Author Topic: PMA VS. AXIAL FLUX WINDMILLS  (Read 15339 times)

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Yianie123.

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PMA VS. AXIAL FLUX WINDMILLS
« on: June 01, 2014, 09:27:39 PM »
Trying to figure out the best way of going off grid?  Many small PMA's or 8ft axial flux.  My understanding is that PMA's can handle the storms, built like tanks, reliable and set it and for get it.  Large axial need maintenance, much stronger tower and high wind sensitive.  Please give me good reasons for your preference, that is, after you stop laughing.  Thanks

oztules

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #1 on: June 02, 2014, 01:45:20 AM »
I've built a few axial flux 4m units.
1. In a marine environment, it seems simply impossible to protect the magnets.... so will never build another one... high powered but useless over the longer term.

2. The very best mill I have witnessed up close is the African Wind Power 240v unit with ferrite magnets. It will last forever, and produces it's 1.5kw day in day out  and can't be burnt out... the back MMF stops it even short circuited, it does not over heat, cannot overheat. It is sited in a very windy site, an axial would not last as the updrafts would beat it in the end.

3. The next unit I build will follow the design philosophy of the AWP..... never again will it follow the axial flux version.

4. If you can find a genny that will current limit below destructive heat, then that is the way to go.... just make STRONG blades, as you will struggle to control it if you try...... dump load is much better at it than a short circuit... it will just run away with a short.... but no damage.

5. An axial with excellent furling system, and some way to protect the magnets in marine environs would be fine.... but it does not happen here.

6. PMA's are not created equal either. The Bergy units overheat and blow up with extensive corrosion here as well, I have been given 2 to rebuild recently Compared to the AWP, the bergy design is a poor joke as been tested here. The AWP had QC problems 10 years ago, don't know what it is like now, but it has not looked like failing from design in the past decade. The Sorma's have been no better  either...... big names, poor designs.... I have one of those to rebuild as well if I get around to it.

Carefully designed PMA's with neo mags to keep a compact design, are just fireballs waiting to happen from our experience.

Make it big and rugged and ferrite and it will last as long as the bearings and blades hold on... it's that simple.


...................oztules
« Last Edit: June 02, 2014, 01:54:51 AM by oztules »
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Yianie123.

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #2 on: June 02, 2014, 07:07:15 AM »
Thank you for your imput.  I am assumming to dislike PMA's?  Is there a need for great wind for them to be worth putting up?

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #3 on: June 02, 2014, 12:02:05 PM »
Trying to figure out the best way of going off grid?  Many small PMA's or 8ft axial flux.  My understanding is that PMA's can handle the storms, built like tanks, reliable and set it and for get it.  Large axial need maintenance, much stronger tower and high wind sensitive.  Please give me good reasons for your preference, that is, after you stop laughing.  Thanks

Going off-grid?  What for?  If you have utility power now going off-grid is only going to cost you more money and headaches.  Unless you live in a location where there is no utility lines, it is not worth the hassle.

When you say "PMA" I assume you mean an iron or laminated steel core radial flux generator, as opposed to the air core axial flux.  Ummmm..... the axials aren't quite as bad as oz makes them out be.  They managed to take an incredible beating here for many years and work fine.  I've seen plenty of both types with windings melted into a black crispy mass.  And the axials generally have higher electrical and mechanical efficiency.  So if it was me I'd go with the axial design.

oztules

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #4 on: June 02, 2014, 03:28:06 PM »
Chris has said nothing I can disagree with. He has seen what he has seen.

What I am trying to point out, that set and forget is possible, but only with a specific iron cored PMA.

It's inductive reactance must be such that it will current limit at less than destructive temps.

The AWP ferrite HV model does this.... I don't have experience with any other AWP versions. I did hear they were going neo, which would make them as useless as all the other commercial offerings.

It is drop dead easy to build an alternator that is efficient, it is just as easy to build one that will not fail under any circumstance, but you will sacrifice the efficiency, which is a who cares if you don't pay for the wind, and the thing cannot burn up.

