Homebrewed Electricity > Frequently Asked Questions (FAQs)
PMA VS. AXIAL FLUX WINDMILLS
Yianie123.:
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:
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
Yianie123.:
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:
--- Quote from: Yianie123. on June 01, 2014, 11:27:39 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
--- End quote ---
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:
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
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