Of course Ken is correct. DC motors are widely use in just such applications as Ken talks about.
Marine refrigeration is one of them and marine propulsion is another. Norm S/V Bandersnatch Lying Julington Creek 30 07.695N 081 38.484W > [Original Message] > From: ken <nauti...@centurytel.net> > To: <liveaboard@liveaboardnow.org> > Date: 3/13/2009 7:25:38 PM > Subject: Re: [Liveaboard] electricity > > Sorry, that last email got screwed up somehow. > > Norm wrote; > > Tesla was a sad genius. If he had just a little of Edison's interest in > marketing he would have been wealthy enough to finance his all of his > scientific investigations to his heart's content. > > Reply; > Well, as I recall, according to an article in "Invention and Technology" > magazine some years back, he DID have a big percentage of Westinghouse's > profits by contract for his poly-phase AC generating stations at Niagara > Falls, but they soon realized that their future investors would not be > happy with that deal and reneged on the contract. If they had not, > Telsa's ancestors today would probably be very wealthy indeed! > > Or maybe he would have just built even larger wireless transmission > towers and burned through all that money also. > > Norm; > > DC has many disadvantages. DC motors must have brushes, which are > > maintenance intensive, a common point of failure, and a source of RF > > noise, or have an internal inverter (such as used in "computer" fans) > > to produce ac. DC cannot produce the rotating magnetic field used in > > virtually all industrial motors. > Reply; > Many motors now, even some in washing machines and such like, are > 'brushless' DC motors. And the fact that DC motors need to commutate or > rectify power is not a problem with todays semiconductors that have a > better conductivity that solid copper! > The fact is that both AC and DC have advantages and disadvantages, > depending on application. > Some of the most efficient, compact, and most powerful motors in use > today are DC permanent magnetic motors. One big advantage to using DC > here is the ability to control the impeadence of the motor much more > precisely than could be done with AC, which means less loss (and less > heat). Another big advantage of DC motors is that in general they can > have a much wider speed range, so a transmission may not be needed. > Better control of torque throughout their range yields a smoother > motion, where that is important. > The biggest dis-advantage of brushless DC motors it that they cost > significantly more and controllers can also be a bit more expensive. > > I would add, that if we ever do get a true 'energy super-highway' or > that is a nation wide power transmission grid capable of sending > humongous amounts of power across the continent from wind and solar > production points for example to consumption points when and where > needed, a critical part of that new grid will be DC transmission lines. > This will allow small suppliers to connect on or off grid very fast > without the cumbersome processes needed today and go a long way to make > the grid more stable than it is now. It will also mean greater > efficiency than AC transmission. > > In the future it may well be AC that is relegated to the back seat! -Ken > _______________________________________________ > Liveaboard mailing list > Liveaboard@liveaboardnow.org > To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard > To subscribe send an email to liveaboard-j...@liveaboardnow.org > > To unsubscribe send an email to liveaboard-le...@liveaboardnow.org > The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ > > To search the archives http://www.mail-archive.com/liveaboard@liveaboardnow.org > > The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html _______________________________________________ Liveaboard mailing list Liveaboard@liveaboardnow.org To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to liveaboard-j...@liveaboardnow.org To unsubscribe send an email to liveaboard-le...@liveaboardnow.org The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/liveaboard@liveaboardnow.org The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
