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Forum Index : Windmills : 7 phase problem
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Highlander Senior Member  Joined: 03/10/2006 Location: AustraliaPosts: 266 |
Hi Glenn, this reminds me of what Dr Chalko was talking about. Have a look at part 6 2007-12-15_095605_SD_modification.zip Is this relevant?   Central Victorian highlands |
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Thanks Glenn, Being the curious type I did more investigating today. First was to remove the links between the 3 star points - made no difference as I expected. Then I disconnected all the phase inputs from the diode bank, rectified a single phase (the 6 others left open cct.)with the other input taken from the star connection. This still had a perfect sine wave AC input to the rectifiers when the DC side was loaded. I tested all phases individually in turn to check if any were differend - not so. It appears that when more than one phase is rectified the distortions appear on the AC waveform. Now I'm leaning towards Gordons suggestion and individually rectify the 7 coil groups, requiring 28 diodes. Got to get myself more of them, the 3A ones are only 50 cents ea. It will be interesting to see if that connection still distorts the AC waveform. The stator might have to be re connected to 3 pole to keep the volts up, more fun  .
While your published 7 phase star connection obviously works and produces a useful output, I feel the waveform distortion is the culprit of heating up my diodes. Klaus Klaus |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
[quote="Tinker"]It appears that when more than one phase is rectified the distortions appear on the AC waveform. [/quote] Klaus, I imagine that when current is allowed to flow in the second phase it introduces a change in the magnetic circuits of the stator, the metal of which is shared by all phases. I would not be suprised if this distortion evened out when all phases are loaded equally. I would have thought that any distortion caused by diode action would show near the zero crossing though I find it not inconceivable that diode noise in one phase could introduce distortion to other phases which due to phase difference would show up at a different point in the cycle. Presumably each phase goes effectively open circuit from the point when the conducting pair of diodes turn off just before the 180 degree phase point and when the other pair of diodes turn on some time after 180 degrees and Doc Chalco's capacitors smooth this transition. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Yeah I still think those ripples on top of the phase peaks are normal. When a AC source is loaded down with a DC drain, you will get a flat top to the sine wave. What we see on that flat top is just the other phases switching in and out. I've made a few changes to the rewire page, the 3 phase rewire. Just a mention about cogging and how we can reduce it, finishing off with a mention of the 7 phase conversion. Hopefully this will clear up some confusion for beginners. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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dazler Newbie  Joined: 21/10/2007 Location: AustraliaPosts: 37 |
hi glenn thanks the update, but apart from going out and buying a new hub (i have the old 14 magnet hub) is there a way to decog the f&p more?? like this link http://www.thebackshed.com/Windmill/images/Dscf0548.jpg i have done this a bit but by doing it more than this "link" would it reduce the power?? thanks guys just trying to get my F&P in the sky:) darren |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Hi Darren. The rounded stator poles is really the only way to reduce the cogging without changing the magnet hub. Its a bummer, but there's not much else we can do to the stator. Yes there is a slight reduction in output power by rounding the poles, but we also gain because the windmill starts in lighter winds. If you stick with your current stator and hub, there are other ways to overcome the startup cog problem. One way is to use a floating hub, where the turbine can free rotate for a few degrees before it engages the shaft and hub. I dont know much about this technique, but other forum members have used it. The other way is to get more start up power from your turbine. My current windmill is a dual stator, not decoged, 3 phase setup. It cogs badly, even though I tried to offset the stators to cancel the cogging out. I couldn't get the alignment spot on and it feels like it cogs about the same as a single stator. But my turbine is built to run in low winds, its a 6 blade at about 2.5 meters diameter, and with its large surface area it starts in the lightest of winds. Another forum member, Adelaide, has added plastic sections to the root of each blade. These increase the area to make starting easier, while at the same time have little effect on high speed performance. Hope that gets you pointed in the right direction. Glenn I should add, on the subject of rounding the poles, it is possible to go too far. There is a sweet spot, like in the photo, go past that and the cogging starts to get worse, AND you loose power. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Highlander Senior Member Joined: 03/10/2006 Location: AustraliaPosts: 266 |
G'day Klaus (Tinker), those bannana shape ripples are interesting. It may be a waste of time, however it would be interesting if you connected some caps (50-150uf) and had a look at the wave. If those bannanas are the peak of each phase then wouldn't it be harder to have an even current when you increase the number of phases? Central Victorian highlands |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Hi Highlander, The ripples only appear when more than one phase is rectified and supplies a load current. I left the star connection intact and tested with one only (of the 7) phases connected to the diode bank and there were no ripples at all on the AC, perfect sine wave. The ripples & wave distortion starts appearing as soon as more phases are connected to the diode bank. BTW, with all connected, at no load there is no distortion. When loaded, there was little difference in distortion at 2.5 or 5.5A. Which lets me to the assumption is caused by the interaction of the phases in star connection. What I will try is not increasing the phase numbers, rather making them independant by removing the star point. The power would be tapped from each end of a coil group and I would still have 7 groups. In theory this would give 7 time displaced AC peaks per revolution, just like the 7 phase star did but, hopefully, still sine shaped and without those ripples. This means more wiring links, basically duplicating the links that are now on one side of a coil group to the other side as well. This requires 28 diodes for full wave rectification. 3A, 40V schottky diodes are 50 cents at Oatleys so it not a big expense. I have a few small (50V) non polarised 100uF caps, was yot yet game to see what happend when they are connected. Klaus Klaus |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
I have a hunch that if you seperate the star point, rectify one phase,and apply a DC load, you will see a flat top sine wave. If you rectify all the individual phases, and combine them together on a DC load, you will get the same result as before, with a flat top sine wave with those little ripples. But I could be wrong. 
