The stator is the very important electrical part of the wind
turbine. It contains all the coils of wire which will have voltage
induced in them as the magnets pass over them. It's defined as the
'stator' because it is the 'stationary' (it doesn't turn) part of the
alternator. For this project you're building a 3 phase alternator and
the stator will have 9 coils. Each phase will consist of 3 coils in
series and you'll make a star connection between the phases. You'll
build this in our stator mold and the lines on the bottom of the stator
mold will help to know the the coils are the correct size, and that
they're placed correctly.
- 6 pounds magnet wire. (best is to use double insulated 200 deg C
- 15" diameter disk of fiberglass fabric, qty 2
- Thin viscosity Cyanocrylate glue (super glue) with
- 1/2 Gallon polyester resin
- electrical tape
- heat shrink (optional)
- 3 brass 1/4 - 20tpi screws 1.25" long
- 12 brass or copper 1/4" washers
- 6 brass 1/4 - 20 tpi nuts
Winding the Coils
Pictured above Scott's winding with two strands of wire. This
is necessary for 12 Volt machines.
The magnet wire you need depends on the voltage of your
system. Roughly speaking, every time we go up 3 sizes in magnet wire
then the wire has half the cross sectional area. The voltage of the
machine is directly related to the number of turns in the coils. If we
double the number of turns, then we double the voltage. No matter what
the voltage of the machine, the coil size and weight needs to remain
about the same. 12 Volt machines require very thick wire, so thick that
it makes sense to wind with two strands in hand. (so for 12V machines
we need two spools of wire and we're handling two strands as if they
- For 12 Volt machines you need to wind with two strands of
#14 gage wire in hand and each coil should have 36 turns.
- For 24 Volt machines wind with 1 strand of #14 gage wire
and each coil should have 70 turns.
- For 48 Volt machines wind with 1 strand of #17 gage wire
and each coil should have 140 turns.
If you follow the guidelines above, and the coil winder is
made according to the plan then the coils should fit nicely in their
alloted space, and the whole stator should require about 6 pounds of
wire. If the rest of the alternator is assembled properly then the
machine should start charging batteries at about 140 rpm which is nice
for a 10' diameter blade.
Start by creating some kind of fixture to hold the spool of
magnet wire. I usually use a vice with a piece of threaded rod, or a
wooden dowel sticking up to put the spool. Clamp it to the work bench
Clamp the coil winder to the workbench with a C clamp as
shown in the picture.
You'll need a pair of side cutters (to cut the wire), a pair
of needle nosed pliers (to bend the wire) and some electrical tape. If
the coil winder has a wing nut holding it together then you can use
your fingers to take it apart. Otherwise you'll need a 1/2 wrench. When
you bolt the front on the coil winder finger tight is fine, but after
all the wire is wound on the spool the nut will be tight so - if you
dont have a wing nut, you'll need a wrench to get it apart.
About 10" from the end of the wire bend it sharply 90 deg
with the needle nosed pliers.
Drop the wire in the slot of the coil winder and bend the end
around the nut. (A wing nut helps here too..) This will hold the wire
from slipping when you wind the coil.
Hold the wire tightly in one hand (keep tension on it) while
turning the crank with the other hand. Be careful to keep constant
tension on the wire and try to turn the coil winder at a constant
speed. I notice lots of folks tend to turn it faster on the down stroke
and slower on the upstroke - this will usually result in a lop-sided
coil (one side of the coil wider than the other). It's important to
keep constant speed and consistant tension. Try to wind the wire in
neatly but don't obsess over perfection. I've seen some folks take over
an hour to wind a coil trying to pile the wire in perfectly. It should
take no more than a minute or two to wind a coil.
Once you've got the correct number of turns, pull the lead
out of the slot and twist the two ends together (1/2 twist - just
enough to hold them together). Don't twist more than you need because
later you'll undo this and it's nice not to bend up the wire more than
necessary. Grab the wire between the spool and the coil with one hand,
and clip it so that there's about 10" of wire out of the coil. (both
leads coming from the coil should be about 10" long) Take the loose end
that's coming from the spool, put it on the workbench and set something
on it (the side cutters are handy since they're probably still in your
hand) so that the wire on the spool doesn't unravel.
Take the end of the coil winder. The coil will come with it.
The coil should pretty much fall off the end if you just turn
it over. Do it carefully so the coil doesn't fall apart.
We refer the longest sides of the coil as the 'legs'. Tape
the legs of the coils with a couple wraps of electrical tape to hold
things together. One coil is finished.