If you build or buy this type of PMA it will certainly be less efficient in every way to an axial even a poorly built one... but it will last forever, and the power from the wind to cover efficiency  discrepancy is free.

It will never be in a crispy mass even under indefinite short circuit condition.... it just can't be broken if the blades stay on.

Any other sort of pma will require decent furling, careful siting, and hand over your heart when the big winds come for days on end..... sooner or later it will wind seek, and something bad will happen...... even those dinky commercial offerings from supposed world leaders in their fields.... just toys in this environment... and don't get me started with their tacky electronics.... that can't handle surges from their precious neo alternators.... those surges cannot happen with reactance limited designs.

I bet Chris has a few crispy circuit boards from his electronic controllers to show that is the case.....



..........oztules
Flinders Island Australia

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #5 on: June 02, 2014, 04:21:52 PM »
I've seen all of them with burnt up stators.  Bergey Excels, Provens (which is actually a type of axial with a toroidal core), as well as homebrew axials.  I'm a little skeptical of using core losses to control output of a wind turbine, and I think the most successful ones have used some type of reliable furling mechanism, whether it be side furling or feathering blades.  So I think it's a horse apiece and the inherent simplicity and efficiency of the air-core axial is pretty hard to beat.

Yeah, I got plenty of crispy stuff.  Collection of 4 AWG crispy wire.  Rectifiers with stuff hanging out of them that I don't even know what it is.  Stators that were on fire until what was burnable was all gone but they looked really cool on the tower, sort of like a P-51 that got shot down.  Got rare earth deposits in the field from magnets that flew off and never found them.  Got pieces of blades that I never did find the rest of the pieces for.  But overall I think this is the nature of wind power.  If it ain't built like a tank it'll break.  And that goes for the biggest utility scale turbines too.  So I find it a little hard to say a "PMA" is "better" than an axial, or vice versa.  It's all in the design and how well you build it to stand up to the elements.  Light duty wind turbines do not stand the test of time.

oztules

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #6 on: June 02, 2014, 04:52:25 PM »
"I'm a little skeptical of using core losses to control output of a wind turbine,"

Sorry Chris, I have not made the point properly.

It is not iron loss/core loss or any other loss that controls the output.

It is simply a matter of the amp turns generated in the windings, reacting against the magnetic flux of the magnets ( amongst other things ).
The net result is when the max power is gotten to, the magnetic fields all but cancel out further flux getting into the windings... so it uses no more power... it ceases to increase the load on the blades and they can try to run away. As the rpm increases, the magnetic fields stay in a steady stand off, and no further power is absorbed by the genny, and so no further heating can occur, The AWP did this at 1.5kw... it behaved like a normal alternator, until it got near 1.5kw... and it just sticks there day in day out ( that one is on a 1000 foot ridge, ALWAYS windy.... it cannot crispy critter... it just can't.... not physically possible.... nor can it over power the control electronics, as the output cannot exceed that max point.... everything is protected naturally.

They have 3.7M blades, but you will never see crispy stators from this thing.

It shares the same Hugh furling, and is very very heavy.

When I say inefficient.. I should say it does not use the available wind effectively once the reactance has cut in fully... it just does not use any more wind than it needed to get to that point. It then does not see the next 200mph of wind, thats for the blades to deal with....  the alt cannot break if it goes off wind seeking on it's own, ignoring the furling... blades need to be decent to handle high speed rotation in these circumstances, but the normal furling should handle this in nearly all cases.

Put simply... it  is idiot proof..... no other alternator style can claim that as an intrinsic part of it's inheritance. The F&P washing machine motors are of this type as well... cannot be burnt.


........oztules
« Last Edit: June 02, 2014, 04:59:29 PM by oztules »
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ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #7 on: June 02, 2014, 06:24:27 PM »
The AWP did this at 1.5kw... it behaved like a normal alternator, until it got near 1.5kw... and it just sticks there day in day out

oz, yes I knew what you were talking about.  I just used the wrong terminology.  Air-core axial generators also experience a significant amount of reactance at higher rpm's.  So it is not unique to the iron (or laminated electrical steel) core radial generators.  And reactance must be compensated for in air-core axials when setting the power curve on MPPT turbines to prevent over-speed of the rotor as the flux "bends" more and more at higher output and speed.

