New Rotor for 1st genny

[Jeff]

This is going to start out sounding normal for a small 1st genny. Dual Rotor, 15 mag, 1/2inch dia. by 1/2inch long N52's. Instead of the usual steel rotor, I have a machinist (my Dad), making "pots" to mount the mags in, providing a path for the flux. A simple 1-1/4inch diameter steel rod stock, with a 1/2inch hole reamed thru. Cut-off to just over 1/2" length tubes, then ground to only 0.002-0.003" Less than the lencth of the mag. The same bar stock can be cut off & ground to 3/8" thick for the backing on the "tube". This will make a "pocket" that the mag can fit into, with a 3/8" backing providing a nice & neat package to mount the mags into. Preferably a very mild press fit on the diameter where I can put the mags in the freezer, and only WARM the pocket assembly to make installing the magnet into. That should make a nice path with plenty of backing and even a 3/8" per side outside path for the flux fieled. Now this can be mounted on almost anything for a rotor, magnetic or not! Even 3/4" hardwood, as long as it has some extra bracing in case the magnetic field tries to distort the "rotor". I'm still searching to pick the best (and cheapest) rotor material. I have some old friends still working in the injection mold industry, and hope to luck out with a couple of 10-12 inch dianeter carbon fiber/graphite discs the can be mounted to the existing shaft & bearings I have.

Like I said, the plan is for 15 mags per rotor. Although the mags are only 1/2 inch diameter, the mounting "pot" will provide 3/8" all around making an effective "magnet and flux field" of 1 1/4" diameter. So...the coils will be just under 1/2" inside diameter and 1 1/4" outside diameter. I planned on going with 9 coils, so 3 phase is the goal. Also, 5-10 amps max out @ about 14v would be preferable.

Now comes the strange part. Forget cut-in, blade size, and even HAWT or VAWT!

My first will be a VAWT however, BUT, this will NOT be directly powering the genny! They will be powering a very small air compressor. I'm talking about those cheapies you can buy at any Auto store or WalMart for $15-$20. With just some minor modifications, and aiming for 100-120 psi. max. And NOT expecting to try and run the thing at 2000 RPM from a small windmill. Even if it took half a day just to get a small 5gal. tank up to 100psi.!

I have 4-5 small air tanks, and very small compressors that will be run by the VAWT/HAWT. It doesn't matter how much or how fast they compress the air into the storage tanks, as long as it does. I have the "stuff" to make a small, simple, motor that will run from two small dual-action air cylinders with a 6 inch stroke. I already have a nice 20" flywheel, and air regulators to controll the RPM's to a nice steady 180 or 200 RPM. The plan is to use this as a "demand" system to add a little extra charging power when the inverter is running something large like the fridge. It will only have to run 15-20 minutes at a time, and have plenty of time to add a little more compressed air to the storage tank. I have 3-4 of those small compressors which when connected the "normal" way, draw about 1.8 amps, or around 24 watts. It sure seems like a small VAWT could handle at least that, and I can always add more windmills and extra tanks to extend the storage capacity. BUT, I can gear the Vawt to run the little compressor wayyyyy down, so literally NO cogging.

Although there will be some losses here & there due to efficiency, the storage & use on demand seems like it would be a great help during those peak use times.

[fungus]

First thing I see 'wrong' is the number of magnets - 15 ? It really has to be an even number of magnets, otherwise at one point you have two likewise poles next to each other, effectively being a single magnet ..

[ghurd]

First thing I saw wrong is placing the magnets in steel pots.

The flux will be shorted.

Next thing is the cheapie compressors only run a couple hours tops, at 30PSI, before they are worn out.  They will not last long at 110PSI.

I figured the 15 was a typo until it showed up again with 9 coils.

G-

[electrondady1]

ok, it seems your understanding of how the alternator works is flawed.

so you should keep reading on that.

 but its interesting if your looking to just compress air

perhaps you could run the compressor right off the mill.

around here they have windmills to bubble air into ponds

perhaps you could rig up something that would compress the air .

[Jeff]

Sorry about the mis-calc on mags -vs - coils. I wasn't going back to my HUGE WORD doc to get the mag/coil ratio right for 3 phase, just a minor adjustment.

