Commercially produced microturbines typically run at 20,000rpm or higher (I think some are 100,000rpm). Check out Capstone's website http://www.microturbine.com/prodsol/techtour/index.asp Perhaps that alternator is made for that.... but probably not.
On 12/8/06, Hakan Falk <[EMAIL PROTECTED]> wrote:
Joe, Yes I got messed up with language, circumference, area and wind speed, because circumference is not really interesting. Regarding relations between area and wind speed, you have a table on my site. If you double the circumference the area goes up with the quadrate and if you double the wind speed the energy content goes up with cubic. The best we can do is to try to find some tables on car alternators, to see their data. As I understand it now, after looking at data, a high performance car alternator would give around 200 amps at 12 to 22 VDC, which give at the high end 22x200= 4.4 Kw. You can get more by having a multiple generator system, mounted on single drive axis and can buy those as standard up to 800 amps . It looks like the upper limit for single generator is around 5 Kw and standard one axis multiple generators 17 Kw. Probably the rpm set to 18,000 is a mistyping and it should be 1,800 rpm, but what is a zero more or less between friends. After looking at some existing generators, they recommend to not go over 2,500 rpm. It looks like the recommendations is to have the generator at half the speed of the engine. It is however possible to rev up an generator to give more power, because the limitation is the current not the power, if it is revved up to give a higher voltage and power, it will also give a higher power output. It is however questionable that the windings and other components would stand for it, see, http://www.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm It describes quite good the design and limitations and it confirms the worries that you had, maybe not exactly but it is component problems that limits the output. What would we do, if we did not have Internet and the wealth of information. I found the link to be a good primer to generators. A table that allow you to rev up the generator to 18,000 rpm will probably give you hight voltage and high power output, but does not seem to be realistic, if the generator is not specially designed for this speeds and high voltage. Hakan At 20:49 08/12/2006, you wrote: >Hi Hakan; > >If the diameter of the pulley is doubled the circumference is >doubled. Not 4 times. You must be thinking of area. Now if you >double the diameter on a wind turbine you do get 4 times the >power. Is this what you were thinking of? If a 3 meter turbine >produces 1kw ( a safe guess for a home made unit? .... with average >wind....whatever that means) so then a 12 kw output would require >sqrt 12 or about 3.4 times the diameter so about 10 meters >diameter? Does this sound reasonable? Yes when you get into the >10's of thousands of rpm things do tend to fly apart. Explode is >not technically the right term but equivalent in effect. I have >seen a saw blade disintigrate into dust when it's rpm was increased >from 16,000 to 24,000. It was very exciting. Lucky nobody got >hurt! No peice of the blade existed which was larger than a grain of sand. > > >Joe > >Hakan Falk wrote: >> >>Joe, >> >>Twice the diameter, would be close to 1 to 4, right (THE SQUARE OF >>2)? Agree that 2,500 might be close to normal speed. That would be >>something like 10,000 rpm for the alternator at normal speed. Talking >>about that the alternator would explode at 18,000 rpm is maybe an >>overstatement? >> >>With the use of alternators in wind generators, I have never seen >>them classed at more then 6-8 Kw, but would not be surprised if they >>would not explode if you under extreme conditions get 12 Kw. >> >>With 10 m diameter, you would get a lot more than 12 Kw. I would >>guess, without calculations, that we are closer to 4-5 m diameter. >>This after looking at existing wind generators. When we talk about >>large wind, we are talking about 100's of Kw and diameters around 30 >>m. It was a while since I looked at wind, but it is a section on my web site. >> >>Hakan >> >> >>At 19:06 08/12/2006, you wrote: >> >>> >>>Hi Hakan; >>> >>>I bet the pulley on the crankshaft is less than twice the >>>alternator's pulley diameter. Also the amount of time your engine >>>is reving above 2500 rpm is short compared to the normal. Anyways >>>they talk about low losses but the gearbox required to turn the >>>alternator that fast would be very lossy and what diameter of >>>propeller would be required to extract 12 kw from the average >>>wind? 10 meters? more? lol! >>> >>>Joe >>> >>>Hakan Falk wrote: >>> >>>> >>>>Joe, >>>> >>>>How much are they spinning in a car? To me it looks like the wheel on >>>>the alternator is much smaller than the wheel on the car engine, >>>>could it be 1 to 4 or more? 4,000 rpm for the car engine is quite >>>>usual, so the alternator can not be far from 18,000 in normal >>>>conditions. Just a thought about the normal conditions for an >>>>alternator, or maybe I am wrong? >>>> >>>>Hakan >>>> >>>> >>>>At 17:09 08/12/2006, you wrote: >>>> >>>> >>>>> >>>>>Read that page carefully! It says the alternator can produce 12 >>>>>Kw........at 18,000 RPM!!! Good luck spiniing that thing that >>>>>fast. I'm sure the bearings would catch fire if the whole thing >>>>>doesn't explode first. Speeds that high require incredible >>>>>balancing and air bearing spindles. 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