SMALL 2 FOOT MILL

[richhagen]

A while back I posted about the blades.  I put one set together about a month ago and connected it to a NEMA 17 stepper motor.  The stepper motor contains a magnet rotor and it is two phase.  This configuration does not require brushes.  I do not know the operating voltage of the motor but I would venture that it is not too high based upon the results.  

Below is a picture of the hub components I put together.  






I coated the blades liberally with linseed oil, soaking them through for the most part.  I decided on using a 4 blader because I was concerned that there would not be enough start up torque from these as a 3 blader.  I made the blades from 1 by 2 inch stock, and that is thinner that what the blade designers call for in a 3 blade set with a reasonable tip speed ratio.  The shaft adapter that attaches to the motor was made out of 1/2 inch round stock aluminum.  the generator end was bored out to .2 inches.  That was a mistake on my part for the stepper has a .185 inch shaft.  I added more set screws which worked for this one, and that problem will be corrected on the next batch of these.  The set screw hole was bored with a #21 bit and threaded to accept a 10-32 thread.  The blade end of the shaft adaptor is milled to a .34 inch square on the outer 1 inch to hold the rotor disks (squares in this case) and the blades.  The end is drilled with a #7 bit and tapped 1/4 inch 20 threads per inch.  The Rotor Disks are actually squares which I milled from 2 inch by 1/8 inch stock on my mini-mill.  I made two holes per blade to bolt the blades through and a square .34 inch hole in the middle to fit the shaft adaptor.  I hit that lightly with a file to square the corners and make it fit as it was usually a tad small and the corners were rounded right off of the machine.  The assembly was put together and the blades lined up, I snugged up the bolt in the end enough to hold the blades and lined them up as best I could.  I then tightend the end bolt a little and drilled the blades on my drill press with a 9/64ths bit through the existing holes in the rotor disks (squares).  I then bolted each blade on with two 1/8 inch screws 1 and 1/2 inch in length, held with a washer and nut. I later added additional washers in an attempt to balance it.  I never did get it perfect.  It has a slight vibration at higher speeds.

Below is a picture of the mill on my roof on the test stand that has been its home for a month or so now.  

The stand was made using a couple of ten pound weights that came free in the basement of a building I purchased.  The pole is a 3/4 inch schedule 40 pipe and is about 4 feet in length.  The pipe is welded to the weights at the bottom.  The pipe is topped with a piece of 1/2 inch EMT welded into the pipe sticking out another couple of inches.  The Mill is mounted on a piece of 3/4 inch EMT which has been smashed in a vise at both ends and a little in the middle and attached to the top of a piece of 3/4" galvanized pipe with a washer welded to the top of it.  The pipe over pipe bearing is well greased with axle grease.  The tail is made from a piece of scrap acrylic, and the stepper motor is clamped to the EMT with hose clamps.  I made two bridge rectifiers out of scrap 4007 diodes and soldered them together.  I simply taped this assembly to the 3/4 inch EMT for the testing and soldered the leads to the motor and to the wire carrying down the DC.  The lead wire is allowed to rap around the tower.  

I had tested the assembly before I put it up and found that at approximately 60 rpm it only puts out just under 3 volts or so.  The test turbine was ineffective for charging 12 volt banks because the required rpm was just too high.  But I figured it might be useful to light some LEDS, or for an ornamental type wind turbine, or even a remote out house light.  

I had a pre-existing wire from the roof to my laundry room which was about an 18 or 20 guage two conductor wire.  I connected that to the mill on the roof and to a test rig in the laundry room consisting of a volt meter, a 15 farad 15.3V capacitor bank, and about 10 LEDS connected in parallel.  I added a bunch of 3.9V zeners to limit the voltage to 3.9 volts later after I cooked a couple of LED's.

At approximately 60 rpm it only puts out just under 3 volts or so.  The test turbine was ineffective for charging 12 volt banks because the required rpm was just too high.  

