Generator with ferrite magnets

[scoraigwind]

Just for comparison sake I quickly designed a direct drive ferrite magnet generator for a 3.8 meter turbine with the following specs:
..... the big three phase would be able to produce about 47 amps before it maxed out the windings - I am delivering power on four wires, the three phase only uses three....
Chris

I have tried to reproduce this design and I find that I can use much thicker wire and also the flux/voltage is somewhat stronger due to the larger holes inside the coils, but I am not about to build one and prove it.

There is a flaw in the logic of this comparison because the current in the two single phase stators is working in pulses - one at a time effectively - which means that the resistance and the losses of this winding are effectively much higher, relative to the 3-phase example given.  I think that the relatively high losses in the 2 single phase units are helping to produce a the optimum loading on the blades and make this machine very successful, but you could also build a 3-phase, direct drive one with the same losses.  

The obvious virtue of direct drive is that we don't all have a machine shop to build a chain drive.  So far as I understand it, bearing life is measured in revolutions, so a lower rpm helps with that and so does the ability to mount the rotors directly on the bearings rather than cantilevered out on the side of a gear case.  

So much for theory.  I gave up building ferrite machines in practice ten years ago, but I have noticed that they seem to last longer than neo ones.  The biggest axial flux one we built was a ten footer with 12 2x2 magnets on 16 inch rotors.  

That is still going strong on its original bearings about 12 years down the line.  The stator has never burned out from overload yet.  That one has a very long wire run that helps to push the blade speed up and keep them from stalling.  It's horribly inefficient in strong winds, but the long wires take it up to a very windy spot, and wind energy is free!

Hugh

[ChrisOlson]

The biggest axial flux one we built was a ten footer with 12 2x2 magnets on 16 inch rotors.

I happen to have one of those turbines hanging on my wall in the shop by a piece of chain (it was a neo though).  The blades are in a box for it but the stator burned out a long time ago and destroyed several magnets when it locked up and I never fixed it.  It think that is my next project - get it flying again but this time with a ferrite 12 pole three phase.

The place where I got these magnets sells them cheaper in a box of 60 so I bought another box just so I won't run out for awhile.  All 60 magnets cost less than six 2 x 1 x 1/2 neos   
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Chris

[ChrisOlson]

I have tried to reproduce this design and I find that I can use much thicker wire and also the flux/voltage is somewhat stronger due to the larger holes inside the coils, but I am not about to build one and prove it.

I think this is probably correct.  I left plenty of room in there for more wire, but I know dual 15 gauge will fit in it.  Perhaps dual 14 would fit too.  But I would caution against making the internal resistance too low or you will be back to the neo problem of stalling blades.  I have found these ferrite generators really let the turbine run as it should, but you can get carried away and make it too efficient and "stiff" with ferrite magnets too.  And that will actually hurt overall performance.  I suspect it is harder to burn out a winding with ferrite magnets than with neos so it might take some experimentation to find the right "match".  With your experience, Hugh, I think you could probably get it right the first time, so I think you should build one    

There is a flaw in the logic of this comparison because the current in the two single phase stators is working in pulses - one at a time effectively - which means that the resistance and the losses of this winding are effectively much higher, relative to the 3-phase example given.  I think that the relatively high losses in the 2 single phase units are helping to produce a the optimum loading on the blades and make this machine very successful, but you could also build a 3-phase, direct drive one with the same losses.

This is all very true, probably.  I have the loading characteristics of a polyphase due to the whole outfit being paralled'd at the DC side of the rectifier.  But I think the built-in "inefficiency" of the dual single phase windings is working good because it lets the turbine run instead of stalling it.  On the bench it seemed very "stiff".  But on the turbine it runs.

So far as I understand it, bearing life is measured in revolutions

Bearing life is measured in revolutions x loading.  A lightly loaded bearing at very high revolutions per minute will last a long time (example: the little 6203 bearings in automotive style alternators).  You take that same bearing and try to use it for an axle bearing on a lawn tractor turning at very slow speed but heavily loaded, and it won't last 15 laps around the lawn.
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Chris

[scoraigwind]

I have tried to reproduce this design and I find that I can use much thicker wire and also the flux/voltage is somewhat stronger due to the larger holes inside the coils, but I am not about to build one and prove it.

