Generator Problem: Too many coils?

[Savonius Man]

Hi Everyone,

This is my first post on the forum.  I have been building savonius turbines and fiberglass generators for the past 4 years.  I'm a mechanical engineer, and I have been trying to develop a fast, inexpensive, and easy way to make complete wind energy systems.  

My recent generator design involved a single rotor with 12 n45 magnets, and two stators on either side of the rotor. Each stator has 12 coils so there were 24 coils total. In test trials I found the device to produce about 10 amps and 70 volts with the stators in series, but this was only possible at 10 revolutions per second, which would require pretty aggressive gearing because my VAWTs typically rotate at 1 rps. I cant seem to find any cheep 10:1 chain drives without resorting to bicycle parts which really can't handle the torque given by 1kW.

I decided to remove the 12 magnet rotor, and make two new 6 magnet rotors to rotate on the outsides of one stator.  This is a technique I have used in the past and found to create a lot of power due to the two rotors concentrating each others fields through the single stator.  So rather than having a 12 coil stator, 12 magnet rotor, and 12 coil stator sandwich,  I now have a 6 magnet rotor, 12 coil stator, and another 6 magnet rotor sandwich.  

Unfortunately, this design seems to create No power.  I tested the stator, and found that it completes a circuit well, so its not burned out.

All I can think of is that a 6 magnet rotor will not work with a 12 coil stator because the fields are passing into the inactive coils and inducing a current that opposes generation in the coils that have magnets passing over them at any given moment.  

Have any of you encountered this before?  am I going to have to pour another stator that has only 6 fat coils to get this thing to work?

Thanks in advance,

--- Ryan ---

[jimjjnn]

If you use the Google search feature on this site, you will find the answers to your dilemma and more than you can believe.

It looks like your design is faulty because oof the ratio of coils to magnets.

[Savonius Man]

I took your advice and tried searching the forums, but like you said there is a lot of info to sift through, and there isn't an obvious set of key words to search with for this specific problem.  I did however find this page where a newbie was going to make a 5 mag rotor with a 10 coil stator.  The replies weren't very helpful.

http://www.fieldlines.com/story/2007/9/20/22058/0188

also on otherpower.com projects page there was a hamster wheel design that used many magnets and only one or two coils.  

It just doesn't make sense to me.  Why would removing 6 of the 12 magnets cause the whole thing to stop producing power?  

Each counter clockwise coil (ccw) still sees an increasing North pole field as each cw coil sees a decreasing North pole field.

Do I need to make a 6 coil stator???

[vawtman]

 More info on size of all the gizmos and pics would be a plus.You seem to be goin about this backwards.

 Thanks

[Savonius Man]

I'm sorry, I thought I gave enough info.  I don't have any pictures at the moment, and my camera is at the office.  

I can tell you that the rotors are 14" diameter, they have 6 magnets each.  The stator is 14x14 and has 12 coils made from about 3 lb of 18 AWG wire.  each coil is wound in an opposite direction as the previous. here is a crude diagram of the sandwich, the O's represent the common axle c=coil n=north pole of magnet s=south pole:

       N                        C                     S

                           C         C

S             S          C             C       N             N

       O               C        O        C            O

N             N         C              C       S             S

                           C         C

       S                        C                     N

My question is simple:

will a 6 magnet rotor work with a 12 coil stator???

[richhagen]

I can't quite make it out from your drawing, but if originally you wired up your magnets and coils for 12 magnets, and reversed the magnetic field at each pole to maximize the change in the fields as it would spin, and wire up your coils so that these induced voltages add, then by removing every other magnet, and fliping the fields on every other of the remaining magnets, aren't you in fact causing the currents induced by the changes in the magnetic fields from each pair of magnets as they pass over every other coil to exactly cancel each other out?  If it is as I suspect you will need to flip the magnets so that each magnet has the same pole facing out, which is less than ideal, or change the wiring orientation of the coils in the stator so that the voltages will add instead of cancel to correct this.  If you can access the leads from each coil, the latter is the better patch.  Rich

P.S. I see that you had wired this in single phase, I would recommend that you review the stator, wiring, and three phase setups from the Wind link on the bottom of the Otherpower front page, or get the Dan's and/or Hugh's books on the subject.  