One day, shortly after I put it up, I noticed there was no output and the capacitor bank had gone down to about 2.5 volts.  I walked out and away from my building so that I could see the turbine on the roof.  It wan't there!  I climbed up and found that the wind had apparently blown hard enough to knock the mill over.  To my amazement, the blades were not broken.  I figure they had to be going at a pretty good clip!  The blades were however bent.  It appears that the Linseed oil made the blades resilient enough to not break, and maybe it fell in such a way that the skimmed the surface of the roof.  They were marked in black where they had apparently rubbed the roof.  I set it back up and kind of bent the two bent blades kind of back to straight and it started up.  I moved a large planter and weighted it on the edge of the iron weights that form the base of the mill, and since then no problems with that.  

Another day, I noticed no power, and climbed up on the roof.  The blades had become disattached from the hub.  I guess the set screw had not been tight enough, or the vibration of the machine was enough for them to work loose.  I found the blades on the roof, again not broken and re-attached them.  The tips are a little scuffed up and one of the blades is still a little bent from the first mishap, but other than that the are fine.  This blade set has nine lives, or maybe thats just three so far.  I am amazed the blades didn't break, and really have to attribute that to luck---and linseed oil (Thanks DanB)  

They spin well most days, and provide a little more light in my laundry room, but it is really only practical as a toy, or an intermittent utility light or something.  I like to keep the little mill busy so I've made a few blade sets over the past few weeks when I didn't have something else to make.  

Ghurd, the assembled set in the photo is yours.

Anyway, it was a fun little project, hope you enjoyed the post.  Rich Hagen

[richhagen]

Oh yeah, I forgot to put any output numbers.  The power is really tiny.  It only makes about 3 watts or so in 10 Mph and maybe 15 watts max in a 30Mph gust.  I've never been around when it's been windier.  So far it hasn't exploded, as it doesn't have any furling on the test rig.  Rich

[nothing to lose]

Wow, good job on the blades and an excellent post.

So do you think those blades would have enough power for a little larger mill with higher output. Maybe charge a small 12V or 6V deepcycle battery and run a CFL lamp with Light sensor for a yard light. Charge with small mill and only run the CFL in the dark?

If so, you might have a product there, replacement tops for all those junk rattle traps Wal-mart and places sell for yard ornaments. People who buy those things already have a  6-8' tower when those whirly heads come apart. They just need to replace the top and drive a couple stakes to ancore the bottom better maybe.

Very interesting post!

[97fishmt]

Hi Rich, I too have been going to a four prop arrangement for smaller machines.

It is a trade off but, for the output and the material of the blades, I think its a winner. I've come up with a nice system of carving blades out of warehouse stores lumber lately, and will try to get some pictures together.  I'm going with 2' of 1"x8" and 3' of 1"x6" and 4' of 1"x4". All laminated together and then tapered. The end result is an 8' prop that has a width of 7 1/4" to 3 1/2" with a twist from 20 degrees to 2 degrees. One I am working on for more torque. Your blades look great keep it up!

[commanda]

Led's are current operated devices. They need a series resistor to limit the current.

If your stepper is what I'm thinking it is, it has 4 wires coming out. Each pair of wires is a coil, with no electrical connection between each pair. If this is the case, build 2 bridge rectifiers, and connect the rectified dc in series. This should give you 6 volts, where you only had 3 before.

There is also a rectifier configuration called a "voltage doubler". Uses 2 diodes & 2 capacitors. Basically, the positive going half cycle charges one capacitor, and the negative going half cycle charges the other capacitor. The 2 capacitors are in series are far as the dc is concerned, thereby adding voltages. With one of these off each coil, and then connected in series, you could make 12 volts. But nothing for nothing. The output power will be the same, or slightly less. So the available current will decrease proportionally with the increasing voltage.

