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Pole to coil counts..
By windstuffnow, Section Mechanical Posted on Fri Jun 23, 2006 at 11:45:31 PM MST
Just to create discussion and a little contraversy

I found an alternator that has an extreemly odd pole to coil count, 46 poles / 51 coils. It completely threw me for a loop. I decided to disect it but didn't want to destroy it because it works so nice. Even with the laminants there is 0 ( yes Zero ) cogging. The metal/magnet drag is around 180 grams of force to start it turning. A laminant that runs almost as smooth as a dual rotor for start up definately needs some intense investigation.
Without actually unwinding it coil by coil I started following the coil groups the best I could but was easily lost and confused. Well, it gave me an idea that I had to follow up on... I started with my little educational wind turbine stator, has 18 slots for a 6pole/18 coil arrangement. But could it actually work with an 8, 10 or 12 pole arrangement? Sure enough !
I came up with an idea that you can wind almost any combination pole/coil to come up with a 3 phase alternator as long as your coil count can be divided by 3 any amount of magnets can be used.
First I worked out the degrees the magnets were placed and then a list of degrees the coils were laid out and found there is always a pattern of which ones will line up for each phase.
Some times you have to use small groups of single phase windings spaced all over the place to complete each phase but it almost always follows a pattern.
I'm building a 14 pole 8" alternator with 15 coils to make a 3 phase output. Can you figure out how it will be wound for a 3phase output... I was pretty amazed when I finally figured it out.
Playing with the plastic stator rewinding it to use 8 poles instead of 6 increased the open voltage by almost 50% and reduced the resistance by 25% per phase. Each phase used 121 ft of wire for the 6 pole, the 8 pole used only 91 ft of wire for the same 6 coils.
I'm sure this isn't something new but it definately opens up a whole new world for different configurations to make smaller more powerful alternators...
Try making up a chart with different pole/coil counts using degrees, you'll be surprised how things line up. I'll get some pictures of the little stator as soon as I get some more time...
.

Pole to coil counts.. | 21 comments (21 topical)

Re: Pole to coil counts.. (3.00 / 0) (#1)
by zubbly on Fri Jun 23, 2006 at 06:40:20 PM MST

thats quite interesting, sort of reminds me of the dual rotor with 12 mag 9 coil arrangement or 8 and 6.

it would "i think" end up having part of the mags in different position to the lams, so cutting out or eliminating the cogg.

any chance of you taking some close up pics of the stator winding and mag arrangment?

damn, now i gotta try something else, what a disease ;) lol!

zubbly

Re: Pole to coil counts.. (3.00 / 0) (#4)
by windstuffnow on Fri Jun 23, 2006 at 06:54:52 PM MST

Darn zubbly... I was sure you would come up with a name for that kind of winding. I must say it's opened up an whole different way of thinking for me. Seems like whenever I get to a point where I feel like I'm stuck something comes along and creates a whole new set of ideas and in this case changes the rules a bit.
I've put the machine back together and didn't take any pictures. It's chucked in my lathe where I've been running a bunch of output tests on it. I still haven't figured out how it's wired but it sure gave me a flood gate of ideas and so far the first few have worked extreemly well.
Your right about the disease part... addiction.. compulsion... all of the above
.
Have Fun! Windstuff Ed
[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#2)
by zubbly on Fri Jun 23, 2006 at 06:46:10 PM MST

it just struck me,

sometimes a client would request a pole change in their motor. perhaps to speed up or slow down their production line. if we were not carefull, we could end up with producing a cogg, cusp, or high electrical noise if we made the pole change in the stator with out checking to see if the rotor bar combination would also be compatible with the new number of poles in the stator.

the design you are speaking of Ed may be very similar in design. i am gonna think a little on this as well.

zubbly

Re: Pole to coil counts.. (3.00 / 0) (#3)
by zubbly on Fri Jun 23, 2006 at 06:51:50 PM MST

i'm not gonna sleep tonight :) lol

mag poles
coils

how many stator slots-what coil span (s)

zubbly

Re: Pole to coil counts.. (3.00 / 0) (#5)
by jimjjnn on Fri Jun 23, 2006 at 09:35:00 PM MST

I want to see where you Gents go on this one. I cant do any of this in my Condo but sure enjoy what you fellas are doing. Keep it up cause no problem seems to bother you. Fun watcghing you solve what seem like big problems with KISS. Go gents GO
Denver,CO
[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#6)
by Flux on Sat Jun 24, 2006 at 12:53:15 AM MST

Ed
If you can check the waveform on a scope you will likely find it to be a good sine wave.

