Maximum efficiency of an axial flux PMA?

[JohnMason]

Hi Fieldliners,

I'm in the midst of writing a paper on wind power and I'd like to know what the maximum efficiency of an ideal axial flux PMA.
And if you can, a URL where I can find documentation for it

If any of you know please let me know

Thanks John

[SparWeb]

You may not realize, but there seems to be something vague or maybe cryptic in your question.

Three possible answers:
1) 99.99%
2) 50%
3) should you be writing a paper on wind power if you don't have available to you the way to work out the answer yourself?

It's not really fair for me to answer your question with a question like that.  There's a range of interpretation of your original question that can get you a wide range of answers.  Need to narrow down what you really mean.
A much better place to start: what's the intended audience of this paper? 

[JohnMason]

HI SW

The reference I have below is what I am using for now, its a white paper by a commercial entity but I am looking for something better. any knowledge passed along would be helpful.

Moreels, Daan and Peter Leijnen. 2018. High Efficiency Axial Flux Machines. European Union: Magnax.

Accademia doesn't care about what the writer of the research knows, it seems to only care about what other research supports the writer's. If my research was on Axial Flux PMAs, yeah your right, I  should already know...but it isn't. My research is on the siting wind turbines in urban environments.

Thanks John

[SparWeb]

Your experience with academia differs from mine.  I hope you experience improves.

Motors differ from alternators, so the Magnax document isn't very helpful.  It also isn't academic - it's commercial and the self-promotion is cranked pretty high.

Without the time to explain, you are probably looking for "electrical efficiency" rather than any other measure of efficiency of the PMA.  In that case, input mechanical power at the drive shaft has to be converted into electrical power.  At low power, the efficiency is high, but the output is just a trickle.  Turn it faster, get more power out, but the efficiency gets lower.  At some point the heat lost become a threat to the alternator. 

Simplest answer is 50%

[JohnMason]

Hi SW

Well that is helpful but not exactly what I wanted to hear.

Thanks John

[bigrockcandymountain]

Generally, an axial with no iron in the stator is somewhat less efficient than an iron core from what I understand.  That would be all things being equal etc. 

That being said, I saw a test someone did on here a few years ago and I seem to remember the axial doing 88% at low power and down to 50% at very high power.  I think it was maybe chris olsen or kitestrings.  They both have nice axial flux machines. 

Search through some old posts and I'm pretty sure you will find a few examples of tests like you are looking for. Lots of people 10 years ago were building and testing axial flux. 

I drank the cool aid on 3 phase motor conversions and a can't see myself building an axial.

[JohnMason]

Thanks for the update BRCM.

I had read at one time that an AF PMA was/is considered the most efficient for wind turbines, I just wondered how efficient?

I sort of figured that there was an efficiency curve at work and wanted to quantify the generation loss.

I also wanted a better reference than a commercial white paper which made motors/generators but as it stands I just took the reference out of the paper.

 Not critical to the research so...meh. 

Thanks John

[SparWeb]

I seem to remember the axial doing 88% at low power and down to 50% at very high power.  I think it was maybe chris olsen or kitestrings.  They both have nice axial flux machines.

Your memory serves you well.  My experience is much the same.  A little lower efficiency with motor conversions used as generators.

[Adriaan Kragten]

The efficiency of a certain PM-generator of a certain type depends very much on the load conditions but also on the frame size. For a certain type, the efficiency generally increases with increasing frame size. This is also the case for asynchronous motors. I have performed very extensive measurements for a radial flux PM-generator made from an asynchronous motor frame size 90. These measurements are given in my public report KD 78 which can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports. The measurements have been performed for a range of constant voltages, a range of constant currents and a range of constant load resistances. It appeared that the efficiency curves depend very much on the load condition. Only for a resistor load, the efficiency is high for a large rpm range, at least if the voltage drop isn't too large.

I have also performed some measurements on a Chinese axial flux generator for a 12 V battery load. These measurements are given in public report KD 595. The really measured efficiency is much lower than the claim of the manufacturer. Manufacturers generally only supply measurements for a resistor load but most generators are in practice used to charge a battery and for this load the voltage is almost constant. The efficiency for for a constant voltage is only high for a small rpm range.