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Forum Index : Windmills : visual effect of capacitors
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
My 24VRE setup with battery inverter loading and grid connect inverter for diversion load had been more than sufficient to handle all generated windmill power for months of testing, including many stormy periods with high winds, prior to the adding of series caps to the F&P windmill. Following the last mod, of allowing the AC of the F&P mill above the series caps to be unrestricted, [removed the rectifier directly to the grid inverter], the output power has increased to a point where I now have too much power and the windmills are shutting down. Total kWhr back to the ACgrid has maxed as well on 2 days. My total windmill system has produced 8.5kWhr over the last 2 days. The F&P was probably just over half of this. Both mills were electrically braking during the peak winds of 35-40kph. The adding of capacitors to the F&P mill has changed my system from dynamic adequate handling of power, to one with more surplus, where the diversion loads cannot cope and the windmill systems have to shut down. I am prepared to increase the diversion loading capacity, but this illustrates that more power is produced to the loads. I intend to mod my Axial flux mill with a similar setup when I get a chance to service and photograph it. May need to extend the Yaw box housing. Gordon. become more energy aware |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi all, As a followup, I have exchanged the 470uF 180V series capacitors for some 330uF 400V items [that bryan gave me to test], in the std back to back arrangement. I have noticed only very minimal difference in mill performance. The mill is slightly less loaded, as the mill achieves a slightly higher rpm with the same output. This is a 30% decrease in cap value, for a minor effect. I will have to wait for some stronger winds to see if top end performance is changed. I have a suspicion that the F&P windmill performance will not change much over a wide capacitor value range. If smaller caps are used, the mill will settle on a higher rpm, where the cap will pass more energy. If larger caps are used, the mill will operate at a lower rpm, and pass a similar amount of power. In the extremes, the largest cap will have performance similar to direct connection of the mill to the rectifiers. In the opposite extreme, this is the same as disconnection of the mill from the load. There is probably a perfect capacitor value for the purists, but it seems as though around 200uF per phase leg is a good starting point for a F&P mill that has an upper output frequency of 200Hz. PS I have heard on the grapevine of testing of capacitors being done on a Chinese windmill. Will need to follow up on this. Gordon. PS edit: My AxFx mill has been lowered, photographed and serviced. I will not be testing caps at this stage. Not enough space in the yaw box. The photos of my AxFx mill internals appear on p7 of the F&P@PE thread. become more energy aware |
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Gordon, could you elaborate about the "std back to back arrangement" please? Do you mean 2 polarised caps connected back to back? Thanks Klaus |
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Bolty Regular Member  Joined: 03/04/2008 Location: AustraliaPosts: 81 |
This is a fascinating field of interest! How often can you get something for almost next to nothing?? Although my turbine is a Chinese 1 kW system, and it's characteristics are quite different, I intend to follow up this excellent thread. This will allow me to see if I can learn how to do it with my turbine. At present my grid-connectinverter is being checked under warranty, so I have no load to test the capacitors. Hopefully it will be returned soon! In the mean time I have been experimenting with different values of capacitors. I have started with 2 470 uF, 200 volt electrolytics back to back in series. ie the positive of one joined to the positive of the other. This effectively produces a non-polarized capacitor that allows (polarized) electolytics to be used with AC. As Gordon has suggested, these are placed in series with each of my 3 phase legs from the turbine leading to the bridge rectifier. In other words each capacitor (pair) allows the AC to feed from the stator winding to the rectifier. I am very conscious of the need for the electronic brake to still control the turbine. As I currently have no load my testing has consisted of shorting out the bridge rectifier DC output to simulate the electronic braking. This is what the Latronics turbine controller does to apply the brake. Unfortunately the series combo of the 2 of 470 uF equalling 235 uF is insufficient. The turbine tends to still run away with moderate winds and the brake is ineffective. Near the revs that would normally be maximum power, the turbine produces around 67 volts at about 35 hertz into these capacitors. A rough calculation suggests that I need to increase my capacitance to around 2000 uF per phase. If I use readily available 470 uF capacitors, this will take a significant number to get the desired capacitance... 