As far as making "pots" for the mags, it's no different than mounting a mag directly to a steel disk for a rotor. The idea is to have a thick enough backing, but no larger than it needs to be for the flux field. Wouldn't an outer shell also have the same effect in providing a better path for the flux field? If not, then why do some mount the mags in an extremely thick plate, with counterbores to place & locate the magnet? If an outer shell would not provide a good path for the flux field, then OK, all you'd need would be a good steel disk the same diameter as the magnet.

As for the cheapie air pump, that was hopefully obvious as a temporary unit until I (or my Dad & his machine shop) could make a small, but much more durable & efficient one (I DID mention some minor modifications, such as a Delrin seal instead of the cheap stock ones, much better air cooling, and minimal/metered oiling to the seal & bearings). The whole idea was to slowly build up pressure, then use that as needed to run the rotor/genny maybe 2-3 times a day for a start.

[ghurd]

" it's no different than ..."

It is very different.

It provides a great path for the flux, from the top of the magnet to the bottom, but that flux path will not go through the copper coils.  No flux in the coils, no power.

All the magnets need to be on the same disk.  Placing them on a disk the size of a magnet will not help.  

"On" a thick iron plate is not the same as "In" a thick iron plate.

Some guys make very shallow pockets to aid in placement.

G-

[Jeff]

Sorry about the typo on the # of mags/coils. I ended up with 15 hard drive neos & typed this up without checking my HUGE Word document I have stored about this. The correct # of mags will be 12, with 9 coils.

However, it seems to me potted mags could only help the flux path. Using the FEMM software, it came out great! Even many people use a 1/32" - 1/16" recess for locating the mags, or add some alloy (I forget without checking again!) in the epoxy/fiberglass to "pot" the mags along with holding them in place.

Anyway, with being able to get 48 1/2" dia. mags, if I don't get enough amps at 1/8" thick mags, I can always add the second set to bring them up to 1/4" thick. Either that, or go with the more difficult 3-rotor, 2-stator setup.

Remember, I'm only going for a couple amps at least, but 5 or more at higher wind speeds would be great! Of course, this would have to include a Ghurd dump load controller! (Finally!)

[ghurd]

Something is not right with the FEMM or interpretation of the data.

Potting magnets in iron will ruin the output.

They use 1/32" to place the magnets.

If $10 worth of steel improved $400 worth of magnets in a $5,000 wind system, and saved $50 in resin, don't you think people would be doing it?

Double the 1/8" magnets to 1/4" now.  Without 1/4", or at least 3/16", of magnet on both rotors, there is not enough space for wiggles and coils.

Small is hard.  What looks fine on paper does not have enough space during the build.  Coils get bigger, bearings have more slop, screw heads get fat, etc.

" or go with the more difficult 3-rotor, 2-stator setup."

Do not go that route on a budget.

The same materials in a larger diameter will get a lot more power.  And more efficient.

I recently asked the smartest I never met about a single rotor design.

N45 7/8" dia x 1" long cylinders.  That is some big magnets for a small windmill, and I thought it would allow some serious breaking of the rules.

The stator should be 3/8" thick, and it would not properly load a 3' diameter windmill.

POP!  That is the sound of my bubble bursting.

Might have a deep look at CmeBrew's mini-me-mill.

Maybe it ain't great, but it sure ain't bad for a first try at a mini-mill!

The good and the bad are well documented.  A lot can be learned from it.

I hear it is up to 30W, and I expect it will get better with different blades.

It would be even better if it had a couple minor improvements, before it was too late to make the changes.

http://www.fieldlines.com/story/2009/2/7/194335/8871

[Jeff]

First Savonious and "potted magnets"

I've tried to post 3 times now, and it never showed up! First, it WAS a typo (sort of) on the 15 mag-9coil. I have an 18-page WORD document I've been building from posts not just from this site, but others as well. Due to limited internet time, I didn't go back to check it while I was typing a post. It WILL be a 12 mag - 9 coil 3-phase setup. The main point was to build my first Savonious, and run a small air compressor directly from it. I'll be using the "cheapie" model air compressors until my Dad gets back to his machine shop in NY around April. Then he can build a much more efficient and more permanent air compressor made to run from the Savonious.

