furl at 32 mph.

This is the same turbine with which I had a runaway with 10.8' blades on it and burned the stator out trying to stop it.  When I put the 7.6' blades on, I re-did all my furling calculations - I shortened the tail and replaced everything on the tail boom with aluminum to get the weight down.

It's back to the drawing board on getting this one to furl properly.  I've tried everything except reducing the tail hinge angle, which is the next thing I'm going to try.  It's at 35°, which is evidently a little too much.  The mainshaft offset is already 8.5% with the smaller blades.  I'm also going to put some sort of mechanical brake on it to stop it if it does this again.

--

Chris

Made the photo display. Sorry it is so tough to add photos here. TW

[SparWeb]

The conventional tail hinge angle is about 15-20 degrees, IIRC.  

That must have been one heck of a noise - that tower is attached to a building isn't it?  How far up does it protrude?

I'd be afraid that any effort to ensure reliable furling will be undermined by turbulence over the roof of the building.

[tanner0441]

Oooooh

I bet that was impresive to listen to.  I tried projecting the blade line and it looks very close to the tower.  My turbine is only a foot or two above my house roof and about 8 foot from it, I only seem to get turbulance problems with the lower winds when the thing can spin like a balerina, when the wind is high enough and comming straight down the ridge line of the roof it seem very stable and the blades are fairly quiet. In your case I would think you would have the most turbulance when the wind is hitting the gable end and scattering.

Hope you sort it becaus 2KW looks like a good stator and it would be a shame to cook it..

Brian

[Flux]

Furling depends on the sine of the angle of the tail hinge. With 35 deg you will need half the weight of a 20 deg hinge. I find it difficult to see how you can keep it light enough for the normal 20 deg. With your angle I see no real chance.

Flux

[bj]

   Glad it survived Chris.  From your other posts, etc it sounds like you have come to the same conclusion that I have.  Mine won't fly without some

kind of brake.

   Because I have the parts, I am leaning toward either an adapted motorcycle

disk/caliper, or a band brake.  I like the band, as they are self energizing

and therefore require a lot less apply pressure.  The disk, would however,

last longer.

   Just my thoughts.

[brokengun]

By my calculations you're tip was doing about 238.6 MPH. That's crankin!

Glad you didn't loose it or damage anything/anyone. Must've been a noisy and nervous sight.

[ChrisOlson]

I had the generator on the rear of this turbine to begin with and moved it back to the front (behind the turbine rotor) due to the separate moment developed by the generator mass rotating about the yaw shaft making it hard for the tail to control it in gusty winds.  That's why I originally used the 35° tail hinge angle.

The shaft stub that used to drive the rear mount generator is still there.  I think what I'm going to do is machine a 6" brake rotor on the lathe and mount it on that shaft stub.  The flange that the generator used to bolt to is still there too, which will be handy to mount a floating caliper on pins.

How I'm going to apply the brake is still up for grabs.  I've thought about an automatic system, which would probably be the best in case it tried to overspeed when I'm not watching it.  At 2 kW it'll take a pretty decent brake to stop it - that's the equivalent of putting a brake disc on a 3 hp electric motor shaft and attempting to stop it with a caliper and brake pads.

The generator on this turbine is pretty stout for a 7.6 footer - I wound it with 40 turns of AWG 14 two-in-hand, 9 coils, and I got six 1/2" bolts supporting it - no wimpy stator bolts on this thing.  It actually shouldn't put out over 1.5 kW continuous, but it's stout enough to throw the shorting switch on the control box and it brought the turbine to a crawl, after I took the photo, even in a 32 mph wind.

The danger with relying on the stator is if you'd happen to lose a phase or something, then it wouldn't stop it.  Running unloaded in those kinds of winds I have no doubt it would come apart.  That's where the brake will come in handy.  Might not ever need it.  But if it is needed and it isn't there, it's too late.  If it burns up a set of brake pads and turns the brake rotor red to stop it in an emergency, so be it.  Half worn out motorcycle brake pads are a dime a dozen and cheap compared to losing a blade.

--

Chris

[ChrisOlson]

The blades run about 6" from the tower.  They'd have to flex quite a bit to hit it.  I got a piece of indoor/outdoor carpet wrapped around the tower, held in place with duct tape in case they would though.

I had this turbine on my 24' tower out in the open, but I'm getting ready to put my 10.8 footer on that tower.  The tower in the photo is on the north end of my shop office and the bottom of the blades clear the top of the roofline by about 4 feet.

