|Windmill Kit, no longer supplied..
Now that your windmill is up in the air, you
need to work out what to do with the output power.
But first a word about the windmills "Power
Band". A windmill behaves a lot like a conventional car
engine, at low RPM a engine makes little power and is easily
stalled, and at high RPM there is the risk of premature wear
or breakage. You want to keep your windmill in the mid RPM
range where its making most power reliably.
As a experiment, with the windmill stalled
( pulled out of the wind ) connect 2 100watt spotlamps in
series across the output leads. Allow the windmill to find
the wind, and it will turn slowly ( assuming its a moderate
breeze, a strong wind will overcome the load from low RPM
), and the spotlamps will not light or only glow dimly. Disconnect
the spotlamps. The windmill will speed up quickly to 200-500
rpm. Connect the spotlamps. They will glow at full brightness
with little drop in windmill RPM. The windmill is now in its
power band and will continue until the wind speed drops off.
If you connect your windmill across a 12 volt
battery, the windmill will see no load until the output voltage
increases over 12 volts. Therefore the windmill will be able
to speed up to its power band before there is a load.
This power band is where you need to operate
the windmill for best results.
Regulating windmill power is a little more
tricky than solar cells. Solar cells can be open circuited
when the storage battery has reached full charge. This is
not a good idea for windmills. Say your windmill is pumping
out 20 amps into a 12 volt battery in a strong wind, and spinning
at about 400 RPM. If your regulator circuit suddenly open
circuits the windmill, it has no load and will speed up to,
say, 800 RPM. At this high speed the windmill output voltage
could reach over 50 volts. If you regulator suddenly reconnects
the battery the windmill output current will be excessive
and can cause damage. Remember the windmill is acting like
a big flywheel and will take some time to slow down to a safe
speed. Excessive speed can also increase the wear and tear
on the windmill blades, at 800 RPM a 2 meter diameter propeller
will have a tip speed of 300kmh! Any dust or rain droplets
( or unfortunate insects ) hitting the blade at this speed
will quickly pit and wear down the blade tips.
So a suitable regulator will need to switch
the windmill output from the battery bank to a dummy load,
therefore keeping the windmill RPM down to a reasonable speed.
I use 4 100 watt 12 volt spotlamps, wired in parallel, but
you could use several electric heater elements. Maybe mount
the heater elements into an old hot water urn as a free water
The regulator used for my batter charger uses
a PICAXE chip to switch MOSFETS. Click here for more info. Oatley Electronics ( www.oatleyelectronics.com ) also sell a windmill regulator kit for approx $22 plus delivery.
A better option would be to use a commercial regulator, such
as the Plasmatronic PL regulator, configured as a shunt regulator.
The Plasmatronic regulators are easily programmable and robust,
for more information or sales you can contact Thomas Pluess
from Sun Power Mackay via email at email@example.com.
For more infomation about Plasmatronic Regulators
check out the three PDF files below.
Regulators for Windmills 1.
Regulators for Windmills 2.
Star to Delta switch.
If you live in a high wind area
you could rewire the stator as a delta configuration.
Delta configuration will provide
more output current at high RPM, but output is much less at
low RPM compared to a star configuration. You could design
a circuit that switches the windings from Star to Delta as
the RPM increases.
3 Phase Transformer
The problem with the low voltage
from the windmill is that you need a heavy core ( 5mm dia
or better ) power lead if your battery bank is a fair way
from the windmill. Or you could try leaving the stator as
standard ( output 0 - 300 volts AC ) running a conventional
240V 10 amp extension lead from the windmill to your battery
bank, and then use 3 step down transformers ( 240-24 volt,
10 amp output ) wired across each phase. Each transformer
will need to be fed into its own full wave rectifier, the
outputs coupled together to provide your low voltage high
current output. The problem with using transmormers is they
are designed to operate at a frequency of 50Hz, but the windmill
output frequency would be a lot higher than this, so the transformers
will not run efficiently and overheat.