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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 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.

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.

So...
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.


7Phase 1X6C

7Phase 2X3C

7Phase 3X2C

7Phase 6X1C

This hub is wired as 7Phase 1X6C

And this is a 7Phase 3X2C
The 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 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.

© TheBackShed 2011