[Savonius Man]

Hahaha, Thanks Rich.

You are absolutely right.  By removing 6 of the 12 magnets from the design, I inadvertently flipped the poles on some of them. I feel kind of stupid now for not figuring this out.  I will pour a new stator and save this one for a 12 magnet rotor in the future.  

I have read up on 3 phase wiring, but wouldn't that reduce my output voltage?

I only work with savonius VAWTs so its hard to get a good charging voltage at the lower revolution/wind speeds. Also, I thought wiring multiple stators in parallel or using 3 phases is a good way to drive more current through the same device, but none of my generators have ever produced more than 15 amps on a VAWT so I didn't think I needed to try 3 phase wiring yet.  

When you think about it, power is the product of current AND voltage, and voltage doesn't cause your coils to melt, so logically the best power to cost ratio would come from a high voltage and low current (20Amp) device.  As stated above, this generator was capable of 70 volts at 10 amps and 600 rpm. obviously  you would need 6 batteries to utilize this charging voltage, which isn't cost effective for only 700 watts, but in the big picture, I will have 12 of these generators all charging the same bank, or more.

If I could push this thing to 1200 rpm, then it may produce 140 volts at 20 amps before burning out. thats almost 3kW.  Not bad for the $150 investment and 3 hours of labor.  

The real problem I'm facing is how to get a chain drive that can handle that power without spending over 50$ on all of the components.  I use no.41 chains. the generator sprocket is a 12 tooth, so to get a max 1rps turbine to turn a 1200 rpm generator requires a 20:1 ratio and a 240 tooth drive sprocket (which doesn't exist).  I don't want to use a jack shaft either to reduce losses. Any ideas?

[boB]

Up until just a month ago, I would have said that it wasn't putting out any power

because it was a VAWT.  But, now after seeing a Mariah Windspire actually charge at

just under a thousand Watts, I have definitely changed my mind and have renewed

hope for VAWTs.  Savonius or otherwise.

Good luck !

boB

K7IQ

[ghurd]

Until you understand why a 5 magnet rotor is not a good idea, you will not have much luck.

"If I could push this thing to 1200 rpm, then it may produce 140 volts at 20 amps before burning out. thats almost 3kW."

Wrong.

http://www.fieldlines.com/story/2009/3/12/195239/297

Mechanical engineer translation:

A toothpick is enough with a 1 trillion to one gear ratio,

so a toothpick is enough with one to 1 trillion ratio?

G-

[commanda]

I've got a small vawt on the backburner.

http://www.fieldlines.com/story/2008/4/30/3552/30035

6 magnets 5 coils. Each coil individually rectified and then the dc outputs wired in series.

Amanda

[electrondady1]

savoniusman

 you have come to the right place to learn about wind driven alternators.

an unusual animal to be sure.

 an alternator designed for a vertical machine is a different creature again.

 you need to increase the pole count (for frequency ) to make up for the comparatively low rpm.

 

[commanda]

Amanda,

That's a good idea to individually rectify the coils.  Do you alternate the poles of your magnets too?  What kind of voltage does this produce compared to a normal alternating coil direction design?

Yes, the magnet poles alternate. Having a problem imagining how any coil could produce any emf if the magnet poles don't alternate.

Amanda

[electrondady1]

i like your windmill

most of my alternators experiments are single phase .

i like to use lots of mags and coils  so i can get a charging voltage

at a relatively low rpm using cheesy magnets from hard drives

(three pole)

if you mean 3 phase .

i have only built one so far.

it's a bit of a luxury to only need 1/3rd of your coils.

you would need some very hefty mags or be prepared to live with finer wire more heat less amps less amps etc.

i haven't run across the infamous single phase shudder yet.

good luck with every thing

http://www.vawts.net/index.spark

[wooferhound]

Man that is a huge picture, 15 percent of our users are using Dial Up internet connections or slower in remote locations. Our picture posting guidelines state that pictures should be less than 640x480 and less than 150k bytes in file size. A pictute that big won't fit on a computer monitor anyway.

