Formulas and calculators > Coil winding

Double the coils or double the magnets (single vs dual rotor)

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planetlajord:
Sorry if I'm in the wrong section! Learned a TONNE from this board but it's my first time posting.

Just about to start my 3 phase PMA build but I can't seem to find an exact answer to this question or the physics behind it. Would I get more power from more coils on a single rotor PMA or from less (but ticker) coil positions on a dual rotor (opposing magnets) PMA?

Background: I have 24 total cylinder, neo magnets (1.25" diameter, 1" thick with a 0.5" hole) and near endless supply of pre-made street lamp ballast coils (3.25 x 2.5 x 0.75). I realize these aren't ideal shapes or sizes and it wont be an exact science but these are all free and what I have to work with. Initial experiments passing a single magnet over a coil exceeded all expectations.
Blade size will be determined once I know the forces required to rotate the alternator. The use of this will be to directly power water heating elements (to heat a thermal battery water tank in the winter and a pool in the summer). Total or capacity/number of elements will be determined by the end resulting power. I live on a farm on the open prairie in Southeast Saskatchewan Canada with some of the best wind on the continent and a 50' tower.

See diagram:

<blockquote class="imgur-embed-pub" lang="en" data-id="a/VGlMuyc"><a href="//imgur.com/a/VGlMuyc">PMA for Fieldlines discussion[/url]
--- End quote ---
<script async src="//s.imgur.com/min/embed.js" charset="utf-8"></script>

Scenario 1: Large diameter, single rotor
18 coil stater (6 coils per phase) and 24 total magnets on a single rotor (with an apposing steel rotor to focus the magnetic flux)

Scenario 2: small diameter, dual rotor
9 coil position stater (with stacked coils to make a thicker coil, so still 18 in total), with two x12 magnet rotors opposing each other (connected via steel bolts to close the flux loop).

I just need the direction that provides the most raw wattage and highest amperage. Thanks for your input everyone!

MagnetJuice:
Welcome to Fieldlines,

As you said, those shapes are not ideal. However, if it is all you have, then you have to find a way to work with it.

I can tell you that scenario 2 will give you very little power. The reason for that is that your two stacked coils will be too thick. In that situation, the magnetic flux from magnet to magnet will be minimal.

If you tell us the dimension of the inside hole of the coils, there could be possible to arrange those magnets and coils in a different configuration that will produce more power.

Also, tell us the gauge of the wire in the coil. The wire size determines how much current can safely flow through the coils.

Ed

planetlajord:
Thanks Ed!
I think the diagrams I drew up would help explain this better than my feeble words, got outsmarted on uploading a pic on here when I made the post.

The hole in the coils is 1.25 x 2", they are remarkably similar to the DIY trapezoidal coils I have seen except they are rectangles. They have four leads on them (common, 110v 220v and 277v). I have one that's in rough shape that I can sacrifice. I will cut through it to do a turn count and gauge measurement (pretty small gauge), I'll attach a photo when I get home tonight. Essentially though, one cylinder magnet can fit inside, two side by side is 0.5" too big.

I am not opposed to winding my own coils if there is an optimum shape, turn count, gauge etc. in relation to my cylinder magnets. Any suggestion on how/where to get cheap, bulk magnet wire would be appreciated, all I can find so far in Canada is on Amazon.ca in tiny little roles and outrageously priced at hobby shops. If I do go this direction, I will definitely need help on the coil winding (pretty much ignored that learning up until now because I haven't been able to let go of these seemingly perfect, pre-made coils! haha).

Thanks again!

bigrockcandymountain:
I am in rural southwestern saskatchewan.  Welcome to fieldlines. 

I believe the thickness of the coils will be the most important measure.  I believe the optimum air gap is a function of magnet thickness. 

  I am no expert on axial flux.  I am firmly a motor conversion follower. 

I hope you get it done and flying.  There is a lot of power in the wind in saskatchewan.

MagnetJuice:
The holes on those coils are too long for one magnet. It would be better to use two magnets per coil.



With two magnets, there will be some magnetic flux wasted, because power is produced only when the wire is perpendicular to the magnet. The small section at the end of the coils will not produce power because there the wire is parallel to the moving magnet. But using only one magnet will waste too much copper.

With two magnets, you will get more voltage out of each coil. If the wire in those coils is at least 18 Gauge, you should be able to use them, especially if you settle for a higher voltage, like 48 volts.

The alternator will have 12 double magnets and 9 coils with a blank steel rotor on the other side.

Better yet, magnet4less have 1 x 2 x .5 rectangular magnets (Model: NB056-0) very cheap, about $6.50. Can you use round magnets on one rotor and rectangular magnets on the other rotor? Absolutely. It would look funny but it will work perfectly OK. In addition, it will produce a lot more power that with just an empty rotor on one side. As you already said, utilize what you already have.

If the wire in the coils that you have is too thin, you will be better of winding your own coils. If you wind your own, they should be round with the center holes the same diameter as the magnet. The coil thickness should be between .5 and .625.

Here are two sources to buy magnet wire. They both ship to Canada. 15 Gauge will match those magnets for a nice 48-volt alternator. Those are 10 Lbs. spools. Nice price.

https://www.ebay.ca/itm/AWG-15-Copper-Magnet-Wire-H200C-High-Temp-10-lbs/252569441837?hash=item3ace4fd62d:g:MdYAAOxyXWdQ6xcP

https://www.magnet4less.com/essex-magnet-wire-15-awg-gauge-enameled-10lbs

If you need help calculating the number of turns per coil, just ask. Someone here can help you.

Ed

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