Amanda

[richhagen]

I had thought about a remote lighting use, but it is far from polished.  As it is it won't put out 12 volts until extremely high rotor speeds, but for say 3 nicads in series at 3.6 volts it would probably work fine.  Rich

[richhagen]

I'm working on bigger blades right now, but I havn't graduated to laminated boards yet.  Rich Hagen

[richhagen]

Ideally yes for the LED's.  Its such a low voltage that I didn't even bother.  Since LED's often fail to short, this is not a preferable arrangement.  Your right I should add some resistance there, thats why I fried the first diodes.

As for the motor it is a 6 wire stepper motor.  Basically, there are two wires center tapped.  I pulled out the 4 end wires from the coils and ignored the center taps.  I did put two bridge rectifiers together out of 4007 diodes, one for each coil. This would be the same arrangement as for a four wire bipolar stepper motor.  These motors come in a large variety of voltage configurations.  The one I used isn't that high of a voltage.  I think I'm stuck with what it is unless I want to rewire it or change it out.  Rich

[richhagen]

I am familiar with voltage doubler circuits and cascade multipliers, but I hadn't thought of that here.  I would need one for each phase, and I'm not sure how much it would hurt efficiency.  Currently I'm thinking it would be better to find a higher voltage stepper if I want a higher output.  But if I used it to charge a 3.6volt nicad pack it wouldn't be necessary.  Integrating this to a larger 12 volt solar or wind system wouldn't add much power generation to it anyway.  Rich

[nothing to lose]

So would a little bigger mill and these 2 foot blades be able to make low amp 12V at all? Or is the blade size too small an area to do that at reasonable average winds.

[ghurd]

Hey Rich,

They look great!

Have you tried that 'bio-electrifier' circuit?

I think these will work great on my little conversions if they don't stall. But they will get 12 volts for sure.

G-

[RobD]

Cute project Rich, where did you get the caps?

I built a similar size mill with my own alternator. It did about 50 to 75 watts but was hard starting because of cogging. (single phase) I might go with heavier blades. Also I'm starting to think about mills with cogged belt gearing and multiple blades like used for water pumping or using the slow speed Sandia design Savonius cogged up.

[johnlm]

If you want 12 V with small props at low wind speeds and dont mind not all that great of performance at higher wind speeds then small fan motor conversions with anything from the original fan blades to 2 ft to 4 ft diam 3 blade carved sets seem to do ok for me.  Ive been experimenting on these for awhile with the desire to have a small (and cheap) but reliable charger to keep my camp trailer (12V) battery charged up.  I dont use the camper 24/7 and suspect that when I do use it on weekends I likely use about 30 or 40 AH out of the battery, so it has several days to recharge and get this back.  Right now I have a fan motor conversion running with a carved 3 blade set that is about 2.5 ft dia. The prop is not the best Ive built as it stated as experimental blades with no twist and no taper, just slope, which I didnt feel worked very well so I glued back on some wood and recut them with taper and twist.  The fan motor uses the stock 26 awg windings modified slightly to lower the output impedance and the armature has been rebuilt using ceramic mags.  This unit will get to 12 V output in a 5 to 6 mph wind but due to high output impedance will only put out about .75A into a battery at 15 mph, and probably only .9A at 25 mph.  The inductance, which limits the output current of these little motors, is a bummer, but they at least easily get enough voltage charge 12 V batteries.  Without the winding modifications these units will hit 12V DC at around 200 to 250 rpm which is easily achieved by 2 to 3 ft props at 5 to 6 mph winds.  Even the stock (metal or plastic) blades that are on these fans work pretty well as the prop, so one need not even mess with building props.

On another box fan motor, once again using ceramics, I tore out the stock windings and rewound with awg 18 wire.  It uses a 3.2 ft  3 blade  carved prop and will hit 12 V at about 6 mph but will put out about 1.75 A into a 12V battery at 15 mph, and tops out around 2 Amps.  But charging the camper battery during the time Im not around at an amp or so in a 10 mph breeze will likely be enough to have the battery fully charged when I return a week later.  They are small enough that Im not too worried about a severe wind storm; but I did build a furled tail set up for this 3.2 ft unit.  its not all that pretty, but it is functional.

