The importance of steel around the magnet?

[gotwind2]

This image will hopefully expalin what I am attempting to do, a single rotor axial design alternator, no resin, only sealed with a hi - temp lacquer.
The magnets hopefully will have a cooling effect on the 'naked' coils.



As can be seen the single rotor plate has the magnets placed on the periphery of the rotor plate. i.e the very edge.
My question is,
Would there be much benefit having the steel rotor larger to overhang the magnets? - I know there are programs such as Femm to model such things.

But an 'experienced' answer would be preferred.

Appreciated.

[Flux]

having extra steel by increasing the disc diameter without moving the magnets would give little gain. You may gain by using a larger disc and moving the coils and magnets out to a larger diameter but your magnets already look to be fairly widely spaced.

The whole thing looks very inefficient, single rotors with no return flux path are poor at best. if you must do it that way then use thicker magnets and thinner coils so the return path is not within the coil. I suspect you could halve the thickness of your coils with little loss in voltage.

Flux

[GoVertical]

Greetings, you may want to consider adding a lower metal rotor without magnets to improve output.  Your current configuration will allow the magnetic fields to  create eddy currents in metal parts located close to the rotor and produce a brake affect.  What is the target RPM?

[gotwind2]

Hi Flux.
The single rotor design performs better than you might expect.
I thought it would be a lot worse as well, but in practice I am getting 200 watts into a 12v battery at 1275 rpm.

Therefore a fast 2 or 3 blade (3ft diameter) prop should work well.

GoVertical.
All the components beneath the steel rotor plate (in the photo above) are non magnetic, stainless/ aluminium.

[Tritium]

Greetings, you may want to consider adding a lower metal rotor without magnets to improve output.  Your current configuration will allow the magnetic fields to  create eddy currents in metal parts located close to the rotor and produce a brake affect.  What is the target RPM?

Hmmmm, now where have I heard that before?

Thurmond

[fabricator]

200 watts at 1275 RPMs? You must have an excellent wind resource.

[Fused]

..........and bullet proof blades



Fused

[tanner0441]

Hi

It looks very neat but, 200 W at I assume 12V is nearly 20 A with no encapsulation on the coils and some of the turns look lose I would be worried about the windings vibrating and if there is any heating what hapens to the zip ties.  I used to use them by the bag full and they did not handle too much heat they used to loosen and fail.

Brian

[fabricator]

..........and bullet proof blades




Fused

I'd like to see 1275 Rpms out of a home built and balanced three blade rotor, I think you'd want to do testing in the middle of the Bonneville Salt Flats, from a concrete bunker.

[Rover]

How to tick off close neighbors ..  1275 rpm wind turbine

There is no such thing as a "quiet" mill at those speeds.

Look/listen to an Air-X at full speed.

[fabricator]

How to tick off close neighbors ..  1275 rpm wind turbine

There is no such thing as a "quiet" mill at those speeds.

Look/listen to an Air-X at full speed.

The ones who live through the original blade disintegration might be pretty annoyed alright.

[Fused]

Wonder on the cut in speed........700-800 rpm?

Now THAT would be useful. (lol)

Or you could sell plans to the unaware.

Fused

[electrondady1]

hello gotwind.
like so many of the alternators you build,
 that's a very nice looking configuration you have assembled.
 you have used a mag spacing that appears to be something like 3x mag width.
 i don't imagine  many of the flux lines being drawn so far sideways to the next mag.
using a single rotor like that i would think that a great deal of the flux will be turning around and heading directly for the steel in that rotor.
so whether it is pulled over the edge or not really doesn't matter.

a few things you might consider.
rather than black tie wraps, use a short piece of the same conductor or a finer gauge to retain the shape of the coils .
you can lay it in the coil jig before you even start to turn  the coil.
and when in place it's almost invisible against the copper of the coil

i have been thinking a great deal lately about using steel /iron wire as a flux return.
it would act like laminates but present fewer problems to create.
you could lay your coils on top of it with out revealing it .

i love the use of acrylic as a stater support, beautiful.
it's practicality is directly related to the purpose of the alternator .
if you can let the volts float it shouldn't get too warm.
but if your holding it down and ramming lots of amps through ,
well, it's bound to get a bit buttery.

i know you will put this devise on some sort to  pole or tower out of sight
but consider , if you created a vertical mill just as nice .
people could walk right up to it and see how beautiful.




 

[Flux]

Ben
For what you need it may be good enough. For a 3ft prop you will need to make sure the alternator doesn't load the prop too much. Efficiency is not everything, matching is far more important. I am not happy about the cable ties either but it will be good enough for trial. I don't think you are going to be seeing 200W very often with a 3ft prop and you will have lots of wind cooling when you do.

There are lots of things you can do to improve things but it may raise the first cost, not much sense in making things too expensive just in the persuit of perfection.

The Lucas Freelite ran quite comfortably at 1200 rpm at 6ft so at 3ft your speeds are fairly modest.

Flux

[ChrisOlson]

The Lucas Freelite ran quite comfortably at 1200 rpm at 6ft so at 3ft your speeds are fairly modest.

