Author Topic: proper coil dimensions (Read 9637 times)

ejl7007 · « **on:** February 03, 2009, 12:52:45 AM »

Hey guys, Thank you for your wonderful and helpful comments...Here is a new question. I just purchased 40 lbs of 13 awg magnetic wire. I Plan to make 12 coils with it to match the 16 neo mags that I have. I believe I will use 70-80 turns to get 5-6 VAC @ 120 rpm. What inner diameter should the coils be? Should the Gap be longer and wider than the mags? For instance my mags are Grade N42, 4"x1"x1". Should my coils, therefore, have inner diameter of 1" at the bottom and 1 1/2" at the top and be 4" long? I wish I could paste a drawing of it but I don't know how to do this....

Best Regards

Ejl

TheCasualTraveler · « **Reply #1 on:** February 03, 2009, 04:42:12 AM »

Judging by your question on the size of the coil it sounds like you feel the need to make your coils wedge shaped. Wedge shaped coils are usually the result of having to squeeze a coil to make it fit or that the magnet is wedge shaped. Usually the inside of the coil is about the same size as the magnet, in your case 4" x 1". So your inside dimension of the coil at the top would be approx. 1" and 1" at the bottom if you have room, otherwise smaller if it is squeezed due to space constraints.

What size rotor are the mags going on?

jlt · « **Reply #2 on:** February 03, 2009, 07:36:02 AM »

from reading your other posts it looks like you are using a 18" single rotor. it will probably be enough for 11 to 12 ft blades.i would aim for 85 rpm cut in speed be sure to make a test coil to check number of turns required. if you can't get enough turns.In try using a blank steel disc. and make it a duel rotor. It should raise your voltage about 50 percent.

ejl7007 · « **Reply #3 on:** February 03, 2009, 10:29:35 AM »

Thanks for your help mate. The rotor is a steel disk 1/2" thick & 18" Diameter. I have 16 mags evenly spaced around it. They have not been glued down on it yet. I may have to push the magnets further in towards the center of the disk about 1" from the outer edge so that the outer diameter of the coils overlap the mags and therefore the inside diameter of the coils is exactly that of magnets 4"x1"x1"

cheers Andy

ejl7007 · « **Reply #4 on:** February 03, 2009, 10:43:41 AM »

Thanks for your help jlt. I would rather stick with a single rotor right now as I am low on cash. I paid $120.00 for the steel disk 1/2" x 18" and about $20.00 for each mag. (16 mags x $20.00 = $160.00) from magnet4less.com I did use a test coil 13 awg @ 70 turns inner diameter 1"x1"x4" with a thickness of about 1" and got appr. 4.5 VAC @ 120 rpm though

Cheers

jlt · « **Reply #5 on:** February 03, 2009, 11:23:56 AM »

not to be critical but 16x20=320

TheCasualTraveler · « **Reply #6 on:** February 03, 2009, 01:47:48 PM »

Thats a big alternator.

If you went dual rotor you would have quite a stator to build but I assume for something this size, single rotor, you have many options for securing the stator to some sort of backing with out worrying about fitting it in the air gap.

Not sure why you would move the magnets in from the edge of the disc, it will reduce the area you have for coils considerably. Make the stator and coils align with the magnets, not the other way. You paid for that steel disc, why not use it? With the magnets at the edge of the disc I think you will have about 3/4 of an inch per coil leg. With no disc to return flux I believe you will want the coils as thin and as close to the magnets as possible.

ejl7007 · « **Reply #7 on:** February 03, 2009, 02:45:45 PM »

Ooops!!!

ejl7007 · « **Reply #8 on:** February 03, 2009, 02:54:57 PM »

Sorry I missed your comments, Casual Traveler. Moving the mags in closer to the center is a bad idea. By aligning the coils with the magnets....Do you suggest that I make the outer Coil Diameter the same size as those mags? Or should the coil's inner diameter by as long as the rectangular Mags? Help!!!

Cheers

TheCasualTraveler · « **Reply #9 on:** February 03, 2009, 03:13:40 PM »

the magnets outside diameter should be about the same as the coils inside diameter

ejl7007 · « **Reply #10 on:** February 03, 2009, 03:19:56 PM »

Thank you Andy!!!!

CmeBREW · « **Reply #11 on:** February 03, 2009, 05:55:10 PM »

Hello,

Yes, I think the wedge shape is best. I was curious about how it would look and had a cardboard box handy, so I did the 18" diameter 16/12 layout quickly, the way I would do it. In the picture, the magnets are backset 1/2" from the outer edge of the 18" disc. The dotted lines are just were the magnets travel:

The small plywood blocks are exactly the size of your magnets 4" long by 1" wide. The coil legs in the drawing are 5/8" wide, but I think I would go with 3/4" legs even if there is a little canceling in the bottom corners of the magnets.

Are you going for a 48v battery system?

If so, you might want to look at Dan's older 17 footer (16/12) to get a rough idea of things- but doing only ONE mag rotor would be roughly half the power (and coil voltage)or a little less than half:

http://www.otherpower.com/17page1.html

It seems your magnets are about the same size over-all. You certainly need to do a test coil to see where you are. If you had the same ga. wire, you should get almost half the voltage Dan got with his 17' coil test I would think. This would mean you need smaller gauge wire and more turns per coil in order to achieve the 48v.

I'm not sure 13ga. coils will be able to make it to a 48v system??

Maybe others with more experience would know??

You can also have all the magnets go all the way to the outside of the 18" disc. and use the stainless steel band around it. This would make the stator even bigger, but you could get even bigger coils (and more voltage and/or power) in there.

-Keep asking questions.

Flux · « **Reply #12 on:** February 04, 2009, 01:02:42 AM »

Not sure that I should intervene here, you seem to want to go your own way without telling anyone what you are trying to do.

Cut in at 120 rpm would probably indicate a prop in the 12 ft region. Volts? I haven't a clue. Does your 5-6 v ac refer to one coil? If so then it seems as though you are aiming at a 24v machine.

If you go out and buy things without thought or reason then it will end up an expensive project. You may have had the magnets and disc but why buy an arbitrary size of wire unless for some reason it came dirt cheap.

Going single rotor is not a good way to build a cost effective machine and it is not easy to predict any performance from such a thing. I think if you get it right it might just load a 12 ft machine but with nothing to spare, it may be more suited to 10ft.

At a guess if you keep the coils close to the magnets I think your cut in will be below 100 rpm if you use coils about 5/8" thick ( should be about right with that wire size.

At 24v it will almost certainly not load a 12 ft machine in high winds but if you can control it with proper furling and keep the power out below 400W it might be ok.

It stands a far better chance at 48v.

I suggest you do a test coil and see how the voltage works out then you can decide where to go from there. Just put the magnets near the outside of the disc ( why buy an expensive disc and waste half of it?) make the coils with rectangular holes about 4" x 1" and wind them until the things about touch on the outside ( make a drawing to find the size that will fit).

Keep the coils as thin as possible consistent with getting 70 turns into a size that fits. When you have got a voltage at 120 rpm we may then be in some sort of position to see where to go from there. For 24v I suspect you will have to use 2 in hand #13.

For most people the magnets and copper are the expensive bits, you seem to be unlucky with the price of steel. Normally it would have been far more cost efficient to use 2 steel discs, With those 16 long magnets a dual rotor with magnets on one disc and a plain steel flux return disc would have given you the chance of far more output or you could have got a similar output with less magnets.

Flux

ejl7007 · « **Reply #13 on:** February 04, 2009, 11:47:30 AM »

Thank you for the trouble you went through drawing the mag layout CmeBREW! Very much appreciated. I was finally able to upload a pic of my rotor. Previously, with my 18 mag/9 coil config I was going for a 12 V machine but now (Thanks to your inpout)I may go for 24 V. Or possibly still a 12 V but more amps. I don't know yet. It took my three days to slowly remove and clean the mags off the plywood stator, and I am exhausted. As for the thirteen Gauge wire, It's all I could find in a surplus junkyard. 40 Lbs @ $ 4.00 = $ 160.00 Also in my previous set up A 13 gauge Test coil @ 70 turns (1" Thick) and at a distance of about 1/8" from the mags, I was getting an output of about 5.4 VAC @ 120 rpm

Sincerely

EJL

ejl7007 · « **Reply #14 on:** February 04, 2009, 12:17:39 PM »

Thank you Flux. What I am trying to do is basically simple. I have always been fascinated with generators, especially car alternators. 12VDC @ 100 Amps. Wow!

