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Subject: [a-w-h] Re: Circuitry for a PM D/C Motor?

>Don, I'll try to help.

>
> > A small rotor will only produce a small amount of
>   power in a low wind.
>
>Why? 

Because there is only so much power in a given area of wind.  A rotor
ocupies a given area of wind.  A small diameter ocupies a small area.  A
large diameter ocupies a large area.  If you have a rotor that is 2 times
the diameter, you have 4 times the area.  In a light wind it would normally
be producing 4 times the power.  Most wind turbines rarely operate at full
power.  Because the wind does not always blow, you can never get full power
all the time.  The ratio of full power-full time(in a given time period)
vs. average power actually produced is call the "capacity factor" or
sometimes "utilization factor".  How much you get depends on your wind site
(wind velocity distribution-or wind regime) and the machine design
(primarily rotor size vs. generator size). For most typical wind turbines
this is somewhere around 5 to 10 percent in light wind regimes to 25 to 30
percent for high wind regimes.  They also don't produce full power until
from about 25mph to 35mph, depending on the machine design.


 are being too general here.  Don't get scientific on me, but
>torque and rpm's I can understand .  I thought a small rotor turns
>faster (higher rpm) in less wind than a large rotor would.  This is

This is generally true, given similar blade shapes.  However, like blades,
generators can be much different in design also.  The speed at which they
produce power (their actual power curve- speed vs. rpm) is very important.

>obviously where I'm messed up.  How?  If the rotor is UNDERsized, then there
>will not be enough torque to spin the shaft.  This I understand.  So, the
>rotor would need to be large enough to spin the shaft at some given
>windspeed (say 5-7 mph), or whatever is "best".  

5-7 mph...startup wind?  "Whatever is best" would be to build a rotor which
matches the generator characteristics (of a given generator), given your
particular wind site (wind velocity distribution).  I thought part of the
discussion was based on what generator you should buy to proceed with your
project.    


If it was properly sized in
>this way, why would a larger rotor provide higher rpm (power output) in a
>low wind?
>

With a given generator there would obvously be a maximum rotor diameter
which could be used (without a gearbox) to maximize energy output.  Blade
design can play an important role- higher tip speed ratio design (narrower
blades) would tend to extend the amount of increase in rotor diameter(area
and power) you would get.    
All in all it is not a trivial mater to maximize performance of a wind
machine.  There are allot of tools I use, and some computer programs I have
been working on (part time) for years, and am not done yet to determine
maximum cost effectiveness in regard to energy vs. cost.  I have done
enough to state that larger rotors are definately the direction that should
be taken looking at most present wind machines today.  

For the record, my company does design and build blades for wind turbines,
and I am currently helping others on this list, with thier projects, as I
have time.  The smallest is about 4+ feet long.

Good luck :)
Pat Kelble, Advanced Aero Tech.
St. Paul, MN

>
> > I sympathise with Claus.  It's very hard to explain the
>   things that matter.
>
>Maybe all of my "numbskull" questions, and their answers, can eventually be
>added to the Wind Power FAQ .
>
>
> > And everyone thinks there must be an easier (cheaper) way.
>
>Ahhh, but there IS!  We just haven't found it yet .  Or, it's
>already been designed and patented, but just not developed for production
>yet .  There is *always* an easier and/or cheaper way to do things.
>The key is to make them reliable, and producable.  Remember, at one time
>people thought the Earth was FLAT!  That man would NEVER fly!  That it was
>IMPOSSIBLE to overcome Earth's gravitational pull (rockets).  Etc., etc.
>Man is best known for doing the impossible, including things that previous
>"laws" said were not possible to do.  On the other hand, man has NOT even
>been able to find the most prevalent thing in the entire universe -- dark
>matter .  It accounts for 80% - 90% of the weight of the universe,
>but we can't see it, can't feel it, can't measure it, nothing.  What is it?
>Does it contain energy?  It obviously contains mass.  Really makes one
>wonder ...
>
>-Don
>
>
>
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X-eGroups-Approved-By: tomgray@igc.org via email; 5 May 2000 13:41:46 -0000
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Date: Thu, 4 May 2000 21:52:56 +0100
Subject: [a-w-h] good questions

>When manufacturers and experts talk about coefficients, does that take
>into account the betz limit. By this I mean: When a coefficient is
>described as 0.42cp, is that 42% of 100% of the total raw power available
>in the wind OR 42% of 59% (betz limit) of total raw power in the wind?

Yes, the 'Betz limit' is a limit on the size of the coefficient, and the
coefficient is a % of the raw power.
Betz proved that the max coefficient was 59.6%.

>Secondly,
>I have always thought that the RPM of a rotor increases in a linear
>fashion with the wind. This is due to a fixed TSR. EG, TSR=11 then the
>tips will always go 11 times faster than the wind...
>General observation of some of my rotors (off-load) seems to show more of
>an exponential increase in the RPM?

Rotors (blades) are designed to run best at a particular 'tip speed ratio'
TSR, but in reality they run at a speed which also depend how they are
loaded.  The power from a rotor varies with the cube of the windspeed, and
the power required by an alternator depends on how the current will flow in
the connected circuit.  (yes it is complicated) If rotor power exceeds
alternator power requirements then the rotor accelerates until the 2 are
equal.  If there is no load, then they will run up to maybe nearly twice
their design speed.  If the alternator draws more power than the rotor has
to offer then it slows, and often stalls.


Hugh

Home from Peru.



