New Idea Makes Box Fan Conversion Very Easy

[ghurd]

Looks good!

Hand held is frightening when they get going. With a load they should slow down some, but those are big blades for that conversion so maybe not much.

And they go a lot, LOT faster when the tail is aiming them and you aren't in the way!

Yes. 3 or 4 blades start easier. I think I would go with 4 blades but not that long. A steeper angle starts easier too. More blades or a steeper angle will reduce the RPM or TSR.

I don't know much about blades :/

I wouldn't trust 1" thin wall very long or very high for something that big around.

Don't forget to put 3 or 4 drops of light oil in the bushing pads.

What angle are the blades mounted?

G-

[ZooT]

Angle of the blades?

I used an extremely scientific method to design the angle.....using two one by twos for a hub, I cut an angle on each that was just less than a quarter inch deep on both two create an angled slot just less than a quarter inch deep when sandwiched together.....whatever that angle is....it's one quarter inch of drop over a two inch span.

With the "hub" the rotor measures about 4 feet 6 inches, and once started the thing will continue to spin with just a breathe of breeze, and so far off my multimeter I've gotten readings of 15.6 volts on the DC side of my bridge rectifier.

And if thing'll go a "lot, LOT" faster I'm thinking I better use more than thin wire nails to hold it all together.....oh well....I bought a bandful of 10-24 bolts and nuts for the rotor anyways...and I better put in a setscrew or two rather than just a "poosh" fit to hold the rotor on the shaft.....

[ghurd]

Sounds just like how I make my blades!

There are plenty here now, so if one set doesn't work out, I just put on another set.  I'm getting better at knowing what is wrong, like too steep/shallow long/short fast/slow...

I am just no good at figuring out what it should start with.

G-

[ZooT]

I've come to the conclusion that this thing is not my friend when a sudden gust of wind tried to knock me off my feet with the blade spinning about a zillion RPM's*LMAO*

[ZooT]

And how do you determine if the blades are too long?

Please.....I'm not very knowledgable in this field,.....don't tell me it'll stall or some other technical term that I don't know about yet.

Tell me what the physical manifestation will be and what sort behaviour it'll display, so that I can "see" it going on if the blade isn't very well behaved....

[ghurd]

LOL !

They have to be just long enogh, but not too long!

Seriously, you are surely asking the wrong guy.

I think I can tell you some physical manifestations,

but I have very little understanding of how some guys can say

"Use a 4.3' dia with a TSR of 6.2" and be right on. It just never works out for me.

OK. The blind leading the blind. Here goes.

With the same TSR (Tip Speed Ratio) A long blade will start easier than a short blade.  The trade off is the long blade turns at a slower RPM than the short blade.

Real example...

I have a stepper motor I had high hopes for.  Put on a longer set of Zub-Woofer PVC blades, because they happened to be on the hub that fit the shaft.

Startup was no problem, but even in a good wind the RPMs were not fast enough to get up to charging voltage.

So I put on a shorter set and they worked great.

So I put on an even shorter set, but they were to short to get really started, because of the cogging.

And when they did get started, the RPMs were high enough to reach cut-in BEFORE there was enough power in the wind to make what the generator wanted to make.

So they wanted to turn faster, but the power to the battery was more than the power in the wind, so it almost acts like electric brakes.

That is my understanding of one kind of stalling.

The other kind of stalling is when the first blade to pass a spot leaves a large wake of turblence behind it, and it interferes with the next blade. At a certain RPM, the thing just can't go any faster because the air is swirling every which way, one blade to the next, keeping the blades from working like they were designed.

High TSR and lots of blades do this kind.

The standard 6 magnet 6 coil box fan conversion's BIG problem is the cogging is huge. To overcome the cogging, it takes a big slow blade, but then the big blade has a low RPM, so it takes a LOT of wind to reach RPMs for charging voltage.

So it ends up being a blade that should make 1000 watts (and tower and related strong enough to handle 1000W of wind) all for a generator that only can make 50 watts.  Jerry's garbo-gen with 4'dia "Jerry Blades" makes what, like 1000 or 2000 watts?

I'm sure most people feel, by the time you have the big blades, strong tower, etc, needed to overcome the cogging, you may as well have something that makes some 'real' power.

That's why I thought I'd try it this way. Keeps everything small, cheap or even free, and easy.

It just worked much better than I expected !

