Author Topic: Is this an alternator for a 10 foot blade? (Read 3456 times)

elt · « **on:** August 21, 2006, 11:18:45 PM »

I'm about ready to send my files off to the laser cutter and thought that I'd ask, please, for a review before I do; thank you very much!

I'm looking at a 10" magnet disk with twelve 1x2x.5 magnets

I got a rear hub from a Saturn; its 100mm bolt pattern leaves room for nine 3.2" x 2.2" coils. The leaves .3 square inch of coil cross section for a half inch thick stator. Flux suggested to me that with N42 or N50 magnets that I could go for a slightly thicker stator... if I can go to a 5/8" thick stator, I get .375 square inches for the coil cross section, about the same as that for the 10' turbine in Hugh's booklet.

Using the numbers for 16 AWG, 354 turns per square inch, the half inch thick stator would have enough room for 52 turns, two in hand and a 5/8" thick stator would have room for 65 turns, two in hand. From "the math" and what I've read in posts this seems like what I'd get from Hugh's ten foot plans which use 17AWG 75 turns two in hand (24 volt) but with using a slightly thicker wire to give a slightly higher cut in speed and a little better high speed efficiency.

Does that sound about right? If not, okay... I'm going to take everyone's advice and build the alternator first and then see what blade matches it but I'd have some piece of mind if I thought I was in the right range for a 10 foot or so blade.

The quote from the laser cutter for two rotor disks, the hub mount and the wedge for the tail is about $100 shipped. (I'm sure it'd be a lot less without the 12 little holes in each disk for the screws into the magnets; the laser has to slow way down to make small holes.)

- Ed.

Countryboy · « **Reply #1 on:** August 21, 2006, 05:47:21 PM »

Hello elt,

You magnet rotor appears to have 6 bolt holes at the center. Why?

You need 4 holes to bolt to the hub. You should have an identical sized 2nd magnet rotor, or blank rotor, to conduct the magnetic flux. This second rotor should have the 4 holes for the hub bolts, and 4 more threaded holes for jacking screws.

elt · « **Reply #2 on:** August 21, 2006, 06:18:37 PM »

Yes, I'm intending two rotors with 24 magnets...

I was going to only cut and tap two holes for jacking screws; do you think that will be too difficult to assemble?

- Ed.

Countryboy · « **Reply #3 on:** August 21, 2006, 07:13:07 PM »

I imagine it will be a SOB with only 2 jacking screws. It'll be far easier and safer with 4. Drill and tap them yourself if you are trying to save a buck.

altosack · « **Reply #4 on:** August 21, 2006, 08:17:09 PM »

I was going to only cut and tap two holes for jacking screws; do you think that will be too difficult to assemble?

Yes. It will allow the disc to rotate around the line made by those two and touch (probably quite quickly and forcefully !) on either side. It takes 3 points (or more) to define a plane and this is the minimum you should use to keep control of clearances and for safety. Since you have a 4-bolt hub, 4 jacking screws will fit nicely.

Flux · « **Reply #5 on:** August 22, 2006, 01:02:13 AM »

Is there some reason you are stuck with 10" rotors? You are squeezing things in quite tight. 12" would seem better but 11" would be an improvement.

If you are sure you can get 62 turns of 2 in hand #16 with the 10" discs then it should be ok, but bigger discs would give you moor room to play with at the centre and less leakage flux.

If you are going for a higher cut in, the 62 turns will be ok for 24v and should take a 10ft prop. Do I remember that you were in a good wind area?, if so the higher cut in will help your overall output.

If you can go up to 12" discs and use thicker wire then you will make greater advantage of the higher wind.

I agree with the others, 2 jacking screws will land you in big trouble, otherwise it looks fine.

Flux

dinges · « **Reply #6 on:** August 22, 2006, 03:30:53 AM »

Use AT LEAST 3 jacking screws. I've used 2 in my mini-axial flux genny, and believe me, you do not want to do that with such big magnets and rotor plates. That's one of the things I learnt from building that mini genny.

Please, please, use 3 or more.

Otherwise you'll not only have difficulty assembling, but may have trouble typing in the future...

elt · « **Reply #7 on:** August 22, 2006, 06:57:13 AM »

Okay... I need my fingers for my day job so three or four jacking screws it is. Thanks! - Ed.

elt · « **Reply #8 on:** August 22, 2006, 07:35:36 AM »

I'm not stuck with the 10" rotors but I have read a lot of concern here about damage caused if/when the rotors and stator flex. IIRC, stiffness goes as the cube of length so a 10" disk will be almost twice (1.7x) as stiff as a 12" disk with a similar factor gained in the stator. I htought that the 10" geometry would be more robust.

I am already down one wire size from Hugh's plan which calls for 75 turns #17 two in hand. I don't have any magnet wire right now and part of what I'm trying to do is figure out what size I should buy. If breaking apart isn't a worry on these small machines then that would sway me to a larger disk with fatter wire. (An 11" disk would only net a 25% gain in stiffness.)