I think this is probably correct.  I left plenty of room in there for more wire, but I know dual 15 gauge will fit in it.  Perhaps dual 14 would fit too.  But I would caution against making the internal resistance too low or you will be back to the neo problem of stalling blades.  

The goal posts seem to be moving around a bit here.  If you want to make it less efficient then maybe make it smaller?  Or put some resistance in the line where the heat will not burn the stator?  I have lost track of what you are trying to achieve here.

There will always be the enigma that a more efficient alternator will make the blades less efficient.  Using a chain drive makes the alternator faster and hence more efficient, to compensate for the lower flux in the ferrite magnets.   But using a dual stator loses out on some of that efficiency.  I reckon it's simpler to use a single stator and direct drive and arrive at the same sort of performance.  I guess that's too simple?

[Menelaos]

I am watching this topic for quite a wile now and we have the same problems im Germany... Magnet prices over here are even worse than in the states which made me thinking about redesigning our turbine kits as well. I have ordered some F30 ferrit magnets and will join in with results as soon as I have made up something that is worth talking about. I also feel that the dual stator design is not the best way to compensate for the lower flux. I feel that it is quite a lot more work to do. I agree with Hugh that making the alternator a little bigger in diameter would solve the problem with more ease and efficiency....
I would rather tink about changing the coil geometry to fit moe copper into the stator. Having made some experiments, I conclude that the size of the whole inside the coil is not as important as one would think it is. I have made tests with coils that have no enterspace at all. Of course, the voltage was lower than on coils with holes but as much as I assumed it to be. So on the bottom side of the coil, I make the center space close to zero, on the top as wide as possible to still get the coils attaching each other on the bottom side. The hight will be about 2/3 of the magnet length and the coil legs are approx 2/3 of magnet width. With this combination, I have less coil resistance since I have less unused Material on the top and bottom side of the coil. I therefore can use slightly thinner wire with a few more turns which is already enough to compensate for the lower voltage due to the changed geometry of that center hole.

In the end I end up with basically same or only slightly higher resistance and same or only slightly lower voltage but I can massively save space and easily fit 12 coils in the space that was needes for 9 coils before....

Has anybody else made experieces in that section?

Max

[ChrisOlson]

The goal posts seem to be moving around a bit here.  If you want to make it less efficient then maybe make it smaller?  Or put some resistance in the line where the heat will not burn the stator?  I have lost track of what you are trying to achieve here.

I would like to come up with something that is useful and that other folks can build.  Few folks are going to build a geared 3.8m dual stator ferrite axial turbine because the thing is incredibly complicated to get it to work.  And it works good and will outperform a direct drive of the same size.  But it's more of an exercise in engineering than being a practical design for folks to build.

As I indicated to you in an email, Hugh, trying to reverse engineer it into a direct drive design with ferrites that that the average homebuilder can tackle, is not going to be easy either.  Even you have have never built a ferrite axial turbine this size.  So that is what I would like to come up with - a 3.8m design that other folks can build using ferrite magnets, but it doesn't require two men and a small boy to lift it on to the tower stub.

I suspect many folks are just going to gulp and spend $500 on magnets (assuming you build a 16 pole 3.8m neo with 2 x 1 bars).  But I bought 60 of these 2 x 2 ferrites for only $110, and for some folks the cost is a consideration too.  And you have indicated that the ferrite machines seem to last longer - so there is another advantage.  I can no longer see spending $15-17 on a single fragile neo magnet when I have proven to myself that it can be done with ferrite magnets for a fraction of the cost, and you actually end up with a better and more durable machine in the end.

Lots of folks are thinking maybe the price of the neo will come down because they're going to start digging holes in other places on earth and flood the market with neodymium.  But my gut instinct is that it is not going to happen.  It is like the price of energy once it goes up - it will never come back down.  So pursuing some practical ferrite designs is worthwhile.

That is all.
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Chris

[ChrisOlson]

I would rather tink about changing the coil geometry to fit moe copper into the stator. Having made some experiments, I conclude that the size of the whole inside the coil is not as important as one would think it is. I have made tests with coils that have no enterspace at all. Of course, the voltage was lower than on coils with holes but as much as I assumed it to be.