(I have 20 failures for every success.  No kidding.  But I always do stuff that is kind of strange, and always small.  Bigger is easier.  Proven designs are easier. I wonder if this is a proven design? But I find this strange stuff much more gooder funnlier, and fun is the only reason I do it anyway.  Hardly a place for a 20" windmill where I live anyway.)

I'll post a bad news (rust) here too.

G-

[ghurd]

Well, bad news that is mostly my fault.

I figured on a rewind later to get all 3 phases working and see how it went.  The magnet rotor was handled a lot, it has been very humid, and time has past.  Got some wind yesterday, so I took a 20" fan blade from our working fan for this alternator.

The shaft had some surface rust and the genny hardly turns now.

In front of a 9MPH fan, it only turns about 60RPMs because of the rust.

Maybe it will clean up.

And the newer donor fan's lams are about 4mm thinner than the old fan I converted.  4mm will add up with that many turns. I think.

Keep them oiled!

G-

[ZooT]

Built a four blade rotor today using the same blade size and shape as the two blade above, and while it did start by itself, as you suggested, the blades are too long and it doesn't spin fast enough to produce anything significant.

I'll trim some off the blades tomorrow and try again.......

Once I can get it working right I'm going to laser cut a hub out of either steel or aluminum and build a more than junker rotor....

[ghurd]

Do NOT take off too much at once!

A little diameter counts for a lot of power.

If I recall corectly, the center 1/3 is only 10% of the power.

Laser Cut?  I have a hacksaw.  And it is not even a good one!

The factory put the teeth on the blade facing the wrong way.

G-

[ZooT]

Made up a pair of swastika hubs today configured so the leading edge of the blades will be 1/2" past dead center.

Tomorrow I'll drill the holes and bend the hubs to generate the blade angles and maybe I'll get a picture or two.

Oh and by the way.....did you notice how nicely these motors fit inside a 3 pound coffee can?........you know.....the kind with the resealable plastic lid*grin*

[ZooT]

Got those swastika hubs bent and everything done as far as the prop goes, and welded together the rest of the genny today.

I cut the blades down just past the "trailing angle?" so the blades themselves are about two inches shorter than they were

Rather than what I expected, when I stood my ten foot thinwall conduit tower/pole up with the genny on it, the thing turned into the wind and the rotor started turning.

All I could do was grin like an idiot*L*

Probably had 15 mile an hour gusts today and I was getting readings 15.4-15.6 volts DC.

After that I tore it apart and painted everything, tomorrow, if it's windy enough I'll put it back together and see if I can get "she who thinks I'm crazy for building a windmill" to snap a pic or two....

Yup....today was a VERY good day grin

[ghurd]

Great!  Congrats!

How easy did it start?

If it started very or quite easy, you may want to take off a couple more inches to get some more RPMs. (its not like me to tell someone to cut up something that all ready works)  Maybe 2" at a time if there is no apparent difference in the diffuculty in start-up, then stop at the first sign it starts harder.

But the low voltage reading could say it needs more RPMs.  You were getting 32VAC spinning the 20" fan blade by hand, so it should be getting 40 or 50VDC open circuit without much trouble in the wind.  It sounds like the blade is too slow.

(I'll point out again that I'm not the guy to ask about blades)

My belief, which may not be based on fact. On a day with some wind power, a gust should get it started turning, then it will keep turning a lot easier. And the faster blades will get more power at a lower wind speed after the gust gets it turning past the cogging of course.  I never flew anything that cogs magneticly like I'm sure that does.

""the thing turned into the wind"".  Did you get a tail on it?

With single phase, does it vibrate like a cat with its tounge in a 220 socket?

It might when a battery is connected.

The bridges are high voltage I hope.  Like 100 or 200V.

If the thing gets turning fast, without a charging battery to take the power, the volts can rise very fast and maybe pop the bridges.  I mean, when the blades are right and it really gets spinning, it can just take off spinning much faster than you imagined, the volts can go up a lot faster than many people expect.  And it can shock the s*^t out of you too, which only seems to happen when my neighbors are watching. ("Hey everybody! Come watch! That goofy guy with the fan shocked himself again!")

How much pressure did it put on the mast?  However you can explain it.

G-

[ZooT]

I've never gotten anything over 24.6 volts on the DC side of my bridge but in all reality 13.6 or however many volts it's takes to charge a battery with low wind is more than enough for now.

