Mini 73

[dave ames]

Hello fellow tinkers,

This stuff is a ton of fun!
 
Thought others might get a charge out of a little wind project (a micro/toy class turbine) that we have been goofing around with. The main goals here, besides good clean fun is a small air core machine (38"-42" diameter prop) with a 12 volt cut-in at 7-8 mph wind, with a target of 73 watts at around 20 mph. Looking to build something not much over 10 pounds that will fit in a small suitcase. Although a pmdc motor might get us there much easier and be done with it, I really want try our hand at arranging some magnets and wire and see if we can hit the target with an 8/6 aircore machine worked up on the coffee table with common tools. <- to see if any of this stuff I've been reading here has sunk in... and if what i think will happen/want to happen comes close to what actually happens..........

Afraid there is no project funding, so most everything is scrounged from the curb or stuff i have hanging around..I did manage to scrape up $12 (June 1 2011 price) for 16 N35 neo magnets 1" diameter round disc X 0.125" thick/long. (a cubic volume of only 1.57 inches..just 7 ounces)

Looking at some of the blade calculators it seems that an RPM of about 400 will be a good speed to shoot for with 7-8mph wind ... our blade speed (RPM) wants to climb much faster than with a larger machine, reaching 1000 RPM at around 20 MPH wind speed. so our volts per turn should reflect this working range and the available power in the wind.

My apologies in advance if I tend to bounce around a bit with the building..I have been taking a bunch of pictures of the progress to date, so that may help to bring things together where my 'splanin' skills fall short?

You won't find much new or original here, mostly stuff others have fooled around with... maybe with a few twists here and there.

A look at the magnetic circuit: -> with the available materials of two 5" diameter x  0.187" thick steel disks and 16 pieces of 1"x 0.125" thick N35 round Neo disc magnets.

......A page from our project notes speaks volumes about getting the most from our meager bits of magnet. Note that we manage a full 60% increase (in voltage) with the dual rotor setup..interesting also that we do over 20% better still by stacking these thin magnets on one disk and running a spinning blank return disk.









stay tuned..next post we will try to use this information to fabricate our stator from stuff collected on the side of the road on trash pickup day.

All good fun!
dave

73 KB1MZF

[GoVertical]

Hi, why did you choose to make the coil ID smaller than the magnet OD?

http://www.6pie.com/coilsandmagneticflux.php


I look forward to your test results. Nice project.

[jlt]

     Looks like a fun project.  I would try using larger  rotor discs,and winding thinner coils.7inch saw blades are pretty easy to find. and will give more winding room.

[dave ames]

.... .. Talking Trash .... .. A trash stator that is!

Here is a very common sight these days in our throw away society:


Just a few screws and some cutters yields some very nice magnet wire:


sometimes several hundred feet in a TV or CRT computer monitor:





In our first post we found that we can obtain an AC voltage in our test coil of 3.51VAC with 135 turns at a speed of 500 RPM.

Lets see what a star connected stator might do at that speed: ?
3.51VAC X 2(coils in series)= 7.02VAC
7.02 X 1.73(star connected)=12.14VAC
12.14 X 1.4(AC RMS to rectified DC)= 17.0VDC
17 VDC - 1.4VDC (rectifier voltage drop)=15.6VDC @500RPM
How about 400RPM?
500RPM X 0.8=400RPM
15.6VDC X 0.8=12.48VDC not too bad!
I feel that might still be a tad high for a lowish battery at 400RPM and decided to back it down another 10%
135 turns - 10%=121 turns per coil. (went with 120 turns  ) for what it's worth I would guess that our flux density is just under 400mT..compared to the big machines running about 700mT.

We collected a good supply of AWG#22 wire..#21 might have worked out a little better if i had it.

GoVertical has some eagle eyes and asked this:

Hi, why did you choose to make the coil ID smaller than the magnet OD?

The short answer is->because we found that we could. with some testing we found that we can squeeze the ID down a few percent (12.5% in this case) and still get the same induced voltage. We went this route for several reasons.

1) we are able to get a bit more wiggle room for possible errors (sloppy windings etc) and still fit the coils in the allotted space.

2) 1/8" smaller diameter coils gives us a bit more room (about 1/4") in the center of the stator.

3) allows us to use less wire for the same number of turns and voltage (a total of 252 feet as opposed to 312 feet)

4) a stator with 20% less wire has 20% less resistance.

5) the little plastic spacers that came with the magnets are 7/8" diameter and made for a nice center for the coil winder we worked up for the task 

For the stator we went with a non casting method..just glued the coils down with a total of 3 ounces (6 tablespoons) of resin.

our stator mount to be:



we cleared a salvaged 0.060" PCB board with a dremel and attacked it with a belt sander..ended up
0.050" thick with lots of thru hole traces still on it some small bits of copper plating as well..I do not believe these small traces of conductor will be an issue, Anyone think otherwise?

we notched out some grooves for the coil starts 0.030" deep.


a little loose with the spacing..#21 or a half size between 21 and AWG 22 would have been better.
these coils are 42 feet each of #22..120 turns about 0.7 ohms.

