Author Topic: And so it begins  (Read 11545 times)

0 Members and 1 Guest are viewing this topic.

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
And so it begins
« on: February 03, 2012, 07:47:07 pm »
Look what the Big Brown Truck brought today!



Not knowing where to start or what to do I ordered 40 of these little magnets. They are 1x1/2x1/4 inch and intended for a small alternator. I’m not expecting much power, just getting some experience in building a working alternator. Gosh these little things are expensive! And powerful! I had one stack I was working with trying to separate one of the magnets. I set the stack down on the bench and it pulled one of the change gears for the lathe from almost a foot away! I’m going to have to make sure my work area is very clear of any iron when working with these things.

I hope you guys are up for some stupid newbie questions cause I’ll have a bunch. I don’t even know where to begin.

First I have a lousy site for wind. Most days are 3 – 15 MPH except in the dead of summer when it’s dead calm for July and August. I have lots of trees and there is a subdivision right behind me. I have a half acre but it’s covered with trees, large old maples. The only real place I have for the tower is mounting on the garage, it’s detached so I’m not worried about the noise but I know it’s going to be turbulent. As if the trees weren’t bad enough, all the buildings are going to mess up the air flow. I have to keep the tower low so the fall zone stays within my property boundries (county ordinance).

I don’t know what kind of power to expect out of these little magnets but I’ll be happy with anything that works. I hope to get about 10 watts out of it in a good breeze.

The design parameters I’ve set out to achieve are:

3 foot rotor
Cut-in about 150-200 rpm
At least 2 amps and 15 volts but I’ll settle for .5 amps.
5-6 inch magnet rotor with 8 or 12 magnets, 6 or 9 coils.
Figuring on a 3/8 inch air gap.

What do you think? Is this do-able with these little magnets?

Thanks,
Kevin
As far from the city as I can get but still keep my job.

Offline dang

  • Full Member
  • ***
  • Posts: 86
  • Karma: +5/-3
Re: And so it begins
« Reply #1 on: February 03, 2012, 07:56:13 pm »
First off - magnets are new to our five monkey senses, there is no instinct to follow with them. GET THEM PROTECTED, back in the delivery box and up on a high metal-free shelf. If you must, find one that is already scratched/chipped/dented to play with and leave the others ALONE until the hour & minute you're going to be placing them... in a clean room w/o other metal items.

My shipment of magnets? I was flipping one around and trying to gauge the strength etc. and was disappointed... then went back to the pile of others and watched the whole stack go frictionless away from my hand enough it almost leapt to an ugly situation.  If you've ever used a metal grinder, cut metal or cleaned up rusted iron in your shop the particles will find their way to the magnets. Duct-tape adhesive is about the only way to clean it off once that happens. Littler ones have given me blisters, larger ones like you have can break bones.

EDIT: I see they are smaller than I thought, not quite bone-smasher's but when they attack in packs.... Same rules apply, call it good practice for larger ones  ::)
"It may be that your sole purpose in life is to serve as a warning to others" - Anonymous

Offline WooferHound

  • Technowhiz
  • Global Moderator
  • Hero Member
  • ******
  • Posts: 897
  • Karma: +40/-3
  • Huntsville Alabama USA
    • My personal webpage
Re: And so it begins
« Reply #2 on: February 03, 2012, 11:04:10 pm »
That's a Lot of magnet
 
----- W o o f e r h o u n d -----
My Renewable Energy Projects

Offline Watt

  • Sr. Member
  • ****
  • Posts: 261
  • Karma: +11/-1
  • Over qualified in the inexperience department!
Re: And so it begins
« Reply #3 on: February 03, 2012, 11:08:04 pm »
Where is Sir Flux when you need him?  :(

I come up with just over 8.25" for rotor diameter if you use all magnets, 20 per rotor for two rotors and have .5" spacings at the closer points.  Just over 5.75" diameter with 12 magnets.  I guess you are going to go three phase with this turbine as you have indicated 3 coils for 4 magnets. 

I think I'd decide on the type of bearings, spindle and hub, get the rotors built and get on to a test coil.  I seem to think more magnets is better so, all you have to do is decide on magnet count before you can really start the build. 

Anyway, keep us posted with your progress.   8)
CEO of this Dis-Organization....

Offline Janne

  • Newbie
  • *
  • Posts: 21
  • Karma: +6/-0
  • Turbiini
    • Projects
Re: And so it begins
« Reply #4 on: February 04, 2012, 03:07:16 am »
Hi,

My rule of thumb on designing alternators has been, that when you double the turbine diameter it will take 8 times the amount of magnet to make as stiff generator. That is because the power output is quadrupled, while speed is halved.

