Hi Rob,
Its really excellent to find a few people running similar machines grid tied as theres not much in the way of support for us.
Unfortunately we had a severe wind storm on Christmas eve and my mill self destructed, and I mean completely; I may be able to salvage the tower stub but thats all, theres bits of stator, winding wire, tail, stator star, magnets all over the field- BooHoo!
Anyway, onwards and upwards, Ill build a new one and have it up in a couple of weeks. I had been trying to squeeze more power out of it and playing with tail angle configurations and inverter power lookup tables etc, maybe I changed too much all at once and something happened. I dont quite know yet what because its so windy I havn't been able to bring it down. Im not sure I'll ever truly know as there are so many parameters and the 'event cascade' is difficult to unravel- did the tail boom metal fatigue and bend first or did it bend after the stator roasted and caught in the magnet rotors? I'll never know now. Ive been working closely with Dan Lennox (well known on fieldlines) to develop his 'PowerDashboard' monitoring software and we had just finished a working version on Xmas eve but I hadn't installed it yet, wanting to do more testing in the workshop before I put it on site. Damn, I wish Id installed it because it may have given clues as to what happened to cause such a calamity. Anyway , next time Im gonna have every parameter logged.
I should add this machine was functioning well for two months and putting out 6.5kw in a good wind, then I started getting those dreaded ground faults. I pulled the whole thing apart, completely rebuilding it, increasing the stator gap just in case there was an occasional rub (which Ive been told can cause a Ground fault), adding some bits like a neoprene washer above the slip rings to avoid grease dropping down onto the rings and affecting conductivity. Tweaking is important to get the most from a particular machine but I tweaked something wrong or mis-connected something and payed the ultimate price. $#|+, its so dissapointing to see all that work ruined- excuse me blowing off steam at your expense!
I'll deal with the points you raise in your mail in order-
Great to see another person with a similar setup as mine. Now that their are several of us with 17-20' Axial Flux wind generators with Power one inverters we should be able to learn off of each other. Mine is a 17' based off of the Dans design. Mine is wound a little higher voltage than yours. It's on a tower just under 100' in USA. Here's a link to details of mine. http://fieldlines.com/board/index.php/topic,144309.0.htmlMine is on an 18m hydraulic tower, a big piece of engineering but very permanent and easy to use when made. Its galvanized and will last 70 to 100 years. Its 18ft diameter, Dans design based but with lots of extra development. I wound lots of different coil configs and eventually settled on 81 turns of 3 in hand 0.95mm dia 200*C wire. Each weighed in at 485grams of copper, as much as I could cram in- I will wind my replacement coils with 2 in hand to raise the voltage a little as I see this as a potential problem, it worked fine for a while but I decided to increase the stator gap from 2mm each side to 3.5 mm because of the ground faults.
What increase in voltage would you expect from this change? Going from 3 in hand to 2 in hand I reckon should give me a third extra voltage but is this the way it works?
I made my tail angle adjustable too. I would love to see a picture of how yours is setup. I also added removable end sections of the tail that lead shot can be added to. Currently mine is furled at 25mph and starts furl about 15mph.My design is adjustable from 11 to 18.5 degrees. Ill post pics when I work out how to.
You have done a smashing job on your machine and have tackled some of the problems I see with the original Dans design: namely, tail shocks, lack of slip rings, metal on metal yaw bearings
I set my dump load to switch for the inverter when it comes on. I thought it might be safer for the inverter, but I'm sure it would transition between load and inverter if it was setup to leave the inverter on. I also figured this way the load condition wouldn't be different if the grid was lost. I'm still not sure which is best?I have my dump set to come on in parallel with the Aurora, Im thinking the dump will take off any overspeeding and still allow the inverter to sing to the grid. I have never seen V above 250V even when at full power (6Kw) but as stated I'll wind coils for higher next time. The Powerone is most efficient above 200v (98%) and has a sharp fall off in efficiency below this so Id like it to hit 200V when its putting out anything over 1000/1500W. The inverter applied load seems to keep the voltage way lower than I expected it would; the amperage rises quick and I expected the voltage to rise at the same rate but it seems to rise much slower. Had I known this I would have designed the system differently from the start but I had no experience with inverters to guide design.
The only time I have had a ground fault problem with the inverter was when I first hooked it up. One of the Delta brand lightning arrestors that I had hooked to the power leads at the tower was leaking across the terminals internally. Replaced it and haven't had a problem over the past 6 months.
Would love to see you Aurora Power curve. Mine is posted in the link above.
My dump load is 20.4ohms when measured between any two legs of the three phases. I'm not sure how this compares to your system. I've turned it on at 300VDC and it slows the turbine more than the inverter, but does not make it stop. One nice thing about my dump is that I can wire the resistors differently to adjust the Ohm rating.My dumpload is a commercial 9Kw 3 phase crane braking resistor bank in an enclosure. I worked out my phase resistance was 6.35ohms and ordered a 16ohm total resistor. I feel this was too high and will recalculate for the new stator and probably have to buy another Dumpload to match. Speaking of which that calculation was done by working out the single wire resistance for the length of wire in the coil and then multiplying this by 3 (for the 3 in hand), I reckon this is bogus now as doesn't the resistance reduce with extra wires in hand? I reckon my dumpload should have been a third of the resistance I ordered at about 6ohms. This would have been a much harder brake which I see now would have helped. I find the whole resistance thing decreasing with extra copper hard to get my head around when it comes to multiple wires in hand and 3 phase values etc.
I'm not using the Power-one Wind Box rectifier. I attempted to build a frequency generator to be able to hook to the inverter to see the frequency and rpm on the communicator software, but can't seem to get it to work correctly. Are you using the frequency outputs on the Wind Box? No, the wind box is just an expensive rectifier and does NOTHING else properly as I have found. It need lots more development by Powerone before it could be considered a must have bit of kit. The fusing doesn't work properly, nor does the brake activation.
The PowerDashboard Dan Lennox is working on with me is going to be the BEST measurement, logging and control software available and is designed specifically for the Axial flux machines we build- he has built a mill too and is applying his experience to the problem exactly as I would if I were to develop monitoring software. The PD measures everything without needing to connect the inverter outputs. Itll read volts, amps, watts, RPM, windspeed and direction (with the proper anemometer of course) and allow remote switching and control/shutdown etc.
The way the fuses in the Wind Box are suppose to work is that at around 550VDC it automatically shorts the legs together. This is suppose to blow the fuses, but according Rob Becker of Solacity, just blows all the capacitors in the box. Which I guess is better than blowing up the inverter.Yea, as I said the Windbox needs lots more work.
I've been getting pretty good output out of mine. Average low wind day I get 6-10kwh, windy days 25kwh, and my best day so far was 36kwh. What are you seeing?Ill get back to you with data- Id love to have a graph with every parameter logged, this would be the most informative and remove the guessing Ive been doing so far.
Thats really good output on yours though, well done!
Would love to see more about your system.