     Looks like a fun project.  I would try using larger  rotor discs,and winding thinner coils.7inch saw blades are pretty easy to find. and will give more winding room.

agree with you 100% jlt. maybe next time around with different disk mounting techniques and adjustable airgap..this fixed airgap spacer is a keystone to this build<- more happening with the spacer than it might first appear.

thanks for having a look, to be continued..out of room in this post for now.

It's all good fun!
dave

[oztules]

Dang thats a good post.

It is so nice to see someone trying different stuff.
I agree with the smaller hole, (I found 80% was good for mine).
I like the ditches you notched out for the lead ins.... good idea.

It is fascinating just how magnetic theory does not always come out in practice as you would expect..... who would have thought that stacked magnets in this case and a bare disk would trump two magnet disks......... never ceases to amaze me how variable this stuff is.... change one thing and something else changes. Well done.

I was never game to stack 50mmx 15mm n50's to test your magnet setup. Firstly I would not have thought to try....I'm just.not that smart..... . and secondly I would hate to try to get them apart if I had have tried.... which would have been another reason to ignore the possibility of  trying it.


Looking forward to part two.



............oztules

[dave ames]

...Some more shots of the stator progress. a visual tour can say it better than I can, hope that the sizing is friendly enough for the folks like me using wet string for their web connection

our series connections and output leads..we brought all six out.


another layer of the salvaged PCB cut up and glued down:










close to getting into real time with the project progress..coming up next is some bench tests done today..

I agree with the smaller hole, (I found 80% was good for mine).

It is fascinating just how magnetic theory does not always come out in practice as you would expect..... who would have thought that stacked magnets in this case and a bare disk would trump two magnet disks......... never ceases to amaze me how variable this stuff is.... change one thing and something else changes.

Thanks for your observations oztules..you always seem to find some encouraging words even in times that you may not agree.

these topics have been brought up by some of the gurus here (squeezing the I.D and the stacking of very thin magnets) seems the consensus was the stacking helps with the "foldback" leakage. so nothing new from me..had everything setup to run with a test..and at least in this case we came out ahead not so bad playing with these tiny bits of magnet. a few little "love" pinches when you let your guard down for a split second.

I've got a few big scary ones here that I hope to never loose my fear of the less handling the better!

cheers, dave

[artv]

Hi Dave,...Excellent thread .....I understand that reducing the # of turns in the coil , lowers the resistance....by winding at 120 turns you lose some of the voltage out,...so does that mean your cut-in speed (rpm) will be higher??......At 400 rpm you have  12.48VDC, isn't that just below cut-in??..........how is that a tad too high??......Also whats the reason for using a pcb??.....just for thickness allowing the magnets to be closer to the metal blank, creating stronger flux??....looking forward to more test results.....
Thanks for putting this out there.........artv
 

[dave ames]

Hey artv,

thanks for having a look and taking time to comment. Tell ya, I waffled quite a bit with the final turn count determination and made the call to go with the lower turn count..we shaved a few fractions more off the resistance and felt better about avoiding a too early cut-in. Glad we did now that it's together and we have some solid numbers. -> ends up that we could have dropped another 10% of our turns per coil and still be ok.

"Also whats the reason for using a pcb??....." after working a bit with this scrap PCB material I can highly recommend this method as a starting point for an easy glue up stator fabrication method..just like the model ships and planes we used to build as kids! we lay in one piece at a time at our own pace  ...while on that subject, I wanted to add a note before the thought passes.

I did most of the building here in my small apartment (380 square foot studio flat) and when we combine my long hair with my hippie tie-dye shirts, the last thing I wanted was strong chemical smells coming from the apartment at 3:00AM (I'm a night owl). this fiberglass resin has a distinct foreign odor to it that could be mistaken for other nefarious activities..we found that adding a few drops of floral scented acetone based nail polish remover to our resin masks the weird odor and helps thin out the glue. <- with a very nice penetration for soaking the coils into a solid mass.

OK so we had a chance to do a run up with my 3/8" black and decker variable speed drill. using cheap meters and a photo tach.


unloaded, unfiltered DC voltage is totally linear at 0.032 volts per RPM after rectification this is connected star..unloaded VOC @ 400 RPM right at 13 VDC

Into a 12 volt battery: (found it a little more of a challenge to hold a constant RPM while loaded)

410 rpm 250mA 12.5VDC    3 Watts
570 rpm 1.42A  13.35VDC  19 Watts
680 rpm 2.67A  13.45VDC  36 Watts
990 rpm 5.00A  14.20VDC  70 Watts  
1200rpm 7.19A 14.6VDC   105 watts

some other measurements of less importance but interesting to see:
Voltage into a 3 Ohm power resistor after rectifiers.
310   rpm  4VDC
400   rpm 5.7VDC
600   rpm 8.8VDC
690   rpm 10VDC
1200 rpm 18VDC

And shorted current into the meter:
240  rpm 2.4A
450  rpm 4.5A
960  rpm 9.2A

we ran it for an extended period of time between 5 and 7 amps into the battery (about 15 minutes looking for heat and it (the stator) did get good and warm, not what i would call hot.
the drill was the hottest followed by the rectifier block (in free air)with two phase legs then the stator then the rectifier with one phase leg.

time for some blades!

it's all good fun!
dave

edit: weird spellin'

[jlt]

I was looking in Altons blade calculator. and it showed a 3.5 ft 3 blade with a tsr of 7 to be about the right size.

