Today I watched the small video on YouTube called: "Exx-027 Wind Turbine Generator - Unboxing & Product Review - Triphase A/C rectifier DC - Energy". In this video, a small 100 W, 12 V, 3-phase, 12-pole PM-generator is disassembled. What surprised me is that both bearings are mounted in the front bearing cover. As the distance in between the bearings will be very small, the radial bearing load must become high if the shaft is loaded by a moment. This moment can be the gyroscopic moment or the self orientating moment or it can be caused by the rotor weight or by imblance of the rotor. The back bearing cover is also machined inside to keep both bearing covers identical but therefore there is a big hole in the back bearing cover. Mounting of one bearing in the front cover and one in the back cover would make the generator almost not more expensive but the bearing loads would be much lower. Other disadvantages are that the tags on the three wires don't match with the supplied 3-phase rectifier and that the box contained almost no specification and no measured characteristics. It is even not mentioned at which rotational speed the 100 W is supplied.
The usefullness of a PM-generator for a wind turbine is determined by two things. The peak on the cogging torque at zero rpm and the shape of the Pmech-n curve for a 12 V battery load. So if someone buys this generator, he has to measure it himself. If the peak on the cogging torque is too high, the rotor won't start at an acceptable low wind speed. If the required rotational speed is too high for a 12 V battery load, the cut in wind speed will be very high and the matching with the rotor will be bad. So the whole thing can be useless. Many Chinese PM-generators are offered without proper specification and measured characteristics for the correct load.