You have the old AWP3.6?

I'm somewhat familiar with the African Wind Power turbines and I believe Hugh was involved in their design.  I seem to recall some problems with the early ones, but can't remember all the details.

oztules

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #8 on: June 02, 2014, 06:55:30 PM »
Yes, reactance in air cores is very low, particularly if you are using neo's. Ferrites as in your higher speed units will see this more so...... but not enough to protect them at all.

The AWP was an early awp3.7. There are a few stories I have written on here somewhere, and they show what woeful quality control they had in the early days. The machine literally fell to bits because of terrible/ woeful/disgusting  workmanship..... the design was brilliant, but the implementation was hopeless at that time.

That said, when we fixed the machine up as per design, rather than the butchery that was perpetrated to this machine originally, it became a set and forget unit.
I still had to rewind it ( all 90 coils!!)  because they never sealed the coils properly.... and they corroded badly.... but never any sign of over heat ....except where the corrosion broke down the insulation..... this is a 500v machine, so corrosion from stupid and lax sealing shows up very quickly in a salt air environment. ( island).

The electrical controller was wired with the wrong look alike components, but still sort of worked, never any blowing up though.

So they are the problems with the early ones..... they were real problems with quality control... or any control from the looks.

If I were to buy a commercial mill this would be it by a country mile...... but  I would pull it to bits first, and rebuild it to spec. It will then last forever... as it was a few weeks was enough to kill the massive ( they are huge)  bearings in it........... over sized shafts made "lumpy" bearings.... that s how tight they were.


.... john
Flinders Island Australia

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #9 on: June 02, 2014, 08:54:47 PM »
I still had to rewind it ( all 90 coils!!)  because they never sealed the coils properly.... and they corroded badly.... but never any sign of over heat ....except where the corrosion broke down the insulation..... this is a 500v machine, so corrosion from stupid and lax sealing shows up very quickly in a salt air environment. ( island).

So the AWP uses a step-down three-phase transformer like the Bergey Excel-R?  I didn't recall they operated at that high of a voltage.  That's pretty cool, really.  Morningstar (which I think builds a pretty robust controller) has a 600V MPPT controller that now has wind curve programming capability.  I'd love to try one with one of those turbines to see how it works.

oztules

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #10 on: June 02, 2014, 11:42:34 PM »
Like every other mill, you can wind for whatever voltage you want.

This one is high impedance, and winds up to over 500v as the transformers come in and drag it down to the 300v or more mark. Simple SCR control to pull in the transformer.

At cut in it in the 260-300v region, you can guess how high it can go once it get roaring..... but the batteries keep the voltage pegged once the scr's have pulled in.

This means it runs at nominal 300v or thereabouts, depends on the battery SOC and the taps used. It will be kept at that voltage regardless how fast it spins, and it will not suffer at all. It will top out at 7-8 amps in the mill windings... and never more... it magnetically cant.

It you were to use the mppt you talk of, then you could harness a lot more power out of it, as the amp turns will be the same for current limit, but the watts can double without a problem if you let the voltage rise.... this makes it very silicon friendly, as no high current spikes can ever happen, unlike the axials, and other PMA's with strong magnets and small iron circuit.


1200v silicon is freely available, and only needs to handle surges of 10 amps or so.

On it's current site 24kwh per day is a walk in the park, and probably below average.... just amazing really.

The 3.7m blades are way oversize for the rating, but that and the current limiting allows it to make more power than comparable units..... it is all about swept area, and being able to control it..... and this cheats and does it easy.


............oztules
Flinders Island Australia

kitestrings

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #11 on: June 03, 2014, 06:37:15 PM »
Did/have they continued in some fashion (AWP)?  I remember following the early development and some related discussion on Hugh's old site I believe it was.

