Need some help to choose right cut in parameters

[Menelaos]

Hi there,

Some people might have already read about my grid tied turbine project. Besides, I am planning to also build a 20 feet Turbine to charge batteries.

My Prop is supposed to have a TSR of 6.5 and the Generator will have an Resistance between 2 Phases of about 0.2 Ohm, wound for 48 Volts with 15 coils and 20 pairs of magnets.

I was reading through manny topics and also uses the search function but got a littlebit lost...
I am not quite sure how to choose the cut in speed for the calculations of the windings of the generator in order to have an early cutin and not to hit stall too early.

I know that the prop, if unloaded, will have an TSR higher than designed TSR but I find it hard to estimate how much higer this would be.

So for the calculations using the designed TSR, what are ur experiences about the windspeed to adjust the turbine for?

Should I make all the math to set the alternator to reach battery voltage (50V) at 8 mph?
Or would that be too early and result in heavy stall in still low winds?

I was actually thinking about 9 mph an I've read about some folks here who did it like that without finding reports about the results. Also the resistance of the alternator is quite low I think and the power curve will thus be quite steep?!

What are the values that other 20 feet builders have used in therms of designed cut in wind speed for designed TSR and also for the resistance of the alternator?

It would be nice to get some hints.

Max

[SparWeb]

I suppose it would be easier to understand if I had a graph to show you.

Every time I measure simultaneous RPM, wind speed, and power output of my turbine, I use a spreadsheet to sort the data in bins and make curve-fits of the data.  These curves can be created to answer any particular question, so Power-vs-Windspeed is obviously useful, but I can plot the RPM-vs-Windpseed just as easily.  The result of doing so usually gives me a particular type of graph.  At low wind speeds, there is obviously no data (no power, variable wind speed data)  Higher wind speeds, the generator reaches cut-in speed and the data clears up.  At wind speeds where the generator is just about to cut-in, I regularly see very high TSR; above 10.  At slightly higher wind speeds, it does turn faster, but the generator loads up the rotor too, reducing the TSR rapidly.  At wind speeds closer to 10 m/s, the blades are truly running at the design TSR around 5 or 6.

With some logic I can explain how this occurs.  At low wind speed, the wind energy captured by the blades is rather small.  Fortunately, cut-in of the generator has not been reached, therefore the genny places very little load on the blades.  There is some friction and in my motor-conversion generators there is also magnetic attration to the iron laminations, but this is not an impediment.  The speed at which the incoming wind power is consumed by the resistance of the generator is a RPM that corresponds to a rather high TSR.  Also, it is worth noticing that the blades are a a low angle of attack (it's almost saying the same thing as high TSR).  If it helps, I often see it higher than 10.

Once the wind gets strong enough to push the blades faster - fast enough to cut-in - then the electrical load of the generator is added on to the idle load.  this is where the required power to turn the generator increases.  The RPM still rises, but no longer as rapidly as the wind speed rises, causing the TSR to drop (and hence increased angle of attack).  If the blades and generator have been designed to match, then the resulting TSR at a "useful" range of wind speeds will correspond to the TSR selected in the design, and congratulations are in order.  It's not easy.

These considerations really only apply to a fixed-pitch rotor like mine.  I have seen your variable-pitch rotors and I'm not familiar enough with that system to know off the top of my head just what is the ideal way to make them function.  Presumably it would be possible to have the pitch self-adjust the angle of attack so that the TSR is FORCED to match the design TSR at all wind speeds and most conditions.  Tuning the pitch control to do this is quite another matter.

Yes it does seem like the resistance per phase of your alternator is low.  Surely you have spun it unloaded, and found the RPM at which it can begin to charge the battery?  You need this speed to make sense of everything else.  If you want to "engineer" the match between rotor and alternator, you will need to conduct loaded tests of the alternator to learn its power input and output curves.

And then you have to decide how far you want to go...  Compute inflow wind speed and make the proper deductions from wind speed to fine-tune the TSR match, hopefully getting a few more % of Cp...

[Menelaos]

Thanks a lot for your response!

I think i had already posted the link to our german site where you can see pictures of the alternator. That one was tested in Belgium with loads. I do have a table which exactly indicates the efficiancy of the alternator at a number of voltages and with different loads. As a result I found out, that the results were estonishing close to what I calculated in advance.
Unfortunately that generator is not mine anymore :-(

A have now started to build another 2 pieces with slightly different parameters.
For the blades that I use I have a programm that gives me all nthe numbers I need.

for the 6 m prop with TSR 6 I have created a table of CP versus TSR shown below:



I first of all want to finish the grid tied project and later set up an independant battery system.
What I really wanted to get was confirmation on that kind of tables that I showed above. And as you say that you saw your prop spin with TSR 10 or more, this confirms me those numbers.