If we use that rule of thumb, and compare it to the early 10' machines, which had 24 pcs of 2*1*0.5inch magnets, your magnet lot comes in about 1/5 of that. Cube root of 1/5 = 0.58, so your magnet lot should be able to support a 5 footer, mayby even 6 if you'd be pushing it a little.

There are of course other factors that play, like how efficiently the magnets are being used, are the (turbine)rotors going to be the same performance etc.. It's important to compare it to something, that makes good use of magnets and also focus on your own design into doing the same. In the end it will only give you an estimate with all the variables in play, but these "rules of thumb" have worked quite ok for me.

The first you'll need to do is to figure out suitable size of magnet rotors. It would be best if you can size the rotors so, that there is space for one magnet in between of each magnets, but a bit smaller gap(like Watt suggested) than that is ok too. That will get you most out of your magnets.

When your magnet rotors are complete, you will then need to make the final design about the rotor size, as suitable cut-in voltage depends on the rotor size. Once you get there. This includes wounding a test coil, and then calculating the number of turns based on the required cut in voltage, and selecting a wire that you can fit into the stator with the required amount of turns.
Beyond the wolf border

Offline rossw

  • Senior Moderator
  • Hero Member
  • *******
  • Posts: 879
  • Karma: +35/-0
  • Grumpy-old-Unix-Admin
Re: And so it begins
« Reply #5 on: February 04, 2012, 04:22:32 am »
I asked Flux in email - his reply follows:

Quote
I spend too much time on Otherpower to think about other boards.

In answer to the question, there is no details of the intended prop and this will have a big effect on the alternator design. There is no energy in wind at 3mph and designing for it would be pointless. For a small 3 ft machine I suspect you will struggle to get anything at 6mph but that may be a sensible cut in point.

For a fairly fast prop I would cut in about 300rpm, but 200 would be sensible to aim for and you could increase the gap if it is too slow. To get down to 100 rpm you would need a slow high solidity prop but this may be the way if he intends to use something like pvc blades.

12 magnets will be enough electrically but I see a big issue with space at the centre of the stator and no way could you get a hub in there, it would need to be a overhung design with only the shaft going through.

I think generally i would favour 16 magnets but the hub would still need careful thought. If you use 20 magnets it will stall and you will need external resistance.

Personally I would go for 16 magnets if you can solve the bearing problem. It should take a prop of tsr5 and it may stall a bit in the higher winds.

I think you will be looking at something near 80 turns for cut in at 300rpm.

Sorry I can't help more but no prop details. You should get 24w or more at 15mph if you can get it out of stall.

Flux

Offline bj

  • Hero Member
  • *****
  • Posts: 735
  • Karma: +23/-0
  • Lamont, Alberta, Canada
Re: And so it begins
« Reply #6 on: February 04, 2012, 06:09:18 am »
   Well Kevin, it looks like you are fully addicted. ;D  And us addicts love company.
You have some good advice to start, so keep us posted.  My site has more or less
the same wind restrictions, and I haven't quite settled the design yet.
   You mention a lathe, so some reading on Chris O's builds might be worth doing.
   Best of luck!
"Even a blind squirrel will find an acorn once in a while"
bj

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: And so it begins
« Reply #7 on: February 04, 2012, 09:00:26 am »
3 foot rotor
Cut-in about 150-200 rpm
At least 2 amps and 15 volts but I’ll settle for .5 amps.
5-6 inch magnet rotor with 8 or 12 magnets, 6 or 9 coils.
Figuring on a 3/8 inch air gap.

Kevin, if it were me I'd use a bigger rotor.  With those magnets, about 6 feet.  And use all 40 magnets to build a 20 pole 15 coil generator.  I did some rough calculations on this and you should be able to get about 40 watts @ 10 mph, and around 280 at 28 mph.

If you use a 3 foot diameter rotor I'm afraid you will be very disappointed on your marginal wind site.  If you build at least a little size into the machine you will have a lot of fun with it because it will actually make some power.
--
Chris

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
Re: And so it begins
« Reply #8 on: February 04, 2012, 09:16:11 am »
Wow! Thanks for the replies, guys.

Dang: Yes, while fiddling with a stack my finger got pinched. Yes, it hurt. Lesson learned. I will only work with one magnet at a time. The stack will not be anywhere near the work area. I’ll also need to work on some way to anchor the rotor while working on it. I don’t need tools and parts to go flying around the shop unexpectedly. The shop vac is my friend. The magnets are back in the bubble wrap and box, they were only taken out for the photo op and inspection.