Also, like I said, I'm not looking for a huge output either from the air compressor, or the genny. I know I've said dozens of times, 5 amps into my battery bank would be enough to eliminate the grid entirely. Optionally, using the air already compressed into the tank, I could run it only when a large load comes on (like the fridge). Since it would be only for 10-20 minutes, I felt this was a good option.

Using the FEMM software mentioned in other places & posts, either the "potted" magnets" or a 3 rotor - 2 stator setup show a really nice mag flux field. I have already ordered 48 N52's, ½" dia. by 1/8" thick. If testing various coils doesn't produce enough, I can always double-up the mags. BUT, like I said, I'm only looking for 5 amps under normal conditions/winds for this area. Higher winds will just be extra gravy for the biscuits. Also like I said, there's still plenty of options as far as stacking the mags 2-thick, messing with the "potting" aspect, adding a 3rd rotor and 2nd stator, and I'm sure there's still many more options I haven't mentioned or had time to look into yet.

The main idea is to GET STARTED! The only thing I may not have is enough of the right size wire for the coils. Of course, once things get actually going and putting out power, hopefully I'll have saved enough & have all the current & working specs for Ghurd to come up with a dump load controller (probably a 3-way due to diverting to a heater for a 55 gal. drum of water, and possibly a 24v output for my wheelchair & a spare set of 24v battery array).

I may stick with a 24v dump load setup even though my main array is 12v. I'll have to make "sets" easier to disconnect, charge as 24v, & replace into the main array & as 12v again. But I think the 24v sets will work better with an old clothes dryer-heating element used to heat the 55 gal. drums of water. This won't be the main heating system of the water tanks, which will be solar. It'll just be a good use of any extra power & a good 3rd stage dump for the controller.

I know, sounds like a lot of trouble, but when you have the time, and the need to get off-grid is so important, it'll just be something I'll have to put up with until I can make it easier.

The mags should be here in about a week, and I know I won't have the Savonious up & running by then. Especially since I just found out I broke my coccyx (tailbone) a couple weeks ago. As if I wasn't getting things done slow enough already! LOL.

Well, I hope this post comes through. If not, at least this time I typed it up in WORD first & saved it. LOL. I might even upload it to my files in case the post doesn't work again.

Cheers all, and again, all comments good or bad are welcome!

jp

[Jeff]

Gotcha Ghurd! Thanks for the simple & direct explanation!

As I will be using old 10 1/4" dia. saw blades for the rotors, and the mags (already ordered 48 - N52's, 1/2" dia. by 1/8" thick, they may need some extra backing on the front (or back) of the saw blade. I have some 7/8" and 1 -1/8" dia. stock to make these with. Any suggestions on these?

ps.: You may want to read the last post I just made 2-26-09 2:30am EST, as this may change things. I will drop the outside pots idea now though. Thanks! And hopefully in a few months, a somewhatb custom dump load controller from you!

jp

[Jeff]

Thanks once again Ghurd! My Dad & I (well, he's the one with the maching shop), have no problems whatsoever keeping run-out, concentricity, square-ness, etc. to tolerances of .0002". Even on a 16 or 18" dia., a .0005" tolerance on all aspects mentioned is no problem. We're sticking with the 10 - 1/4" saw blades for now though. This is just due to availability ($0 cost), and the lack of need and even direct limiting RPM's to 150-200 whatever is needed. No need to worry about furling, wind speed, and all that good stuff. A simple pressure relief valve to keep the storage tanks from going above 150 PSI, and adding extra tanks for extended/longer run time.

Thanks again, and I apologize for what looks like a double post. Oh, by the way, I AM removing those darn teeth on the saw blades!

My Dad even has balance capability up to 12,000 RPM as he made racing engines that frequently ran in that range. Could you imagine a genny running that fast?!?!?!

[Jeff]

The new mags have been shipped & should be here any day now.

First question: Any suggestions on wire gage and thickness of coils? Remember, 12 1/2" dia. by 1/8" thick (stacked to 1/4" thick) N52 mags per rotor, 9 coils on the stator, wired for 3-phase.