For alternators feeding rectifiers, any old waveform will do and simple coil slot combinations are good enough.

For cheap low power(low cost) alternators intended for ac the same seems to go, and sometimes the waveform is from poor to bad and this does affect certain awkward loads.

There would be no intentional attempt directly to reduce cogging as for anything other than wind power it is of no consequence, but it is also related to slot ripple.

Rapidly changing flux linkage as the poles pass the teeth will result in harmonic voltage ripple. The first step to reducing this is to use an odd number of slots, then use a bit of skew if needed. Other things used to improve waveform are short pitched coils and distributed windings.

The case for motors is different, but the issues show up in a different way. The harmonic waveforms tend to lock the rotor speed at the harmonics during start up and if bad enough the thing may lock into a crawl and not reach the full speed.

As Zubbly mentioned, pole change motors have to satisfy this requirement with 2 speed combinations and there are less available slot pole combinations that will work properly.

For a low cog alternator, choosing an odd number of slots would be a good starting point, but low cost simple motors normally don't provide this option.
Flux

[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#7)
by Flux on Sat Jun 24, 2006 at 12:56:21 AM MST

Don't know where the italics came from, there is no significance in this.

[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#8)
by kitno455 on Sat Jun 24, 2006 at 06:01:37 AM MST

scoop tries to auto format things you do, it thinks that slashes or underscores are calls for italics. you had two slashes in your story, with spaces outside of them. if you had left out the space next to the slash, it would have worked.

space / word / space = word
space _ word _ space = word

allan

[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#9)
by Flux on Sat Jun 24, 2006 at 08:06:09 AM MST

Thanks allan, I was wrong when I blamed the cat. Cat typing screws up computers bad.
Flux

[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#10)
by fred480v on Sat Jun 24, 2006 at 08:32:18 AM MST

extra coils may be for some kind of aux. output, metering, some kind of control circuit, maby output for a brake coil. how many terminals are there
fred480v

[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#11)
by windstuffnow on Sat Jun 24, 2006 at 08:44:28 AM MST

Its wired in star with the basic 3 wire output.

.
Have Fun! Windstuff Ed
[ Parent ]

14/15 layout (3.00 / 0) (#12)
by windstuffnow on Sat Jun 24, 2006 at 11:33:49 AM MST

Here is the 14 pole / 15 coil 3 phase layout. Single layer of coils, makes it easyier. Each section is wound like a single phase ( cw-ccw-cw etc ). This forms 3 single phase windings, one right after another.

Using the 12/9 arrangement I found it was sometimes quite difficult to get the turns/resistance correct with only 3 coils per phase. this allows for the addition of 2 extra magnets and 2 extra coils per phase. Smaller coils, fewer turns etc. Following the "rules" the 14 pole disc was awkward and required lots of coils to get it right ( typically 14/42 ). The 14/15 gives you the best of both worlds and keeps it simple...
.
Have Fun! Windstuff Ed

Re: 14/15 layout (3.00 / 0) (#13)
by kitno455 on Sat Jun 24, 2006 at 11:42:51 AM MST

ok- what does this do to the waveform? i guess it makes it more broad and short? it seems that all the mags over a single phase are in slightly different relative positions to the coil.

on an air-core machine anyway, it would seem that the mag at 12 o'clock is linked strongly to the green phase, while the mag at 4:30 is doing very little for the green phase. does this not mean that the coil leg at 4:00 is just adding resistance?

or does an iron core machine behave so differently that this is not true?

allan

[ Parent ]

Re: 14/15 layout (3.00 / 0) (#14)
by Flux on Sat Jun 24, 2006 at 12:51:47 PM MST

This will most likely make the waveform much nearer to a sine wave.

If air gap the waveform would already be close without using distributed coils. with an iron core the waveform would be much better,

I can see no advantage for battery charging, the distribution is so severe that one coil will be contributing nothing but resistance ( and inductance if iron cored).

You could probably leave one coil out of each phase to advantage.

