Coil Turns

Coil Turns determination:

Copied from www.fieldlines.com/

Originally submitted by hugh piggott www.scoraigwind.co.uk

Reposted here with his permission.

Here is a rule of thumb for finding how many turns of wire you need in the coils.

I am going to assume that you are wiring the coils in 3-phase star (wye). I am going to give you a number of 'turns per phase'. If you are winding 12 coils for example then you have 4 coils in each phase. If you need 500 turns per phase then you can do this with 4 coils each of 125 turns in series. Or you can connect 4 coils (each with 500 turns) in parallel but I do not recommend this so much.

To find the turns per phase using my formula you will need to know the following things:

System voltage V (for example 12 or 24)

Desired cut in speed RPM (for an eight foot blade try around 200 rpm or less)

Strength of flux in Tesla (Ferrites could give you about 0.2 or 0.3. Using neos you can expect 0.5 or better for dual rotor machine but it does depend on the air gap and stuff like that)

total area of magnet face in square inches (This will be the number of magnets times the face area in sq inches)

Turns per phase = 17000 x (System voltage V +1.4) / ( Desired cut in speed RPM) / (Strength of flux in Tesla) / (total area of magnet face in square inches)

Example.

You plan to use 12 magnets that are each 1" diameter. Total area of magnet faces is 12 x 3.14 / 4 = 9.4 sq inches

System voltage is 12

You want to use a fast 8 foot rotor, so cut in rpm is 200

You are using neo magnets but the magnet thickness is only 1/4 inch while the gap between magnets is 3/4 inch so we can guess flux density is 0.4

Turns per phase = 17000 x (System voltage V +1.4) / ( Desired cut in speed RPM) / (Strength of flux in Tesla) / (total area of magnet face in square inches) = 17000 x 13.4 / 200 / 0.4 / 9.4 = 303 turns.

If you have nine coils total and thus 3 per phase then you should have 100 turns per coil. Connect the coils in series and then the groups in star and feed to the rectifier. Your maximum output will only be about 1-200 watts, but that's another story

Hugh Piggott http://www.scoraigwind.co.uk