48 in fact for the 3 phases! I am slowly collecting these capacitors to continue my testing. If my inverter returns shortly, I will conduct some tests using the existing 235 uF, but being very watchful to prevent run away! |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi tinker, the capacitor arrangement was shown back in a post on 28/9/08, p8 of this thread. This was the connection I used to convert polarised electrolytic types to an effective non polarised type, that is good enough for testing. My ultimate goal is to replace this with a polyester/other type non polarised type, once the cap size is settled on. Polarised caps are common and large sizes are found in junked SMPS. All of my testing on the F&P is done after the mill shorting switch, that is on the AC and the first component in the wiring from the mill. I also have a 3phase switch across the caps, so I can simply put them in or out of cct, without risk of mill runaway. My high power testing has to be done on the mill, in a blow, so safety comes first. Safe testing. Gordon. become more energy aware |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I have finally set up an anemometer in reasonably close proximity to my mill, within 2m. I have not been able to get any objective graphical data yet, but I have so far confirmed that the power output from my F&P mill does not follow the wind energy curve very well. Even though I have recorded 600W from this mill and the cutin is at low windspeed, All I can confirm is that a boost cct definitely gives additional current at the low end[<100W power level], and capacitors increase current at the top end[>300W power levels], measured at the same comparison windspeeds. The capacitors if too small do reduce the mill output at the low end [<50W power levels]. The capacitors do work across the full range of mill output power, and I have used 160uF and 235uF with good effect. I have yet to try 470uF, but I think this may be an even better match for my mill. A sensor in the middle of the rotor may still be the only way to measure the windspeed, that the rotor sees, to allow accurate wind power measurement. I may be persuing a futile exercise with this, as the best testing may only be achieved on a test bench, or in a wind tunnel. I will leave this to someone else. Gordon. become more energy aware |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Well the use of capacitors has progressed to another level. I had tried a third rectifier across the mill to load the mill when the rectified AC voltage of the mill on my 24V system rose to >48VDC, so I could directly feed my PVE1200. This reduced total output by effectively clamping the top end rpm and giving current limiting again. I have added additional capacitors to AC couple to this third rectifier. The rectified AC has been up to 130VDC so far. This is the same 100S in delta stator that is still connected to my boost cct and the 24V battery and now the 48V grid inverter. I have recorded first level, up to 3A in the boost cct, then the 20A into the battery at 28VDC directly, and then an additional 5.5A into the grid inverter at approx 60VDC. This is a total of 890W. I still have some work to get the cap sizing right. I have now 165uF in each output on the rectifiers connected to the battery. I have an additional 165uF in each output of the rectifiers connected to the PVE1200. I will increase the 165uF to 330uF and then to 470uF. It maybe that 1kW output for a single F&P stator with ferrite magnets on a windmill is possible. Remember that the mill has had no changes to the furling or blades or location etc. I have merely controlled the loading at each voltage level. What this means is that my 24V nom output windmill starts charging my battery when the mill output first reaches 12VDC. If the battery SOC is low then output is clamped by the battery to approx 600W. As the battery SOC increases to a point where diversion occurs, then power increases to approx 890W so far. As the battery becomes fully charged, all the power is diverted to the grid inverter, or backup diversion loads. This is a seemless process, with no switches. There is a 12V-28V variable boost converter on the mill to the battery. There is a 24V-75V fixed boost converter on the battery to the PVE1200. I still need battery voltage limiting protection and an additional voltage limiting protection on the PVE1200 at 95V. It is hard to imagine the capacitor coupling able to simultanously provide current to the battery at 24VDCnom and at 60VDC+ to the inverter, from the same inductor. The caps provide DC isolation while still allowing power transfer. This is like having a whole series of windings in parallel, but there is only 1. I do not think there is much benefit in any extra cap ccts past 2, as the mill is running out of output. I cannot make more use of any additional voltage either. This has been a very useful exercise so far. The output loading is now getting closer to the wind energy curve and the power levels are pretty useful as well. I may have to replace the chinese battery controller as it interferes with operations now. Gordon. become more energy aware |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I