[hvirtane]

i haven't run across the infamous single phase shudder yet.

You are using many small magnet poles and coils?

What about iron in your stator? Do you use iron or are your generators air core?

It would be interesting to get more knowledge about your savonius turbines. Have you published somewhere more about them?

- hv

[Norm]

picture properties:

1638 x1229

goofs up the text width too as a result

you could have cropped the picture and

made it only as third as wide....who

needs a picture of all that dirt on both

sides of the savonius?

[TomW]

Norm;

I fixed [removed] it.

I guess some folks just don't care about the image posting guidelines. They are there for very good reasons..

Tom

[MarkYarbro]

Hey Savonius, here's some excellent newbie info that I found enlightening:

http://rapidshare.com/files/210370740/AXIAL_FLUX_HowItWorks.pdf.html

http://rapidshare.com/files/210371381/AXIAL_FLUX_Testing_V1.pdf.html

It's geared toward windmills but the lessons are widely applicable.

Enjoy,

Mark

[ghurd]

OR...

Instead of being subjected to the advertising and 30 second waits, we could find it somewhere else.

I wonder if SparWeb bothered to wait 30 seconds to view his own files?

Steven, Curious if you did?

G-

[TomW]

G;

I never clicked thru cuz I knew what happens on rapidshare but recognized the filenames as  being from "here" couldn't recall who, tho.

At least they weren't offered "for sale" ;=>

Tom

[SparWeb]

HI

My eyes are still blinking away the glitz.

Try this instead:

http://www.sparweb.ca/Forum/AXIAL_FLUX_HowItWorks.pdf

And

http://www.sparweb.ca/Forum/AXIAL_FLUX_Testing_V2.pdf

Good luck

To all Mechanical Engineers out there: read the instructions carefully.

To all the other forum members out there: please forgive us ME's the only thing we learned in university was how smart we are and even that information is becoming obsolete...

To anyone else who doesn't know: I'm also a ME and I've asked plenty of newbie questions myself!

[ghurd]

I never had the pleasure of the 30 second wait to get a better link.

Or I just closed it 29 seconds too soon.

G-

[ghurd]

My eyes have not been right since Dec 26 07.

Often it takes an ME to translate EE.

Thank you for the translation,

G-

[Ungrounded Lightning Rod]

Geez.  What are the bearings/supports on that puppy like?

[Savonius Man]

Please read my comments more carefully.  I do understand why odd numbered magnet configurations are counterproductive.  I was merely referencing someone else's thread.  

Also simply quoting me and stating "wrong" then referencing a link isn't helpful.  I read through the entire thread you were referencing, and I don't understand the correlation you were trying to make.

I have built more generators than I can count over the past 4 years, and I think you all need to consider higher voltage devices in your designs.  If there is one thing I learned from all of the electrical engineer courses I have take it is:    Power = Voltage * Current

Considering that statement, Current is the limiting factor because as you increase amps, you take the risk of burning out your generator.  Voltage on the other hand does not destroy coils.  

I used to work for the Ames power plant.  Why do you think utilities use high voltage transformers to step up to 161,000 Volts, then they step down once the power gets to a switch yard?  Its to save on cabling costs because a small diameter cable can carry 200 MW of power if the voltage is kept high and the current is low.

[Savonius Man]

I used 5/8" diameter threaded rods which pass through sealed plate bearings on the top and bottom.  I experimented with industrial caster wheels because I had a few laying around, but they got chewed up after only 2 months.  The new sealed bearings have been turning with this guy just fine for the past 8 months.

[Savonius Man]

All it takes to induce a current in a wire is a changing magnetic field.  if the coils were far enough apart, you could have all of the magnets facing the same way, assuming you use individual rectification.

[Savonius Man]

Im really sorry,

This is my first time posting a picture to the site.  I didn't realize some of you guys are using dial up.  I will repost the picture at the reduced size you indicated.

