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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 09:42pm 06 Jan 2009
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Hi oztules,
The AxFx magnetic rotor disc and Al plate idea. This would allow the rotor to spin with low coupling at low rpm, and overcome starting cogging. I suspect to go to this length, the effort may be better spent to just make an AxFx alternator in the first place.
Gordon.
become more energy aware
Robb Senior Member Joined: 01/08/2007 Location: AustraliaPosts: 221
Posted: 11:55pm 06 Jan 2009
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How about a DC-DC converter with a programed power curve mapped to RPM. Sounds like a job for a PIC expert.
The car clutch if slipped is basically throwing heat into the flywheel = waist. They don't have oil coolers on auto transmissions because they are efficient.
KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691
Posted: 01:31am 07 Jan 2009
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Thats true but both the car engine and the wind turbine suffer from inability to make serious power at low RPM, in both cases let it slip a bit and give it a chance to get up to speed and make some real power.
SparWeb Senior Member Joined: 17/04/2008 Location: CanadaPosts: 196
Posted: 07:46pm 07 Jan 2009
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Hey I want to jump back to the mention of a magnetic rotor plate for another second. I remember putting my axial flux rotors on the lathe, and instead of the stator being in between, I stuck various things in between as the lathe spun the rotors. Solid blocks of aluminum produced significant amounts of torque, yet strips of aluminum, taped together to have the same volume as the solid, had much much less. The same laminated piece, when turned 90 degrees caused just as much torque as before. It was lots of fun, food for though, but I didn't dwell on the science or practicality of it at the time.
If you wanted to make a coupling like this, it probably wouldn't take much aluminum (start with a disk 10" diam and 1/4" thick) to make a coupling that would freewheel at low RPM and then "catch" at, say 100 RPM. Testing on a lathe would allow fine-tuning of the disk, and to learn the speed ratios to expect.
The blades would always turn faster than the generator. Usually one wants the opposite to happen...
Steven T. Fahey
Robb Senior Member Joined: 01/08/2007 Location: AustraliaPosts: 221
Posted: 11:14am 08 Jan 2009
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100% right. And thats why a car has a gearbox not just a big clutch.
Now the load in a car and the load in a PM alternator is vastly different.
The car is a heavy mass that must be accelerated from stationary. Most of the engines power is used to move the car along and the gearbox helps get it up to speed.
Now a PM alternator on the other hand.......
Open circuit and the alternator provides little load and we all know about over RPM issues on open circuit turbines. So we don't need clutches or gearboxes to get an unloaded PM alternator up to the ideal RPM range of the turbine.
So my point is a mapped DC - DC converter in the context of a wind turbine is what a clutch and gearbox is to a car.
No need for a clutch or torque converter in a diesel electric locomotive either
KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691
Posted: 02:35am 09 Jan 2009
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Nothing much there to argue with Robb though I feel some of your comment does assume a neglibible friction/cogging alternator.
If we are going to use smart electronics we should be using more than RPM as the input. Comparing RPM to wind speed (from an anemometer etc) would give relative wind angle and from that we could determine if the load should be increased or eased for best output. Lots of ways to vary the load, circuit switching, PWM, switching in reactance........ probably more.
The anemometer has to be right at the mill, maybe on a pole sticking up above the blades?
Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1461
Posted: 06:44am 09 Jan 2009
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Ok time for me to add my 2.2 cents worth in this useless thread...
<rant>
If this so-called idea was a real goer don't you think it would be on commercial wind gennies ???. The basic concept of DIY wind gennies is USE THE KISS PRINCIPLE.
It well known here in Oz 99% of the time the winds are low to meduim but once in while we get 100K+ blows. The F&P wind genny has come a long way with the use of caps and twisting the poles, the gennies most guys do use the KISS principle. Guys have tried with some success gearing up but reality states a 1:1 ratio between the blades and genny work the best.
The more complexity you add to a wind genny the greater the chance Murphy will come pay a visit.
<-end rant>
Cheers Bryan
KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691
Posted: 09:09am 09 Jan 2009
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You dont like the idea Bryan, well thats OK.
You see, the idea is to discuss and kick around ideas no matter how wild they may seem and sometimes something useful drops out.
Bolty Regular Member Joined: 03/04/2008 Location: AustraliaPosts: 81
Posted: 02:49am 14 Jan 2009
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What this thread does not seem to discuss is that although a torque converter can increase torque, it does so by a reduction in revs. It also suffers a significant loss in power transmission as has been mentioned. Any attempt to use an automotive torque converter (TC) is likely to be a failure due to excessive losses. Remember that a TC is designed to transmit probably a minimum of 40 kilowatts, of course up to several hundred kilowatts. This means that transmitting say 700 watts will be rediculously inefficient! Add to that, that a TC is designed to "slip" at rotational velocities up to about 700rpm and the turbine would need to spinning really fast before any energy was transmitted. Perhaps it is true that a special small scale torque converter could be designed and manufactured, but I would like to see that done in a back shed.
In effect my capacitors, lightly loading the turbine at low wind speeds, and then being voltage doubled, does this with a minimum of hassles. Although some people have observed capacitor failure, mine have proven very durable. This is even though my turbine produces up to 1250 watts. After all, with the voltage doubler capacitor arrangement, the capacitors are bypassed at higher power levels. This in effect is working the same as a torque converter at low revs, but without the losses!