And yes I did put a tail on it....I C-clamped a 2x2 foot piece of 1/4 birch plywood to the angle iron that I'm using for a "body".

Tomorrow the new "tail" cut from the old one(just trimmed some off to give it a better shape) gets bolted on....But it gets bolted on about 8 inches further back to give a tail a bit more leverage for steering

As of right now the alternator is offset 4 inches from the center of the tail so I can add a side furling tail later.

And yes it did push against my "tower/pole" but it wasn't hard to hold or anything.

Needless to say I duct taped my multimeter to my pole so I could use two hands to hold the pole

And after building my new swastika hub, I think I might have done something good rather than bad as the something seems to have either added a flywheel effect of sorts or lowered wind drag caused by the old 2 inch thick wooden hub (X shaped) and it seemed to start easilly, and it keeps spinning at a lower windspeed than before.

Whatever I did it starts a lot easier....it still cogs though

The one thing I did do wrong was I gave no thought to the balance of the entire unit and it's tail heavy. Maybe phase two, the furling mechanism will use a piece of square aluminum tubing to lower the weight on the tail

The bridge is rated at 200 volts......I used heat sink paste and drilled and tapped a CPU heat sink and mounted it to that...

And I've never seen a cat with it's tongue in a 220 socket*L*

[ZooT]

Here's a pic of the latest incarnation of my box fan*L*

[ghurd]

I'm "gone" for about 2 weeks. I won't be ignoring anyone.

No phone, no grid, no road, no internet, no radio station...

http://www.caesarslodge.com/trophyfishing/littlebenny.html

Taking a break from packing now. Gave up on finishing any work left to do.

G-

[nothing to lose]

"Laser Cut?  I have a hacksaw.  And it is not even a good one!

The factory put the teeth on the blade facing the wrong way."

Ya they sell anything these days. I was putting in a new floor and the store sold me ceiling nails instead of flooring nails. Both boxes had the points on top and heads down

Have fun on the trip if you read this before you go, OR, I hope you had fun on the trip if you read this after you get back

[nothing to lose]

"Sure wins the ugly contest!"

No, I think mine still wins, and though moved several times after the trees bloomed it was still flying untill I went to Canada to visit Picmillian. I took everything down before leaving though so no problems while I was gone for the wife in case of storms and such. Time to fly again

[OlBuzzard]

Hey team!

I just finished a conversion of my own last week.

I used the original windings and 2 hard drive mags snapped in half.

So I started messing around with one coil pair and Here's the tale...

I threw in a diode in series with a small capactor to sustain charge and a 1kilohm resostor for a small load, nearly open ciruit. Now with this half-wave rectifier I hooked up a cheapie cordless drill and read 2VDC, 10 milliamps short-circuited. I figured that this baby needs more power, so I brung out the ol' electric AC drill spun it up and read 4VDC open, 30 milliamps shorted.

Now I would bet this drill would likely spin the motor faster than the wind will, so this would be a disappointing project.

I am thinking of rewinding the coils, but will it really generate more power?

Where the power? I WANT POWER!!!

[ghurd]

"I threw in a diode in series with a small capactor"

That could be a problem. Once the capacator is charged no current will flow.

Rewinding with more turns will make more volts.

Rewinding with heavier wire (lower resistance) makes more amps.

The 'power' comes from the magnets. And those hard drive magnets are very tiny.

I am quite surprised it made 4V!

The magnets I used are 30 times bigger than half a hard drive magnet.

A good set of blades in this size range will turn faster than the drill.

There are plenty of turns.  It takes more magnet than you have.

G-

[OlBuzzard]

Thanks, man.

I knew it. But don't be scared of the cap. when you short it out to measure short circuit current, it doesn't matter. Plus it was wired in parallel to act as a filter to improve the DC characteristics of the half-wave. THe reason I used the diode is because those hefty bridges will eat a volt of sweet energy, while the diode I used was a shottky, which drops only one-fourth that.

[ghurd]

Try 4 scottky's for a bridge.

Or a 25~35A bridge, at low amps the Vf will be much lower than at Irated, maybe less than 0.4Vf per diode.  Even 6A diodes will have a low Vf at such small amps.

These fans have a LOT of turns (voltage).

With more magnet, the Vf of the diodes is fairly insugnificant compared to the losses in the high coil resistance.

If the thing is complete, try it wired 3 phase star.

I am quite curious about the Vopen.