So what I plan to do now is:

1. make a new set of coils wound to fit the Aurora grid tie inverter making all the calculations using my excel tool that I once introduce here. It now has many new features and got prove several times that it now usually works on the spot :-)

2. I am planning to wind the coils for a cut in of designed TSR of 6 for 4m/s about 9 mph. I can then end up with a resistance of about 0.2 Ohms between the phases and thus have very low losses in high winds and no worry about glowing stators :-)

3. I know the losses of the bearing hub at various RPM and the losses that occour in the inverter and the alternator at various currents and loads. So in hand with that table on the picture, I am then able to make a good match of Alternator and prop and get a cot in about 5-6 mph considdering the loss of cp shown from the table.

From about 10 mph upwards, I will try to follow design TSR and thus get maximum efficiancy. If I trust that graph, TSR 10 or even 11 should still give me some power, at least it sould be possible to have the blades spin that fast to make those assumptions.

If everything works out fine, I want top use the same alternator to charge batteries and forget about gridn and hope to still have a good match if I set it to reach 50 Volts at design TSR for 9 mph in order to have real cut in about 7 mph or so and not to hit stall too early.

If there are problems occuring, I can still change design TSR in the range of 5-7 and make adjustments that way without having to play with the airgap.

According to my calculations, at an output of 6 KW to the grid, I would have less that 0.5 KW of losses in the stator which is like nothing for such a big stator as i think...

The pitch controll you mentioned has nothing to do with all of that. My prop is basically a fixed prop like the one you have. Angle off attack does not change with wind speed!

The mechanism only starts to release when the blade speed reaches a set RPM. I will adjust this to about 11-12 m/s
Only if that speed is reached (f.i. 250 RPM) the blades will start to turn and thus limit RPM. Below that, it is a normal "fixed prop".

I hope it is clear what goes through my mind these days... I basically want to increase efficiancy of the alternator using less wire by optimising it for a higher design cut in and live with less efficiancy at verry low winds.

Just what I didnt have experiance with was prove of how fast beyond design tsr blades can spin when no or only little load is applied.

Please comment :-)

Max

[Flux]

This will always be a compromise with battery charging with direct connection.

Much depends on the type of blades but typically a prop of tsr 6.5 will likely reach tsr10 on no load. For larger machines there tends to be more worthwhile energy in the lower winds. I suspect a good starting point would be to aim for cut in at 8mph with tsr 8. You may start to pick up some power even at 7mph.

There is no doubt that you will drop tsr fairly quickly and will eventually stall. If you can get a good energy capture from 8 mph and hold it reasonable to 20 mph then you will do well. if you start to hit stall hard below 20mph then much will depend on your site conditions. You may get better overall results opening the gap and loosing some of the light wind results if it is a reasonable site. On a very poor site you may be better accepting the stall.

It is a good idea to keep the winding resistance as low as possible to avoid heating but there is good reason to have extra resistance external to the stator to keep you from stalling hard so I wouldn't make any big effort to keep the line resistance very low.

For small machines you need to think about a reasonable top end performance as there is little to be got in low winds, but for bigger machines it is likely better to start worrying about performance at 7 mph even if it starts to knock the high end as with batteries you will need an enormous bank to accept the currents that are potentially possible in high winds if you are matched correctly. That is why i wouldn't worry if you hit hard stall much over 20 mph. You may be better off pushing the top end up with external resistance and keeping the low end rather than opening the gap and avoiding high end stall at the cost of winds below 8mph.

External resistance will cost you but will still let you keep increasing power in high winds with very little effect on light winds.

Wider gaps will give you higher efficiency in the high wind but at a price in low wind. I think the bigger the machine the more use the light wind end will be.

Interesting to see what others have found but I suspect most will have opened the gap to avoid stall rather than try the extra Resistance as low value resistors of kW rating are not easy to come by and once you have chosen your cable you are pretty much committed.

Flux

[Menelaos]

Hi Flux,

I do not really care about hitting stall above 20 mph but woud rather have good performance at 7 mph maybe even already a little at  6 mph( if I trust the table i posted, that should be possible in theory with TSR about 11)...but OK, thats the disadvantage about direct charge of batteries. So grid tied machines can start up a lot earlier and also have better efficiency.

