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Wind Generators – AC v. DC Output and Blade Design Effects

Thank you for the mostly accurate article about wind generators in the
Feb, “All At Sea”.  I do want to point out some things you said which
are generally accepted as true, but like many urban myths, are not.

First was your statement that the generators with A/C output are more
expensive (“because more components are necessary”).  It’s the same
number of components.  The KISS is the only one that makes the
conversion to D/C in a remote location, and it is less expensive than the other high-output wind generators..

The smaller bladed wind generators do not start turning in lower wind
speeds.  The Air X, for example, needs 12 knots to start turning.  The
generators with more than three blades start turning in lower wind
speeds, not because because the “blades are lighter”, but because there
is more torque placed on the shaft by the multiple blades.  As usual,
compromises must be made, and the generators with more than three
blades (GWMTTB) are not as efficient in higher wind speeds.  The big
advantage to GWMTTB is the effect of surface area and drag.  In higher
wind speeds, GWMTTB have more drag due to larger surface area, which
tends to limit the maximum speed (RPM), a big advantage for generators
designed for use on farms in England, which is where most of them come
from.  They also do not “cut in” at lower wind speed.  They (generally)
start turning at lower wind speed.  Generator voltage is a function of
RPM and load.  “Cut in”, sometimes called “start up” speed is the wind
speed where generator RPM produces voltage above battery voltage to
start charging, and some manufacturers use 12 volts (which in my
opinion is too low).

The amount of energy a wind generator can produce is a function of
blade swept area, with a slightly larger diameter significantly
increasing swept area.  If you look at the power curves, you will see
that “generators with smaller blades” do not produce more power in “10
to 15 mph”.

Hotwire Enterprises
102 W. Fulton St.
Tarpon Springs, FL 34689
(727) 943-0424
hotwiregam@aol.com
www.svhotwire.com

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