 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Windmills : Why are the 7p vs 3p windings different ?
| Author | Message | ||||
Steve9R Regular Member  Joined: 24/01/2006 Location: AustraliaPosts: 72 |
Just a quick one.. checking the windings diagrams Glenn did for 3phase2pole compared to 7phase2pole.. why is it that on the 7p they're now terminating star points from the right hand side of the pole whereas it was left hand side on 3phase ? is there a reason ? will it make any difference ? |
||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Nah no difference, it was just the way I drew the diagram. Using either the left/outside/ending or right/inside/starting wire from each coil as your star point doesn't matter, so long as you stick with the same end for all the coils. Hope that helps. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| Steve9R Regular Member Joined: 24/01/2006 Location: AustraliaPosts: 72 |
Thanks Glenn.. One other question then ... while looking carefully at your dscf1080.jpeg (the picture you took of the 7P2P) www.thebackshed.com/windmill/images/FPCogless/Dscf1080.jpg Right at the bottom of the stator, you've labelled, 1 - 2 - 3 etc.. above the 3 (beneath the serial number sticker) there is a cut white wire, and to its right there is a bunch of other wires sitting in the bottom of that stator ? I have to assume these are offcuts that you left there by mistake ? You havent got your star points joined too do you ? Steve |
||||
| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Yes that white wire was a off cut, and bit of scrap I didn't clear off before I took the photo. In fact there is also a red yellow and brown wire to the right of that white wire, there were off cuts too but you cant see the ends. I should go and doctor that image to hide them. There are 3 star points on that stator, very crude looking. One is just below that white wire, you can see the 7 wires connected together. There is no need to connect the 3 stars together. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| Steve9R Regular Member Joined: 24/01/2006 Location: AustraliaPosts: 72 |
cool.. thats what i thought.. I just looked at that bunch of wires down there and thought 'what could they be for'... Thanks Glenn.. |
||||
Robert_VK2BBR Regular Member Joined: 31/12/2006 Location: AustraliaPosts: 67 |
Hey Glen, on the subject of 7P, is there any reason that 7P3P wont work on the old rotor hub? regards Robert. ps lots of wind today but of course one of my mills is down for mods! 1555 W grid connect system since Jan 08 both vehicles running on modified, used vege oil. |
||||
| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
I've fixed that picture now, did a bit of Paint Shop touch up work. The difference between the 7 phase and 3 phase is the magnet count in the hub. The 7 phase conversion uses a magnet hub with less magnets than intended for the stator we use. Basically we are using old model stators with the later model hubs. This means they no longer work as a 3 phase alternator and have to be re-wired for 7 phase, the advantage is slightly better output and no detectable cogging. If you re-wired a stator for 7 phase and used a old hub, you would get no output, it just wont work. At first the 7 phase conversion takes a bit to grasp, but I wont use any other combination now, the extra work and cost of the new model magnet hub is worth it. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| Robert_VK2BBR Regular Member Joined: 31/12/2006 Location: AustraliaPosts: 67 |
Glen can you elaborate on this please "If you re-wired a stator for 7 phase and used a old hub, you would get no output, it just wont work." If it is wound in 7 phase, why does it care how many magnets there are, or is it because they overlap etc and cancel each other out as well as adding additional cogging. I just "need" to know. cheers Robert 1555 W grid connect system since Jan 08 both vehicles running on modified, used vege oil. |
||||
| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Yeah its because they do cancel out, more or less. The "old" motors used a stator with 42 poles and hub with 56 magnets. Every 3rd stator pole lines up exactly with a magnet, so we connect every 3rd coil together because we know they are all in sync with eachother. On the 7 phase conversion ( 42 poles but this time only 48 magnets ), every 7th pole lines up with a magnet. So we connect every 7th pole together, and this gives us 7 phase power. If we connect a 3 phase stator/magnet combination as 7 phase, then we are connecting together stator poles that are not in sync. While one pole could be making +5 volts, the next one could be making -2 volts and another one -3, I could draw up a vector diagram to work it out, but you'll just have to trust me on this. One of the best ways to visualize this is draw up a stator and magnet hub on paper, or use a CAD program ( As I did when I first came up with the 7 phase idea ). Then rotate the hub past the stator and look where the poles line up with magnets. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| Robert_VK2BBR Regular Member Joined: 31/12/2006 Location: AustraliaPosts: 67 |
Thanks Glen, I do trust you in this. I can visualise what you are saying. So I will order a new rotor asap. cheers robert 1555 W grid connect system since Jan 08 both vehicles running on modified, used vege oil. |
||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