Woof: I ordered enough to make two machines. I just know I’m going to mess one up someway, somehow. It’ll happen.

Watt: Thanks a lot. This is what I really need, some rules-of-thumb to base starting points on. The parameters I started with had no basis in fact, just some assumptions I’ve made based on the descriptions of other projects. I assumed a spacing of one magnet width, maybe a little more. My plan is the first device will use 8 magnets per rotor, 16 total. Yes, it will be three phase. I’m trying to follow common practice, not blaze new trails. This first machine is a learning laboratory for me. I’m hoping my expectations are more conservative than overly optimistic.

Janne: More rules of thumb. Many thanks. That’s really what I need, critique of what I’ve set out to do, suggestions to avoid mistakes and to define reasonable expectations.

Ross: Thanks for forwarding the info on to Flux. Please pass along my appreciation for him taking the time to help me out. Of course the parameters set out above are just a starting point and will be adjusted as warranted. A 5 foot rotor is do-able, I think. 7 foot will likely start running into issues with the neighbors (not to mention the county bureaucracy). More than that and I’ll start running into structural issues and trees. Though something tells me my wife will start complaining before any of the above get a chance to :)


Bj: Thanks for dropping by. I don’t know about addicted (yet). But it is something I’ve wanted to do for a very long time. I have a smallish machine shop in a corner of the garage: 7x14 lathe, 9x20 lathe, X2 type bench mill and a larger knee mill. I also build small engines: steam, stirling and repairs around the house. The plan is to document the project here. Perhaps some other newbies will find it useful.

By the way, this is likely to be a slow build. Time, materials and motivation may not always be available at the same time. I'm on call 24/7 and of course family needs always come first. I have the motivation and would like to be flying ASAP but a more likely timeline is first wind around mid to late summer.

OK, design changes:

5-6 foot turbine, but I still want to get away with as small as possible.
Cut in ~300 rpm
Hub 8 poles, 6 coils, 6-7 inches in diameter
Bearings yet to be determined.
Wire gauge and turns yet to be determined.

Any suggestions on bearing size or style?

Coil:
I’ve read where the core should be the same size as the magnet. Is there and advantage/disadvantage to going slightly larger or smaller? Is wider better than longer?

Is there any advantage to building a pair of small test rotors first, say with four poles to help determine what coil parameters to use?


Thanks,
Kevin
As far from the city as I can get but still keep my job.

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
Re: And so it begins
« Reply #9 on: February 04, 2012, 09:39:01 am »
Thanks for the leg work, Chris. Looks like I've been talked into at least 5 feet on the rotor. I'd like to stay small to be unobtrusive to the back neighbors. They are fairly close as the garage is built towards the back of the property, but still plenty of room from the fence line as long as I keep the tower low. Their properties are slightly bigger than the usual subdivision postage stamps, but not much, maybe a third the size of mine.

The only overhead clearance I have is from the garage and directly back, or above the house. And it is NOT going on the house!
As far from the city as I can get but still keep my job.

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: And so it begins
« Reply #10 on: February 04, 2012, 09:45:36 am »
5-6 foot turbine, but I still want to get away with as small as possible.
Cut in ~300 rpm
Hub 8 poles, 6 coils, 6-7 inches in diameter
Bearings yet to be determined.
Wire gauge and turns yet to be determined.

Assuming a 5 foot rotor cutting in at 6 mph and 8.5 TSR you have 285 rpm.

With only 8 poles using those small magnets you need 140 turns of wire to get 12 volts @ 285 rpm.  You need to use more poles with those small magnets.  With 20 poles and 15 coils, for instance, you can get the coil turns down to 22 @ .650 air gap, and get the resistance of the winding low enough to actually get some power from it.

If you had bought 1 x 2 x .5 mags, then yes, you could build a 8 pole.  But the magnets you got will not work very well with 8 poles.  I see you mentioned buying enough magnets to build two machines, so you could build a 10 pole single phase as well, which would take 20 magnets.  A 10 pole single phase would require 38 turns per coil, which would also be very doable and yield a low enough resistance to get decent power from it.  With the small prop the single phase configuration would also keep the prop out of stall at higher wind speeds because it is only loaded when the voltage is high enough for the diodes to conduct.

So there are several options.  But I'm afraid that a 8 pole three phase is not one of them with those mags.