Check your coils, they should fit in the stator mold as shown
in the picture. It's OK if they're a bit smaller we used #16 gage wire
in the coil pictured. If you use #17 wire as called for, they'll be a
bit smaller. Remember the stator mold has 9 radial lines that tell us
the maximum width of the coil, and it has two circles (8" and 12"
diameter) that show us the path of the magnets. When checking the size
of the coil center the hole in the coils center over the 8" and 12"
circles. In that position the coil must fit in between two of the
If the first coil fits well, then wind 8 more like it. In the
picture we've put all 9 finished coils in the mold, you can see how
they're almost a perfect fit. Again - you might have them come out
slightly smaller than those pictured which is fine.
Wiring the stator
The drawing shows how we'll wire the coils together. Each
phase is numbered and consists of 3 coils in series. We define each
coil (and each phase) to have a 'start' and an 'end'. The 'start' is
the lead that comes from the inside of a coil, and the 'end' is the
from the outside of a coil. The only thing not shown in the drawing is
the 'star' connection. (In the drawing the starts are labelled A, B,
and C, the ends are labelled X,Y, and Z) To make the star connection
you'll connect the 3 starts (A, B, and C). The only difference between
the drawing and what you're going to do is that you'll make all the
connections on the inside diameter of the stator.
Take 3 coils and put them in the mold in their proper
position. Pick 3 spaces which are 120 deg apart. If you coud
superimpose and image of our magnet rotors over these three coils you'd
see that they are seeing an 'identical' magnetic situation, therefor
they are 'in phase' with one another. (when one of them is at maximum
voltage so will the other two be). Be sure all 3 coils are same side up
(the start of the coil is the wire that crosses over the inside, and it
should be facing up - you need to be sure that no coils are 'upside
down'. We are about to wire up 1 phase of the alternator.
Take the 'end' of one coil, and wrap it around so that it
points towards the outside of the mold - and tape it to the leg of the
coil. (Basicly you're adding 1/2 of a turn to the coil when you do
this). It used to point towards the inside of the mold, now it should
point to the outside. Then take the inside of of the same coil and bend
it around the island in the middle of the mold to the next radial line
in the mold, and cut it off about 1/2" past that line. This wire will
connect to the end of the next coil, and the start of that coil will
need to connect to the end of the last coil in that phase. So what your
doing is making sure you have just the right amount of wire to connect
the coils and cutting off the excess. It's better to be a bit on the
long side than a bit on the short side so give yourself a little extra
length to be sure - but not much because there's not much room for wire
on the inside of the mold. Once this is done to three coils you have 1
phase ready. Repeat this for the next two phases.
The insulation on good quality magnet wire is fairly thick
and very hard to scrape off. I find that it's usually double insulated
and the inside layer of insulation is almost invisible, so even though
you might think you've done a good job of stripping the wire - it can
be decieving! The best way is to burn the insulation with a propane
torch, about 1" back from the end of the wire. I usually heat it enough
so that the wire itself becomes red hot. This also anneals the copper
and makes it easier to twist together. Do this to all the leads that
you've cut. You've not cut the end of the 1st coil yet (it sticks out
towards the outside of the mold) and you've not cut the inside of the
last coil yet so leave those be - you'll deal with those later.
Let the wires cool down, and then clean the burned insulation
off carefully with sand paper.
Put the 3 coils back in the mold and twist the wires together
tightly. You can see in the picture how the connections are pretty much
centered in between the coils. Then solder the connections, and bend
them over with pliers so you can insulate them with electrical tape and
keep it all as thin as possible. You can also use heat shrink here for
neater appearance - if you do, be sure to put that on before you twist
the leads together!
If you're building a 12 Volt machine with multiple strands of
wire it can be tricky to twist things together nicely. For machines
that have multiple strands, it works well to make your connections by
inserting the coil leads into small copper, or brass tubing - and then
crimp and solder.
Once you have one phase connected together, carefully remove
it from the mold and do the same thing to the other two phases.
Once all three phase are finished, put all three back into
the mold as shown in the picture. Do it such that your three 'ends'
(those wires that are pointing towards the outside of the mold) are
beside each other. Those three 'ends' will be the leads out of the
stator (the output from the wind turbine).
Now you need to make the star connection between the phases.
The 3 inside leads should be brought together so that we can connect
them together. Leave enough slack in the wires so that we can make this
connection, and then push it down between the coils and the island in
the mold. So figure the length, cut them off, burn the insulation with
the torch, sand it, twist them and solder them. Then insulate the
connection with electrical tape or heat shrink.
Pictured above is the finished star connection, all that
needs to be done is to poke it down so it doesn't stick up above the
Even though the coils fit well and are the right size, once
we make all these connections things are kind of springy and surely the
coils are not in their perfect place. The connections we made and all
that wire around the inside is sure to push some of the coils out
further than they ought to be. Use duct tape and go around the stator 1
coil at a time, and tape it exactly where it belongs. Keep the tape off
the 'legs' of the coils as shown in the picture.
Cut 9 little rectangles from fiberglass cloth about 1.5" wide
and 2" long. Before you cast the stator you'll need to remove the coils
from the mold again. We'll use these squares of cloth and superglue to
hold everything together so that we can move it.