[TomW]

OK, I will bite, mister Savonius Man;

You say:



I have built more generators than I can count over the past 4 years,

First, I am fairly sure you can count into the thousands?

I see one file in your uploads:

http://www.otherpower.com/images/scimages/12656/T3_Right_Isometric.JPG

If you have built so many generators, where is the electrical generation happening in this picture? I see no "head" or wires. So what gives there? Seems a guy with countless generators could have easily jury rigged one up for the photo?

Looks to simply be the "usual" pic of a vertical from folks pimping them [no alternator].

I think you are so far off on the facts of generation that it is not much value in us trying to explain to you.

The "reasons" the grid is done the way it is Do Not Apply to DIY alternators charging batteries, which is what we do here. Unless and until you understand that you are in the wrong place for "advice", either giving or getting.

BTW, the voltage we are forced to use is the battery voltage so the statements about current being the limiting factor in this application completely apply. Think about it. Obviously you haven't or you wouldn't be so confused.

Just my opinion.

Tom

[wooferhound]

No Problem

 We really like pictures

   Just not big ones . . .

[Madscientist267]

This seems to be the thread to sink teeth into, so following in with my typical two cents - here goes...

Why would you keep the poles facing the same way, only exploiting a present vs not present magnetic field?

That's like taking half of the batteries out of your flashlight and then wondering why you can't see anything with it. Alternating poles cause flux reversal, a key concept in real world alternator design.

Hang around a bit longer and read... building things blindly is more or less reinventing the wheel. Why put yourself through all that when the information is all around you, much of the pain of doing the inventing already done for you? It just needs to be absorbed and understood properly to be of use.

While you seem to understand the basic concepts, it appears that it is more in a 'pass the magnet near the wire and watch the microammeter' kind of way. Great for theory, but almost meaningless if not taken only for what it is, a concept. Real world uses for things go way beyond what made us all "ooh and ahh" as kids.

Grab a chair, monitor, keyboard and mouse and hang out for a while and let these people teach you the ways. Coming off as a know-it-all and then unwittingly revealing to us that it's actually just a front will only irritate the people you are asking for help. I can say this... did it early on and got put in my place... Right Ghurd? LOL

Steve

[Savonius Man]

Tom,

Its really unfortunate that after starting my first thread, there are so many negative comments.  This whole experience has left me with a bad taste in my mouth. You should really try to be nicer to people.

The reason why you only see one picture in my file is because I have only uploaded one so far. The reason why I can't count all of my generators is that they each have evolved so many times, it's difficult to say how many designs I have experimented with. The reason why you don't see a generator mounted to my 15' savonius is that I came out on a later day to mount the generator when I didn't have my camera.  I didn't think it was necessary to prove myself.  Also it isn't easy to get to all of my client's locations as they live all over Iowa.  That 15' turbine is in Kelly Iowa and takes me over an hour to drive to.

Here is a smaller turbine I built in Nevada Iowa.  It only peaked 600 watts at 25 mph winds.  I have included a shot of the generator mounted at the base, which didn't get done until after dark.

Please don't be a nay sayer for savonius designs unless you have actually built one.  And try not to use phrases like: "until you understand".  That just boils my blood.

And final, Yes the principals utilized by a utility are the same electrical principals that apply on a small scale.  Power = Volts * amps in both cases, and current IS the limiting factor.  This guy in Nevada Iowa had 3 deep cycle batteries on hand, so I designed the turbine to push 40 volts and 10 amps in 15 mph winds.  He has a switch to alter the wiring of the stators to be in parallel when the wind is blowing harder (soon to be automatic).  

It seems like the only way I can convince you HAWT guys that VAWTs are feasible is to post a video where I show my turbine turning, anemometer readings, current measurements, and battery bank all in one continuous shot.  Would that make you happy?  Let me ask you this: Can you build a 1kw HAWT without a welder? in 3 hours? for under 150$?  Be nice to me, I can help you.

[Savonius Man]

Like I said, I'm sorry, I'm new to this site.  Here is a cropped version.  This rotor was built with 4 scoops.