Homebrewed Electricity > Wind
Report KD 718 about 16-pole PM-generator available
Adriaan Kragten:
Another new chapter is added to report KD 718. The title of this chapter 9 is: "Ideas about a 20-pole PM-generator using a 4-pole motor frame size 112". This alternative makes use of the same magnets size 40 * 15 * 5 mm as used for the original 16-pole generator.
Adriaan Kragten:
Another new chapter is added to report KD 718. The title of this chapter 10 is: "Ideas about a 30-pole PM-generator using a 6-pole motor frame size 160L". The magnets of this generator are even cheaper than the magnets of the 16-pole generator frame size 132M as described in chapter 6. The generator frame size 160L has a shaft end with a diameter of 42 mm and can therefore be used for a 3-bladed windmill rotor with a diameter of maximal 5 m. This report KD 718 contains now the description of six PM-generators with different frame size. For all generators, the original motor winding can be used. The fluctuation of the sticking torque is only little.
SparWeb:
Sorry I missed this when you first posted it. I have often thought that if I were to carry out a conversion with re-winding of the stator, that I would multiply the poles on the rotor at the same time.
Can you walk me through the pole orientations on the rotors you have drawn?
As I look at a figure like the first one you posted (figure 1) or the new one from chapter 8, I see (for example in the upper-right quadrant) two or more N oriented magnets with an iron-only pole between them. I would have expected that iron pole to be S oriented, not N. Can you describe how you determined that? By test? Have you built a detailed model of this rotor to confirm that the field will develop as you expect it to? (I think you say in your introduction that this hasn't been built or tested yet).
Perhaps my intuition is fooling me.
Adriaan Kragten:
Figure 1 out of KD 718 gives a side view of the armature and the stator winding. In this figure you can see that there are 36 stator slots and so 36 stator poles. The armature has eight grooves but the magnets are glued such that two adjacent grooves are filled with magnets with the north pole to the outside and two adjacent grooves are filled with magnets with the south poles to the outside. In between two magnetic poles there is an iron pole. This results in four mechanical poles for one magnetic pole. The magnetic flow pattern is given in figure 2 of KD 718. In this figure you can see that you get four magnet flow bundles of which two are rotating right hand and two are rotating left hand. Each flow bundle consists of two magnetic loops. Every magnetic loop is flowing through one pole formed by a magnet and one pole formed by the remaining iron of the armature. So this is the situation for an armature with sixteen mechanical poles used for a 4-pole stator winding laid in a stator with 36 slots.
Figure 4 of KD 718 describes the armature and the magnetic flow pattern for an armature with 30 mechanical poles used for a 6-pole stator winding laid in a stator with 36 slots. So you should not combine figure 4 with figure 1.
For all six options as described in KD 718, a special ratio is realised in between the number of mechanical armature poles and the number of stator poles. This ratio is 4 : 9, 5 : 9 or 5 : 6. The number of preference positions per revolution depends on this ratio and on the number of stator poles. It is rather high and this reduces the fluctuation on the sticking torque. The number of preference positions is much higher than for an armature for wich the number of mechanical armature poles is the same as the number of magnetic armature poles.
The advantage of all six options is that the original motor winding can be used (if the generated DC voltage after rectification matches with the chosen battery voltage). If you want to use the original motor winding, the number of magnetic armature poles must be equal to the pole number of the original asynchronous motor. So a 6-pole motor requires an armature with 6 magnetic poles but it can have more mechanical poles.
The armature given in figure 1 of KD 718 has 16 mechanical poles and you get 4 magnetic poles if the magnets are glued such as given in figure 1. However, if you would fill one groove with magnets with the north pole to the outside and the adjacent groove with magnets with the south pole to the outside, the armature will get 8 magnetic poles. If all eight grooves are filled with magnets with the north pole to the outside, the south poles will be formed by the iron poles and so the armature will have 16 magnetic poles. But an armature with 8 or 16 magnetic poles can't be used in combination with the original winding!
Adriaan Kragten:
I just realised that something isn't logic in figure 2 of KD 718. The mechanical poles are numbered right hand starting with a magnet pole. This results in an iron north pole N4 at the right side of magnet north pole N3 and in an iron south pole S8 at the left side of magnet north pole N1. But with the same right, it can be assumed that there is a north pole at the left side of magnet N1 and a south pole at the right side of magnet N3. This second option results in a similar magnet flow patteren but it is only rotated 22.5° left hand. The real magnet flow pattern for an armature without stator will lay somewhere in between both options. The real flow pattern is more difficult to describe and figure 2 is therefore maintained.
The real magnetic flow pattern in the stator iron also depends on the magnetic resistance. The magnetic flow lines will follow the path of least resistance which means that if the stator is saturated somewhere, a part of the flow will follow a different path and it may even be that the real flow pattern in the stator varies in between the two options.
The iron pole in between two magnet north poles will certainly be a north pole. The iron pole in between two magnetic south poles will certainly be a south pole. But the iron pole in between a north and a south pole can be a north pole, a south pole or partly a north and a south pole depending on the where the stator is saturated.
I will add a new chapter 11 to report KD 718 in which I explain the non logic aspect of figure 2.
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