Coil:
I’ve read where the core should be the same size as the magnet. Is there and advantage/disadvantage to going slightly larger or smaller? Is wider better than longer?

All the homebrew books claim you should make the hole in the coil the size of the magnet.  However, there are some trade-offs in performance doing that.  The book designs will yield a high resistance generator that gets hot at high outputs.  If you "scrunch" the poles a little closer together the flux leakage at the corners of the poles is insignificant compared to the gains in internal resistance you can make by using wedge shaped cols.

When you use a lot of turns of wire, the outer turns add resistance real fast and performance suffers accordingly.  So keeping the turn length as short as possible is important, especially when dealing with small units like this where you'll wind with small wire and internal resistance ends up being the killer in getting any amps out of it.

So I would tend towards a design using wedge shaped coils with probably about 1" top to bottom, about 5/8" wide at the outer part of the coil and about 1/4" wide at the inner part.  Using this wedge layout will require about two more turns per coil, but the gains in less resistance will be significant compared to using a winder configuration that has a rectangular hole.
--
Chris

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
Re: And so it begins
« Reply #11 on: February 04, 2012, 10:23:42 am »
OK, 20 poles with 1/2 inch spacing puts me at a ~8.5 inch hub. Still not bad. Funny how this thing keeps getting bigger :)
Flux also mentioned more poles to make it work. Guess I better defer to experience :) 20 poles it is.

I'd rather stay with 3 phase to get power from the lower wind speeds since that's what we have most of the time. Wouldn't a single phase need more torque to overcome cogging?
8.5 TSR seems rather optimistic with all the obstructions I have, but I really have no basis for that opinion. I just assumed I'd have lousy efficiency no matter what I did.

You built a multi-stator machine at one time, didn't you? How did that work out?

Thanks,
Kevin
As far from the city as I can get but still keep my job.

Offline Janne

  • Newbie
  • *
  • Posts: 21
  • Karma: +6/-0
  • Turbiini
    • Projects
Re: And so it begins
« Reply #12 on: February 04, 2012, 12:06:16 pm »
For 5' you're going to need all that magnetic material you have - so 20 pole is a good way to go forth.

To add to Chris's post, the only time your design would suffer from smaller than a magnet sized hole in the coil, is when the magnet is coming to the middle of the coil.. At the time when the voltage is at the lowest. With battery charging devices, no current is flowing at that time, and no loss will be made. So that coil geometry would probably be a good way to go, in fitting the most copper wire possible into stator. A good thing to remember, is the more copper you put into the stator, the more less you're going to lose power internally in it.. Meaning less chance of burnout and better electrical efficiency.

I'd avoid single phase. You will get better electrical efficiency if you go 3 phase. This is because in 3 phase the maxium current is less - hence smaller I^2*R losses. If stall becames a problem I'd rather deal with it externally(longer wire, or resistors in series), than heat up the stator. Not saying single phase cannot also be succesful - my first machine was a single phase 5 footer :).
Beyond the wolf border

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: And so it begins
« Reply #13 on: February 04, 2012, 12:43:19 pm »
You built a multi-stator machine at one time, didn't you? How did that work out?

Beautiful.  They're two-phase 10 pole geared units, driven with 3.8 meter rotors.  I"m flying three of them as we speak.  They use ferrite magnets and are considerably more powerful than the three phase single stator neo generators they replaced on my 12G turbines.  They will develop 1.8 kW continuous without overheat and I've pushed them as high as 4.3 kW.

The rear stator is skewed 90 electrical degrees from the front one and they use IRP (Individually Rectified Phase) configuration with four wires down the tower

422-0

They're also heavy.  The generator assembly weighs about 80 lbs.

Here's another photo of a complete 12G turbine head with a dual stator generator laying on its side in the wheelbarrow - this is the one I took down a couple week ago when I put up my new 3.2 meter MPPT turbine:

423-1

That turbine head weighs about 340 lbs.  Those generators will take anything a set of 3.8 meter GOE222 blades can put to the shaft.  It is one heavy duty sucker.
--
Chris


Offline jlt

  • Newbie
  • *
  • Posts: 19
  • Karma: +1/-0
  • No Personal Text Set by User
Re: And so it begins
« Reply #14 on: February 04, 2012, 09:37:06 pm »
I would use 2mags for each pole shaped like a t. And shape the coil's in a wedge shape.

  And use 12 poles and 9 coils.

That would be a lot simpler to build than with 20 poles and 15 coils.

You can push the mags on each pole within about 1/4 " apart as long as they are seated on the steel rotors. 
  Or use for 8 poles and 6 coils