Has anybody else made experieces in that section?

Hi Max,

Yes, I have experience with this.  It is why you see my designs are using wedge shaped coils instead of making the coil hole the size of the magnet.  I have experimented with it as well and found that the very slight drop in voltage is more than made up for being able fit more copper in a smaller size if you design a coil geometry that allows the fitting of the coils in a tighter space.

I have gone as far as to place a piece of plexiglass over a rotor and sprinkle iron powder on it, then turn the rotor and watch what the lines of flux do.  The lines of flux, in what I have found, do not follow the shape of the magnet as much as one would think.  It becomes a thing of blended magnetic beauty when all the magnets are on the rotor and it is the change in the flux as the thing rotates that causes the current to flow in the wires.

I know this is a discussion of a topic that could be controversial.  But that is what I have found and why my designs use the wedge coils.
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Chris

[Menelaos]

Hi Chris,

Good to see that you have made the same experiences. For a long time I as well build with wedge shaped coils now. The theory on what is the most efficient solution differs a lot from what pracical results have discovered...
The magnetic fields do definitively look not even close to what can be simulated in various tools...It is more of a mess :-D

...so sticking to the theoretically most efficient coil design does not give as much advantage as we would assume it to do...
So I have gone over to making the holes verry narrow, basically as small as I can bend the wire to on the bottom and as big as I can male it on the top without the coils just touching each other on the other side so that I do not have to move them appart on the bottom side where they basically directly touch. Also I found for myself that the coil legs should not be to wide. It is quite a difference if you compare the length of the wire on the first turns with the ones on the last turns...it can be more than double...only adding resistance. So making them about 2/3 of the magnets width is the most I would go for.

I better don't tell people how manny stators I have build and then thrown them away after making tests on them as they crowded my tiny workshop and how manny magnets I have messed up...but it was definitively worth it for learning from it.


This does not really relate the the ferrit topic but on the other hand side it does because it saves a lot of space which we need for compensating the lower flux of ferrit magnets without getting giant alternators...so with going back to ferrits, those issues become more important...

Well, this is my way of approaching the problem ;-)

Max

[Tritium]

Chris,  Where are you getting your magnets?

Thurmond

[ChrisOlson]

Chris,  Where are you getting your magnets?

Hi Thurmond,

I bought them from Master Magnetics in Castle Rock, Colorado.  They have a website at www.magnetsource.com.  I called them and talked to a gentleman named Travis Ranney at ext 149.  The 2 x 2 x 1" thick magnets come packaged in a box of 60 and if you buy the whole box you can get them for $1.89 each.  If they have to split the box down then they will charge a little more for them, but not much.  They actually make the magnets there, and magnetize them there.  You can get custom ones made too, if you want.
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Chris

[ChrisOlson]

I better don't tell people how manny stators I have build and then thrown them away after making tests on them as they crowded my tiny workshop and how manny magnets I have messed up...but it was definitively worth it for learning from it.

Max, do not feel bad.  I have somewhat the same collection of stators, but I have not thrown them away.  I should take a picture of all the stators I have hanging on my shiop wall and post it.  Folks would think I am running some sort of stator store or something   
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Chris

[Menelaos]

Don't worry, I dodn't throw all of them away, I still have plenty in Stock, I kept the good ones ;-) ....but manny were not worth keeping, were cracked, came up on the sides or burned up in tests...so why keeping them...?!

Anyway, I will join back in when I have some results on the ferrit tests :-)

Max

[ChrisOlson]

Anyway, I will join back in when I have some results on the ferrit tests :-)

Max, definitely looking forward to your testing results!  This has turned in a project of great interest to me, as it is not in any of the books.
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Chris

[jlt]

I understand that proven wind turbines are still using ferrite mags, and build some pretty large  machines using them.
         I have tried to find out how they are built, or if they could be  home built.

[Flux]

Their windings or on a toroidal core. You can do it if you have a source of high quality strip wound core material and you have a toroidal winding machine or infinite patience. It is in fact a very good design and one that suits the low flux density of ferrite magnets.