- Ed.

willib · « **Reply #9 on:** August 22, 2006, 11:26:53 AM »

you might consider adding more support for the stator,

if you are worring about everything flexing i would think that four or five mounts for the stator would help in that area.

also how thick is the steel in the rotors ?

i suspect it is not 1/4" , the price quoted would lead me to believe it is too thin?

elt · « **Reply #10 on:** August 22, 2006, 04:37:46 PM »

well... I asked for a quote on cutting the pieces out of 1/4" plate. When I saw that the quote included shipping I sort of assumed that included material but maybe that's just the way they quote cutting time (because it has to end up in my hands eventually.) But his charge for steel is .63 USD per pound so if the quote doesn't include material, it'll be about $20 more.

- Ed.

willib · « **Reply #11 on:** August 22, 2006, 05:57:34 PM »

do you have a link to this place?

elt · « **Reply #12 on:** August 23, 2006, 06:44:55 AM »

Using the number "305 turns per square inch" for #15 wire, it looks like I can get 65 turns two in hand (with a 5/8" thick stator) by going to an 11" diameter rotor. Each coil would have about 1/2 (.54) of the resistance of the coils of the published one, .45 ohm versus .83 ohm ... is there any point to going on with an even larger (diameter) alternator and even larger wire? (When is enough, enough?)

I realize that they are electrically equivalent but other than the difficulty in winding, is there consideration in using 65 turns of #12 wire versus #15 two in hand?

Thanks alot!

- Ed.

elt · « **Reply #13 on:** August 23, 2006, 06:53:55 AM »

I found this on ebay -

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250021492664

Here's the website -

http://www.acssteel.com/

Hope that helps,

- Ed.

Ungrounded Lightning Rod · « **Reply #14 on:** August 23, 2006, 05:00:39 PM »

Very slightly more eddy current losses with a single wire. I believe it's usually such a tiny difference that it's not an issue.

(Now if you wanted to wind with thin copper pipe so you could water cool the stator the thickness WOULD be enogh for eddy currents to become an issue. B-) )

Flux · « **Reply #15 on:** August 24, 2006, 12:36:36 AM »

I am not sure what thickness discs you intend to use, but I wouldn't use less than 5/16 for magnetic reasons. I think most of the trouble with flexing is due to the way that most people build things backwards.

I like to mount the front disc direct to the hub flange and the prop direct on to that. Most people mount the back disc on the hub and carry the front disc and prop on a conglomeration of allthread about 2" in front of the hub flange.

Perhaps there is problems doing it my way without machining facilities. A 12" diameter 5/16 thick disc is not going to flex from gyroscopic force on its own, ( it may flex from magnet pull but that is fixed once assembled).

The gyroscopic load of a 10ft prop on 2" of overhanging allthread needs consideration.

Stator load is mainly torque and again long bits of allthread flex as cantilevers with torque and bring the stator nearer the back disc.

elt · « **Reply #16 on:** August 24, 2006, 10:04:40 AM »

I like to mount the front disc direct to the hub flange and the prop direct on to that...

Are you suggesting putting one rotor and the stator between the front of hub and the rear flange? I gave that some thought but it looked like I'd have to take the hub apart to get the rotor in there... how do you do it?

- Ed.

Flux · « **Reply #17 on:** August 24, 2006, 10:24:30 AM »

Yes that's what I do, but I have no idea if it is possible with your hub. I suspect there must be snags as everyone seems to hang the things over the front.

Most early hubs have tapered roller bearings and it is easy to remove the hub from the mounting plate. Not so sure about newer hubs as these seem to have special bearing units that are pre loaded and not adjustable.

I see in your reply to Willib that you are thinking to use 1/4" plate, I wouldn't use that above 10" and not with magnets 1/2" thick.

nothing to lose · « **Reply #18 on:** August 24, 2006, 11:04:48 AM »

"well... I asked for a quote on cutting the pieces out of 1/4" plate."

If you want the most power you might like thicker disks? If it just adds more material cost and not more cutting cost it might be worth it? Only looking at a few pounds.

Did I see you are using N42 2"x1"x0.5" neos? I have those stuck to 1/4" steel now and I can feel the flux loss on the back side using a wrench. Not real bad but it sticks enough I kinda wish I had ordered 3/8" disks now since I'm not going to use a ring on the 12" size.

I have 4 more on the way a bit different that were laser cut. The used ones I have here now were not cut perfect but good enough, and a used hub, I'll use those for a permanant coil/stator tester.