think this thread is reaching a conclusion. After some initial early discussion not much feedback comments from the posts has happened recently. I can see that the thread has been viewed a lot, but has not stimulated much more discussion. I had thought it may be worthwhile to spend some time and draw up the electrical wiring diagram for the multiple capacitor rectifier configuration I am using and present it here. This seems of little point at this time. This seems a good time to give this a rest, maybe come back with some more findings next year, unless other readers reveal results of related testing. Gordon. become more energy aware |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Yes we have battled on with just about every concievable angle that could be covered. You have done excellent research and work, but I agree, there is not much more to discover. We know that caps work, and work well, and provide a very flexible coupling system to high pole count generators, allowing for wildly better matching to the batteries, and just about anything else too.... heating (Zubbly), grid ties (Gordon), and batteries (Bryan and Gordon). In my mind it would be sad for you to have established as much as you have, without tieing it all up with useful F@P circuits and uses, and for Glen to put them in the archives..... beats the Bonox out of rewiring. The inertia of people being happy with their current systems will continue for a time, but sooner or later when upgrades appear necessary, we may find more mills better matched to their loads..... via caps. Well done. .........oztules Village idiot...or... just another hack out of his depth |
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| Jarbar Senior Member Joined: 03/02/2008 Location: AustraliaPosts: 224 |
Gordon , I for have been looking forward to seeing a wiring diagram and some photos.I have followed every post you presented here but feel out of my depth in commenting on your achievements.Well done and thanks for taking the time to relay your experiments. 
Anthony. "Creativity is detirmined by the way you hold your tounge".My Father "Your generation will have to correct the problems made by mine".My Grandfather. |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
Hi Anthony, Wiring the caps up couldn't be simpler, just get atleast 6 high voltage polarised caps(ie: 250-400 volt) solder the negative terminals together on each pair. Then connect them is series with each phase of the genny. If you have a dmm that reads uF even better as the uF will halve and thats a good check to make sure you've done it right. I used 470uf for mine and I gave Gordon some 330uf caps to try which he has spoken about already. Thats how easy it really is. Cheers Bryan 
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Don B Senior Member Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Gordon, With your DSO, is it possible (or have you been able) to measure the angle between the current in one phase, and the phase to neutral voltage of the same phase from the alternator (ie phase to neutral voltage before the series capacitor)? I imagine that this angle should approach zero when you have the optimum value of capacitors in series. This is the resonance case (or, if you prefer, 100% power factor correction), and should be the point at which you get the maximum output for a given shaft speed. Regards Don B |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Don, A final death throw. I have previously looked at AC voltages and currents, independently. I was interested purely in levels and the what the waveforms looked like. I am probably more interested in my 100S being able to simultanously charge my 24V battery and grid inverter at approx 60V with no DC-DC converters, with the same mill winding. I have to be careful with the DSO, as the inputs are not optically isolated like a FlukeMeter and there are specific voltage limitations. I may be able to cap couple the voltage onto channel B, while measuring the current from the voltage drop across a shunt in the same phase with the channel A. The arrangement I have now consists of more complications with additional caps and rectifiers. There is an uneasy balance I have to achieve in order to maintain maximum power at a particular windspeed/rpm range. Since I have been monitoring windspeed and power at >20 readings/sec, I have been able to compare output with different configurations. I have been switching caps on/off and comparing outputs and also maximiser on/off, and other combo's. With the additional caps, I cannot easily measure total outputs, as the currents are at 2 different system voltages. In an ideal test environment, the input power and loadings are completely controlled. I only have the option of comparing measurements from my mills up on the tower in the wind. I have been hoping that someone with a test setup that can operate to power levels above 1kW outputs, and are not concerned about what happens to the energy would step up and perform the bench testing to satisfy the academic readers. Bear in mind that much changes when tests are compared from the bench to a working windmill. I see no simple solution to this