The [permanent magnet axial flux] alternators displayed at otherpower.com (and a few other places) are intended to satisfy a few requirements: - easy/inexpensive to build/acquire - high output at low rpm - self-starting output They seem to primarily be directly coupled to things that turn at low speed... wind turbines, slow-speed diesel engines, (exercise) bicycles. Automotive alternators tend to fall short in the second and third category. They like to turn at high RPM (~10k or so), and they require their field windings to be excited before they produce output. Sure, you could build some type of gear/pulley assembly to mate your driver's RPM (windmill blades, slow diesel, pedal power) to your automotive alternator's design RPM, but then you have losses in the drive train. These folks would rather have something that's dead simple, works, and is easily repaired if problems arise. To solve the inefficiencies created by an arguably poorly engineered design, they throw extra magnetic flux into the mix. It's an easy solution, and seems to work well enough. Then they use some rectifiers and off-the-shelf inverters to clean up the output... not much different than how most portable generators produce (somewhat) clean AC these days. I suspect there's quite a bit of satisfaction in having "built" the thing with your own hands from scratch, too. The automotive alternator would be too easy from that angle :) Being hand wound, these things are also fairly easily adjusted for other voltage outputs... 24v and 48v designs seem popular too, for feeding the larger inverters, and reducing line losses. There's also a bit of safety factor with them... tie all of the outputs together and the things pretty well lock up... helps to provide some additional safety factor if you're performing maintenance on a wind turbine, or if you need to have the thing shut down in high wind. I don't believe you easily get those benefits with an automotive alternator. On Wed, May 21, 2008 at 3:42 PM, Herbert Graf wrote: > On Wed, 2008-05-21 at 13:30 -0600, Cedric Chang wrote: >> Sorry if this has been asked. Are these alternators more effective >> than an automobile alternator ? >> cc > > I was wondering the same thing. > > The typical automotive alternator pumps out around 50amps at 12V, pretty > close to the 500W mentioned. > > Heavier models can pump out 100amps or more. > > Obviously they are not optimized for size/weight, and they also drop off > in output quite a bit at lower speeds. > > TTYL -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist