13' mill questions

[cdog]

I have a question about the stator and mags for a 13' mill, similar to the one Chris recently posted about.
I would like to build a robust stator and mag assembly for a 13' mill using 48 2"x1"x.5" mags and 18 coils, 6 per phase.
This is just because I have the materials handy, and it will be something different.
The other reason is I would like a machine that makes little heat in the stator, even though this will be an obvious waste of the mags.
I know the 12' piggott machine is 32 mags and 12 coils.
Any direction or opinion on this would be greatly appreciated, as usual!
Cdog

[jarrod9155]

I could be wrong but I believe that the 12 coil 32 mag is a 14 footer in the recipe book . 

[cdog]

Could be, been a while sincie I checked, but the question remains!!

[cdog]

The piggott book I have had recipes for 4, 8, 10, and 12 footers.

[ChrisOlson]

I have a question about the stator and mags for a 13' mill, similar to the one Chris recently posted about.
I would like to build a robust stator and mag assembly for a 13' mill using 48 2"x1"x.5" mags and 18 coils, 6 per phase.
This is just because I have the materials handy, and it will be something different.

While I always like different things, my machine ran in 25 mph winds yesterday, survived a thunderstorm last night with 60 mph+ gusts, and continuous 25-35 mph winds all day today, that are still blowing at 30+.  It's been putting out 1,400 - 1,500 watts all that time and it runs just super-smooth.  All I can hear in the tower is a bit of humming coming from the generator.

Even though I sort of messed up when I wound it I'm pretty happy with it.  So I can see no real advantages to going to 48 mags on a machine this size.  I think the key is to pack the most copper in the smallest space it will fit it so the magnets stay busy all the time and don't traverse any gaps in the stator, and if you can do that the number of magnets doesn't really matter.
--
Chris

[cdog]

Thanks Chris, I guess my train of thought was that many poles would give me my voltage and few turns per coil would let me handle big amps worry free.
That being said, observing your mill, how many turns would you suggest for a set of blades identical to yours and for 24 volt??
Cdog.

[ChrisOlson]

Thanks Chris, I guess my train of thought was that many poles would give me my voltage and few turns per coil would let me handle big amps worry free.
That being said, observing your mill, how many turns would you suggest for a set of blades identical to yours and for 24 volt??
Cdog.

Mine is 48 volt so I think you'd better do a test coil.  I bought a set of those PowerMax blades and they need to cut in at lower rpm than flat-face because they don't spin as hard on the top end and tend to naturally stall in high winds anyway.  Mine isn't even getting to 200 rpm in 35 mph wind and I haven't seen the ammeter move all day.  it stays right on about 25 amps.  That's all she'll do.

I'll know more when the wind lets up so I can see it run some more in lighter winds.  But I know that if you use PowerMax blades you need to have it cut in around 90 rpm.  They are low wind speed blades and they don't perform all that well at higher wind speeds.  The possibility exists that I wound properly for those blades.  While I didn't get the 2 kW I expected out of it, it seems to maintain its rpm even when the wind dies down to 20-25 mph during the more "calm" periods we've had the past two days.

I've only had a chance to watch it run on Sunday at idle (10-12 mph breeze) and then the wind went to full throttle and hasn't let up so far.  So I don't really know how it performs in between yet.

But I have to stress that those PowerMax blades are NOT high rpm blades.  They only run at about 4.5 - 5.0 TSR at cut-in (if you wind the generator properly) and they'll pick up to about 6 TSR at 18-20 mph, then they go downhill from there.  They have a very flat power curve.  Keep that in mind when you do your test coil.  I guess with a 16-pole 24 volt I'd wind a test coil with 50 turns and check it with the generator air gap at .725 and see what you get.

For 24 volt I assume you're going to want about 17.8 volts at cut-in, so that means each phase has to make about 10.3 volts.  If you got 4 coils per phase you need to see around 2.6 volts out of that test coil at 90 rpm.
--
Chris

[ChrisOlson]

Thanks Chris, I guess my train of thought was that many poles would give me my voltage and few turns per coil would let me handle big amps worry free.
That being said, observing your mill, how many turns would you suggest for a set of blades identical to yours and for 24 volt??
Cdog.

Another note on these blades, if you get the cheaper ones (WindMax) they run at higher rpm's than the PowerMax blades do.  I don't have any experience with those other than what other people have told me.  But they have a different root on them and they don't have the cup on the front trailing edge of the airfoil so they tend to want to want to run faster (and quieter) than the PowerMax blades.
--
Chris

[cdog]

HMMMMMM
This makes me wonder if I wanted to pursue my arrangement, what size blades would I use.
I like making my own so thats no problem, what do you think?
Cdog.

[Flux]

16 pole 12 coil should take 12 ft with a sensible winding. Hugh's blades generally run at near tsr7 so if you run slower blades you will need to be careful pushing things to 13ft.

I think 24 pole is going over the top for 13ft, you will be so tempted to squeeze them on to a small disc to reduce size and weight that I doubt you will come off any better than starting with 20 pole 15 coil.

Cut in will depend on your blades and how much you value the few watts available in very low winds but for 13ft I would try cut in at 100 rpm if you make your own blades. You could always raise it to perhaps 120 later if it suited the blades better.

Even using 20 poles you will have something that will stall very hard. If the main concern is stator heat then there are two factors. The heat depends on the loss in the stator, using thicker wire will reduce the loss but with very powerful alternators you also reduce the high wind capability and that will also limit the stator heat.

Once you have the thick wire you can run the stator at a rating determined by the wire and get more out than a lighter alternator but you won't get more unless you take steps to avoid hard stall, in fact you will get less.

With 20 poles and a sensible cut in and built on a sensible disc size you will probably get poor performance above about 15 mph unless you introduce enough line resistance to get the stall speed up. This resistance doesn't heat your stator but it does let the prop perform better, you then get much more current and at some point you still reach the stator heat limit and the furling has to cope with this but in fact it will furl easier and your tail weight becomes more manageable.

Without added resistance on a 48v machine I suspect the 20 pole would always stall limit in any wind but no way would I want to try it and I really can't see how you could set the furling for a condition that you may only see once in a year or more.

The stall control is much more constant than any furling and it would be difficult to know when it was furling or stalling in lower winds.

Flux

[ChrisOlson]

16 pole 12 coil should take 12 ft with a sensible winding. Hugh's blades generally run at near tsr7 so if you run slower blades you will need to be careful pushing things to 13ft.

Flux is right, here.  You can't use the recipe book if you use these low-speed PowerMax blades.  They're a different animal.  They don't light up and spin at a high TSR around cut-in.  They start up slow and don't come into their "prime" until the wind is blowing at 18-20.  But the advantage to that is that they make more power in low wind IF you wind the generator for it.  They have torque - not rpm.

If I had it to do over on mine I wouldn't change anything.  The wind died out last night here and Doc Wattson says it's putting out ~6.2 amps this morning.  My little anemometer broke awhile back so I don't know what the exact wind speed is.  But going by our flag flying in the yard I'd say 10-12 mph.  The batteries are at 56.4 volts so I think 6 amps is pretty darned good for 10 mph wind - that's like 1/4 of what the machine can put out with just a light breeze blowing

I do have to fix the furling on it though.
--
Chris

[jarrod9155]

My generator is a 12 coil 32 mag 18 inch rotors with the powermax 13.1 blades  coils are 19 awg 350 turns . The blades seem to perform best around 15 to 25 mph winds I was able to  peak out at 2,000 watts before furling . I will say these blades are a little loud at higher rpms I have my inverter set to cut in at 185 volts on a windy day . So far really happy with theses blades .

[ChrisOlson]

I will say these blades are a little loud at higher rpms I have my inverter set to cut in at 185 volts on a windy day . So far really happy with theses blades .

You must have like a 208 volt system.