I really need to make myself a F&P test rig. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hmmm, I still suspect the little ripples are caused by the magnetic circuit of one phase interfering with the magnetic circuit of the others. |
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Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
G'day Gents, I feel this subject has been covered before. It is the reason Herb suggested IndeS earlier in this thread. Consider this, We start with a Y but as one phase rotates past 0 it's diodes no longer conduct at 0.7 V(silicone type) either side of the 0 line. This is an imbalance in the other two phases and shows as inductive reactance. According to Dr.C this can be corrected by the addition of capacitive reactance (capacitors) but this reactance varies with frequency and therefor is most suited to micro hydro where the rpm (hence Fq) is more stable. Note: Single phase = not rectified & no other phases to imbalance. Multiple phase @ no load = no current passing through diodes so no imbalances. Multiple phases with load = As explained above. I have noticed most old wind-millers here and abroad use Inde be it IndeS or IndeP or switch between the two. What Tinker has just discovered (even if he doesn't know it yet) is the solution to the bumpy trace for wind mills. Unfortunately he is not the first, but well done. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
[quote]Consider this, We start with a Y but as one phase rotates past 0 it's diodes no longer conduct at 0.7 V(silicone type) either side of the 0 line. This is an imbalance in the other two phases and shows as inductive reactance. According to Dr.C this can be corrected by the addition of capacitive reactance (capacitors) but this reactance varies with frequency and therefor is most suited to micro hydro where the rpm (hence Fq) is more stable. [/quote] As Tinker has observed one phase alone is not distorted and distortion is there even with the star points disconnected. As far as I can see the only remaining connection between the phases is the magnetic lines in the stator core. When there is current in one phase the associated magnetic flux passes through some of the same metal of the other phase, for most of the cycle this flux is smoothly changing as current changed but the diodes switching cause the current to suddenly change and hence the associated magnetic flux. A rapid change of flux acts like a transformer and induces the distortion in the other phase(s). Thats my theory! 
The addition of capacitors would smooth the sudden change in current and significantly reduce the transformer effect as relates to the distortion. |
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herbnz Senior Member Joined: 18/02/2007 Location: New ZealandPosts: 258 |
Hi I have no experiance 7 phase. I have been looking at reconnections that you do all makes sense but I could not find any referance to type stator used 100,80,60 ?? Is this why some are experiance problems using different stators The ones in the photos above nearly look like 60's. The flaterning of the waveform under load is the current limit when the stator mmf is approx egual to rotor mmf this point voltage will fall to maintain constant current Happens about 200 ampere/turns. with old rotors but these new rotors I dont know strength of. The humps would be when another phase supplies some of the dc load and current in this phase goes down voltage up. I am assuming you are using a resistive load not a battery. Confirm the type stator and load . This is my opinion Herb ps on your scope bring the two traces together and see if the humps line up with a hollow if not swop one trace to another phase i think you will find one that lines up not all three at once. Edited later been giving some more thought and some aprox calculations voltage drop not current limit but due to impedance in winding when that peak is supplying current in my opinion |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Herb, the winding wire of my F&P stator coils measures close to 0.7mm. This would make it what you call an 80 series according some info on F&P elsewhere on this site. You are right, I did my tests with a big resistor, unfortunately it has only 2.3 & 4.6 Ohm tappins but it can take the load without getting too hot so I'm using it. I will try to do that trace swapping you suggested soon, also using a battery with a load connected to have a more realistic load. Glenn, watch this space, I am working on a F&P test setup and post details soon. Klaus Klaus |
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| herbnz Senior Member Joined: 18/02/2007 Location: New ZealandPosts: 258 |
Test setup mount either drive motior or generator so housing is only stopped rotating by a spring balence. Then accurate input power can be assest. (like a dyno tester ) nearly .7 dia more like 60 re Id of stator Herb |
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aussiekiwi Newbie Joined: 08/12/2007 Location: AustraliaPosts: 10 |
hello everybody well had a good weekend got my 7 phase rewired and it works good no cogging just got a couple of questions this is going on my wind turbine got 13ft prop and is going to be gear 3 to 1 any suggestions on want to rewire stator too have already got one rewired to 7p2p and what sort of controller or regulator to control in high winds thanks any help would be great |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Herb, close to is not the same as nearly . I measured MORE than 0.7mm eg. close to. But precise measurements are not possible after scraping off the enamel insulation.
Re your test setup, I am not interested in adding that complication. Not interested in input power at all nor in efficiency. I AM interested what sort of power I can get out of a F&P wether its driven by my lathe or, later, a propellor. Klaus Klaus |
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