Unfortunately these tiny Alternators require 2,000 - 3,000 rpm to produce such power. So, when I accidentally discovered your website, I was particularly awed with your wooden alternator, and so many other wonderful d.i.y. projects. A home made alternator that produces as much power but only spins at 120 or 300 rpm? I was hooked. I have no direct plans of raising a tower or building any blades - yet!

But I love the idea of home brew energy. And all you guys over there dedicating your lives to it is truly inspiring.

Anyhow, In my previous and wrong set up of 18 mags to 9 coils, I originaly tested one coil. 13 Gauge 70 turns 1" thick and was getting about 5.4 VAC @ 120 rpm

Then I went further and tried 11 Gauge wire 200 turns 1" thick, though this test coil was more circular (The core of the coil was about 1/2 inch in diameter only)and as a result when placed near the mags at a distance of 1/8" I was getting about

7 VAC. What a waste of wire and time. So i think I will stick with 13 gauge, make more of wedge shaped coil and go from there. I apologize if 13 gauge may not be as ideal as say, 14 - 16 but I found a large spool of it in a surplus junkyard. 40 lbs @ $4.00 = $160.00

So I will try again This time hoping for: 12 coils -3 phase- 4 coils in series.

and increase my turns of 13 gauge to 100 - 120 turns to get perhaps 6-7 VAC per coil. 6-7 VAC x 4 = 24VAC-28VAC per phase and wired in delta. Or add a regulator to bring it down to 13.8 VDC and increase the Ampage. I'm not sure yet how to go about this as it has become a rather expensive hobby. I hope you can see my 16 mag config on a steel plate pic that I just submitted to CmeBREW.

What do you mean by a second steel disk as a plain steel flux return disc? How would that work? I wouldn't mind considering!!!

Once again Flux, I thank you!!!

ejl7007 · « **Reply #15 on:** February 04, 2009, 02:38:45 PM »

Hey CmeBREW. Here is a pic of my stator layout for 12 wedge shaped coils. I will experiment with coil turns to get the right voltage.

Thanks

CmeBREW · « **Reply #16 on:** February 04, 2009, 06:18:29 PM »

Good going cleaning those nice magnets. It is looking good. It looks like your photos are too big and above the 100K size limit per photo. It takes too long for dial up fellows to view.

HINT:

If you want, you can shrink those photos down under 100k using "PAINT" program on your computer if you use microsoft. Just go to: 'Programs'; Then 'Assessories'; Then "PAINT" ; then load up your photo there from file and goto 'Image'; then to 'Stretch/Skew' and simply shrink it 60-80 percent and re-save. Then re-upload it here.

But One thing looks to be concerning to me from the photo. I see you are not using a heavy duty trailer hub. That support shaft looks like it is only 3/4" bore which is too small I believe. That big diameter rotor and those big mags have An ENORMOUS amount of force with a 10' prop. You might want to consider using something much stronger like (at least) inch and a quarter (1.25" diam shaft) BORE pillow block bearings.

Now to the alternator. Just a word of caution you may already know. If those magnets are not epoxied down yet you better be MEGA careful with them or two of them could crush your fingers off in a micro second. BE CAREFUL!

I would epoxy the magnets on - out close to the outer edges as Flux says.

It would be smart to put a steel strap around the disc as DanB does to hold those heavy high center of gravity magnets on very well.

You must choose which Battery system voltage you want in order for those in the know to help. It makes a big difference for the coils.

Many here say that for a serious Re-house system, 48v system is best with the least losses. But A good 24v/48v power inverter costs a lot more than a common 12v inverter. Many here say it is more than worth it for a serious system.

Hopefully, others with more experience than me will help you approximate your 13ga coils. (BTW, thats a good deal on the mag wire. Looks like half price to me)

Guessing from your first test coil, it looks like you are in range for the 48v system, even though 1" thick coils are very thick coils.

So lets say with 16 mags you get 5 volts with your test coil at 120rpm.

