Coil basics

[thrilla]

I can't seem to find what I'm looking for searching, so maybe I'm using the wrong terms, but here goes......

I'm working my way into understanding the building of an axial flux alternator (aka, reading a LOT for the last few weeks).  I'm to the point of being ready to do some testing using a drill press to spin a makeshift rotor over some coils to get a better grasp of how it all works (and maybe to convince myself that I can make it work ).

So far, I've gleaned that the hole in the middle of the coil should be the size of the magnet(correct me if I'm wrong).  Things I'm fuzzy about or I have no idea on:

1. How do you estimate the # of turns in a coil?
   
2. How thick should the coil be?
   
3. What direction should the coils be oriented in relation to the direction of the rotor?
   
   

I'm sure these questions have been answered someplace, but I've haven't had much luck finding answers.  Again, I'm easing my way into this piece by piece.  Correct me on any assumption I've made, I'll appreciate it.

Thanks!

[electrondady1]

3. / there is no relationship
   
2. / the thickness is usually the same as your magnet.
   
1. / what sort of rpm does the drill turn at?
   
   

the coils must all fit together on the stator and that

dictates the outside dimensions.

you  need a specific number of turns to reach a charging voltage at a specific rpm

prop speed in a given wind

if your just messing around, put on 50-100 turns

[thrilla]

Thanks electrondady1!

I'm just messing around for now to get the basics in my head.  The drill is variable speed, so I'll probably try it on several different speeds to see how much difference it makes.  Nothing drives a point home like experiencing it first hand.

Thanks again, and I'm sure I'll be back with more questions

[SparWeb]

Hi,

Welcome to the world of producing your own electricity!

Take a look at this, maybe it will help you (requires Adobe Acrobat)

http://www.sparweb.ca/Forum/AXIAL_FLUX_HowItWorks.pdf

Something else I could mention about the coil orientation is that when they get wired together in one phase, they must all work together to produce voltage.  The voltage is induced in the coil when the magnet passes.  If the magnet pole goes from N to S, then one voltage polarity is induced, but if it goes from S to N, the voltage is opposite.

I doesn't happen often, but some builders discover that they have wired up a series of coils with one backwards.  The result is a "weak phase" or no power at all.

The way to keep things straight is by watching the wires go "clockwise" or "counter-clockwise around the coil.  A N-S magnet pole going over a clockwise coil will produce the same voltage polarity as a S-N magnet pole going over a "counter-clockwise" coil.

[thrilla]

Extremely helpful PDF!  Thank you for sharing!  I'll be reading it a few more times.

[willib]

I believe that is a common misconception ( about the coil hole )

On my second minigen i made the hole 0.445 dia. and my magnets were 0.875 dia , ( 7/8).

This enabled me to make my coils thinner than i would have been able to otherwise.

my two cents

Bill

[thrilla]

I'd like to thank everyone for their comments!  I was able to do some testing (playing) this weekend with magnets, coils, etc.  

So how did I do?

Not real great, haha!  It was my first try and I learned a lot.  For instance, have a plan to get the coil off of the winder.  I could open it up, but the copper was so tight around the mold (plywood) that it wouldn't slide off.  I'm thinking a few wraps of paper should fix that.  Another is that I should base my coil shape and size not entirely off of magnet size, but on the shape and size from one leading magnet edge to another (larger shape, and a little more triangular).  

I also ran across another post that recommended looking up the user Electric Ed and checking his drawings, very useful, and illuminating!

http://www.fieldlines.com/story/2003/4/10/221932/659

http://www.fieldlines.com/story/2003/5/8/113141/6796

I'm sure very basic and rudimentary knowledge, but some things you have to learn the hard way.  I figured I'd share what I learned for others that are starting out to learn from.  I'll post some pictures when I get some.  I didn't really take many as I was keeping my cellphone and wallet well away from my work area so that nothing got ruined with the magnets.

Thanks to everyone that posted thus far with info, I appreciate it!  Hopefully I'll have a little time during the week to make a new center "mold" for my winder, or a new winder all together and try again next weekend.