You can build anything if you want to but I notice people will put a lot of effort into some things and reject others. When it comes to obtaining magnetic core steels you will have real trouble unless you want a ton of the stuff. The torus also has a few tricky mechanical issues to deal with/

Flux

[jlt]

There is a transformer Rebuilding Place That sell old transformer steel to the scrap yard . My idea is to cut small pieces and cast them with resin in a mold to form the core..
     then to wind one coil to see how many turns will be needed. and then to measure the length of wire needed. then it would be simple to put each coil onto a spool and then to the core.

[GoVertical]

Anyway, I will join back in when I have some results on the ferrit tests :-)

Max, definitely looking forward to your testing results!  This has turned in a project of great interest to me, as it is not in any of the books.
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Chris

http://practicalaction.org/docs/energy/pmg_manual.pdf


Hi, I found this link when searching for a magnet and coil configuration that I could use for the project I am working on. It appears to use ferrite magnets. How does it compare with your results? It is not the same but seems similar.

[ChrisOlson]

Hi, I found this link when searching for a magnet and coil configuration that I could use for the project I am working on. It appears to use ferrite magnets. How does it compare with your results? It is not the same but seems similar.

Hi, yes it is similar but not the same.  I looked at that (it is in Hugh's PMG Manual).  In that design, as near as I could decipher it, Hugh was passing a magnet over every coil at a rate of 24 times/sec at cut-in and getting 12 volts DC from a 4:3 pole/coil ratio three phase unit in wye with 100 turns of wire.  Mine is passing a magnet over every coil at a rate of 42 times/sec.  I get 25 volts DC with the same number of coils in each phase as poles (every other coil in each stator is wired reverse polarity) using individually rectified phases, or "jerry rig" with considerably lower internal resistance.

And, of course, my ferrite generator is considerably more complicated with the 10 pole dual stator design, and much heavier and more powerful than the 8 pole shown in those plans.

The ferrite magnets are quite heavy.  This block of 60 magnets sitting on the bench weighs within a few tenths of 50 lbs!



The center rotor alone in my generator weighed 23.3 lbs and it is only 11" diameter!



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Chris

[GoVertical]

  Hi, have you determined the RPM of your blade rotor  for a output of about 15 amps, what is the chain drive input RPM for about 15 amps output? I believe my project could be easily altered to use ferrite magnets. I would be able to fabricate more than one and just add more units as needed. If I limited the output to 15 amps or 10 amps it may reduce the weight. 

[ChrisOlson]

  Hi, have you determined the RPM of your blade rotor  for a output of about 15 amps, what is the chain drive input RPM for about 15 amps output?

It produces 15 amps (at around 26 volts) with the rotor turning at 155 and the generator at 355 rpm.  However, that is the output of both stators using the IRP configuration.  So each stator is delivering a portion of that.

15 amps is easily gotten with just a single stator too at higher rpm.  But I didn't record enough readings to determine what that was when I was running it single phase.  Before you get too excited about this design I came up, I should caution that it is pretty "stiff" and will produce 60 amps with the turbine rotor running at 260 rpm.

I dropped the gear ratio one "notch" with this thing to give the blades a little more "run" at it before they come against a wall and lean into their torque curve real hard.  But as it is right now the TSR is down in the high 4's at around 25 mph wind speed.

It's a little trickier because I got two air gaps to mess with, two stators with different numbers of turns in each one, and for peak performance the power efficiency between the two stators has to be balanced.  The 50 turn section is slightly more power efficient than the 53 turn so it tends to deliver more power at higher outputs.  I've determined that I need to open the air gap on the 50 turn a tickle to get a better efficiency balance between the stators.  If I can get the rotor up to 300 rpm by increasing the rpm/volt a smudge, I'll get the same low wind performance and improved midrange to high end output.

As to how all this would apply to a VAWT I don't have a clue.  But I do know it would take one hell of a big VAWT to drive this dual stator generator.
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Chris

[Tritium]

15' tall by 6' wide blade lenz type VAWT wide might do it. 

Thurmond

[GoVertical]

Hi, I have it working, it just needs some fine tuning. Thank you for the information.

[ChrisOlson]

15' tall by 6' wide blade lenz type VAWT wide might do it. 