Here in the states the early pioneers (those with the arrows in their backs) of the "stronger than an elephant" (always liked that ad) turbine had trouble getting delivery or parts or anything that resembled service.  The US franchise/rights were bought by a guy named Richard Preus (sp?) in Oregon, and with some alterations sold under the name ARE (Abundant Renewable Energy).  The smaller unit still had a pretty good reputation, but IIRC the output went from 1.3 kW to a 'rated' 2.5 kW - same rotor size - and the price more than doubled.  They went out of business, must be nearly 15 years ago, and it was again bought by a company called Xzeres.  Not sure how they've faired...

Not much to add on the OP question.  A lot seems to depend on environment, availability of materials/resources, skills, preference to -or from electronic solutions.  PhilM on the back shed site has some similar conclusions to yours, Oz, and some crafty work I'd add.

There are many, many examples of AF burnouts.  A lot of them though were direct-ties with little or no place for load once the batteries were full.  I'll still suffer some lumps the hard way, like other before me, but why invite trouble?

Regards, ~ks

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #12 on: June 03, 2014, 09:11:33 PM »
There are many, many examples of AF burnouts.  A lot of them though were direct-ties with little or no place for load once the batteries were full.  I'll still suffer some lumps the hard way, like other before me, but why invite trouble?

Yeah, but most of those were/are amateur built and designed too.  And a lot of installations where things aren't matched in wiring resistance, stator resistance, blades, etc..  It's not the fault of the design.

I never really posted much on these turbines, as it seemed turbine building had gone out of style, and most of my designs ended up being too controversial because they went against everything the homebrew books said.  So I eventually just quit posting the details on them and moved it all to my own website.



These are 3.5 meter machines and they produce 3 kW continuous @ 12 m/s wind speed on a 48V system.  They are over twice the overall efficiency of a AWP3.6 or 3.7.  And you cannot burn one of these out.  They will free-spin at 20 m/s wind speed at over 1,000 rpm with no problem (although they are noisy when doing that).  They can run fully shorted in 20 m/s wind with no problem, and in fact that that is method I use to keep them online in high winds, running them shorted with a mechanically engaged voltage clipper, with the clipper keeping the power output and voltage to a level that the Classic 150 controller can handle.  They can also be wound for any voltage you like - this stator is a 180V unit:



And they actually will furl in very high winds running unloaded, just like a Bergey Excel will.  Although they will furl earlier if the machine is fully loaded and producing full power:



Just to show you that there is a little more advanced design in axial turbines than what is shown in the homebrew books.  I've been building them for years, and departed from the trailer hub turbines after the first one I ever built because they were problematic and not too durable.  You'll probably notice that my design sort of follows Gordon Proven's design, except mine is upwind with side furling while Gordon's machines were downwind with spring loaded blade feathering.

Regardless, these machines have proven to be extremely durable - can't break one.   So don't fault or discount the axial flux generator as being "inferior" somehow.  You run them at high enough voltage, just like the AWP's radial, you can't break it or burn it because the more copper you put in the stator, the higher the reactance and self limiting becomes as it reaches full power.  The axial designs with those big round magnets on 9 tiny little coils, then strap 10 foot blades to it should have "burn out" stamped right on them.  It is a flawed design from the word "go".  But it is not the axial's fault.

oztules

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #13 on: June 04, 2014, 03:33:34 AM »
Excellent work Chris.
Intrinsically, your axial has better efficiency than the radial iron core.
The output power differential is more to do with matching the load via your exotic controller than much else in the design I think.

What I am surprised about is the "reactance limiting" your experiencing.... for a start  I assume ferrite magnets?... as I can't see neos doing this.
When you say "short" do you mean terminal volts=0 or the controller is holding it at X volts and that behaving as a X voltage shunt, and feeding off the 3kw as well.

Very nice outcome, and beautifully executed as usual.

If it will current limit without any fancy control ( ie straight into a 180v battery bank sort of thing) you have my vote as best mill around.
 If it cant do it without the classic and voltage clamp, it is still way in front of the "normal " axials, but not truly current limited natively.... thats my test of invincible.


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

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Flux

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #14 on: June 04, 2014, 10:41:05 AM »
Some interesting discussion, little of which I disagree with. Site conditions and your requirements have a lot to do with the choice.