*#*

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From: hugh piggott 
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Date: Tue, 7 Nov 2000 11:22:47 +0000
Subject: [a-w-h] Re: H40 Success & Thank you all

At 4:08 pm +0000 6/11/00, georges  wrote:
>--- In awea-wind-home@egroups.com, hugh piggott 
>wrote:
>>  did you note down any figures?
>
>Yes, but I do not have them with me as I write. I can read 1 v
>accuracy on a 0 -40 v range. The peak voltage never got higher than
>40. It was fun watching the rotor speed up. I set the time interval
>to 10 ms/cm (100 ms total), and the volts to 5 v/cm. As the rotor
>speeds up you can see both voltage and frequency rising. From memory,
>the peak voltage was ~ 40 v, when the frequency was ~ 30 Hz, It was
>about 20v at 15 Hz (I still have to count the poles in the motor)

It would be nice to know that number...  Meanwhile, I am puzzled by 
the 40 volt figure you mention.  If the voltage exceeds 26 volts then 
the wind turbine should start to charge the battery.  the voltage 
will then flatten out.  it should not be possible for the voltage to 
reach anywhere near 40 volts.  Maybe you mean 'peak to peak' voltage 
(which is a different matter)? Peak voltage is the voltage relative 
to 'zero'.  It is the highest voltage reached between the two wires.

>
>I live on a great island. My neighbors came over to congratulate me
>(even ones I do not know, some windsurfers  from a coulpe of blocks
>over). I offered to turn it off if it bothered them, and they said
>don't think of it. Time will tell, someone might get a bug up their
>tail.

Good.  The noise can't be that bad, then.  Last night I was speaking 
on the phone to a man on an island near here.  He said he could 
hardly believe that the noise from his AIR could be legal.  I know 
what he means.  There is one about half a mile from here and we know 
all about it.  One night it frightened the ponies and they charged 
right through a fence.

>
>As to the noise, I believe it is the karman vortex sheding off the
>blade elements in "stall" at non design tip speed ratio.

It's not actually stall, it's overspeed.  Stall is when the speed is 
too low.  Overspeed seems to cause more of a 'whistle' or swish, and 
stall causes a 'whump' or roar.

>
>(broad band). The second method is to sweep the blades so they look
>like scimitars. It works in much the same way. The problem with sweep
>is the non radial strain on the line of centers of the rotor blade.

This is the type of tip Proven use.  I am told that a 'sword point' 
is also good for low noise (Danish research).

>
>On the whole, I don't believe it is an issue. Once the winds pick up
>it is hard to distinguish the rotor from the wind.

It's a BIG issue when the blades go into flutter, but this ought not 
to happen with the whisper, because it has the angle governor.
-- 
Hugh

Scoraig Wind Electric
Scotland
http://www.scoraigwind.co.uk


*#*


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Date: Wed, 10 Jan 2001 00:34:14 EST
Subject: "Robert E Sparks" : [a-w-h] 

Bob-- Marcellus Jacobs claimed he and his brother experimented with the
multi-bladed water pumper rotors in their early days--even to the extent
of making a wheel where the angle on all of the blades were made to
"feather". Mr Jacobs stated all those blades just get in each other's
way".  The water pumper rotors are considered a "drag" device, not an
airfoil. It is unusual for a drag device to run a tip speed ratio above
1:1, whereas an airfoil will run typically 4--10:1.  They do produce lots
of torque, but at quite slow speed, compared to an airfoil rotor.
Therefore, the water pumper rotor runs so slow, the step-up gear will eat
up too much of the power it produces before reaching the generator.
At least a couple companies made a rotor resembling a water-pumping
rotor, and ran a belt around the entire outside of the rotor as a "large
drive pulley" . At the moment I don't recall the names, but one was at
Stillwater, Ok, I think. Maybe American Wind Turbine. Apparently they
weren't successful, but I found the idea intriguing!
btw, working water pumpers are in demand and you might sell it for enough
to buy a used wind generator.
John Parsons--windpower4jp@juno.com
 ---Keep looking up!--JP---  PLEASE SEND ME NO ATTACHMENTS- thanks.
--------- Begin forwarded message ----------
From: "Robert E Sparks" 
To: 
Subject: [a-w-h] 
Date: Tue, 9 Jan 2001 16:27:54 -0700
Message-ID: <001c01c07a93$df5d78c0$64560e3f@oemcomputer>

Does anyone know if it is possible to convert an old cattle ranch water
pumping windmill into one that will generate electricity.  If so where
can I
get info on how to do it.
Blessings,
bob sparks

Isaiah 64:4
For from days of old they have not heard
or perceived by ear,
nor has the eye seen a God besides You,
who acts in behalf of the one who waits for Him.


*#*


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Date: Thu, 18 Jan 2001 14:29:55 -0800 (PST)
Subject: Re: [a-w-h] Article in Home Power #65, June/July 1998


--- jnetter781@worldnet.att.net wrote:
> On Page 25 ofthe article titled Apples and Oranges,
> under the section 
> Number Of Blades, it states " A certain amount of
> torque is necessry 
> to get the rotor spinning from a stopped position.
> However, torque is 
> inversely related to rotor conversion efficiency."
> 
> Can someone explain why the second sentence is true.
> 
The energy efficiency conversion of a stopped rotor is
zero.  The energy efficiency of a low solidity rotor
will not rise to a reasonable number until it gets
close to its design tip speed ratio, which could be
anywhere from 5 to 14.  

There is torque even with zero power (stopped rotor).

Robert W. Preus

This is: http://davd.tripod.com/TipSpeedRatio.html#top