Having searched the bord, I somewhere found an article in which you mentiones that you are using a grit tied jacobs and have made your own "grid".

That would be the perfect solution, using the inverter for maximum output and low losses in high winds ans dtill somehow get that power stored into batteries. Is that what you do?

If so, I would be very interested in how you got that working.

Max

[SparWeb]

Sometimes projecting the same information on a different form of graph will illustrate better what you want to know, ie using different axis definitions.  For instance, I have recently started using this format of graph to understand blade - generator matching:



http://www.sparweb.ca/1_Blades/Aero.html   Read the rest of it here.



This makes the comparison of turbine and generator much more obvious, and the data are easier to show, too.  To focus solely on the TSR is misleading, you should look at many parameters instead.  This is as far as I have gotten with it now.  There is more for me to learn too.

[SparWeb]

Where did you get that WindKraft program !?  Is the software available?

[jimovonz]

Hi Menelaos, Some time ago I developed an Excel workbook that used a Cp v TSR curve to determine the actual output of a given alternator/blade combo by seeking the point along the curve where the available power matches the load from the alt. I could vary certain alternator characteristics to see how the output might be affected. It had a similar layout to your typical alternator power output spreadsheet (windspeed vs power into the battery), but rather than using the fixed design TSR at all windspeeds, some VBA code searched for the specific TSR that matched power available from the blades to the power required to turn the alt. As I recall, the Cp vs TSR curves I was using dropped off faster with higher TSR compared to yours - but our blade profiles may be quite different. The algorithm I used started off at an arbitary max TSR of 12 and searched back from there. The impact of choosing this arbitary maximum TSR was minimal as before cut in the RPM was not relevant and after, the TSR drops fairly rapidly. Unfortunately I am about four PC's down the track from when I last used this workbook and I'm not as organised as I should be. I'll have a look for it as soon as I get a chance. If I remember correctly it was not that complex...

[Menelaos]

In my tool, the section where power is calculated actually does not interest me at all.
I am using the workbook to calculate number of turns and to estimate generator size, amount of wire needes and resistance. All of that works very well but for the power output section there is still a lot to do....but as it does not change the results of the working machine, I do not really care :-)

I will have a look at the site you posted, spareweb, thanx for that!

The programm I uses is freeware by litz hermann and can be downloaded here:

http://www.bitpilot.de/

It is also verry useful for making blades as you can printout the shapes of airfoils for all sections of the blade. It is possible to load many difdferent airfoils  or insert own data, just have a look at it and try to understand the german :-(

Also there are 5ways to choose from in oder to simplyfy the blade profiles which makes it easier to build them. All the results from those nsimplifications and stuff also nresult in the tables. That is why my graph has the shape it has and is not steeper towards the beginning at low TSR.

To use the tool, it makes sense to read the instructions...which are in germand...undfortunately :-(

Max

[jimovonz]

In my tool, the section where power is calculated actually does not interest me at all.
I am using the workbook to calculate number of turns and to estimate generator size, amount of wire needes and resistance. All of that works very well but for the power output section there is still a lot to do....but as it does not change the results of the working machine, I do not really care :-)

The purpose of my tool was also to determine the best alternator design to match a given blade set. My definition of best match was the configuration the gave the best power curve (into the battery). If you are not designing your alternator to extract the maximum power then what is your goal?

[Menelaos]

I do not want to go too far off topic...but the goal of my tool is only to quickly try manny different options, play with different magnets and wire gauges, determinde the airgap and find out if the stator would fit into that gap, calculate nflux and thus get all the numbers needed for winding the perfect coils on the spot.

On the mspot means that I know in advance who to adjust prop and Generator.

It is not a tool for dummies. One has to have a basic knowledge of what is important to consider. So for example I have to know that I have to choose a windspeed higer that the actual cut in because the tool calculates with desin tsr and things like that.

It is nearly impossible to consider all the Tings like steepness of rise in power of the alternator, wire run, change of cp...all it could be is a guess...practical results for sure will be different, so I do not bother with that and rather determine those things from experiance.

Experiances like the ones I now got from spareweb and flux regarding unloaded TSR.

