Planning a new turbine, Toshiba 7.5 kW Conversion

[Mary B]

Mary, after I uploaded that post I thought; “there is no humor in having to put up with any kind of noise”.

If that noise bothers you, there could be an easy and inexpensive fix for that. If you can get someone to take a picture of the bracket that is attached to the house and uploaded here, we might be able to come up with a fix.

SparWeb, I don't want to hijack your thread, but if there is any interest in an isolator to eliminate vibrations from a tower, I have been working on a design.

I can post the drawings here when I'm done or I can start a new thread.

Ed

Brackets are hard bolted to the house for a reason. ANY flex could lead to failure when one of the infamous 90+ mph wind storms rolls through. I have a rather severe weather site when it comes to wind... Rohn recommends 1 bracket at around 25' I have one at 12 and 25... made from that adult erector set angle iron you can buy at hardware stores. My homemade brackets are ten times stronger than the Rohn house bracket. In fact you can stand on them for a work platform!

[kitestrings]

I also haven't figured out what the best connection scheme on the ground would be.  My battery stack could take the juice with the DC hooked up directly, but I'd like to experiment with MPPT (finally; I'm like the last luddite hold-out).

A robust battery bank solves many problems.  Many are undersized IMO, and it is understandable; batteries are expensive.  MPPT affords you flexibility.  In the end the challenge of course is not whether the thing will produce enough power - it will - it is what to do when there are the three-day blows.

I prefer a strategy that reduces power to the rotor.  Midwoud has an ingenious design, but any variable pitch design will add complexity in a difficult location.  We've of course tried a power furling approach, and this has worked well for us.  It is soft, simple and essentially is just a supplement to the furling tail design.  Ours is binary, but it could also be modulating over the full range of travel to match the need.  Either approach I think is preferable to an electrical solution.

Have you thought about blade material?  I'm dying to carve a new (next generation ;>) blade set, but the summer is short and my list is long this year.

~ks

[SparWeb]

I certainly have considered the blades.  In fact, I may be doing blades for BOTH the Zubbly conversion and this one.
It started with an opportunity to try out new features in an online CAD software system called Onshape.  I recommend you try it if you are at all interested in CAD or have even a small amount of experience and want to see what's new.

There have been many distractions this spring.  Here's a screen-capture from my rotor design as it was a few months ago.  I've pushed this farther along to the draft drawings stage.  I stopped here because I began to wonder if it would be better to relocate the turbine with a new tower.  Well, you can see now what I've decided, but that made the planning more difficult.



And if I'm going to be raising a new tower, then it might as well be for the Toshiba conversion.  So the tower becomes a priority for later, because I'm digging into the work I did long ago, to see what I've learned since then about sizing/matching of rotors.  The Zubbly conversion of the Baldor has proven that I can make the blades larger - probably 10 feet instead of 8.  The Toshiba 7.5kW conversion will handle 12-foot blades easily but probably better with 14-foot diameter.  It's not settled yet.  So I flip back and forth between designing blades for the Toshiba and the Baldor...

The experience you shared with power furling has been very valuable.  Something like it may be incorporated in my future project, but I also can show that motor-conversions are more robust than the axial generators.  With slightly under-sized rotor blades, there is rarely any need for furling at all.  The motor housing can absorb and radiate much more heat than the disks of an axial.  This was made abundantly clear to me when I opened the housing of my motor-conversion after years of operation, to find some thermoplastic parts inside.  They were part of a tachometer experiment that I'd forgotten to remove.  The thermoplastic parts were completely intact and undisturbed, but if they'd been exposed to any heat above 150F they would have warped and caused damage.  No such thing happened, so it was a tell-tale that this motor conversion doesn't get hot inside.

[SparWeb]

It's actually a bit farther along than what I was showing earlier:

[mbouwer]

Very worthwhile to consider your plans in this way from all sides.

[bigrockcandymountain]

I highly recommend active furling as well.  It has worked well for me and I would absolutely not be without it now that i have had it.

Do you have numbers on your blade set for the toshiba?  I am pretty curious.  Tip speed ratio, airfoil, diameter, thickness, etc.

The drawings for your 10' are awesome.  What is the tsr to make those cut in on the baldor?

[SparWeb]

I don't do things much differently from the Hugh Piggott blade carving plans.  The laminating and the hub business are extra fun bits, so I indulge a little.  Hugh doesn't care much for airfoils, and he has good reason.  Airfoils are great at the scale of airplanes and helicopters, but not so important at smaller scales of wind turbines.  The key things are angle of attack and low drag, and you can get that from a smoothed wedge.  A true airfoil will have much lower drag still, and from there it's diminishing returns.
So I have picked an airfoil type, kinda old-school, something from the NACA 6412 to 6415 range.  I'm not sure if the thickness changes much.  If it doesn't matter I'll go for thicker blades for strength.  It doesn't need a concave surface, which I prefer to avoid to simplify carving.

For the current Baldor:
The 8' blades have a TSR about 4 or 5 but I had intended 6.  I discovered after making them that I'd goofed and put even more curve in them than necessary.
No matter, though - the data logger tells me that they actually do run about TSR=4 or so, but that's due to being too small, not strictly because of the twist.
The turbine does need a decent breeze to get turning, but that's fine.  It saves bearing life and the breeze that can start them generates only a pitiful amp or two, anyway.
The replacement blades should be TSR 6, and at 10 feet diameter they will be much more effective.  The extra diameter will make up for less twist to start up in light wind.

For the next Toshiba conversion blades:
These are settling out at about 14' diameter, needing TSR about 5.  I feel like it's worth the effort to put in the work trying various combinations and see what the result would be, but there are lots of them.  Diameter, TSR, and wiring connection between Star, Delta, and Jerry (rectifying phases independently).  And then there's the possibility of converting my system from 24V to 48V.  Not likely to happen but there is a possibility, then I'd like to know that it will be as simple as taking the parallel phase coils and running them in series instead.

Power furling:
Hey, I may be getting complacent with how well the furling works on the Zubbly conversion right now.
I have an unused garage door opener.  I wonder if I could use that with a cable running up like KS and BRCM have done.
I'd have the luxury to activate the tail furling from inside the house!

[SparWeb]

Sizing up the converted generator.  It weighs 125 pounds.  The driveshaft is 1.375" diameter, and is 3.5" long.  It also has a stubby rear shaft.

[kitestrings]

Maybe a good spot for a parking brake, or...?

[SparWeb]

or...?  ...water pump!   

I used the think it would be good to have a parking brake, but this motor locks up tight when the leads are shorted, just like the one I have flying now.  And I don't need to attach a tachometer since I now have a datalogger that can read any speed through the noisy mess of the output waveform.

The rear shaft was originally used for a cooling fan, being a TEFC motor.  I doubt I need that fan, but I could put it back on if I could convince myself that the generator would run any cooler with it.