Since you have 4 coils in series per phase, that is 5x4= 20vac per phase.

Then you multiply that times 1.73 (Star connection) which =34.6vac

Then you multiply 1.4 with that number due to the rectifiers - which = 48.44vDC

130-150rpm which is a good cut-in for a 10' mill I believe.

If you want a 24v system you may be able to make thinner coils (5/8")and less turns with the same 13ga wire. Looks like you would then need half the coil voltage or 2.5v with a test coil. Or you may have to wrap the coils 'Two in hand' as Flux said.

For a 12v system you will HAVE to do the 13ga 'two in hand coils' and less turns.

No matter what you do, always bring out all 6 wires out of the stator for more options if need be later.

-Looks like you too have the addiction. It is SMART to have some RE now.

Flux · « **Reply #17 on:** February 05, 2009, 01:51:45 AM »

That wooden alternator was an interesting experiment to show what can be done but otherwise it has probably caused more confusion than help to many people . It really is a toy to demonstrate what can be done with modern neodymium magnets. it is so inefficient that without the powerful neo magnets it would be virtually useless.

Using magnets in alternators with no closed magnetic circuit will give some results but at large costs in terms of material and at low efficiency. Sadly the single rotor construction is not a great deal better but there is at least a useful flux concentration through the steel disc. The return path through air is still very ineffective.

The dual rotor arrangement completes the flux path on both sides and forces the flux through the air gap between the magnets. You don't need magnets on both discs to get most of the benefits, having magnets on one and leaving the other blank has the same effect except that for the same gap flux density you need thicker magnets. Your 1" thick magnets should let you use coils about 1/2 to 5/8" thick with a plain return disc.

Using very long magnets in axial designs is also not a good use of materials as the magnets are crowded at the centre and widely spaced at the outside. If you make the coils wedge shaped you increase the wire length and resistance goes up. You probably are worse off than keeping the coils rectangular. The gain in voltage from radial coil sides is small and the added resistance will be considerable. Long magnets work much better on axial machines with constant spacing.

If you want to make a good 24v machine then think of at least 2 strands of #13 in hand. If you want to get down to 12v then at least 4 in hand. Using several strands in hand is fine and it the #13 wire came cheap then use it but not a single strand.

Regarding your other question about a voltage regulator, Oztules covered that. You will have to use a battery, trying to run things directly without a battery from these type of alternators is just not viable.

Flux

ejl7007 · « **Reply #18 on:** February 05, 2009, 02:53:38 AM »

Thank you Flux for your help. However winding two strands of wire at once? I would have to unspool some wire from the main spool onto another empty spool and then use those two spools to wind up the coils. I would end up with four leads;

or I bend, twist and fold the wire in the middle and then wind two wires at once....I am sorry to confuse you but I am lost. Should a coil not have an end and a begining?

I am still thinking of your reply, as I still may have more questions for you.

Cheers

ejl7007 · « **Reply #19 on:** February 05, 2009, 03:05:55 AM »

The shaft that goes through the rotor is 5/8" I have it set up and hooked to a motor that spins the alternator to speeds of up to 300 rpm. A variable transformer lets me control the speed of the motor and a tachometer tells me the rpm. So I am sorry if I confused you a bit. And yes I will epoxy down those magnets. I will also consider purchasing an 18" Diameter 1/4" thick steel disk to place behind the coils so that I can get the maximum flux return. (I still don't know what that means exactly) AS well as a steel strap to place around the mags. Still don't know if I want a 12 or 24 Volt system, as I am still expirementing. I love the whole process. Please bear with me. You have already helped me tremendously.

Cheers

Ejl

oztules · « **Reply #20 on:** February 05, 2009, 04:09:35 AM »

Perhaps this will help you to visualise the effects of the steel behind the magnets, and the steel disk in front of the magnets (but behind the stator).

(Forgive me Tom, but I think this is worth loading up on 54kbs even if it is a little big, if you disagree then kill it)

The more purple the color, the higher the flux. yellow is low flux. and green is lower... then blue is background.

The lines joining the magnets are ideal flux lines. Note as the gap gets further from the magnets, the leakage between magnets rather than through the stator becomes a problem. You can imagine what happens when the disk is removed completely.