I agree with the problems of corrosion of neo in marine environments. You can make any machine reactance limited by adding series reactors if considered necessary.

In a really good wind area then simplicity and robustness means a lot. Another factor is how much the weight issue is a problem.

I grew up with dynamos and later wound field alternators, the problem there was obtaining enough load without an electrical machine being ridiculously heavy. For larger machines a geared drive was virtually essential.

Neo changed all that and introduced a new problem of stall that was never an issue before. Although I welcomed the potential for output in low winds I was frustrated by the dismal performance in higher winds. This lead me to write an article about matching the load and the ultimate conclusion of this is the spectacular performance Chris has managed to get from his designs and the Classic controller. That is not to suggest that in a good reliable wind area the the direct charging approach is not suitable.

If you accept the limitations in high wind and get enough power in lighter winds then the simple approach is fine. Whether you can get furling to work depends on many factors and if you can't then reactance limiting is no bad thing, it can reduce stall issues in higher winds and offer ultimate protection if furling fails. Again it is a compromise and a part of good design.

I still like the radial slotless design, a compromise between the slotted radial ( Bergey/ AWP) and an axial, magnet protection is easier, cooling is better and it justifies overlapped coils. It suffers from the same problem as other radial designs, it is not forgiving on design errors but as long as it fits together most of this would be solved with the Classic.

Flux

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #15 on: June 04, 2014, 11:41:19 AM »
If it will current limit without any fancy control ( ie straight into a 180v battery bank sort of thing) you have my vote as best mill around.

If you had a 180V battery bank, oz, it would do that.  The magnets I used are neo but they are little 1/2 x 1 x 2 N42's and the air gap on these is quite wide (22mm).  You get more reactance that you would suspect from that setup and the generator will go to about 3200-3300 watts or so and it just won't put out any more, no matter how fast you spin it.  These dual rotor axial generator designs make very bad use of the flux compared to a radial with an iron or laminated steel core.  So the design is not really commercially viable because it throws too much materials at the problem and uses the magnetic material inefficiently.  But the electrical efficiency of the generator is right around 90% at full power output.  The 180V stator at a "clamp" of 144V will only put out 21 amps.  For whatever reason, that's all she'll do and it does make the windings warm up a bit but they won't burn.

You can fully short it running unloaded in high wind speeds, but the generator is too powerful and it will stall the blades.  The best is to use a three-phase resistor on it (voltage clipper).  This dissipates some of the power in the resistor and lets the turbine continue running in high winds without stalling it.  By matching the clipper properly the turbine can continue to run in high winds and stay under the 150V operating limit of the Classic controller.  I did burn out a few of those "clippers" until I figured out how to build one out of some garage door springs that has held up really good.  I haven't really come up with a better way to keep the voltage within limits, other than maybe making a variable pitch hub like Frans has on his turbine.  But I haven't gone there yet because even the Jacobs' blade governors had their share of problems.  So to keep it simple I've just been using the resistors and turn them on with the Classic's AUX1 port when the voltage gets too high for the controller.

As I said earlier, Morningstar has a TS-MPPT60-600V controller that can be programmed for wind turbines.  I got a TS-MPPT60-150V here that I have been testing with a little 2.6 meter turbine.  I'd love to turn one of my 3.5 meter machines loose on a 600V one and see what it's really got.  But they get around $1,100 for those 600V controllers so I haven't bought one yet.

oztules

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #16 on: June 04, 2014, 01:34:59 PM »
"If you had a 180V battery bank, oz, it would do that."

That makes it best on ground, and is a giant step forward.
The auto burn out designs as seen on this site would do well to learn from you.

I have not burnt out any of  my 4m neo machines, so it is not sour grapes from that....... but rotted out 96 2x.5"  n45 and n50 magnets in various states... sour grapes from that

So I won't emulate your exploits.

I may try another version of Flux's with the slotless radial, and will use this construction, this was a slotless radial made from fencing wire for the core, and power pole struts for the drum and ferrites...it was high voltage and good for 2-3kw depending how it was loaded... reactance limited


I gave that one away as I was chasing more power with the axials.... as it turned out....power was easy with the axials.... but magnet longevity here was not... wish I had kept it now.