I'm thinking of using a 10mm drill bit (this is the largest my 3/8" rechargeable screwdriver/drill will go), and winding until approx. 3/4" dia.. The thickness though will have to be somewhat thinner than the stator plate to allow for epoxy'ing in the coils on both sides.

The mags are currently marked out to be placed on the center of a 7" diameter circle, every 30 degrees.

Any statements or suggestions always welcome.

OH, ps.: I'm doubling up the saw blades to add thickness for the magnetic flux, since each are only about 1/8" thick. Since It looks like I'll be doubling the mags also, to make a 1/2" dia. by 1/4" thick mag. I looked up the pricing, and came out cheaper with the 1/8" mags, but I'm also probably loosing a little on strength going this way rather than one 1/4" thick mag.

[Jeff]

I got the mags tonight! Remember, these ARE N52's!!! Should have gotten 4-5 extra, these things are HELL getting apart! Already broke 3 and only have 32 apart so far. I could order extras, or go with 18 per rotor.

[Jeff]

I'm in the process of cutting the teeth off the saw blades. BE VERY CAREFUL doing this! Definitely safety glesses if not a full face shield. A leather apron wouldn't be a bad idea either! I'm laying it out for an 18 mag - 12 coil setup. Single thickness on the mags though like I said I broke 3 trying to get these suckers apart! Being the prototype if it works out well things will only grow bigger from there!

Still haven't heard any suggestion on wire gage or # of turns. I'm pretty limited to a 3/8" inner diameter at the smallest, 3/8" thickness also. Since my CAD computer is down I'll have to finish laying it out on the blades to get a max dia.

[Jeff]

Well, things are still slowly going along on my small test VAWT.

My CAD computer broke down, so I'm using my Mom's laptop, which is "CAD-less". On top of that, the keyboard doesn't work very well on it, so I have to use the one from my CAD computer.

My tailbone (coccyx) fell apart on me a month ago, and it's still as sore as ever.

Anyway, I have 3 - 10 ¼" saw blades done (de-fanged) and made sure they fit together nicely with no gaps. With just one blade, and one of the N52 ½" dia. by 1/8" thick, it failed the paperclip test miserably. So, I'm still going to have to use 2 saw blades together so you don't feel any "tug" on the side opposite the magnet. The fourth & final blade has been de-fanged, but still needs a good smoothing out just so it lays flat on its mating half of the rotor.

Without my CAD computer, and the 18-page WORD document I made for reference/instructions, I've had to do it all over again "manually".

I came up with a 20 magnet - 15 coil setup. 20 magnets put them 1.095" apart center-to-center. I have a small piece of ¼" hardwood flooring board I've started laying out a template on for placing the magnets. I'm making 3 holes for the magnets even though I could get away with two. I figured this way I could always flip the template over to double-check the magnet placement. I'm laying it out with digital vernier calipers, center punching the intersection of lines that need it, and using a precision "V-Block" for both the center punching & drilling. I've also made a test fixture I can put 1 coil into & spin it up with my cordless screwdriver. It claims 320 RPM, so I'll have to "guesstimate" the output at 200 RPM.

Since this will be set up for 3-phase, and I can go as small as 0.04" air gap on 1 side (it'll actually be 0.05", but I'm allowing a little fiberglass covering on the stator), any suggestions on coils like wire size, I.D. and O.D.? There will also be a "brake" 0.01" less than the air gap that will give some notice if things get close to rubbing. Again, the center-to-center distance on the mags is 1.095" (there's 20 of them on a 7" diameter circle. I had to allow not only some room for the flux path, but also what's left of some slits built into the blades.

I'm working on a drawing, but WORD is about the best thing I have on this computer. You can set grid size to as small as 0.01", and snap (move) objects to the grid, so there you have it.

I have barely started on the VAWT. Have the boards cut to size, barrels cut in half, and the mounting hardware for those. I'm having my Cabinet-maker friend use a router on a fixture I'll make, so the barrels will have a small recess to fit into (and make location a LOT easier!). He even has a sanding "planer" to make the mounting boards nice & flat and parallel. Not to mention he's got a spray painting room so he`ll water seal the boards & add a second coat of some nice white paint that has some kind of vinyl in it!