A "little loud" is an understatement.  I've disconnected the load on my smaller ones before to see how fast they really will spin and they are VERY noisy at high speed.  I think it's caused by the slight cup they have on the trailing edge - which gives them better slow speed characteristics and detracts from high speed performance.  I would suspect that if I had less turns of wire in mine that it would get close to 2 kW too.  But I don't know what that would do to the low wind performance - I think it would be less.

I kind of scaled what I learned on my 10 foot to the 13.  But it was still somewhat experimental.
--
Chris

[jarrod9155]

On my inverter grid tie I have been setting the voltage around 190 thats what it locks the wind mill at I have been thinking of lowering the inverter voltage to 160 for every day winds around 12mph . Maybe this will improve my low end power with theses blades .

[cdog]

Thanks guys, this is a great learning tool for me.
I still do not understand how you calculate number of mags, coil size and stator diameter for a given size prop?
Perhaps I should be asking what size blades should I build to use the entire 48 mags I have on hand, and make the stator accordingly??
I would still like to do the 24 pole 18 coil arrangement, so what size blades and stator diameter and number of turns for 24 volt??
Thanks to all,
Cdog.

[ChrisOlson]

I would still like to do the 24 pole 18 coil arrangement, so what size blades and stator diameter and number of turns for 24 volt??

You have to know what blades you're using first.  Assuming 13 foot homebrew that run at 7 TSR I'd start with 22 turns in a test coil (again assuming the mags are 2 x 1 x .5 bars).  That should cut you in around 110 rpm and give you some air gap adjustment either way to get it spot-on.  But that's why you need to do a test coil - you're not using any recipe that can be found anywhere and you're designing something new.

What I have done is use the dimensions of the test coil to determine how many will fit in a circle.  Wind one, measure it and draw the thing out on a piece of cardboard or paper.  If it looks like you can fit 18 of them in whatever size it takes to do that, with a little room to spare for error, then go with that for the diameter of the generator rotors.  Build the rotors, run your test coil, and if it's close you're in business.

Unless you've built this design before, it's best to err on the bigger side to give yourself a little more room in case you end up needing more wraps in the real coils than what the test coil had.  After you build one, then you know and can adjust it accordingly for the "perfect" (next) one.  I have never built what you're talking about, but that's the way I'd go about it.
--
Chris

[ChrisOlson]

I still do not understand how you calculate number of mags, coil size and stator diameter for a given size prop?

I used a method called an "educated WAG".  I based the educated part on past experience and what I've built and what I've gotten out of it, then apply the WAG part.

I attached a picture of an 18 coil stator that I built once (hope it works - can't figure out how to insert a picture here).

This thing had 19 turns of AWG 14 wire in it and it fit 10" generator rotors and was only .450" thick.  It was a feat of flat stator engineering that has probably not been matched either before or since.  But it was not easy to do.

I ran this thing with 12 poles and it reached 18 open volts at 260 rpm.  So using the educated part, if you put 24 poles to it you need half the rpm - 130 rpm.  But you're going to have bigger generator rotors with faster moving magnets at the same rpm, so now the WAG part comes into play.  130 down to 110 is quite a bit - more than bigger rotors will make up for - so I threw three extra turns at it.  That's how I came up with 22 turns.

If anybody has a better way to come up with a starting point, feel free.
--
Chris

[cdog]

Good stuff Chris, I think I follow what you are saying.
I guess I should ask it this way....
If a set of blades is known to be able to produce x amount of power, how do you determine the cubic inches of mags needed and the corresponding amount of copper?
I am also curious as to how much difference the speed of the mags flying by the coils matters.... as in having a 14" stator compared to an 18" one, all else being equal...
If I am suggesting using twice the mags and copper that my 10' machine uses, should I not be looking to match that to a prop with double the ability?
Thanks for putting up with all my grade school questions, but I have never understood the bare bones of this !
Cdog

[ChrisOlson]

Good stuff Chris, I think I follow what you are saying.
I guess I should ask it this way....
If a set of blades is known to be able to produce x amount of power, how do you determine the cubic inches of mags needed and the corresponding amount of copper?