I can then go into the tool and select a planned cut in for design TSR of lets say 4 m/s, knowing that it will be lower and about knowing the factor. Now the tool can do all the math and I can try various magnet sizes, wire diameters and stuff to get the best ratio of cost, size and Resistance. And the results of open voltage will be about 5% correct from what was calculated. It does save a lot of time for optimisation....but still, I have to know what I want to do!

[SparWeb]

Thank you sir!

Ich werde versuchen, mit Google zu übersetzen!   

[Flux]

Hi Flux,

I do not really care about hitting stall above 20 mph but woud rather have good performance at 7 mph maybe even already a little at  6 mph( if I trust the table i posted, that should be possible in theory with TSR about 11)...but OK, thats the disadvantage about direct charge of batteries. So grid tied machines can start up a lot earlier and also have better efficiency.

Having searched the bord, I somewhere found an article in which you mentiones that you are using a grit tied jacobs and have made your own "grid".

That would be the perfect solution, using the inverter for maximum output and low losses in high winds ans dtill somehow get that power stored into batteries. Is that what you do?

If so, I would be very interested in how you got that working.

Max

Sorry, not sure werer you found that but it wasn't me.  I can't think who it might have been but someone does post here under the name of Jacobs and seems very familiar with their machines, perhaps you could check his posts, it might have been him.

Flux

[jimovonz]

Menelaos, sorry I thought I was on topic. From your initial post I took it that you wanted advice on TSR at cut in and over a useful range of RPM up to stall point (which may or may not occur). The typical fixed pitch blades used here may never actually see their design TSR in use and if they do will see it at only one 'sweet' spot where it it optimally loaded for its wind speed/RPM. For me, predicting the match of an alternator to these blades based on a fixed TSR falls a long way short. Since you have a Cp vs TSR curve for your blades (which is rather rare in these parts) I simply suggested a way for you to more accurately match your alternator to your blades. If you are happy doing it using a fixed TSR then all is good    

[SparWeb]

Having searched the bord, I somewhere found an article in which you mentiones that you are using a grit tied jacobs and have made your own "grid".
Max

Sorry, not sure were you found that but it wasn't me.  Flux

That sounds like Chris Olson, on a recent thread started by Yiannie.

[Menelaos]

yes, thats right, Thanx :-)
I will ask him about that.

What I will do now about the generator is this:

I will wind it to cut in at design tsr at 4 m/s (about 9 mph).
And I might be able to push some power into the battzeries at about 7 mph. If the turbine stalls too early, I can still add line resistance or even better, change design TSR of the blades as I can adjust that easily. I will see how that works. Anyway my blades are not twisted and the width is the same all over the profile. Therefore they should not hit stall as easy as those who are designed for higher Cp with twisted profiles etc. since at some point, the angle of attack will always be right. We will see

As things also depend on various types of profiles, line resistance, size of battery bank, resistance of alternator and many more things, I have to wait for the practical results and I will post them here for others to have another example of how it should or should not be done :-)

Max

[SparWeb]

Max!
That WinKraft is fascinating - I'm slowly picking up the german terminology.

Just what I was suggesting to you before - about matching generator RPM to rotor's curves - I can find it now in WindKraft under "Bettriebskennlinien".

If you plot your generator's power curve directly on that plot, you will know how well it matches the rotor design - and you can adjust the rotor to improve any problems.

As you say, other factors in the installation will affect it, but this is a fine head-start you have with this program.   Danke!

[Menelaos]

I do not quite agree with you.
If I plot my generators power curve into that table, numbers are not korrekt. I have to sum up electrical output, rectifier loss, line loss, loss in an extr reiststor (if used) and the loss inside the stator coils which I can only calculate by ohms law. I then can see at which points I have room for improvement, thats right  but I can not see it directly.

On the other hand. If I take the graph that I postes for various windspeeds, so TSR versus Cp I can always see strait if the prop is too slow or fast and what the resulting power of the blades will be.

You might have seen that factor on the bottom of all the graphs in the programm. If I take the table of TSR/Cp (in the programme ´named "Cp-Kennlinie" I can always quickly determinde the theoretical power of the blades at any TSR and wind speed by simply multiplying the according TSR from the curve with the " Bezugsleistung" on the bottom of the page and I have the power in Watts.

The best and easiest way would be, to overlay both graphes so that on x-axis I Have numbers for TSR and RPM and on y-axis power in watts and cp. One graph for each windspeed...but that is only to correct things once they have been build and testet. For now its important to try and make nthe best match in advance!

