Author Topic: Question about rotor disks  (Read 4323 times)

0 Members and 1 Guest are viewing this topic.

gsw999

  • Full Member
  • ***
  • Posts: 209
  • Country: 00
    • kernelpower Ltd
Question about rotor disks
« on: December 07, 2016, 12:53:58 AM »
I am experimenting at the moment and I have just received some magnets , I have them coming in 2 lots of 14 ( shipping rules ) , all along I have been planning to make standard 12" DISKS with 12 magnets and 9 coils , what I wish to ask is , how would it make things different ( potentially ) by having 14 magnets , they would fit in ,  I intend to wind my coils very tight with 80 winds of 14AWG, Thanks.

Adriaan Kragten

  • Hero Member
  • *****
  • Posts: 1154
  • Country: nl
Re: Question about rotor disks
« Reply #1 on: December 08, 2016, 04:09:00 AM »
For a standard 3-phase winding of an axial flux generator, the number of coils is chosen a factor 3/4 of the number of armature poles. So for anarmature with 12 magnets the number of coils is 9. This means you have three coils of phase U, three coils of phase V and three coils of phase W. As 14 isn't devidable by 3, it isn't possible to make a 3-phase winding. The number of magnets must be even, so the next larger number of armature poles is 18.

You can make a generator with a 1-phase winding with 14 armature poles but a 1-phase winding gives a very strong fluctuation of the rectified DC-current and this isn't good for the battery if the battery is connected to a load during charging.

gsw999

  • Full Member
  • ***
  • Posts: 209
  • Country: 00
    • kernelpower Ltd
Re: Question about rotor disks
« Reply #2 on: December 08, 2016, 05:09:10 AM »
Many thanks for your reply , that is what I thought but glad someone knowledgeable could confirm the reason, I am on a steep learning curve here and feeling a bit out of my depth , so if I wired a stator single phase would all 9 coils be joined together? Thanks for your help.

The chinese have supplied me with 24mm magnets (*28) instead of 25mm and the 12" disk looks empty maybe thats why sometimes people use the 46*30*10 what size magnets would you reccomend for a 300mm disk , I have wound a couple of really nice test coils which are 80 winds of 14awg.

Appreciate any advice

Thanks

Gavin

kitestrings

  • Hero Member
  • *****
  • Posts: 1376
Re: Question about rotor disks
« Reply #3 on: December 08, 2016, 01:31:16 PM »
Quote
The number of magnets must be even, so the next larger number of armature poles is 18.

Wouldn't the next multiple be a 16-pole alternator  - 16 pairs of magnets (assuming a dual axial) and 12 coils?

~ks

Adriaan Kragten

  • Hero Member
  • *****
  • Posts: 1154
  • Country: nl
Re: Question about rotor disks
« Reply #4 on: December 08, 2016, 02:09:53 PM »
Yes, I made a mistake. The next armature pole number is 16 with 12 coils and then 20 with 15 coils. If coil 1 is of phase U, coil 2 is of phase V, coil 3 is of phase W, coil 4 is of phase U, coil 5 is of phase V, coil 6 is of phase W and so on.

It isn't clear to me why most people use rectangular magnets and trapezoidal coils. I have designed an 8-pole generator with circular magnets and circular coils which are easier to manufacture than trapezoidal coils (see manual VIRYA-2.2). I think that the variation of the magnetic field in the coils for circular magnets and circular coils is more sinusoidal than for rectangular magnets and trapezoidal coils. Gluing of circular coils to the steel sheet is also easier because you can use a gluing jig with circular holes in it.
« Last Edit: December 08, 2016, 02:33:25 PM by Adriaan Kragten »

kitestrings

  • Hero Member
  • *****
  • Posts: 1376
Re: Question about rotor disks
« Reply #5 on: December 08, 2016, 03:43:46 PM »
Adriaan,

I suspect it may have more to do with availability and cost.  It's been awhile since I looked, but it seems like there were many more choices for large, rectangular magnets - not necessarily do to home-built wind turbine market ;) - and less round types.  It would seem logical that they would be lower cost to manufacture, but I'm speculating.  The last time I looked the prices had really risen a lot for NdFeb's pretty much across the board.

gsw999

  • Full Member
  • ***
  • Posts: 209
  • Country: 00
    • kernelpower Ltd
Re: Question about rotor disks
« Reply #6 on: December 08, 2016, 04:36:17 PM »
I think I am going 16/12 I actually measured the magnets the Chinese company sent me and they are only 24mm !! not 25 as they should be lol

gsw999

  • Full Member
  • ***
  • Posts: 209
  • Country: 00
    • kernelpower Ltd
Re: Question about rotor disks
« Reply #7 on: December 08, 2016, 10:46:41 PM »
nice turbine b.t.w kitestrings !! great work.