Ive found that I have to be pretty creative about getting the cogging down if I use (small) NEOS on these units, but the ceramics havent been much of a problem.

If anyone is interested, I can put together some pics of the units.

Johnlm

[johnlm]

Actually I think the 2.5 ft unit above may do better than I stated.  I had only put that (pretty fast with tsr of around 8 to 9) 2.5 ft prop on it a week or so ago and had not had this fast of prop on the motor conversion before.  Well there is a storm blowing in today and I was out in the shop where this unit is up on a 25 ft TV mast tower and was watching the meters while the ac output was connected to a 15 Ohm power resistor.  During one gust, I think was around 25 mph +/- , I saw it putting 30Vac into the 15 Ohm resistor , thats about 60 Watts with the stock 26 awg windings.  Open ckt the ac output would have been about 60 Vac.  I did not have my frequency meter connected at the time but hooked it up and later saw 20 VAC at 1500 RPM with about a 15-20 mph gust.  Ive just not had alot of opportunity to check these units out at higher wind speeds.  I realize the rectified current into a battery will not be the same here but 60 W in a 25 mph wind and a 2.5 ft prop with about 2 hrs of blade making time and $3 worth of magnets and a few more dollars for misc on a scrap motor is not bad.  I just bought 2 more of these 20 inch box fans to play with the other day (in real nice shape- hardly used?) for $2 each at a thrift store.

John

[Trivo]

Rich

Just a thought.If you take off two of the blades you may get a large increse in speed,. Worth a try

Trivo

[richhagen]

I believe that the amount of power in watts is equal to the voltage multiplied by the amps.  The amount of power in the cross sectional area is limited.  You could get 12 volts with a properly configured alternator, however your amps would be low and the overall power in watts about the same.  Rich

[richhagen]

There was a surplus auction for 95 or so on E-bay about a year ago.  They are the 1F 5.5 volt variety.  I had collected a few others previously from other sources.  Rich

[ghurd]

That makes me feel pretty good about the little conversion I'm playing with now.

With stock 20" plastic blade and not much wind (10? 12?) I get about 250ma.

With a 20" steel 3 blade (central air?) and better wind it got over 500ma.

Stock starts and runs, parelleled outputs, neos, 50 and 100 ohm coils!

Horid efficiency.

I may have to take one to the motor shop for a rewind.

G-

[ghurd]

Rich,

Did you think about using 2 motors?

Looks like it should not be hard to get them rear shaft to front shaft.

Then feed 4 caps in series. 4 X 3 = 12

Or maybe even 3 motors for 18v.

G-

[richhagen]

At first, I wasn't sure how much power the motors would use, or how much of a drag on the turbine.  I did consider that as an option, but it wouldn't work in this case I don't think because the startup torque is not that great and coupling a second motor would cause it to start up even more poorly.  As it is it does OK, but it takes a good breeze or a small gust to start it up.  Once it's going though it seems to be OK.  Rich

[nothing to lose]

Low watts around 15 or so at 12V in average winds might work ok?

What do you think? 12Vdc 15watt CFL or less, 7-20 amphr SLA battery like UPS or rechargable aircompressors, Circuit to charge 24HR but only light after dark.

You got 24hrs to produce 6-10 hours of 15watts useage plus losses?

For extra options include a motion sensor also, only light at night when detecting movement, turns off in 5 minutes of no movements.

20amphr battery good for 240watts at 12V provides 24hrs backup power at 15watts, used 10hrs a night that's 2.5 days of night time only back up if no wind at all.

Much better than those dim little solar yard lights right? How often no wind at all for 2-3 days in a row?

