For a wind mill I've settled on a Savonius design optimized by UC Long Beach. It is a full blown lift motor with a TSR of 1.6. The choice is because I live in a class 2 wind zone in Florida. The design appears to have good torque and decent speed that would be advantageous to gentle coastal breezes.
http://www.energy.ca.gov/2005publications/CEC-500-2005-084/CEC-500-2005-084.PDF
Your theoretical output curve is attractive because it ramps up fairly quickly at the low end and reduced cogging is always a benefit.
I to am flying in the face of popular opinion on windmill design. Hopefully we can be helpful partners in this crime.
Viron
That change in the power curve is interesting. It's something that has not been seen before, as far as I know. It should be possible to hit the power curve of the mill at two points instead of one. Keep in mind that curve was hypothetical. While the shape is correct so will any curve scaled up or down from it be correct. The ramp up at the low end depends on the resistance of the alternator. In general a lower resistance requires a larger alternator. Probably larger than with the regular design. Keep in mind that in this design the coils are not spaced tightly, so a larger rotor would be expected. In other words go into this with your eyes open. That said I am willing to give any help and insights that I can.
This might be a good place to suggest a plan of attack for a first case design. Use circular magnets. Decide on a coil diameter. This will determine the size rotor you will need. Pick a number of wire diameters. Wind coils of the specified size with all the wire sizes (the number of turns will depend on the wire size). Mount the magnets on the rotor and make stators using the different size coils. Try the different rotor stator combinations and evaluate each one. From this data you can predict what size magnets and coils you need to meet your design specifications. It would also be nice if you presented your results here. Good luck!
GeoM[ Parent ]
Here's my technical partner's, Larry Ludwig's, assessment. In general he thinks it would be good for producing power at very low wind speeds as it would reduce EMF drag.
Skimmed the discussion and drawings. The only serious advantage to this is that low wind speeds will still produce pulses (less system EFM drag) which can be rectified so that you can always produce some voltage. Electronically the voltge can be built to a higher level with a chopper circuit. This might be useful in a battery based system where trickel charge (high voltage, very low current) helps to maintain the charge. If you were to look at there diagrams and draw lines to the top of each pulse you would get a sine wave which is what overlapping coils whould produce. In an alternator, these three overlapping coil voltages are rectified to a pure dc. The three coil set allows for less ripple smoothing to have to ocur so that less loss occurs in the rectification and smoothing circuit. If our desire is to always generate some voltage, even at low wind speeds: we could have our PIC keep a low drag PM pulsed alternator engaged at low RPM and a High drag, High voltage generating alternator swithched in ( and the other swithed out) at higher RPMs. Then we could have retification circuits for each one designed around what were doing with the outputs. The High RPM could be a direct feed to the system under use, with a small bleed to the batteries. The low RPM system could only feed/charge the battery. This is typically the type system I had envisioned for a home power system. A high voltage battery set with an inverter for producing AC at high output periods and a low current, high voltage electronic circuitry for just charging the batterys during low output periods. I could talk to Pete about an electriclly actuated clutch system or a mechanicat RPM activated clutch system the we could read electrically to determin system operation parameters/switching. [ Parent ]
I presented this design for the case of charging a battery where pulsed dc doesn't matter. That is, while this will have more ripple than a three phase system, for charging a battery it doesn't matter.
I don't see any reason why this alternator couldn't be made to produce more power at higher wind speeds by introducing centrifugally operated iron cores for the coils. At low rpms they are retracted. At a certain point they are inserted in a controlled manner. This would be easiest to do if the coil assembly rotated. With the magnet assembly rotating it would be necessary to mount the centrifugal weights on the back of the rotor and transmit their effect through the shaft by the use of a rod. The question is how something like this would compare in cost to adding a second alternator?