Adriaan Kragten

  • Hero Member
  • *****
  • Posts: 1154
  • Country: nl
Re: Question about rotor disks
« Reply #8 on: December 09, 2016, 03:39:06 AM »
I have bought my magnets at the Polish company Enes, website: www.enesmagnets.pl . They offer a large vareity of circular neodymium magnets and their circular magnets are only a little more expensive than rectangular magnets with the same magnet volume.

gsw999

  • Full Member
  • ***
  • Posts: 209
  • Country: 00
    • kernelpower Ltd
Re: Question about rotor disks
« Reply #9 on: December 09, 2016, 08:24:19 AM »
I have bought my magnets at the Polish company Enes, website: www.enesmagnets.pl . They offer a large vareity of circular neodymium magnets and their circular magnets are only a little more expensive than rectangular magnets with the same magnet volume.

Thankyou I will check their website , with regards to the N grade of the magnet have you any info on is higher better ie is N50 better than N35 , does it really matter, I keep checking back on your website, cheers.

Adriaan Kragten

  • Hero Member
  • *****
  • Posts: 1154
  • Country: nl
Re: Question about rotor disks
« Reply #10 on: December 09, 2016, 11:53:14 AM »
Information about the N grade of neodymium magnets can be found on the following website if you follow the following path: www.supermagnete.de, select English, select: Good to know, select: How much Gauss has a N42 magnet, select: Go to data. Here you find a page with all relevant data's.

The higher the N number, the stronger the remanence B in Tesla and the stronger the magnetic flux flowing through the coils. In most of my KD-reports about PM-generators you find a simple methode how the flux density in the air gap and in the stator iron can be calculated.

gsw999

  • Full Member
  • ***
  • Posts: 209
  • Country: 00
    • kernelpower Ltd
Re: Question about rotor disks
« Reply #11 on: December 13, 2016, 12:31:48 PM »
I have bought my magnets at the Polish company Enes, website: www.enesmagnets.pl . They offer a large vareity of circular neodymium magnets and their circular magnets are only a little more expensive than rectangular magnets with the same magnet volume.

Is there any advantage to circular magnets?? thanks

Adriaan Kragten

  • Hero Member
  • *****
  • Posts: 1154
  • Country: nl
Re: Question about rotor disks
« Reply #12 on: December 13, 2016, 02:04:48 PM »
There are several advantages of using circular magnets.
1) If the magnet is circular, the coils can also be made circular and making circular coils is easier than making trapezoidal coils because the wire speed for circular coils is constant and therefore you can wind the coil with a higher speed. I have designed an axial flux generator for which the coils arn't cast in epoxy but then the coils must have flanges. Making flanges to a circular coil core is rather easy.
2) If the magnets are circular, one can use a glue jig with circular holes in it. So positioning of the magnets to the steel armature sheet is simple as circular magnets alway fit in a circular hole.
3) If a circular magnet is pulled along a circular coil, the variation on the manetic flux throug the coil varies more fluent than when a rectangular coil is pulled along a trapezoidal coil. This means that the generated voltage will look more like a pure sine wave and this may prevent torque vibrations.

Up to now I have tested only one very small 8-pole axial flux generator with circular magnets (see report KD 608 of the VIRYA-1 for drawings). I have built a complete armature with eight magnets but a stator with only one coil to determine the required number of turns per coil for a certain open voltage at a certain rotational speed. I have not yet tested a complete generator so its not yet proven that it has no torque vibrations. This generator has only one steel armature sheet with magnets. The stator sheet with the coils is made from phenolic fabric so no heat is dissipated in the stator sheet like this is the case for my other axial flux generators with a steel stator sheet. You need rather big and thick magnets if the stator sheet isn't made of iron but this was not a problem for this small generator. Drawings for a much bigger 8-pole generator with circular coils and a steel stator sheet are given in the manual of the VIRYA-2.2.

gsw999

  • Full Member
  • ***
  • Posts: 209
  • Country: 00
    • kernelpower Ltd
Re: Question about rotor disks
« Reply #13 on: December 14, 2016, 04:46:51 PM »
Thanks I shall read those reports on your website