I have finaly built my first axial flux (outer rotor) coreless generator rated at 3 kW for grid conection. Very happy about it but some problems did occure....
The nominal power of the generator was measured at 2700 W rather than 3000 W that was found in my FEMM-Matlab simulation. After measuring the generator's dimensions I found out that the airgap was larger. I executed a new simulation and the results were very good (1.5% error in the EMF and about 4.5% error in output power). But the problem is that the airgap was not uniform. In fact, the two steel discs (outer radious 480 mm) were not flat and so the airgap was difficult to be set at the correct value. Any comments on how to avoid this problem in future generators ?
Another problem I encountered had to do with the thickness of the rotor discs. I had (and still have) no idea on how to calculate this. Just some advice (the thickness should be equal to the thickness of the magnets for example) that I found here and some research on Hugh Piggot's and other constructed machines in order to find some kind of equation between the force of attraction and the thickness of the iron. In the end I just chose the 10 mm thickness thinking it's a safe choice. But now, wanting to build a larger machine, with more powerfull magnets than the N40 I used, this knowledge is essential. So I am asking your help for any information in order to produce a tool of general use...
In addition, I think that there is also a heating problem in the generator... "I think" is becouse I can't measure the temperature now that the machine is built and while it is working and mostly becouse I don't have any clue of what the impact of the (physical) ventilation of the generator will be on the temperature... Just to be sure, I was thinking of drilling some symetrical holes in the rotor.... Any comments on how to control the temperature?
Thank you very much!