These animations are part of a series Peter Dingesman has kindly done (Dinges) here: http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1458&PN=1

This is well worth spending some time on. He has animations of all kinds of combinations, and you should come away with a pretty good understanding of magnetic circuits.

..........oztules

Flux · « **Reply #21 on:** February 05, 2009, 06:43:26 AM »

"However winding two strands of wire at once? I would have to unspool some wire from the main spool onto another empty spool and then use those two spools to wind up the coils. I would end up with four leads;"

Correct. You end up with 2 start leads and 2 finish leads. Just connect the 2 starts together and 2 finishes together. The end result is a coil with the equivalent of 2 #13 wires in parallel. It will behave exactly as a single coil of #10.

Another way to look at it is you have 2 identical coils of #13. Each will produce the same voltage so you just connect them in parallel to halve the resistance.

For coils with more than one wire in hand the number of turns is the number of times you turn the former. It is not the number of individual wire loops.

Flux

ejl7007 · « **Reply #22 on:** February 05, 2009, 11:49:10 AM »

Thank you for taking the time to help out a newbie oztules, from down under....AS I understand it, it should be something like this:

Where the mags are 1" thick, the gap between the magnets and the stator is 1/8";

The Stator itself is 1/2" thick;

The gap between the stator and the Plain Steel disc is 1/8"; while the Plain Steel disk itself is 1/4";

Therefore, Overall adding it all together I've got: 1/8"+1/2"+1/8"+1/4" = 1" Which is exactly the thickness of the magnets.

Is this the correct way to look at it? Or must I use the same thickness steel disc as the one onto which the magnets are on? i.e. 1/2" ?

Cheers

oztules · « **Reply #23 on:** February 05, 2009, 02:24:00 PM »

Your gap is 1/8" + 1/2" + 1/8" = 3/4" which looks good enough to try for my money.

Any thickness steel disk is better than no steel at all. You can see that with the animation.... but you need physical strength as well... those magnets will have some serious ability to flex anything less than 1/4" I should think.

I use #13 as well,... but for 48V so I use 1 in hand. For 12v, you will want 4 in hand as Flux has pointed out... 4 pieces of wire wound together as 1.

So 4 starts and 4 ends per coil in parallel... not easy to do with this thickness, but just persevere. They need to be wound from 4 rolls.. all at the same time to keep their lengths near identical, otherwise you may get circulating currents when you join all the starts and ends together.

With smaller wire, I have laid them out and twisted them together to form a "twisted rope" and then wound that into a coil. Not sure how easy that would be with #13 though, but it would minimize the chances of coils seeing different flux lines and generating different emf resulting in circulating currents that will cause excess heating, but more importantly make it harder to get the prop moving. (would show up as drag)

Perhaps read this http://www.fieldlines.com/story/2006/10/21/61110/798 to see an extreme winding feat. Even after that , this would not suit your disk setup as it is so assymetric, that the inner turns would see much more flux than those further away. For you, a messy random wind will be better I think, where the wires randomly change position from inner to outer of the coil.... this of course messes up the packing ratio's and results in a bigger coil for the turns... sigh..... see nothing is simple with this wind business.

This would be excuse enough for me to go 48v single wire :-)

All the best with it.

........oztules

ejl7007 · « **Reply #24 on:** February 05, 2009, 03:11:11 PM »

Thank you, Sir!!!

Cheers

EJL

CmeBREW · « **Reply #25 on:** February 05, 2009, 06:48:19 PM »

If you really want a 12v system, you may be able to use your single wound 13ga. wire and "Jerry rig" the 3 phases individually with 3 (probably 6 for more amps) bridge rectifiers up at the mill and parallel the outputs. Then you would have only 2 run wires. -Just an idea.

Here is some info about your 'coil placement' question:

Look at this very helpful page:

http://www.otherpower.com/stator.shtml

Just make sure all your coils are placed down in the SAME WINDING DIRECTION.

The coils in the diagram below are all placed down in a Counter-Clockwise winding direction. (I always look at the outside wire of the coil as to which direction it is coming around. Obviously, you can just flip a coil over and it's winding direction is reversed. It took me awhile to realize that...Dah)

Your 16/12 stator is exactly the same- except you have to add one more coil in series per phase. But it is hooked up the same way.