The only good way I know of to do that is by experimentation with a totally new design.  Theoretically you can use a gauss meter to measure the flux of a particular set of magnets, then do a bunch of calculations to figure out how much wire you need.  But I've never been able to get that method to work out.  The old test coil will tell you more than anything.

The speed of the magnet does matter.  If you have one coil and one magnet and move the magnet over the coil really slow nothing will happen.  But if you move the magnet over it fast it'll cause current to flow.  If you move it over the coil faster yet i'll make more current flow.  I don't know the relationship there either - I just know thru experience that bigger rotors with the same mags take less turns of wire than smaller ones.

In theory, a 10 foot machine that's 30% overall efficient should make about 1,800 watts @ 25 mph wind speed.  A 13 foot machine at the same 30% overall efficiency should make 3,150 watts at the same wind speed.  My 10 foot will make about 1,400 watts in a good 30 mph wind.  My 13 foot only makes about 100 watts more than that - about 1,500 watts.  But the 13 foot has proven it puts out more power than both 10's combined at 12-14 mph wind.

I suppose there's some way to apply some sort of formula to all this, but I don't know how accurate it would be.  I made a spreadsheet awhile back that used complicated formulas to predict power output of a design, but it's only accurate within a certain range of like +/- 20%, which is quite a bit of error.  The reason it's hard to predict, unless you're working with a known design, is because the volts you get per rpm do not stay constant.  When I built my 13 I tested it at three different speeds and got like 6 rpm/volt at 60 rpm, 5.2 rpm/volt @ 150 and 4.8 rpm/volt @ 450.

Again, I suppose there's a way to apply scientific formulas to this.  But how accurate it would be is questionable.  A bench test will always tell you more than 16 pages of mathematical formulas.  So to sum up, when you're working from a known, proven design you have something to go by.  When you're designing something new you have to be able to accept failure if it doesn't work, say, "Well, yeah, that didn't work worth a darn", redesign it, learning from your mistakes, and hopefully the next one will work better.

I have a couple or three stators laying around here that are labeled "Top Secret - Experimental" because they didn't work.  If you're not willing to start a Top Secret Experimental stator collection like I have, then you need to work with a known or proven design.  And that includes furling systems too - I got another collection of stators that don't have any smoke left in them.  Those have accumulated in my High-Output Stator Display. 
--
Chris

[cdog]

Head spinning.....................
If I use my 24 poles, I would put them on a 17" circle....
My machine is 24 volt....
15' prop.....
100rpm cut in......
1.7 volts per coil....
18 coils....
1.7x.7x12x1.7=24.2 volts???
13 ga wire???
PALEEEZEE tell me I am on the rite path or in the ballpark??
Cdog.

[ChrisOlson]

1.7x.7x12x1.7=24.2 volts???
13 ga wire???

I'm not sure what those numbers mean.

1.7 volts per coil times 6 coils per phase is 10.2 volts per phase times 1.732 (for star configuration) = 17.7 volts RMS times 1.4 = 24.8 volt cut-in.  So that's about right.

13 gauge wire is .072 diameter so .072² x 4869.48 = 25.2 amps / .77 = 32.8 amps max continuous.  32.8 amps x 28.5 volts = 934 watts.  For a 15 foot prop you'll probably want at least dual strands of AWG 13 in a 24 volt machine, which would be the bare minimum.  AWG 13 is not all that easy to work with.  I'd probably use triple strands of AWG 15 if I was doing it, which will give you a much heavier duty generator.  Even triple strands of AWG 16 would give you more capacity than dual #13.
--
Chris

[Flux]

I am also curious as to how much difference the speed of the mags flying by the coils matters.... as in having a 14" stator compared to an 18" one, all else being equal...
If I am suggesting using twice the mags and copper that my 10' machine uses, should I not be looking to match that to a prop with double the ability?
Thanks for putting up with all my grade school questions, but I have never understood the bare bones of this !
Cdog

The speed that matters is the rotational speed or angular speed not the linear speed. All the bigger discs do is give you more room for more copper and that helps to get more output from a given set of magnets.

