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#Post#: 153--------------------------------------------------
Alternators for high speed wind turbines
By: lynx wind Date: July 31, 2013, 3:40 pm
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It is true 3 phase alternators put out a more even rectified
voltage. There is less ripple. But it is common for engineers
to be refrencing 2 to 4 pole alternators. But what if the
alternator is 18 or 24 pole?
What does the ripple of rectified DC look like?
A high speed wind turbine can put out 60 hz easily in a modest
wind. At 60 hz you wouldn't notice any ripple at all with
single phase.
I started by making 3 phase alternators, and gradually made them
stronger with more and more copper. With this I was able to
achieve good voltage at slow rpm. But then as I started
experimenting with faster turning wind turbines I noticed that I
needed to reduce the voltage at low rpm so the turbine could
reach a good speed above TSR1.
When experimenting with a radial alternator with few turns I
noticed the turbine simply raced up to the point where the
output (minus losses) equaled the input from power in the wind.
The complexity of trying to overlap 3 phases in a permanent
magnet alternator is daunting.
So one day I tried a single phase alternator. The turbine raced
up to an rpm where the output (minus losses) equaled the power
in the wind. What happened to the ripple?
Voltage off an alternator is talked about as RMS or Root Mean
Squared. If you charge a capacitor off a Gull 160 alt at 120
rpm you will see 55 vdc on the volt meter, remove the capacitor
and you will see 40 vac. That is because the capacitor is being
charged by the peaks of the sine wave, and the meter is showing
RMS.
There is power in the peaks. A battery or a load will absorb
these peaks un-noticeably, but there is some power. A very good
way to charge batteries is with pulse charging instead of just
straight hard amps which can cause overcharge, or heating of the
plates, boiling of electrolyte.
The other benefit is that instead of a hard point at which
charging occurs, the cut-in is a soft point. I noticed this
with the first single phase alternator I made. The volt meter
showed 7 volts and yet the battery was showing charging at that
same rpm.
And instead of stalling the turbine in light winds, the turbine
can operate up and down in that rpm range.
I have seen charging in winds as light as 1-2 mph. And with
just inertia I have seen charging at .5 mph .
I feel the complexity of a three phase alternator is not merited
for high speed VAWTs. The idea that they are more efficient
applies more to hard amperage work.
Another benefit of single phase is that it is possible to run AC
lighting directly. CFL and LED lighting for instance.
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#Post#: 837--------------------------------------------------
Re: Alternators for high speed wind turbines
By: rrattink Date: November 17, 2013, 12:06 am
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I was looking at serpentine windings on youtube and was
wondering what your opinion was on using this these for your
wind mills? They appear much easier to produce.
Another point I was thinking on was using multiple or
alternately stacked windings to take advantage of both sides of
the magnet plate thus duplicating the power potential from the
same rotation.
Wadaya think? :)
#Post#: 838--------------------------------------------------
Re: Alternators for high speed wind turbines
By: crazyguy Date: November 17, 2013, 9:17 am
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Welcome.
Single phase is more economical to build also.
I think it's a toss up on serpentine windings being easier to
wind than the multiple single coils. The serpentine has to be
wound by hand (or some new fangled machine). The single coils
can be wound very fast on a drill motor. Either way considering
an axial design, the shape of the coil and magnet cannot be made
to produce the most power from your materials. That is because
of how the magnets enter and exit the coil legs. You get sort of
a sine wave or some other complex wave shape. I figure a radial
alternator can have square magnets passing over square coils
producing more power, because entry and exit angles are
parallel. Shown below is a radial alternator.
Stacking coils and magnets produces more power but also requires
more power to spin.
IMHO
#Post#: 839--------------------------------------------------
Re: Alternators for high speed wind turbines
By: lynx wind Date: November 17, 2013, 9:55 am
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I have made all types of alternator. Radial, Axial, 1, 2, 3
phase. I have made some awesome alts with nearly as much copper
as is theoretically possible to jam in.
Serpentine doesn't save on resistance and can be easy to wind on
a big round diameter and then the shape force formed after.
Hopefully you can visualize what I am going to say now. A
single coil will come off a form tight and with square sides.
There is more area in a square than a circle. It is really hard
to maintain the same amount of copper in the serpentine shape if
it is post formed. It is really hard (if even possible) to
pre-form it on a serpentine jig because of the way the wire goes
on - first on the inside of a turn and then on the outside of a
turn.
So I would say if the aim is to maximize wire in a single phase
alt don't use serpentine. I would recommend it for 2 and 3
phase though because the phases can be crushed down together to
form a dense coil.
Keep in mind this single phase alt really only pertains to
keeping manufacturing simple and costs down and simple for a
DIYer and suited for a high speed VAWT that will automatically
match peak rpm to wind speed. That's a lot of conditions to be
met. Obviously for certain applications other alternator
designs could be more suited.
#Post#: 841--------------------------------------------------
Re: Alternators for high speed wind turbines
By: rrattink Date: November 17, 2013, 12:52 pm
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Thanks for the input. The serpentine example I saw was for
three phase with an offset between three windings. I get what
you meant about coil density. I also appreciate your quick
response. Great job on the mini joule thief BTW. The ferrite
component really make sense when I see the stuff lasersaber is
doing nowadays. Keep up the amazing experimenting.
#Post#: 844--------------------------------------------------
Re: Alternators for high speed wind turbines
By: lynx wind Date: November 17, 2013, 3:32 pm
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Here is a picture of a Boreas Alternator stator. You are
looking at 4.5 Lbs of copper squeezed down to 3/8" where the
magnets pass. Note how the three phases nest together.
Now if this was a single phase alt we could get much more copper
in by winding individual coils.
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