Pole numbers that are not divisible by 4 usually cause a lot of trouble.
Flux

[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#15)
by tecker on Sat Jun 24, 2006 at 06:02:45 PM MST

Eddy

Got those mags and the mini gen all is well .
Frankly I'm scratching a little at that mgen I'm going to replace my current wind gen pulse charger with the unit and readjusting the voltage to 80 volts . Wind is not available for a good test but . I know I'm going to let it run as is Reading the pulse charge ,llet you know on the wegys. Like I said I 've been coveting those for a while .

other 14 pole layouts (3.00 / 0) (#16)
by windstuffnow on Sat Jun 24, 2006 at 09:56:13 PM MST

Here are a couple diagrams added to the list...

Using the 14 pole ( or other pole combos ) you can use 3, 6, the above, 21,24,27,30,33 coils to name a few and they'll all work. Some better than others obviously.

The point is, It can be done with any pole/coil count using a mix of single phase groups and following a pattern for a 3 phase layout.

.
Have Fun! Windstuff Ed

Re: Pole to coil counts.. (3.00 / 0) (#17)
by scoraigwind on Sun Jun 25, 2006 at 07:14:37 AM MST

I have seen this type of winding on alternators and assumed that it was to avoid coggng, which it does very well. It doesn't get rid of the magnetic drag of the core, but it at least smooths it out. The sine wave thing is very interesting but presumably of little importance for battery charging.

When you group the coils to make 3 phase you will lose out compared to a proper 3 phase winding, because some of the coils ar not really very close the the correct phase, and they will not add up to as much voltage as if they were all in the same phase. The worst case is where a coil is 30 degrees off phase and its voltage will only contirbute 86% of the desired voltage to the phase group. some of windstuffnow's groupings look as if they have larger deviations than 30 degrees. Try turning some of the coils back to front - this gives you more options.

So overall I would say there is no avdantage to doing this with a machine that has no core. However you can put a rectifier on each coil and get a many-phased machine that works well for example my 5 phase design in my plans.

I am not sure that increasing the number of coils helps beyond a certain point. Sure they are smaller but they do not span the magnet pitch so well and therefore they will have lower output voltage. This is counteracted to an extent by their lower resistance, but the flux they catch is less than a bigger coil.

don't make things more complicated just for the sake of it unless you just enjoy the mental exercise. I sometimes regret my ten coil design. It works fine, but has no real advantage over 3-phase and it forces the rectifier to be at the alternator, which is not always the ideal place to put it.
Hugh Piggott http://www.scoraigwind.co.uk

Re: Pole to coil counts.. (3.00 / 0) (#18)
by windstuffnow on Sun Jun 25, 2006 at 11:11:25 AM MST

The basic idea was to reduce the coil size and turns and as well open up an option for odd pole count ( other than groups of 4 ) to achieve a better output.

Calculating the differences between the 12/9 and 14/15 I can cut the resistance in half over the 12/9. The 12/9 requires 40 turns per coil of #14 wire where the 14/15 only needs 18 turns per coil to match the same open voltage. The reduction in coil size and the lower turns helps to keep the overall resistance very low and in turn making the alternator more efficient as well as increasing output. It may not be the best wave form but it still outperforms the 12/9 by over 40% in the same small package.

And, yes... I enjoy the mental exercise very much. When there is nothing to challenge you there is no learning....
.
Have Fun! Windstuff Ed
[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#19)
by WXYZCIENCE on Sun Jun 25, 2006 at 04:47:05 PM MST

And, yes... I enjoy the mental exercise very much. When there is nothing to challenge you there is no learning....
Ed maybe this is the pill that feeds the addiction? Very interesting read :-0 Joe

[ Parent ]

Re: Pole to coil counts.. (3.00 / 0) (#20)
by tecker on Mon Jun 26, 2006 at 02:29:31 AM MST

If this axial stator could evolve into a smaller footprint with amperage . The uses would be staggering . Outbuildings ,Docks , Long Cable runs ,remote locations and inner city to name a few . I think the stators will have to remain thin to take advantage smaller magnets. The tighter wire turning radius with wire in the 20 to 40 amp density will have to be addressed . I am thinking that mags 1/2" thick saturate 90%or better at 3/4" leaving space between to focus the flux across the air gap you come up with an interesting arranging task no doubt.

Re: Pole to coil counts.. (3.00 / 0) (#21)
by ghurd on Thu Jun 29, 2006 at 05:40:34 AM MST

Did it start as an alternator or motor?

I have seen quite a few strange magnet/coil combinations in motors from small items like VCRs and DVD players.
G-
Ghurd.info

Pole to coil counts.. | 21 comments (21 topical)

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