It's possible it could.  I don't know about matching it for torque and speed though.  My generator reaches 15 amps at about 14 mph wind speed so the turbine rotor is running at 5 TSR.  If my calculations are right a 6' diameter VAWT would only be running at about 65 rpm at that speed so it would take a lot more gearing to get the generator up to speed.

The higher the gear ratio, the more torque loss there is in the speed change.  My 3.8 meter rotor is developing approximately 21.8 lb-ft of input shaft torque at that wind speed.  A VAWT running at 65 rpm would have to develop 52 lb-ft of torque to match it for power.  I don't think a 6 ft x 15 ft VAWT style machine can make that kind of torque at 14 mph.  The formula for wind pressure on a 1.0 TSR wing in Psf = .00256 x wind velocity².  I think it would have to be bigger around to get the required torque.
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Chris

[Tritium]

Chris, I pulled that number   out of the blue sky just for discussion's sake which you granted me.

I am building a 8' tall by 6 foot diameter three wing lenz type though. We will see what it will do but the testing certainly will not be as refined as you typically accomplish.

Thanks

Thurmond

[ChrisOlson]

I am building a 8' tall by 6 foot diameter three wing lenz type though. We will see what it will do but the testing certainly will not be as refined as you typically accomplish.

Well, that's pretty cool.  The bigger around you make it the slower it will go but it will make more torque.  I think the height only increases power (torque) at any given diameter.

I got a half-built VAWT that I started working on about two years ago that's 6 x 6.  One of these days I'm going to finish it just to say that I got one   
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Chris

[keithturtle]

I got a half-built VAWT that I started working on about two years ago that's 6 x 6.  One of these days I'm going to finish it just to say that I got one   

Well at least I'm not alone in the delay.

Here's the blade, sort of a curved LENZ 2, hub goes on a piece of 1 1/4" threaded rod with 2 flange bearings about a foot apart [pic not found]

Turtle, slow

[GoVertical]

http://www.youtube.com/watch?feature=fvwp&NR=1&v=lbpRdme4Tpg


Hi, interesting video of ferrite PMA project.

[fabricator]

That is interesting but I don't think he's ever had blades one one, with that bearing setup and his tight air gap he's gonna be scraping coils big time, if the TRB gets a little slop in it same thing, long blades in a stiff wind will deflect that bearing enough to scrape coils, a machine like that done right with proper bearings and a properly sized shaft would be a pretty bullet proof machine.

[ChrisOlson]

I agree that on a wind turbine that bearing system would be quite maintenance intensive to keep magnets from rubbing the stator.  On a hydro application it's probably pretty good.

I'm working a geared radial three-phase 14 pole, 42 coil ferrite generator that's very similar to that one, although I haven't decided what to use for the core yet.
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Chris

[scoraigwind]

That alternator in the video does not seem to even have a core.  It's rather like the old brakedrum design, except that he has not filled the available space with wires and he has not used a core (apart from a couple of laminations to hold the casting together)  He could use those same magnets on a dual rotor axial with a blank steel disk opposite the magnets and get much better output.  Easier to build too.  He'd need to work out a way to stop the magnets flying off, but no big deal.

And yes the tiny bearing hub is a bit comical.

[vawtwindy]

I intend to reply few of my observations hugh, but my inferiority pretends them, whether it is good observations or not? i dont know

here it is
compared to magnet size the coil size (thickness) is pretty small, may be 3/4th of the magnet size? but at 2.06mins duration in the video he shows something like a core, but it has inner core structure?

[ChrisOlson]

He could use those same magnets on a dual rotor axial with a blank steel disk opposite the magnets and get much better output.

That's one thing I'm running into playing with a radial.  I've tried three different things for a core, with just a test coil to see what I get for voltage.  None of them - not even an old electric motor core - can match the axial for magnetic performance.

At the cost of ferrite magnets (really cheap), even if you have to throw double the number of magnets in an axial, you still get better performance and not much more cost.
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Chris

[vawtwindy]

Like few of those achived 3kw to 6kw in axial using Neo's, could it be possible with ferrites in axial model?, if so just imagine the amount of weight your bearings have to hold. thats where my concerns are rolling out and still thinking of radial's could do it.