Fwd: Re: Fwd: [a-w-h] Several Important Questions (I believe....)
- You bring up a good point Hugh.
I was in too much of a hurry to explain well....
I still like the method I described, however it has to be done very well,
or else it may be worse.
The wood blade has to be sealed in a way that is essentially
waterproof. The wood blade should also be dry to begin with (about 10% to
13% moisture content is good. The epoxy and urethane does breath, it just
breathes very slowly or little. If there is not a break in the finish, the
blade will last for many years and will not have to look "ratty" at all.
The key is to never let the wood stay saturated by moisture (30% or
more). When it is saturated, fungi will grow and decay will proceed, if at
normal temps conducive for plant growth. The reason having a highly
breathable finish works is that it doesn't spend much time saturated, as
the blade dries out very quickly after it gets wet on a wind turbine.
This info comes mainly from the days when I was building aircraft with
wooden structural components and for obvious reasons had to learn how to
keep the plane from falling apart.
I have seen some of my wood/fiberglass blades (inside mounting holes,
etc.) after about 15 years and was surprised at how they looked brand new,
as if they were just drilled.
Sticking to my story, so far ;)
>At 1:28 AM -0500 24/6/03, P Kelble wrote:
> >One way: Seal the wood with epoxy or similar material. Top coat with a
> >good exterior polyurethane paint.
>I do not recommend you seal the wood in this way. My experience with
>epoxy coatings is that the wood cannot breathe. Any moisture in
>there will centrifuge out to the tip, and I have seen the tip explode
>with accumulated water. A good hard wearing paint is helpful (not
>varnish) but really I find that wooden blades last pretty well
>anyway. The situation is dry and clean so they do not rot. The
>worst thing is if they run too fast and do not have leading edge
>protection. Then they will not last long.
>Wooden blades here on Scoraig last from ten to twenty years in my
>experience. They get to look a bit tatty, but they still work OK.
> >Put urethane tape on the leading edge for added protection protection.
>That's a good idea if you plan to run them fast.
> >Building the blade with a hard-
> >wood leading edge wouldn't be a bad idea either.
> >There are many other other ways such as fiberglass over the wood, etc.
>Wood lasts longer if you let it breathe.
> > >2-We know that inside a car's alternator there isnt a real magent;
> >>coils are wound up so that they make a magnetic field. How are these
> >>coils connected to the battery so that they don't discharge it when
> >>the car is stopped. In other words...why isn't the power in the
> >>battery lost as heat?
>TYou can feed the field coils from a separate rectifier - that is how
>some cars do it and it means that only the ignition warning light is
>on when the alternator stops. The warning light provides a small
>current to the field and that helps it kick in.
>Do not use a car alternator anyway it is not a good idea.
> > >
> >>3-I've got an old AC motor (similar to a car's alternator); u know the
> >>one with no metalic armature but with coils wound up even in the
> >>middle (try to understand....i know that my english isn't very well!!).
> >>When this machine is used as a motor, the coils making the magnetic
> >>field have a voltage of 30 V across them (each) and they stay normal
> >>after long operation. When i connected these two coils in parallel to
> >>12 V battery they both got very hot in a short time.
>To connect to a battery you should use a rectifier to convert the AC to Dc.
> > >
> >>4-Did any of u use a car's alternator on a wind generator?
>yes, long ago.
> > How
> >>efficient was it?
>very inefficient. Also the rpm is very high, so it only worked in
>strong breezes or half gales.
> > and what regulator did u use?
>I did not use the internal regulator. That tries to keep the voltage
>at 14 max whereas you need more than that if you have a long cable to
>the battery. I did not use a regulator at all. It worked only in
>high winds and I had a big enough battery to keep an eye on it myself.
> > >
> >>5-Aren't there some companies that make autos' alternators that need
> >>relatively low rpm's? (Japanese or Korean motor companies?) I'm asking
> > >about these alternators since they have matching regulators.
>don't bother with car alternators. Everyone seems to have to try
>them first, but they are not a good way forward.
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