[SparWeb]

In my eagerness to try out the program, I did not write my last posting carefully.  You are right, you must measure or estimate the required mechanical input power at different speeds for the generator, before trying to show a match to the rotor.  I have measured this data directly for my generator, so for me it is easy to plot.  Corrections for losses in the lines are also simple.  You might have to estimate it if you have not tested your alternator, but the axial flux machines seem to lend themselves to reasonable accuracy in estimating the required input power when the output curve is known.

I have noticed that WindKraft has (I think) assumptions about alternator efficiency built into the input data table.  I would rather use pure rotor mechanical power and concern myself with alternator efficiency afterward.  It would be easy to work around this, but the rotor diameter is sized automatically therefore some trial-and-error is needed. 

[Menelaos]

you can ignore that alternator CP. All the graphs only apply to Blade efficiancy. Its just a bit stupid one has to play with output power oder wind speed or cp to get a prop diameter desired. I wish there was an option to choose that value directly...

If you manage to read all the manual, you will find that there is an option to import your own profile data. If you have the angles of attack and the cp and ca values for those angles of any profile, you can make a table in a certain outfit and then import it into the programm. Thats what I like most about that tool as there are books with those informations on a lot of common profiles...

Max

[SparWeb]

Yes.  In fact I just finished dragging the manual through Google's translator and though not perfect, I get the point.
If anyone reading this wants a copy of the english version, just send me a message and I'll e-mail a text file, with some extra notes and translations that I've found helpful.

I have other airfoil data that I could use, but the NACA airfoils are suitable enough for learning how the program works.
Interesting that the planforms can be changed, too. 

[tecker]

Most of the calculations are a stretch the whole thing has a some calibration issuse that seem to be over looked
When the Alternator is grinding on a Charge or grid load there is some data that's really important in the form of alternator max min and heat buildup .You pretty much have to calibrate your alternator or live with what you have now when it's running . What data do you have now with respect to amperage at 48 + voltage .
 

[Menelaos]

What kind of data are you taling about?

Max

[DanielInSweden]

Menelaos, I much appreciate your hard work that you generously have shared with us, thank you! I'm planning to build a 20´turbine and have used your latest(maybe there are later versions now..?) excel calculator trying to get the numbers in there and understand the relations. I have attached a file with the numbers I have on magnet size, number of poles  etc. I will wind my stator "star". May I ask you to have a quick check on my numbers to see if I have made any obvious mistakes filling in the numbers or if you see that the coils can be slightly adjusted from your knowledge and preference. I.e. I'm asking for your opinion if you where to build with the magnet size and number of poles as I'm planning.

I'm living in Sweden and understand some German.

Thank's

/D

[DanielInSweden]

I found this calculator the other day that you might find interesting. It's Swedish and not translated yet on the website but I think you can figure it out.

http://24volt.eu/generatorkonstruktion.php

[Menelaos]

Hello Daniel,

We already have a new version of the tool. The one you downloaded was online for only two days until we discoverd some mistakes.
Wires in hand were not taken into account when calculating the resistance between 2 phases. Ich changed some things in your spreadsheet. First of all the resistance is now 0.3 ohm. Thats is verry low resulting in you winding 3 in hand. I also changed number of coils and magnet poles to 15/20 which is far enough considering the new resistance. From experience I have added a factor of 1.2 on the formula with number of coils as the resulting voltages semm to always be a bit lower as calculated. You should be on the safe side now.
That also depends on how thick your rotor disks will be. I recomment at least 12 mm, better 15 to get maximum flux, but 12 is probably a good middle between costs, weight and flux density.
I also changed cut in from 3.5 to 3.6 as stalling will be not such an issue then. With the powermax blades that I am building with now I even take 3.7 m/s for cutin as they have abvout TSR 8 on light loads.

Have a look at the spreadsheet ant tell me what u think about my changes.

I know the tool from 24 volts.eu
We made our own tool as we werde not satisfied with that one :-D

 Kopia av scheibengenerator-berechnung-1_6.zip (67.84 kB - downloaded 141 times.) Kopia av scheibengenerator-berechnung-1_6.zip (67.84 kB - downloaded 141 times.) Kopia av scheibengenerator-berechnung-1_6.zip (67.84 kB - downloaded 141 times.)

[DanielInSweden]

It's a great tool you have built!  I'm grateful.

I have read somewhere that the generator run more smoothly(less vibration=longer life..) if the magnets are closer together. I't seems by looking at yor coil sketch that you prioritize to get the hole inside the coil to fit a full magnet width. I have seen coils where they have a smaller width of the coil towards the rotor center. What's your opinion of what to prioritize? You get a cleaner sinus but does a cleaner sinus push more energy into your batteries?

