Report KD 730 about 28-pole PM-generator available

[Adriaan Kragten]

Report KD 730 can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports. The title of this report is: "Ideas about a 28-pole, 3-phase permanent magnet generator using the housing and winding of a 4-pole asynchronous motor frame size 80".  This generator makes used of 28 neodymium magnets size 40 * 7 * 3 mm and the magnet costs are only about € 25. It is expected that this generator can be used with the original 230/400 V winding for 24 V battery charging if the winding is rectified in delta. Figure 1 out of this report is added as attachment.

[joestue]

this could be interesting, but i think that it would be worth it just to rewind a concentrated winding. its also rather easy to make such windings.

unfortunately, most 4 pole induction motors are 36 slots.

[Adriaan Kragten]

The number of stator slots depends on the frame size, the number of armature poles and the manufacture of the stator stamping. For manufacture of Kienle & Spiess, 4-pole motors have 24 slots up to frame size 80. 4-pole motor of frame size 90 and 100 can have 24 of 36 slots. 4-pole motors of frame size 112 and larger have 36 slots but very big 4-pole motors can have 60 of 72 slots. 6-pole motors have 36, 54 or 72 slots, 8-pole motors have 24, 48 or 72 slots.

I don't agree that rewinding is easy for an amateur. It is just easy if the original winding can be used. A 2-layers winding as given in figure 1 of KD 730 is most common for a 4-pole motor with 24 stator slots. There is another way for which the coils are laid as tiles but laying the coils this way is rather complicated for a small stator as then one has to work with all phases at the same time. For a 2-layers winding, one can first lay two coils of phase U, next two coils of phase V and next two coils of phase W and all these coils are lying in one layer, so there are no crossing coil heads. Then all coil heads are bent to the outside and the second layer is laid in a similar way.

If the voltage of the original winding is too high, it is rather simple to half the voltage by modification of the 230/400 V winding into a 115/200 V winding by connecting the first and the second layer in parallel in stead of in series. This procedure is explained in chapter 4 of my report KD 341.

[joestue]

When i replied earlier i thought that you had found a coincidence where a stock 4 pole winding could be used with a 28 pole armature. -you've got a 28 magnet machine which still produces 4 net poles which is why it works with the stock winding. 

i looked at it again today and realized it can't. when i suggested just winding a new concentrated winding i meant winding one like this https://www.electricmotorengineering.com/non-conventional-design-of-concentrated-windings/

(minus the non conventional part)

[Adriaan Kragten]

When i replied earlier i thought that you had found a coincidence where a stock 4 pole winding could be used with a 28 pole armature. -you've got a 28 magnet machine which still produces 4 net poles which is why it works with the stock winding. 

i looked at it again today and realized it can't. when i suggested just winding a new concentrated winding i meant winding one like this https://www.electricmotorengineering.com/non-conventional-design-of-concentrated-windings/

(minus the non conventional part)

In the report I explain that mechanically the armature has 28 poles but as you have seven north poles and seven south poles together, physically it has 4 poles. The fact that there are seven armature poles opposed to six stator poles, makes that the armature has 6 * 7 * 4 = 168 preference positions per revolution and this strongly flattens the peak on the clogging torque.

[Adriaan Kragten]

A new chapter 5 has been added to report KD 730. The title of this chapter is: "Alternative 4-pole winding with coils piled up like roof tiles". Figure 3 out of report KD 730 is added as an attachment. The efficiency of a winding with coils piled up like roof tiles is higher than that of a 2-layers winding as given in figure 1 of KD 730. However, mounting of a roof tiles winding is much more difficult as all twelve coils have to be mounted simultaneously. So this type of winding is generally only used for much bigger stators.

[Adriaan Kragten]

I have designed several PM-generators which really have a high armature pole number but then the armature pole number is two more or two less than the number of stator slots and all magnets are mounted with the north pole to the outside. All these generators are described shortly in the first part of chapter 6 of public report KD 341. A 34-pole generator which makes use of the same magnets size 40 * 7 * 3 mm as the 28-pole generator of KD 730, is described in public report KD 580. However, this generator makes use of the stator stamping of a 6-pole motor frame size 80 which has a larger inside diameter of the stator than that of a 4-pole motor and 36 slots instead of 24 slots. This 34-pole generator needs a special winding but this winding is rather simple. Now there are two bundles of three coils for each phase. Figure 1 out of KD 580 is added as an example to show the difference with the winding of a 4-pole motor as given in figure 1 of KD 730.

[JW]

Dude you are good at math.
***Removed PDF per request of owner***

[Adriaan Kragten]

Dude you are good at math.
***Removed PDF at the request of the owner***

What has this to do with this post about multi pole PM-generators and why is Dude asked to say something about my public report KD-382 which you can find on my website but which should not be copied at this forum without my permission. It is only allowed to copy a KD-report for private use and that is mentioned on each report. I don't want my reports be available somewhere else than on my website because sometimes reports change and I want to be sure that someone always uses the latest version.

[Bruce S]

Begin Moderator MODE!!

Adriaan;
That was JW's way of saying you are really good at what you are doing.
I know that sometimes things get lost in translation, "dude" refers to you, not some other person.

We can certainly remove the link to the PDF.

END Moderator MODE

Bruce S
OOPS!! I put GW instaed of JW. My bad

[SparWeb]

The other thing that should be clarified is the meaning of the word itself.  In this context, JW uses it in the friendly way.
You would be correct that some people use "dude" as an insult or a pejorative, but I can tell that JW didn't mean that.
In the United States, the meaning and usage of many words has drifted to their opposite in the past few decades. 
It's just something you have to get used to.

[Adriaan Kragten]

Okay, now it's clear. I thought that Dude was the nick name of someone else on this forum. And yes, you find some math in most of my KD-reports but it isn't of a high level. All KD-reports about the design calculations of rotors like KD 382, are based on the formulas as given in report KD 35. The derivation of some of the formulas out of KD 35, like formula 5.3 for the angle phi and formula 5.4 for the chord c, is very complex and the derivation isn't given in KD 35. But working with the formulas isn't very difficult and examples of the rotor design procedure are given in chapter 5.4.1 for a rotor designed with the optimum lift coefficient and in chapter 5.4.2 for a rotor designed with a constant chord. If someone has problems with understanding parts out some of my KD-reports one can always ask a question about it on this forum and then I will try to explain it.

[Mary B]

Dude came into use in CA as slang for just about anybody "Hey dude, can I borrow your board wax?" and the person being asked might be female! It still persists in use and is rarely a pejorative, more of a generic way to address someone.