[SparWeb]

...when we combine my long hair with my hippie tie-dye shirts, the last thing I wanted was strong chemical smells coming from the apartment at 3:00AM (I'm a night owl). this fiberglass resin has a distinct foreign odor to it that could be mistaken for other nefarious activities...

Very wise!

I once made the mistake of curing an epoxy stator in the kitchen oven.  When my wife found out...!!!

[ghurd]

Nice!  I love little stuff, especially when it uses junk.

Softening CDs in the oven to make Christmas decorations is also not wife-friendly.
The only thing that saved me was the fact it was a Girl Scout project.
G-

[Tritium]

Nice!  I love little stuff, especially when it uses junk.

Softening CDs in the oven to make Christmas decorations is also not wife-friendly.
The only thing that saved me was the fact it was a Girl Scout project.
G-

Heat lamp and cast iron skillet next time G. 

Thurmond

[bj]

   Been following this Dave, fun stuff.  Of interest because I have a grandaughter that is getting interested.  I also have lots of
spare stuff that can be used.
   Thanks for the share.
   P.S. for wife unfriendly, try washing small engine parts in the dishwasher. 

[dave ames]

Hey G- and spar,
Some good chuckles here

I like the idea of blaming the nearest kid when we get caught doing something we happen to think is a GREAT solution to a task, but the better half thinks it's idiotic 

We have to be sure to make a big production anytime we are able to use something from the junk treasure pile...and best to use something from the trash stash when working on some job that she gives you..look honey this is that "thing a ma bob" you said to throw away..it's just what we needed here..and so on, to justify all our "stuff".

Hey bj,
Nice to hear your grandkid is infected with the curiosity gene! could be because they grew up with Grandpa poking around with this stuff? The sidewalk pedal generator comes to mind
 
This little turbine is definitely a kid friendly project. can't get hurt much with the small magnets used here individually-> but still some care needed when we have them in a working magnetic circuit.

OK so a little progress on some kind of blades..
WARNING: I hit my head pretty hard the other day so all this may be nonsense, ...buuut we want to try something that can only be described as goofy for our first set of blades for this project.

we want to do away with the root portion of the blade and start the blade at an outer station and try tuning them in via adjustable mounting stalks then lock them in place with a thru bolt? what   ........sort of like the extruded blade system seen at the backshed forum.

some pics of the progress.....

Bashing some EMT conduit:



some 4" pvc:


adjustable mounting saddle:





we are starting at 44" and will take them down from the hub end stub and adjust the relative angle of attack till we are happy..then drill thru the locking bolt hole.

yep, goofy..if this seems to work out we may go with a set of carved timber using the same method

This is a ton of fun!
cheers, dave

P.S. I want to put in a very short rant here...With all the free information right here I still can not believe that some folks are still just gluing down magnets and winding wire willy nilly when we have a fairly good targeting scope (the forum).

[klsmurf]

Very cool Dave! I see a variable pitch rotor in the making.

[dave ames]

Oops almost forgot..

I was looking in Altons blade calculator. and it showed a 3.5 ft 3 blade with a tsr of 7 to be about the right size.

Right on jlt. wish Mr. Moore had a hit counter on his site. Bet I must have run his program 100 times in the past 60 days. Add that to everybody else screwing with wind and he must be up in the brazillions with his site visits.

We grabbed his data for a 42" blade chord width and made ours from the 6th station out.

Very cool Dave! I see a variable pitch rotor in the making.

hehe..only variable for the tuning. It's neat to poke around with this stuff...maybe an advantage of a toy size machine?  easy to try out wacky ideas...and cheap too!

cheers, dave

[jlt]

pretty neat idea  for building blades.  It would be easy to carve a 2 blade prop out of a 1x4. and see how they compare. I can carve one in about an hour using a 9" disc sander. not much start up torque, but once going spin really fast 

[ruddycrazy]

G'day Dave,
                 Great little project and it does look the goods mate. I do have a heap of those 16x13mm round N50 neo's left after putting a heap on my 4kw motor conversion and now I got the bug for finally building an axial flux genny albeit a small one. I reckon I'll go with 2 mags for each pole and put em longways then wind oval coils. Anyway once I get going I'll make my own diary thread on it.

                Once again great work buddy.

Cheers Bryan