|The 7 phase F&P conversion
One of the biggest problems with the
F&P is cogging, or the amount of effort required
to start the windmill from a stand still. Many a windmill
has been built that refuses to start until the wind
picks up. But once going, the windmill will make power
at much lower windspeeds.
The standard F&P stator has 42 poles,
and the magnet hub has 56 magnets. This gives us a 3
phase output, but cogging is bad.
However later models of the F&P
use a new magnet hub, it only has 48 magnets. If we
use one of these hubs on a common stator, cogging is
reduced to almost nothing. But there is a catch, we
need to re-wire the stator to 7 phase.
Before we go further, I would recommend
you read this page, it describes the process of re-wiring
Ok, the new magnet hub wont appear on
the recycling piles for a few years yet, its only a
new model, but you can buy them new for about $60 to
$80 from your local white goods agent who repairs F&P
gear. The part number you need to ask for is...
Part No. 420 774 P
The old hubs had 14
large ceramic blocks, each with 4 magnets, giving us
56 magnets. The new hub has 16 ceramic blocks, each
with 3 magnets, giving us 48 magnets, and the new ceramic
blocks are physically smaller than the old type. The
new hub magnets lines up with a stator pole every 7
poles ( where it was every 3 poles with a old hub ).
Here you can
see a ceramic tile from a old hub next to the tiles
in the new hub.
the subject of tiles, each tile consists of magnets,
the old 4 magnet tile to the left, and a 3 magnet tile
on the new hubs to the right. There would be two different
new tiles, one that goes N S N, and one that goes S
We can use out standard re-wire naming scheme as explained on the F&P Stator Rewiring page, and just add "7Phase" to make it clear its a 7 phase conversion.
7Phase 1X6C = 6 coils wired in series. Max volts, good for
48 volts systems or 12 / 24 volts on a slow running turbine.
7Phase 2X3C = 2 lots of 3 coils. Less volts more current
than above. 24v systems
7Phase 3X2C = 3 lots of 2 coils. 12v systems.
7Phase 6X1C = 6 lots of 1 coil, all wired in parallel. Max
current, suits a fast windmill. 12v systems
Click on the drawings below to see full
size. For simplicity each drawing only shows one phase,
so you just need to do the same connection for the other
6 phases. The Star connection is a common connection
to all phases.
This hub is wired as 7Phase 1X6C
And this is a 7Phase 3X2C
drawing to the left may make it clearer. Its how
I wired my 7Phase 3X2C above, which I used on my faster
spinning HAWT. To convert your stator, you need
to cut the wires for each coil/pole. I found if
I unwind the outer coil one turn, it was then long
enough to reach the next coil, 7 poles further around
You may wonder what the difference in
7 phase power is compared to 3 phase. 7 phase has a
slightly higher output voltage peak, and less ripple
after rectification. The drawings below may help. V1
is less than V2
Rectification. I threw
together a 7 phase bridge rectifier using 4 cheap 35amp
bridge rectifiers from Dick Smith, like this...
Special thanks to Bruce.