It runs surprising well on that short tower.  With an east or west wind there's a sort of wind tunnel effect from pine trees that are further north of the building and it puts out a lot of power.  With a north wind it's sporadic, and with a south wind it runs fairly well, except the row of pine trees slows the wind a bit before it gets to the turbine.

This is just a temporary deal because of the 10.8 footer going on the other tower.  We got 2 feet of snow here right now so it's kind of hard to set another proper tower for the 7.6 until spring or early summer.  Until then it's going to have to fly on this one.

And yes, it made a pretty impressive whining noise at 880 rpm.  I think most of the noise was coming from the generator though, rather than the blades.

--

Chris

[bob golding]

hi chris,

 hard to tell from the photo but that tail looks a bit on the small side to me.

bob

[ChrisOlson]

It's 3.2 square feet.  After I moved the genny to the front it has no real problems keeping it steered into the wind.  The tail boom is telescoping and I got three adjustment holes drilled in it.  I think in that photo the tail was in the medium length position, which is about 6" shorter on the tail boom than I had it when I had the 10.8 blades on it.

There's probably a tail hinge angle limit where the calculations don't work anymore, and my best guess is that at 35° I'm past what it should be.  Like flux said, I probably got the angle so severe that I can't get the weight low enough to get it to furl when it should.

I remember why I did that - when I had the generator on the rear the tail would hit the generator when it furled.  So I increased the angle of the hinge, which makes the boom climb quicker when it furls, then it cleared the generator by about an inch.

This is what it looked like when I had the generator on the back:

http://picasaweb.google.com/christopher.w.olson/76FtWindTurbine#5430081358178684610

This turbine flew for quite awhile with the generator on the back before I decided that it was causing problems with balance of the entire unit on the yaw shaft.  Moving it back to the front removed about 11 lbs of weight and eliminated two bearings.  It was an experimental deal that didn't really work out like I had planned.

--

Chris

[bj]

   Chris--pretty much my thinking as well.  Chances are if I have to apply

the brake, something is wrong, and the tower will have to come down anyway.

So--what's the big deal to change pads?

   On the disk, I was thinking 18 inch brake rotor, with a 4 piston caliper.

Should be able to stop it at least once.

  Again, just some thoughts.

[ChrisOlson]

I don't think it would take that size of a brake.  I'm thinking just a little 6-8" disc and a spring loaded aluminum caliper would be adequate, and would keep the weight down.  It'd get hot but as soon as the airfoils stall it'll come to a stop pretty quick.

What would be the best way to activate the brake is what I'm toying with.  The trouble with something like that is that it's out in the weather and metal parts tend to rust and corrode after awhile.  If you don't use the brake the disc will rust and have no traction for the brake pads.  If the caliper seizes up with time it's also useless.

--

Chris

[taylorp035]

I once had my 8 footer going in 35-40mph winds, approximately the same speed as above.  It sounded like a propeller off of a turboprop on a small airplane (50 seats).

Did yours sound like this?  

[taylorp035]

Also, congratulations on the 2kw.  Quite impressive.  44 watts / sqft.

My record is only 6 watts / sqft.  Wow!

[ChrisOlson]

Pretty much.  What sounds really impressive is when a side gust hits it and the blades "slap" the wind.

The generator I got on it is a noisy thing too.  It starts humming and whining when it gets above 1 kW.  It's kind of annoying because the tower I got it on right now is attached to the peak of my shop roof and the noise transfers into the building when the generator starts working hard.

We got 20-24 mph winds here again tonight and it's putting out anywhere from 35-40 amps pretty continuous.  I saw it go to almost 55 amps once.  That's more than I like to see going to the batteries but I got a pretty good inverter load on the system right now so it's not too bad.

This is the first time in weeks that I haven't had to run the genset to keep the lights on.  The wind has been blowing steady here for the last week and that little 7.6 footer is keeping up with the load pretty good.  We had the batteries down to about 80% charge last night and it brought all seven of them up to 14.7 volts by the time we got up this morning.

--

Chris

[ChrisOlson]

It did that because I hooked up a DC block heater (used in Alaska for warming up diesel engines in frozen trucks with another truck that's running) to it with some jumper cables.  I don't know how many watts one of those heaters is but it was getting pretty hot because it's only supposed to run on 24 volts.

Basically it took everything the turbine could put out without stalling it like shorting the stator does.  Right after I took the photo I threw the shorting switch and shut the turbine down before something got wrecked either in the stator or lose a blade.