Use the cyanocrylate glue to glue the fabric rectangles to
the legs of the coils. Put plenty in - you'll know its a good glue
joint when the cloth becomes transparent. This will also serve to
somewhat 'pot' the legs of the coils and prevent individual wires from
vibrating against one another - maybe not an issue, but I like to have
lots of superglue in the coils. Also put glue on the fabric between the
coils so that the fabric becomes 'hard' and less flexible. This will
make the stator fairly rigid and easy to handle before you cast it. Try
hard not to glue the coils to the mold!
In the picture you can see all the coils are connected to one
another with fiberglass cloth.
Remove the duct tape, it should pull off easily.
Now you can carefully pick up the uncast stator and remove it
from the mold. Put it somewhere safe untill you're ready to cast the
stator in resin.
Casting the stator
The stator will be cast in the same polyester resin you used
for the magnet rotors. You'll need fiberglass cloth on both sides of
the coils. It might be useful to reveiw the section on casting magnet
rotors before doing this as the proceedure is very similar and safety
precautions are the same.
If you fold the fabric correctly, you can lay out just 1/4 of
the ring and cut out two in one shot. You need two rings of fiberglass
15" outer diameter and 6" inner diameter.
In the picture you can see the two rings of fiberglass. Set
them, and the coils aside for now. Grease the stator mold inside, on
top - and around the edge. Same with the lid - everything should be
carefully covered with grease, or wax. Automotive or wood wax works
It takes about exactly 1/2 gallon of resin to cast the
stator. Find a level place to put the mold. It's important to either
keep the edges of the mold off the workbench - or find a work bench
(like the one in the picture) that allows access for C clamps around
the edges of the mold. When your done you'll need to clamp the lid down
with C clamps so think ahead! Pour about a pint of resin into the mold
and roll the mold around so that the whole bottom and the sides become
covered 'wet' with resin.
Put one of the fiberglass rings into the resin and work it
with a stick untill it becomes saturated. When saturated - the fabric
will become almost invisible. (you won't see any white)
Then pour about another pint of resin in the mold, work it
into the fabric more - try to work out any airbubbles.
Put the coils in carefully, poke at them so resin runs all
around the coils and airbubbles come up.
Then fill the mold with resin and be sure all surfaces of the
coils have resin on them.
Put the remaining fiberglass ring over the top of the coils
and work resin into it - again, it should almost disappear.
Pour the remaining resin over the top of the fabric. Work it
in and try to work out air bubbles. It might not hurt at this time to
beat on the mold a bit or vibrate it with a sander (or something) for a
couple minutes to help air bubbles rise to the top.
Carefully put the lid of the mold down over the casting.
Put a 1/2" washer over the threaded rod, and run the 1/2" nut
down over it. Tighten the nut - this does a good job of clamping the
lid tightly on the mold and assuring that the finished casting will be
Put a C clamp on each side of the mold (use 4 C clamps) and
tighten them evenly. You'll have some idea when the resin is hard by
all the stuff that spilled out the side! Let the stator sit in the mold
untill the resin is hard.
A chisel works well to scrape/peel the resin off around the
outside of the mold. A good time to do this is while it's still a bit
flexible (before it gets really hard).
Once the resin seems hard then remove the C clamps and the
nut in the center. Use a chisel or a screw driver to gently pry around
the lid untill it breaks loose.
Once the lid comes off you can usually turn the mold upside
down and the stator will just fall out. If not then turn the mold
upside down and tap on it with a hammer or pry gently at the edge of
the stator. It should come out easily.
Use a file or a sander (or both) to clean up the edges of the
stator. The inside diameter must be pretty clean because there's not a
lot of extra room between this hole and the wheel hub which will exist
It's nice if you do drill the 3 holes for the studs that hold
the stator to the wind turbine before you do the welding on the frame,
then you can clamp the stator bracket to the stator on center and drill
1/2" holes right through it. If you do it this way, it's very important
that the center hole of the stator be just about perfectly centered
with the stator bracket. Also be sure to have the 3 holes come out
between coils - preferably with the 3 wires coming out between the same
two holes. You don't want to hit copper with the drill bit!
If you've allready welded up the frame then you can center
the stator on the wind turbine frame against the stator bracket and
clamp it there - and drill through the holes.
Drill 3 holes 1/4" in diameter about 1/2" away from the edge
of the stator - one near each of the leads that's coming out.
Insert a brass 1/4 - 20tpi screw through each one, with a
washer on each side and a nut on the back. Cut the leads just long
enough so you can clamp each one between a screw head and the washer.
You can put a couple more washers and one nut on each screw now. These
will serve as the lugs to which we can connect the line to the wind
The stator is finished! We can put that aside untill we're
ready to assemble the alternator.
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