I think 1,200 rpm is a bit on the low side for a 3 foot prop to get 200 watts.  About 1,600 rpm would be a 6 TSR prop at 28 mph.  With a small prop you need speed to get power.  It'll probably sound sort of like a bumblebee AirX but otherwise I don't see why it won't work fine.  I don't really like the zip ties to hold the coils because those things tend to loosen up after awhile.  But otherwise I see no reason it won't work.

I've tested a lot of generators with just one mag rotor and they work fine.  When I built my first geared turbine I tested a stator that was originally wound for 12 volt on a 10 foot prop.  Its rpm/volt was 13.02 with dual rotors in delta, and 30.25 rpm/volt with a single rotor.  Using just one rotor raised its cut-in rpm from 146 up to 330, which with the gearing still kept the prop at ~150 at cut-in.  I plotted a full power curve for that stator, and even with the reduced magnetic efficiency using just one rotor it still had about the same power curve as it did with dual rotors spinning 2.25x slower.

When you can put rpm's to it, that magnetic efficiency becomes less and less of an issue.  And the reduced magnetic efficiency traded for rpm's actually makes it easier to match the prop's power curve and keep the blades out of stall at high outputs.  The trend with most builders is to build the generator way too efficient, which simply puts the prop into stall when the wind starts to blow.  Getting rid of some of that magnet area and putting the rpm's to it gets a better match with every stator I've tested so far on my geared units.
--
Chris

[ghurd]

My mini-ECM with Rich's 12" CNC blades (25.5" dia) make almost no sound at 1800RPM.
I get some resonance or vibration induced noise at about 2000 or 2100RPM, but the sound is not from the blades moving through the air.
It has run away by the time its going that fast.
G-

[ChrisOlson]

My mini-ECM with Rich's 12" CNC blades (25.5" dia) make almost no sound at 1800RPM.
I get some resonance or vibration induced noise at about 2000 or 2100RPM, but the sound is not from the blades moving through the air.
It has run away by the time its going that fast.

Well some people think it's too many rpm's here, but it's a function of tip speed ratio.  If the prop's peak power is at 5 TSR, for a 2 foot prop @ 30 mph wind speed that's 2,100 rpm.  For a 20 foot prop it would be only 210 rpm.  And for a 200 foot prop it would be 21 rpm.  The smaller they are the faster they have to turn, but the tips of the blades are still running at the same speed at the same TSR, no matter the size of the rotor.
--
Chris

[Flux]

I notice comments about the AIR machines and the noise, they were deliberately intended to go into blade flutter to reduce power in high winds. it's this flutter that causes the dreadful noise.

As Chris points out, the tsr is not very high at 1200 rpm and noise should be no big deal. Perhaps those thinking in terms of 10ft machines are not realising that this is a tiny prop.

Flux

[gotwind2]

Thanks for the mixed responses, very much appreciated I've put some time into this.

In the very nature of what I do and this DIY forum, this has all been achieved without a 'kitted out' workshop.
I used just basic tools, a cordless drill, hacksaw and set of hand files (apart from the bearing housing). that was a favour from a friend (Cost £10, $16).

The whole stator will be sealed somehow - I'm open to suggestions on a suitable hi temp dipped resin/ varnish or lacquer??

A couple more images.
Top side.



THe 'viewable' underside.



Ben.

[ghurd]

I have a gut feeling it would work a lot better with 4X the neos.
Double them side by side, and double the thickness of both.
G-

[gotwind2]

Thanks Glen.
This design is a little 'magnet light' (costs).
I see where you're coming from, I had considered trying some standard (stock) 2" x 1" x 1/2" mags.

I drew it up and what with the triangular shaped coils It simply doesn't work out unfortunately.
I much appreciate the input however.

Ben.

[RP]

What kind of rectifier is that on the underside?  Is that a 3-phase block rectifier?  If so I've never seen one like that.

[gotwind2]

HI RP.
Yes it is a 3 phase 35 Amp bridge rectifier in a single package.
Bizarrly it was half the price to import this from Canada (incl shipping) than anything I could buy in the U.K.
http://www.windynation.com/catalog/rectifiers

[Flux]

I presume it is just a case of demand, 3 phase bridges have been around for years but it cost much more to use one than to use 2 single phase ones. I think gradually the price differential is falling. Much more convenient to use the 3 phase version if the cost is not prohibitive.

Flux

[tanner0441]

Hi

Just a post script on the blades at 1200RPM.....

I watched a documentary earlier on the Apache Helicopter, the main rotor on that spins at 1200RPM and they are over 30 foot across.  They do have a fancy end on though do deal with the tip forces.

Brian

[taylorp035]

I'd like to see 1275 Rpms out of a home built and balanced three blade rotor, I think you'd want to do testing in the middle of the Bonneville Salt Flats, from a concrete bunker.

My mini-ECM with Rich's 12" CNC blades (25.5" dia) make almost no sound at 1800RPM.
I get some resonance or vibration induced noise at about 2000 or 2100RPM, but the sound is not from the blades moving through the air.
It has run away by the time its going that fast.
G-

My 30" diameter cnc blades were happy at 10 mph at ~1200 rpm.  I saw over 3000 rpm several times and it had a nice smooth sound.  The pitch on those blades were ridiculously low, so the tsr must of been pretty high and the winds were not 40 mph.