In theory if you use twice the magnets and twice the copper you will get 4 times the output from a given alternator. That at first sight means you can have 4 times the blade area but you will also drop the rotational speed so life is not that simple.

The speed is a linear function of prop diameter but area is a square function.  Probably it would support something like 3 times the area so something like 16ft.  Doubling everything up is probably a bit drastic for going from 10 to 13ft unless you want it to stall really hard.

Flux

(fixed quote code- VF)

[Ungrounded Lightning Rod]

I am also curious as to how much difference the speed of the mags flying by the coils matters.... as in having a 14" stator compared to an 18" one, all else being equal...
If I am suggesting using twice the mags and copper that my 10' machine uses, should I not be looking to match that to a prop with double the ability?
Thanks for putting up with all my grade school questions, but I have never understood the bare bones of this !
Cdog

The speed that matters is the rotational speed or angular speed not the linear speed. All the bigger discs do is give you more room for more copper and that helps to get more output from a given set of magnets.(fixed quote code- VF)

Actually, what matters for voltage isn't really angular or linear speed, but how much flux transitions between one side and the other of the coil wires (inside and outside of a coil) in a given amount of time, multiplied by the number of wires (coil turns).  This usually does translate to higher RPM and/or higher linear speed - but mainly because of the geometry changes you need to do to make it happen rather than there being anything inherent about the relative speed of the magnets and wires.  (For instance you could have used a lower speed but a bigger magnet with more flux lines and gotten the same effect as a higher speed.)

Now doubling up on the frequency means you double up on the power you get from a given set of magnets and coils.  You can do this by spinning the machine faster.  Or you can do this by changing the geometry.  One way to change the geometry is to double the radius and double up on the number of coils and magnets, while holding the same RPM.  You get one doubling of power by doubling the frequency (making twice as many poles go past each coil in a given time) and another by doubling the coil/magnet combo.  (And you raise the torque needed by a factor of 4:  2 for doubling the radius to the magnet-coil drag, 2 for doubling the number of coils/magnets.)  In this case the relative speed of the magnets and coils doubled, due to the geometry change.  But if you could squeeze the stuff in closer to the center without losing the field to bypassing "shorts" you'd get the same effect without a full doubling of the  linear speed.  See?

[cdog]

Great stuff guys, I've learned more in this thread than I have for some time...
Underground.....
Is there a point(I hope my mill never sees it) that the mags would not have enough time to "saturate" the coils if they were moving by fast enough?
Do you feel I an in the ballpark with my numbers?
Why hasn't anyone enlse built a machine this way to get the most bang from the mags?
Many thanks, I love this board,
Cdog

[ChrisOlson]

Why hasn't anyone enlse built a machine this way to get the most bang from the mags?

The most bang for the mags would be 16 poles on a 15 foot prop.  I think you're going to find the power curve is too steep to use a 24 pole genny on that size machine.  I think you're also going to find that things are going to get pretty tight for the coils.  With only 17" rotors you're going to have a coil about every 2.2 inches.  Even my 14" 16 pole in my 13 footer was VERY tight to get everything to fit, and my coil spacing was 2-3/4", the bottom of the coils come to a "vee" and the inside dimension at the top of the legs is only 3/4".  It's solid copper, smashed in with a hydraulic press to get it fit in a .650" thick stator.

You need to find a big piece of cardboard or paper and draw the thing out, then wind a test coil and lay it on your template to see if it's going to fit before you get too excited about proceeding with it.
--
Chris

[Flux]

Head spinning.....................
If I use my 24 poles, I would put them on a 17" circle....
My machine is 24 volt....
15' prop.....
100rpm cut in......
1.7 volts per coil....
18 coils....
1.7x.7x12x1.7=24.2 volts???
13 ga wire???
PALEEEZEE tell me I am on the rite path or in the ballpark??
Cdog.

Don't understand this quote thing so no idea where this is going to land.

I really can't see why you want to waste all those magnets to produce an oversized alternator for a say 14ft machine but if you want to do it then this may be a starting point.