Make sure you bring out all 6 wires for more possible options (if need be later)--

And for a "STAR" hook-up, just connect A,B,C together and X,Y,Z will go to the bridge rectifiers and then to the Batteries.

Hope you are casting the coils down INTO the Treated/Marine plywood and not just on top. The stator will be thinner this way and thus the flux will be stronger since the rotating 1/4" thick steel plate on the outside is closer to the mag rotor.

-Hope goes well.

ejl7007 · « **Reply #26 on:** February 06, 2009, 02:29:54 AM »

"Jerry Rig"? Whould that kind of connection qualify as 3 phase? Star or delta? would I be getting a decent output that way? I will definetely keep it in mind.

Thanks for the layout with the coils, I've already read that but clearly, not well enough. And yes I will cast the stator and make it as thin as I can....perhaps 1/2" or 5/8" as the following schematic that I made will illustrate:

Therefore with 1" thick mags, the gap between rotor and stator 1/8", the stator 1/2" thick and the gap between the stator and the outer, rotating 1/4" thick steel disk also 1/8" I have....

1/8" + 1/2" + 1/8" = 3/4" between the two rotors. Enough to maintain a great and powerful Flux. Thank you for convincing me to go dual rotor.

I have got a lot of work ahead of me, and I hope I will succusfully cast a thin 1/2" stator.

I will keep you posted, CmeBREW.

Once again, I thank you.

ejl7007 · « **Reply #27 on:** February 06, 2009, 02:37:16 AM »

Thank you flux. I will let you know how things are going. In the maentime I have to go out to the machine shop and order me a second steel disk. And proceed with the windings and the casting of the stator.

Cheers

TheCasualTraveler · « **Reply #28 on:** February 06, 2009, 05:18:16 AM »

That is going to be a very big stator, roughly 20" or more. I don't know if you can safely make it only 1/2 inch thick. Read up on casting stators, adding fiberglass mat etc. Warping may be a problem. No expert here but you may have to compromise a little on the air gap for the sake of strength.

CmeBREW · « **Reply #29 on:** February 06, 2009, 08:08:48 AM »

'JerryRig' is simply parallel connecting the 3-phases up at the mill for less volts and more amps. It lets you have lower volts than even Delta which looks like what you need with those big magnets to get down closer to a 12v system.

However you do not multiply by 1.73 Or 1.4 to get final volts with 'Jerry connect'. You just multiply the test coil voltage by 4 (4 coils per phase in your case), and allow a little more for Rectifier losses.

You would need something like 3.7vac per coil x4 = 14.8vac (after rectifier(s) voltage drop it will be close to 13vDC cut-in, which is good)

I was thinking about the 'Jerry connect' because later on down the road you might possibly be able to use the same stator and go to a 24v system if you wish by re-connecting the wires in STAR.

You really don't know yet how thick your stator needs to be until you determine your coils and the number of turns. You seem to want 12v which is common.

I agree with Traveler, plywood tends to warp unpredictably. It would be safer to just get a gallon of Fiberglass reinforced polyester resin at Wallyworld and Talc and fiberglass mating and do it the more reliable way since copper wire costs so much.

Do another single wound test coil with the 1/4" rotating steel plate attached. (Be CAREFUL with that!)

You may still need to do two in hand though even with delta OR jerry connection. It is difficult to know at this point. This is not easy when you do something on your own for first time.

Ideally, you want to avoid stall, and you don't want the mill to be spinning too fast either, since it might be too hard to control in big winds.

ejl7007 · « **Reply #30 on:** February 10, 2009, 12:03:35 AM »

ahgr....I am having a hard time winding 2 strands of #13 ga wire. It doesn't look as smooth as say, single strand. I will keep on trying. So far 2 strands of wire call for about 25 or so turns; though it's not as smooth as my previous coil @ 70 turns. Wires overlap; This new "dual coil" has about 50 or so turns. it seems thicker. I am getting frustrated. I really wish I could use a single strand of wire though.....

Help!!!!

Cheers

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Author Topic: proper coil dimensions (Read 9637 times)