Use 4 jacking bolts. Like others said 2 is not enough, it can flop over to one side. 4 is nice and even, with no binding or flopping, and makes it easy to keep rotors in balance too. I had my disks cut with 2 different bolt patterns, total 8 1/2" holes, 4 I will drill out and tap for 9/16" jacking bolts myself. I have the option of using 4 bolt trailer hubs or 4 bolt Ford/Mercury hubs with these disks but I had to have all the holes cut 1/2" to fit the lug bolts in doing that.

I would geuss material was included if shipping was also, you should check.

I was told my 12" disks weigh 30lbs for the 4 total. That would be about 7.5lbs each or 15lbs for 2, so your 10" should weigh less. At $0.63 lb 10lbs would only be $6.30 maybe with your extra parts it'd be around $10 or so??

Not sure the user name offhand it's saved in e-mail, but a forum member here can waterjet cut the disks, I'll be having him make some parts also soon. I got sidetracked on that last trip I made.

This set of laser cut is coming from a Northen friend that was also doing me some other stuff.

elt · « **Reply #19 on:** August 27, 2006, 10:41:18 AM »

Okay, thanks everyone for the feedback!

Based on that I'm going to do for my 10' 24v turbine -

Use 4 jack screws instead of two
Use 5/16" thick plate instead of 1/4"
Use an 11" diameter magnet rotor instead of 10"
Use 65 turns #15 wire two in hand (or 65 turns #12 wire)

instead of 65 turns #16 wire two in hand.

One thing that's confusing me - if I made this 12 volts that'd be 32.5 turns of #15 wire four in hand... compared to Hugh's 8' three phase turbine which has 27 turns of #14 wire three in hand ... #15 four in hand is the same current capacity as #14 three in hand; the ratio of 32.5 turns to 27 turns is the same as 10' to 8' ... I think there's something to learn here but I'm not sure I see it. Since the 10 footer turns slower in the same wind, it seems like the extra turns on the 10 for alternator will just about make the same voltage as the 8 footer in the same wind (while turning slower.) I thought that I went from the #17 wire in Hugh's original design for the 10 footer to #15 wire to raise the cut-in speed and be more efficient at higher wind speeds. But is seems it'll make the same voltage as the 8 footer and with more turns has more resistance... where's the extra power (expected from a 10 footer) come from?

It seems to make sense comparing the two 10 foot designs but not (to me) comparing it to the 8 foot design. Confused.

- Ed.

Flux · « **Reply #20 on:** August 28, 2006, 07:09:01 AM »

Don't worry you are not the only one confused.

With 12 poles of the 2 x 1 x 1/2 magnets on a nominal 12" disc you have an alternator that is pretty stiff for 8ft and a bit on the light side for 10 ft. You can play changes with the cut in speed and tsr to get what you want to some extent, there is no perfect winding that will out perform anything else.

At 8ft with 24v and short thick leads you may have to increase air gap and possibly add a bit of line resistance if you cut in at 7 mph. The 12v case usually keeps out of stall with more diode drop and line loss.

At 12v you may have a tough time holding things down fairly well with a 10 ft prop, but you should make it with 24v as long as you keep the air gap tight.

You will most likely have a similar peak output power from 10ft as from 8ft as the temperature will be the limit.

The 10ft machine will gain by reason of its swept area and will produce more power at all wind speeds up to the thermal limit ( furl earlier for 10ft).

When you have your magnet rotors sorted out you can play with a test coil, your winding ability will have a significant effect on the size of wire you can squeeze in for a given number of turns and your moulding ability will affect the air gap that you can safely work with.

When you are satisfied what wire you can squeeze in then you can select your cut in speed to suit your wind area. If you are prepared to forgo the lower winds you can use less turns of thicker wire and achieve better efficiency in the 12 mph upward winds. You will find that if you do this you will be running faster than the normal stalled state that you reach with a low cut in speed.

For 10 ft in a good wind area I would aim for a cut in speed of 180 rpm at 24v and use the thickest wire you can while maintaining a safe air gap. If you get sloppy with air gaps at 10 ft you will start running into high speeds at full load.

Not sure if this has helped but there are really no exact performance details for any of these machines as far as I know. Constructional ability, magnet grade, line loss are all factors that are a bit unknown, and I suspect that individual interpretation of the blade profile may have as much effect as all the other factors and you haven't even considered that.

Flux

elt · « **Reply #21 on:** August 31, 2006, 03:22:00 PM »

Hi Flux, you wrote:

aim for a cut in speed of 180 rpm at 24v and use the thickest wire you can while maintaining a safe air gap

What's a "safe" air gap?

My magnets are N42. The place where I'm getting the parts cut didn't have ready access to 5/16" plate so I ordered 3/8" thick for the rotors; hopefully that will get all my flux going in the right direction... I've been calculating my windings based on #15 wire in a 5/8" thick stator. I can do a 1/2" stator if I used #16 wire. (Hugh's design called for #17 wire.)

Thanks for everything,

- Ed.

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Author Topic: Is this an alternator for a 10 foot blade? (Read 3456 times)