I consider 17" small but it should do. You are looking at something like 25 turns of near 9AWG wire for your cut in.( way off your #13 single strand)

Virtually all the resistance will be in the line connections, if you connect with very heavy cable it will stall real hard and probably level out at something near 200W. It will only be line resistance that will get your speed up to the point where it will do something useful.

I think you are obsessed with the alternator and have lost the plot with the overall performance. Your alternator is going to be near 70% efficient at 1kW, which is going to run you into stall virtually above cut in and it will settle out at near constant power.

If you can add the necessary line resistance it will work much the same as an alternator with less magnet and copper and will certainly stand a lot of power twice a year when you get those big winds but even then you will have to furl if you get the matching right.

If you don't add the resistance it may stall regulate in any wind but the output in high winds will be miserable and it won't be too bright in the useful 10-15mph region where you most want it.

You can do it with 16 poles if you are careful and with 20 very easily, 24 is just wasting magnet for no useful gain.

Flux

[TomW]

Don't understand this quote thing so no idea where this is going to land.

Flux;

If you did not changes your preferences, all comments go in chronological order at the bottom of the thread. You can make it newest at the top but I found that very odd to track posts.

Quote just lets you show what you are responding to and does not affect the placement. As near as I can tell all posts are arranged in chronological order.

Hope that helps.

Tom

[cdog]

Thanks for bringing me back to reality.
If it would stall as bad as youre saying, why not up the prop size a bit?
I am not stuck at 17", all of this is just trying to get a starting point.
What size mill would you build if you wanted to make the best of the mags I have,
Cdog.

[ChrisOlson]

What size mill would you build if you wanted to make the best of the mags I have,

Two 10-12 footers with 12 pole generators.  The magnets you have are 2 in², which is not enough surface area for bigger machines.
--
Chris

[cdog]

This is just for my hunting camp, I wont be puttin up 2 mils, so I will be going with a 13' like you made or a bit bigger with 20 poles like flux suggested.
Any reccomendations for a 20 pole machine,lol?
Cdog.

[ChrisOlson]

This is just for my hunting camp, I wont be puttin up 2 mils, so I will be going with a 13' like you made or a bit bigger with 20 poles like flux suggested.
Any reccomendations for a 20 pole machine,lol?

You need to cut the number of poles back and keep the prop size down.  My 13 is 48 volt.  You have to realize you're dealing with the limitations of a 24 volt system.  If you built a 3.0 kW peak machine you have to deal with 120 amps and it'll be smoke the first time you get any real wind unless the furling is set to shut it down well below what the prop can put out, and in that case you're wasting the magnets anyway - and prop size.

If you build a 13, then stick to 16 poles - if fact for a 24 volt I'd consider dropping to 12 poles.  The 16 pole in my 13 footer is way too powerful for it.  I opened the air gap to .800 and backed the furling off on it and this afternoon in 25 mph wind it was peaking at 1,700 watts before it would fully furl.  Even at 1,700 watts it's only like 16-17% overall efficient and not putting out everything the prop could put out.  At 1,700 watts you're dealing with like 70 amps peak in a 24 volt.  Again, you'd be much better off to build two 10's or 12's if you want to use all your magnets up.  Otherwise you're going to have to wind with really big wire to get it to handle the amps, and then you have to increase the size of the rotors to get it to fit, then your efficiency goes down while the heating in the stator goes up.
---
Chris

[cdog]

Ok Chris, I think I will do the 13' with the 16 pole setup.
You stated in one of your posts that you feel that you overwould your coils a bit, so what would you recommend for wire and turs for 24 volt?
Thanks again for the advice, I will leave you guys alone for a while!!
Cdog

[ChrisOlson]

You stated in one of your posts that you feel that you overwould your coils a bit, so what would you recommend for wire and turs for 24 volt?
Thanks again for the advice, I will leave you guys alone for a while!!

Check out this thread:
http://fieldlines.com/board/index.php/topic,143174.0.html

Max uploaded a spreadsheet tool that looks really good to me.  I entered in the data for all my machines and it hit every one just about dead on.
--
Chris