can of worms. I am not trying to scientifically establish the electrical relationships, as this would have already been done, but just allow my mill to produce as much power as possible at each wind energy level, and of the power I cannot use from the battery, that as much as possible can be used in the rest of my home appliances, and the minimum is diverted to dump loads, without making any changes to the mechanics of my windmill. Remember that this mill in the original setup produced around 280W max. My 2 mills could barely power the TV. Now I have had the TV on and have recorded 550W fed back through my grid inverter. On the windy days I have used used over 4kWhr in my home this way. I am looking at changing the rotor blades, and the process of capacitor selection may need to be refined again, maybe not. I have tried to at least keep as many variables constant, as if I changed too much, I would not know what did what. I intend to have the same blades on each mill. These will end up being similar to my Lakota blades, but a foot longer. One thing of benefit in the process I have adopted is that I have not needed a complicated electronic maximising system. At the end of the day, there is very little to go wrong, and I have essentially 4 parallel systems. I have built in redundancy as well. This is not a succinct solution, but is one that probably anyone could adapt to. I have just realised that the capacitors can be used in a slightly different way to independently charge 2 series connected 12V systems, effectively in parallel, to give a low cutin, and then as the wind power levels increased and the rpm/output voltage rose, then a separate rectifier could charge the 2 in series 24V combination. This could be expanded to a 4 battery setup as well, for a high rpm range alternator. This just requires capacitors and rectifiers. A 12V stall limited mill could probably still be used on a 48V battery bank, with only the one winding in the mill. As long as the operating rpm of the mill was a 4fold multiple of the cutin voltage. I see this arrangement could easily be adapted to a VAWT, as long as the output frequency was sufficient, where low voltages maybe output, but a high voltage battery may still be needed. I am sure this is not a`new idea, but does not seem to have been exploited much. Now is possibly a good time. Gordon. become more energy aware |
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fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Hi Gordon , As we quite often talk over the phone ,I will add this to this thread , when my present predicament is fixed I will throw whatever support that I can to help to do into getting the most out of caps and F&P Gens , as you know I can set up a fairly good test bed with my lathe , and now have the dual piclog for testing one mill against the other , my electronics skills are not worth 2 bob with this so I can only offer what I am good at , Keep up the Good work , by the amount of hits on this subject there is a lot of people interested but I think like myself it is way out of my depth of understanding and by reading your findings is giving me the knowledge to have a go and see if I can let the smoke out !!! PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi phill, I am sure that with your lathe as a test bench, and me sending some mud maps to try out, that some progress can be made. Hi oztules, The problem with inertia is that eventually the driving force diminishes and things stop. I will wait a while to see is there is discussion on multiple capacitor configurations though. It is a bit too early since my posting. The ability to control impedance with capacitors will open a few doors with better mill loading. This may be a difficult concept for readers to visualize. I will be testing a combination of 12V sub-blocks on my 24V battery in place of the boost maximiser as a start. The prospect of no switching relays, star/delta type switching, or DC-DC converters or controlling electronics, coupled with the thickest single coil type alternator wiring for the desired system output voltage will probably be appealing to many readers. All the electricals are located at the battery, and only normal mill wild AC needs to be transmitted. This will not work if the mill has DC output though. I am looking for a low tech, long life solution to mill loading that will not be dependent on if a particular IC, or transistor, or programmer will still be available when things go wrong. All of these basic components are located between the mill AC electrical brake and the load and should always be available. Gordon. become more energy aware |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Jarbar and phill, here is the basic low rpm/power cut in schematic with caps. This will halve the effective mill cutin rpm. The low end power of approx 5-30W will be gained, where none would normally be available. It is assumed that the usual 3phase rectifier would still be connected directly to the battery, so upper power levels would not be changed much. If the caps are too large, the impedance will be too low and the mill may stall. The formulae Z=1/2piFC can be used to check the cap loading. 