......oztules
Flinders Island Australia

Flux

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #17 on: June 04, 2014, 02:07:05 PM »
I like that, I admire the drum construction. Not sure how good the fence wire is for core material, florist's wire may be a lot better but the iron loss doesn't seem to be a big issue and with ferrite it will be even less. The simplicity again has a lot going for it. I used motor cores but removed the teeth to keep the weight down, just left a ring about 3/8" thick.

My versions have been neo but ferrite doesn't have the corrosion problems, just comes out heavy and a bit greedy on copper. I can see why Gordon Proven used the torus version with ferrite but it is a pig to build.

Flux

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #18 on: June 04, 2014, 02:29:46 PM »
I built some high-powered axials with ferrite block magnets.  But the only way I could get decent power around ~2.5 kW was to gear the things and run them at 1,000 rpm.

I've seen that radial design from oz before - you must've posted that on here one time?  Or you possibly had a website it was on?  I've always liked that and was going to build one when I get time to see how it works.  Except I was going to try a powered iron core.

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #19 on: June 04, 2014, 02:48:37 PM »
I have not burnt out any of  my 4m neo machines, so it is not sour grapes from that....... but rotted out 96 2x.5"  n45 and n50 magnets in various states... sour grapes from that

The corrosion issues of neos in salt air makes them a very fragile thing.  I don't know if you can get it in Australia but I went to treating my rotors with a product called POR-15 several years back.  I machine the rotors for axial runout then leave them setting outside.  The freshly machined steel rusts very quickly.  Then treat it with POR-15.  Then I bolt the magnets on (not glued) with stainless steel bolts.  Then finally treat the magnets and around the edges with POR-15 to prevent any moisture from getting underneath the magnets.  They look like this when they're done



I've found that the corrosion starts underneath the magnet, then it very quickly gets a white cancerous looking growth on it and rapidly deteriorates.  The POR-15 has worked pretty well here.  It is impervious to salt water, solvents, diesel fuel or gasoline, or even battery acid.

kitestrings

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #20 on: June 05, 2014, 06:18:15 AM »
Very impressive Oz.  How did you insulate the wire?

One more thought I'll add, and this may be a design consideration that is somewhat independent of the alternator choice.  I think it illustrates that one size does not fit all.  From what I've followed with some of the F&P adoptions, one of the popular configurations is a 6-phase alternator, typically rectified at the turbine due to the add complexity of transmitting it through a set of slip-rings.

We have a pretty good wind site for our region.  There are two commercial-sized installations located on ridges either side of us.  Last week I made a point of eyeing the highest trees as I climbed our tower.  They're 75' (23m) tall, mostly maple, ash and basswood (a softer, all-white-meat hardwood with very large leave structure).  Our tower is 100' (30m).  The shut-wound unit we've maintain for nearly 30 years here has a stud-diode bridge rectifier in the control box, our axial uses this same design.  A lightning storm can pretty quickly take out the rectifier.  To isolate one in this scheme takes 5-minutes and a VOM; to replace one takes maybe twenty (most of it locating my soldering gun).  Compare that to changing one on the 100' tower.  In one of the worst cases I recall, some of the early Dunlites had a diode ring that couldn't be accessed without bringing the alternator to the ground.  A 600# machine.  I admit its an extreme example.

My point is only that one of the appealing things to me about the axial's is their simplicity.  I'm not underestimating the corrosion issue with neo's, but in our case there's no salt air factor, so the choice is different.  To me three moving parts on the tower is very compelling, and I'm less afraid of the electrical wizardry of controls (MPPT, diversion, etc.) as long as they're on the ground.