I certainly endorse creative and innovative ideas! The torque converter fits this category when used on a turbine, but I believe would be practically difficult to achieve for back-yarders. I would welcome to look at the results of your investigations with an open mind!
Hi, I have just joined the forum, and only started to build a F&P based wind turbine this week, and would like to make the most of low wind speeds. As my weather station I run generally shows 3m/s to 4m/s a lot of the time.
I am thinking that you could switch the winding around series at low speeds, and change to parallel at higher speeds, either using relays or solid state switching to improve performance.
Also has anyone used the F&P speed detect board at all?
trying to build a wind generator :)
KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691
Posted: 06:22pm 14 Jan 2009
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Hi, welcome to TheBackShed, yes you can switch windings series to parallel, star to delta etc to get the best to match your blades and conditions. You will find a lot of good ideas like that on this forum though you might have to search a while to find them all!
John
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 10:21pm 14 Jan 2009
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Hi iceberg,
I have made winding switching, DC-DC converters and now capacitor multiplier arrangements.
The winding switching has mechanical and sensing components. My system suffered from relay click-click noise and short mechanical life, to achieve reasonable power matching.
The DC-DC converter variable boost maximiser works quite well once programmed, but produces electrical switching noise. Careful design and component layout and filtering is required to reduce RFI to TV and radio reception.
The capacitor multiplier arrangements offer the simplest solution without any of the downfalls of the above systems. Like all things, optimum values are required.
Hi,
I suppose the item I really need is a MPPT to suit the F&P motor.
I have been doing some reading on the forum and see some discussion about a MPPT.
Has anyone developed a MPPT that can be used with a F&P, or is it just too hard and not worth the time and effort?
I am back to work this week after leave over Christmas, will only have weekends now for building my first wind turbine.
Thanks for the help.
Peter
trying to build a wind generator :)
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 01:40pm 18 Jan 2009
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Hi iceberg,
MPPT you ask. This has been raised on many occasions for over a year. You will need to read many threads to follow progress. I am unaware of any commercial black box universal designs. Any system that gives a cubic loading profile to an alternator is effectively a wind MPPT. The blade tsr may be a little up or down from optimum.
Measuring the wind energy that the windmill instantaneously sees is subjective and the wind changes the measuring goal posts very quickly. I see a windmill MPPT working with a system that has very low inertia, an analogue processor and analogue measuring. I have a system like this on my AxFx mill, but I still would not call this a wind MPPT. There has been a lot of testing of AC coupling and capacitor doublers, that give a better matching of windmill loading to the wind energy. This is still not windmill MPPT.
A good indication of the loading allowing a windmill to track the wind energy is; the windmill speed closely follows the windspeed. The windmill produces output current across a wide range of shaftspeeds, at least an 8fold change of shaftspeed. The output load current, say to a battery type loading, will be proportional to the wind energy. Obviously this behaviour will only occur if the windmill is not in a furled state.
I doubt the wind MPPT discussion will ever stop. I am not an expert in this field, but I have some very good units that are close to a MPPT, that worked well on a F&P mill. My F&P windmill however, has my latest capacitor multipliers and mixed loadings. I will continue with this loading matching, and not the universal black box.
A significant point is that the cap multiplier systems have no RFI component. This has significant impact on TV & radio reception.
This may not be right thread to continue this discussion for MPPT. I have been reading other threads on the subject.
I think the problem to solve is very complex, as the relations ship between RPM to power produced with a given load and with the addition of blades and wind speed variations it just gets too hard!!
I suppose if possible I would like to get a feel for the power curve of the f&P mill can produce.
I think if you measured the power output for a given RPM, and worked out the max power, at that RPM. Then plotted that, it would be a good start to understand what load at a particular RPM will give you max output.
As the wind mill changes RPM due to wind speed, if you measure the RPM using the F&P detection board (I got one with my motor, just have to work out the connections). You can then track RPM of the wind generator. I think you may be able to ignore wind speed.
With a set of data for RPM vs max power output and the load at which max power occurred.
All you have to do now is adjust the load in accordance with rpm. Also to keep control of the F&P, set a max RPM and adjust the load accordingly so max RPM is not exceed.
I am not sure if this is practical at all, but it is something I have been thinking about in the last couple of days as a way to get better efficiency. It may be simpler than building a MPPT for wind generator.
cheers
Peter
trying to build a wind generator :)
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 09:45pm 19 Jan 2009
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Hi iceberg,
If you hadn't noticed, I have modified the natural alternator characteristic, and battery type loading output to be very similar to the wind energy curve. This is really the aim of the exercise. There may be a bit of slop either way, but the wind/blade combo adapt to fill the gaps.
I would prefer to use a system the just did the job, than something that required complex measurement and computations to find a maximum, that probably will have changed by the time an adjustment to the load was made.
This weekend the wife is off on a craft day, so the two apprentices (two kids) and I will be doing some work in the shed. With some luck I hope to get the basic steel work completed so I can spin the F&P motor on the shaft.
I have also been thinking of using a Vicor module / PSU as the switch mode PSU to convert from high voltage DC down to 12V, you can adjust the output on the Vicor module to give you capability to charge batteries / float batteries.
The power side of things I will sort out in time, I just have to get the mechanical things sorted out first.
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.
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