Cogless F&P

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 the stator....

http://www.thebackshed.com/windmill/FPRewire.asp

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.

On 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 N S.

Now to keep these new 7 phase configurations separate from the old 3 phase configurations, I've come up with a new naming scheme.

7p3p
The 7p means its a 7 phase conversion, the 3p means there are 3 poles wired in series. The new 7 phase alternator has a max pole count of 6 for each phase, where the old 3 phase conversions had 14 poles per phase. We can divide the 6 poles into one group of 6 poles in series ( for max voltage ), 2 groups of 3 poles in series, 3 groups of 2 poles, and 6 groups of 1 pole ( for max current ).

So...
7p6p = 6 poles wired in series. Max volts, good for slow running windmill. 48v systems.
7p3p = 2 groups with 3 poles each. Less volts more current than above. 24v systems
7p2p = 3 groups of 2 poles. The best all rounder, similar to the old SP configuration. 12v or 24v systems
7p1p = 6 groups of 1 pole, 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.

7 phase 6 pole	7 phase 3 pole
7 phase 2 pole	7 phase 1 pole
This hub is wired as 7p6p	And this is a 7p2p
	The drawing to the left may make it clearer. Its how I wired my 7p2p ( 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 the stator.

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.