~kitestrings

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #21 on: June 05, 2014, 08:23:56 AM »
We've been running the MPPT controllers here on wind turbines now for going on three years, and never had one fail yet.  And I've pushed them pretty hard.  I've over-volted the 150V controllers to 200+V several times and never had smoke come out.  The firmware in them has been a little buggy at times.  But I think the hardware is pretty good.  The best thing is that it allowed me to run turbines on 1,000 foot wire runs from the towers to the power room with lower losses and pretty much doubled the energy production to the battery, making the turbine much more useful and productive.  It cuts the current from the turbine over the transmission wires to about 25-30% of what it was when it was direct hooked.  And unlike a transformer with mechanical tap changers, allows infinite programming of the power curve to precisely match the blades to the generator.

So I don't consider MPPT to be "wizardry" anymore.  Anything can fail, but these modern MPPT controllers are pretty rock solid in my book.

Yianie123.

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #22 on: June 11, 2014, 06:47:19 AM »
What is meant by PMA are the Permenent Magnet Alternators sold by various manufactres like Hydrogenappliences.com, Missourri Wind and Solar and others.  They seem very rugged, but claim more power then it seems possible.

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #23 on: June 11, 2014, 08:02:16 AM »
What is meant by PMA are the Permenent Magnet Alternators sold by various manufactres like Hydrogenappliences.com, Missourri Wind and Solar and others.  They seem very rugged, but claim more power then it seems possible.

Rugged?  They're frickin' junk.  I know from personal experience that a 24V one is good for about 20A continuous at about 40% efficiency.  I bought one, from which company I won't mention because they all fight like cats and dogs about who has the best converted car alternator.  I drove it with a Honda GX160 engine for a DC genset.  I figured it should be able to put out 1,200 watts, which was only about 40 amps.  Melted the windings in the little thing within 30 minutes, and they refused to warranty it.

Flux

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #24 on: June 11, 2014, 08:13:23 AM »
PMA is an abbreviation for permanent magnet alternator. It covers any form of machine which uses permanent magnets  to provide the field.  it covers all forms of construction including the axial air gap design and even the simple bicycle dynamo.

The modified alternators you mention are car alternators with the claw rotor and field coil replaced with permanent magnets, they will not have an output higher than the basic car alternator but they don't have the loss from the field winding.

Unless run at very high speed the output is quite small. For some hydro applications they work well where you can keep the speed high but for wind they won't produce much if you accept a reasonable cut in speed in light winds.

You have found some of the sites that make wild claims well beyond reality and they come up with silly ideas such as multiplying short circuit current by open circuit volts and calling it power. Most of the stuff they claim is well beyond the Betz limit.

Flux

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #25 on: June 11, 2014, 11:30:36 AM »
Car alternators are designed to put out rated amps for only a few minutes to recharge the battery after starting.  Then put out low amps to maintain the battery and the vehicle's electrical system.  Otherwise they overheat and fail.

The 24V converted alternator I got had 18 ga windings in it and the rotor claw had been pressed apart and the field coil replaced with a neo ring magnet.  It was advertised as putting out 1600 watts.  After seeing the windings in it, the best I figured it could put continuous is 500 watts, and even then it would be very low efficiency.

That same alternator rated at 62A in an automotive 12V application would have 7 turns (they are a 14 pole unit) of 14ga wire in a skein or serpentine winding, wired delta.  The one I got had 15 turns of 18ga in it and reached 24V at about 1,000 rpm.  I was not too impressed with it after it melted, and I seen what's in it.

ChrisOlson

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Re: PMA VS. AXIAL FLUX WINDMILLS
« Reply #26 on: June 11, 2014, 12:00:41 PM »
Here's an example of what NOT to buy because you're being fleeced (mods, if posting the link to a commercial product is unacceptable, please change the post accordingly)
http://www.amazon.com/12V-Super-Charger-1600-Watt-blade/dp/B00IHRXUFU/ref=sr_1_2?s=lawn-garden&ie=UTF8&qid=1402508658&sr=1-2

1600 watts @ 15 volts is 107 amps output.  There is no reasonable person that could expect to get 107 amps out of one of those little alternators when the 1600 watt power output as shown in their graph is supposed to be achieved at 135 mph wind speed.  I don't know exactly how that was tested, and I'm afraid that if you have 135 mph wind, how much power your wind turbine is putting out is the least of your worries.