Is N42 magnets a good choice for this machine or is a higher grade to prefer (more cost efficient)? When I change magnetic power (grade) in the calc. sheet cellD25, It doesn,t change the generator power very much.. Does this suggest that the match between chosen magnet flux and coil design(resistance, etc) is more important than maxing out one parameter like the grade of the magnet. I guess that at the end of the day it's prio1 to use every tesla available in the magnet and turn it into power in the wires. So, is there a liear relationship between going after higher grade magnets would require more copper in the coils to use that extra flux?

The PowerMax blades do look great. Do you have a set of 20,4ft available? I found them at magnets4sale.com(PowerMax) and magnets4less.com(WindMax) Similar? Where did you buy? Is the 20 poles generator example you sent me suitable for these 20,4ft blades or would you change it a lot? you mentioned going to 3.7 for cutin speed with powermax blades, I don't understand, don't you wan't to get cutin at 3m/s or as low as possible? 

[Menelaos]

I Usually make the holes as long as the magnets and the width same as magnets on the outer sode and about 2/3 of magnet size on the inner size.
Making the hole much smaller does not make much sense as I think. Then a number of disadvantages appear.

1. the magnets on one rotor disks get very close to each other which distracts the magnetic flux. It will basically split off, not only going through the airgap but also to the magnets next on the same disk so that the flux in the air gap will decrease.

2. It is not only about the sine wave that will not be as clean anymore which is not so important as we rectify anyway, the main problem is that if the coil hole is too small, the there is a point when one magnets strike the 2 legs of the coil. At That time the power produced on both sides of the coil will be zero  and thus power is lost. The resulting voltages will be lower but resistance and thus losses will not be decreased.

I always look for a good match of power, size and costs.
Makingbthe holes smaller means that I can build the alternator more compact and cheaper. For me, the measurements I  stated seem to be a good midway but that is only what I have decided to to after having built at least 50 Generators now...


The magnets:

When I started making my first alternators I was always looking for magnets with highest grades. I do not do this anymore. I usually build with N40 or N42 as the rise of flux is not linear to the rise of costs for the magnets. Here in Germay magnets are far more expensive than in the states, at least 3 times more so for me it is not effective to use N50 or even N52. Also there is not a big difference in the amount of copper needed, so in the end using lower grade magnets for a far lower price makes a lot more sense to me.

Yet, I have not used the powermax blades but I will oreder some sets from the USA soon to make my own experiences with them. I am impressed about what chris Olsen wrote about them. I like blades with high torque. On light loads they have about TSR 8 which I matched to about 2.7 m/s of wind which gives me 3.7 m7s for TSR 6 so that is what I typed into the tool. The tool calculates with nominal TSR, not considering that TSR can change under very havy or light load.

3.7 is what chris Olsen has figured out for a good match as well, so there is no need for me to reinvent the wheel :-)
Anyway I will make my own tests and see if I get the same results.

Maybe it is a good idea if we order together?

Max

[DanielInSweden]

Ok, I see, make sense.

Please look into ordering blades together from the US. It would be great if similar blades can be bought in Europe. I have seen similar blades on picture mounted on a turbine in Romania(www.solbergavind.se/Gallery). I have sent him a question of blade type and where he bought them but no answer yet. I'll try to get his number and call him.

A question on the calc. sheet. Maybe it's obvious to someone with more knowledge than I have but under section 3 you wrote "Airgap between magnets"(my translation..=)). Do you mean the airgap between magnets looking down on one rotor disc laying on a bench or do you mean the total airgap between magnets(opposite poles S&N)when both rotors installed and stator fitted inbetween? If the latter is what you ment and the airgap is 25mm, stator thickness 22mm and 1,5mm airgap on each side of the stator(inbetween stator and magnets).

What's your thouts about high temperature in the stator windings? Is it all a matter of furl the machine at the right amperage or is there ways to keep the temp. down except cooling holes and different fillers like talcum powder and aluminum trihydrate(ATH)?

When the voltage increases with increasing rotor rpm, is it the charge and dump load regulator that load the generator more and more as the voltage goes up or how does it work?

/Daniel

[Menelaos]

Hello Daniel,

I am curious on that traders reply,
let me know if you have any idea about the prices and what kind of airfoil that might be


RGDS
Max