I have used 2 x 2 bridge rectifiers. There are a total of 12 caps for a voltage doubling function with polarised caps. This simple mod will allow the mill to be closer to ideal, where if it spins, it produces current to the battery. No switches/winding changes etc. This will even work on chinese windmills and axial flux mills. There will be some diode loss on a 12V system. Gordon. PS edit. As has been pointed out by Gill, in a subsequent post, there is no connection between the rectifiers and the centre connection of the battery. become more energy aware |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Excellent work and a great effort Gordon! |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
So, lemme get this straight..... after years making dc/dc converters, pic programming, double sided circuit boards, ground planes and mosfets............. it comes down to a few skungy caps and some diodes.... how does it feel 
Well done Gordon, It seems you have tied up the last loose ends, and have defined a simple eloquent solution to what has been very difficult problem.... matching the load. Well done. This should go along way to clearing up the benches there. Some of us have too much wind (I blame the beans), too big a prop, and too small a battery bank to require this solution, (we'll see how much the new EV uses yet), but most will benefit from your research.... if they want to improve their systems. Many a good mosfet has laid down it's life in search of the perfect load matching device, only to find that they have been beaten by a humble cap and diode array.... strange world really. 
At one stage I had a great appetite for a high tech solution, but since building my mill, and seeing what potential it had to destroy all things silicon (except for the diodes), the high tech road has lost it's appeal. Furling is never going to tame the mill all the time. Overcorrection will always pull many kilowatts for very brief moments, and will test any circuit to the limit. This simple agglomeration of caps and diodes seems very able to handle the transients that I have worried about. ...........oztules Village idiot...or... just another hack out of his depth |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
[quote=Oztules]In my mind it would be sad for you to have established as much as you have, without tieing it all up with useful F@P circuits and uses, and for Glen to put them in the archives.....[/quote] Oztules, you mean something like a management summary for those of us who got lost halfway through the thread... ? 
Seriously, a short explanation/summary of the idea, theory behind it and how to execute it practically may help a lot for disseminating this (obviously new and working?) idea more widely. Would probably make good stuff for the backshed frontpage too. One must be *very* motivated to read through this entire thread. It was useful for what it was, helping out during the experimental stage, but now that everything is more or less worked out, a good summary could mean the difference between the idea falling back to disuse and obscurity, or widespread use. Would also prevent the same questions being asked and answered about how to execute/implement it dozens of time in the future. Wouldn't have to be a full rigidly-scientific paper... Just a summary and advice on how to practically implement it. A few schematics for clarity. Some capacitor values. Some do's and dont's, etc. [quote=Oztules]The inertia of people being happy with their current systems will continue for a time, but sooner or later when upgrades appear necessary, we may find more mills better matched to their loads..... via caps.[/quote] One necessary condition is that people understand how to do it. For me, as someone who observed from the sideline... can't say I fully comprehend it all. Doesn't matter much anyway as I don't have F&Ps to play with. But still. Bet the first people to whom Einstein explained his Special Theory of relativity felt the same... they sensed it was big but just didn't comprehend it (at?) all. 
Peter. |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi dinges, The voltage cutin boost type arrangement as shown in the schematic above will work on low polecount alternators as the capacitor sizing will be relatively modest to still obtain useful benefits. The F&P can however benefit across the full output power spectrum. No 1 should miss out on some benefits. Oztules has commented above, I could have saved myself a fair bit of effort with the boost maximiser, as the caps pretty well cover this function. I have another similar concept that does the reverse function, that is take a series string of batteries and convert this to a voltage at the single battery voltage, without any transformer. This will have to wait another day as it is not directly related to this thread. Gordon. become more energy aware |
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