Alternator layout

[Roly SA]

Hi All

If i want to design a small alternator (100mm or about 4" diameter), with 2 stator rings (for a start) and 3 rotors (1 on each end and 1 in the middle)with 6 coils on each stator, what would the best magnet layout be?

The coils i want to place in 60degree spaces. Assuming this will be 3 phase, how should the magnets be placed to give best results?

I have read that ordinarely you would have 1.33 magnets for each coil, so that would be 8 magnets. Am i correct in assuming that the magnets just be spaced on 360 degrees / 8 which is 45 Degrees?

The coils will be fairly small, about a wedge that can fit inside a equal sides trangle with 58mm sides.(all 3 sides are the same length)

What thickness must the coil be and will it work in a triangular shape? I have made some drawings with the coils about 10 mm thick with the outsides fitting in the above mentioned triangle. So hopefully they will be sufficient.

So the plan is to have 2 stators in above configuration (if its possible of course) with the 3 rotors on the sides and middle. If the middle rotor is the same thickness as the magnets, can it be made to have its faces open so that north pole one side of the rotor, and south pole other side? There isnt any rule against that is there?

Any suggestions or thoughts?

Thanks in advance

Roly SA

[Roly SA]

As soon as i have posted this, i found the following on the board:

http://www.fieldlines.com/story/2007/11/12/55458/516

This is basically what im after. The middle rotor will be made from composite material, with the magnet faces open to the stators.

Any thoughts still?

Thanks

Roly SA

[Flux]

Your diameter is very small but with the high speed you should get something reasonable.

Yes 6 coils will work with 8 poles.

By using a single magnet in the centre you will not have as much flux as two dual rotor machines stacked, but you have not specified any magnets so you could choose slightly thicker ones. If you have to fix the magnets to the outer discs to stand 3000 rpm then I would personally use a steel centre disc with magnets stuck on both sides. To me it seems easier than making some composite disc but that is your choice, it will be ok.

I assume this is for battery charging. If not you would need to think again as it will be 3 phase and 150Hz so not directly useful for other things.

Flux

[Roly SA]

Thanks Flux.

Initialy it will be to charge a battery bank. I have read that the mimimum voltage generated must be more than the battery voltage otherwise no charging.The battery bank will be connected to an inverter.

I dont know much about inverters or battery banks at all, but want to learn. Am i correct in assuming that if the inverter has a load of 5kW, and the battery bank is 12VDC, the amps needed are 417? All i know is that Watts = volts x amps. Please correct me if im wrong, or tell me that i am.

I also have a small sketch of the coil size i want to use, please check it out and advise.

Roly SA

[hiker]

heres one........

                    http://www.fieldlines.com/story/2006/9/9/175715/7026

[Flux]

Your theoretical amp figures are correct for 5kW, add 20% for real life. I don't consider that practical at 12v.

Your coils would suit round magnets, if you use other magnet shapes I would more or less keep the coils the shape of the magnet but being so small you have little option.

Don't expect 5kW from that tiny machine so you will be doing more charging than running the inverter.

Flux

[Roly SA]

I have redesigned the whole thing. The stator is now larger, with the coils placed between a 200mm diameter and 70mm diameter concentric circles. Still only 6 of them in 60degree sectors. This coils are now slightly larger, about 20mm thick wedge shaped fitting in a 115mm equilateral(spelling) triangle.

If i had 8 wedge shaped magnets, could i fit them against each other? Basically a solid magnetic ring.

I saw in another posting that its better to use laminated steel backing plates for your rotors to redirect the flux back to adjacent magnets. How does laminated steel differ from plain old mild steel? Is it layers with some insulation in between?

[Flux]

"If i had 8 wedge shaped magnets, could i fit them against each other? Basically a solid magnetic ring."

Yes you could but it would not be an effective use of magnet material. Much of the flux would be in the wrong place and be wasted. With the single layer stator you don't gain much with magnets wider than the spaces between them. For a conventional winding then space half magnet width seems about right.

If you rotate the iron with the magnets then there is no need to laminate. You need laminated magnetic circuits when they are stationary as the magnetic field will cut the iron just as the copper. You are mixing up many ideas.

Flux