[richhagen]

You could probably do this with a 7 Amp Hour battery or so just fine.  I had thought of doing something similar in the current setup, only using leds for the lighting, and a lower voltage battery because of the current alternator.  Then build a circuit, probably a couple of comparators with low voltage op amps capable of operating in the voltage range of the battery.  One to go high when the voltage is over a certain amount, one to go high when the light through a cds cell was too low, indicating that it was dark out.  Run those outputs to a cmos and gate or something and use that out put to turn on a FET or two to activate the lights.  that way the lights would only be on if it was dark and the battery voltage was high enough.  You could do the same thing just replace the leds with a circuit to power a flourescent tube, similar to the wonderful circuits posted on here recently.  Rich

[richhagen]

As it is with two 4 amp hour 6 volt batteries wired in parallel, if you only discharged them to 80% state of charge that would give you about 9.6 watt hours of usable energy.  You could build a simple shunt regulator by running enough 7.5 volt zeners in parallel with the battery to eat up the maximum current produced in a gail.  If you had the Leds wired in parallel with resistors, for the light, say 150 ohm to limit them to about 25 milliamps at 7.5 volts, then at 6 volts or so they would consume in the neighborhood of 20 milliamps, if you had a light made from 12  or so white leds, it would consume about a watt and a half on average plus a few milliamps to the control circuitry, and you would end up with about 6 and a half hours of light from it if the batteries were fully charged and there was no more generation.  On a breezie or better night, it would of course stay on all night.  You could probably stretch this further with a larger battery bank and more leds, but the above should be doable.  I may just have to build a model of it.  Rich Hagen

[nothing to lose]

Yep, you probably should if you have the time

 Look at all the power wasted nightly running yard lights for no reason! Many of those homes even have the rattle trap windill decorations I speak of and hate so much.

People have been brainwashed into thinking lighting up a yard runs away thiefs far to much. Maybe in a big city, but not in rural areas so much.

Think of this, People that had the land and new trailer house next to me in the middle of nothing had a yard light installed from the power company. WHY??

They came here for 2 weeks twice a year at most, the rest of the time no-one was ever there. No-one can see the property basically because no-one lives within view. Woods between me and thier place too. But they paid for a security light and wasted all that power all year long!

 Now on the other hand, if it were dark, a thief would need light, a flashlight glowing and flashing around I might see through the trees/woods if I am outside. Put up the security light the thief does not need the light and I'll never know they are there even if total dark night and I am looking straight at the property.

People are brainwashed into thoughs things, makes no sence to have one out here when your not gonna be there! But they were from more of a city area and put one up to chase away burglars???

You could sell a yard light kit!!

[ghurd]

A rich "city guy" bought 50 acres next to some woods my family owned.

Half of his was beaver swamp.

Nothing there but trees and beavers.

I mean nothing.

Nothing for a long ways.

He posted it. (not common in that area- just irratated quite a few folks)

Put up a big fancy expensive gate.

Somebody stoled the gate!

[richhagen]

I put just the rotor for now up on E-Bay, we'll see if anyones interested in using one to build something with, so far no bids.  NTL, don't bid on it, if you want one to play with, just E-mail me.  Rich

[ghurd]

Got some real wind.

Never ready when it is here.

The things go so fast it is scary.

Holding the stepper motor with both hands.

That explains some of the fear.

Also, never finished balancing the assembly.

Obviously no load.

Maybe 15 or 20mph wind. Maybe 1000 rpm.

Hard to count mis-balance pulses at the RPM it was going, But fast.

I was afraid to even turn it out of the wind.

Kept my head down waiting for the wind to subside, slowly furling it.

Sounded like a bunch of mad bees.

Thrust was much more than expected.

The balance and tracking are off, but that is my fault. Never ready.

[richhagen]

At high speed it gets about like holding a sheet of plywood.  I knocked one test setup over because I underestimated that.  For balancing, I just added washers to the light side on the bolts that hold the blades together.  With a load it will hold the rpms down somewhat.  The little things are fun to play with though.  I just sent a set out to a guy in New York state.  It looks like he might be also building a dual axle, I added info about the site here, so hopefully he'll join and post if he isn't already one of us.  Rich