The stator I got in it can probably put out 1.5 kW continuous without hurting it.  It was a dangerous situation because if the stator got hot running the block heater, and the wind persisted, it could take a phase out if I threw the shorting switch to stop it.  So I decided to play it safe and throw the switch before the stator got too hot.

--

Chris

[Perry1]

Hi Chris,

What improvements have you made to the stator such taht it can sustain a 1.5 kW output?

Perry

[Fused]

...and how does wrapping "carpet" around the tower protect the blades from hitting it? Seems it would only reduce clearance between blades and tower even more. I'd hate to be in the house and underneath those blades when they hit that carpet, for sure.

Good luck

Fused

[SparWeb]

I'm having a hard time with the carpet idea, too.

Either you put the carpet on because you were concerned about the blade tips (but it won't do any good) or the carpet is for some other purpose and not about the blades at all.  

It's one of those "unwritten" ideas:  when you first get your genny on the tower, you push and pull on the blades a bit to get a feel for what's going to happen.  Did you ever try this?  

[coldspot]

 Chris-

 "to activate the brake"

My $0.02 on this.

 A flap hanging down so that when the

high winds come this flap would then get

pushed back and up by the wind.

 This could then be used to apply the brake with a cable maybe.

 Ive been thinking about this as a way to

 click a relay to then short the phases

 and stop the turbine or maybe a switch

to go from star to delta.

 but remember I'm a bit crazy like that

 so don't do what I might be thinking I'm just

thinking here.

[Boss]

Speaking of fantastic power output due to late furling our 11 footer 6"offset 2" inch magnet, 24 volt setup. The readings I saw during a particularly strong wind were 60 amps at 33 volts = 1980 watts! We haven't any method for measuring wind speed.

Here's an excerpt from my blog  http://outfitnm.com/2010/01/29/bmn-nice-little-snow

Our wind turbine pegged the ammeter during the wind storm of last week. I had to use the new alternator kill switch to shut it down. The machine was fully furled when I went out to the shop to check up on it. I was in the house when I started noticing things clanging outside on the walls. For example, the cover on the electric circuit panel needed the latch fixed and it was making a sound not dissimilar to a large wind chime. That sound usually signifies the wind is coming from a north-westerly direction. Anyway, when I got to the shop the volt meter read 33 volts! Nominal voltage is of course 24 (two 12v batteries in series). So 33 volts isn't good and will boil the liquid in the battery cells.

A quick look out the front door of the shop showed a completely furled mechanism, meaning the tail and the blades were parallel and the blades were perpendicular to the wind direction. A quick look back around the corner of garage door, and I noted the ammeter pegging with 50 amps being the highest amperage the meter will read. Crap, well cool and crappy at the same time, if this makes any sense. Cool because for the first time I saw our little 11 foot diameter bladed turbine kick out and sustain 1.5 kilowatts, double the normal output. Bad, because this level of power generation will burn the alternator in short order.

Yeah I had to shut it down or it was going to destroy itself, even though it was fully furled, it was still spinning way too fast. I'm glad I was here to shut it down. It is still shut down. We still do not have the wind turbine hooked to anything purposeful and I don't have the new bank hooked in yet.

[ChrisOlson]

I burned up the first stator I had in this turbine.  When I wound the new one I used two-in-hand AWG 14, 44 turns.  It's a 9 coil, only 11" diameter.  I had to beat on the coils some with a rubber hammer to "fit" them, and when I put the whole thing in the mold the bolts wouldn't pull the mold all the way shut.  So I put the mold in the press with a 1/2" steel plate top and bottom and smashed it to compress the coils and get everything to fit.  The stator ended up .450" thick and I'm running a .010" gap between the magnets and stator.

This generator has custom wedge magnets in it too, which make more power than 2 x 1 x 1/2 bars because they have more surface area.  The generator is a sweet runner, but it's sort of noisy at full load (makes a sound that's sort of between a groan and a low whine).

--

Chris

[ChrisOlson]

This is a temporary tower for this machine and there's some sharp edges at the top that the blades can hit if they flex far enough.  The carpet saved the blades once already, just two days ago.  It doesn't prevent them from hitting the tower if she gets snapped around in the wind, but it softens the blow so it doesn't blow the tips all to pieces.

The tower has a telescoping mast, but I don't have a bracket welded to it to use the come-a-long to jack it up for more blade clearance.  Like I said, it was a temporary deal because I put my 10.8 footer on my big tower and this one had no home so I put it on this old chopped down TV tower.  It works for now.  In the spring when I can set a new tower for it, it'll get a decent tower.

--

Chris