gEDA-user: Calculating a linear self excited induction generator

[John Doty]

On Jun 11, 2006, at 3:40 PM, Samuel A. Falvo II wrote:

> On 6/11/06, Karel Kulhavy <clock at twibright.com> wrote:
>> I read about self excited induction generator, homopolar generators,
>> liquid metal dynamos, interstellar plasma dynamos, linear motors
>> and electric meters.
>
> Ummm . . . Interstellar?!

Sure. That's where the galactic magnetic field comes from. Natural  
dynamos are common in the universe: there's lots of conductive stuff  
in electrical contact and in differential rotation.

About 3 years ago I heard a talk by Roger Blandford on the  
electromagnetic physics of stellar collapse forming a black hole. The  
dynamo saturation condition for the accretion disk a few seconds  
after the initial collapse suggests there should be zetavolt  
potentials driving exaamp currents around! Roger tweaked his  
physicist audience by using SI units rather than the Gaussian units  
physicists usually use: after all, he was analyzing the star as  
electrical machinery. The only trouble is that the SI doesn't define  
prefixes high enough to handle the power (something like 10^42  
watts)! That power can make a gamma ray burst that's still intense  
enough to be detected by an instrument you can hold in your hand  
after traveling 10 billion years!

I expect to use gEDA to design the electronics for a new generation  
gamma ray burst detector starting later this year.

>
>> I got an idea of placing two coils almost touching the aluminium  
>> rim and
>> wiring them somehow obscurely with capacitors (how people do in wind
>> power plants with squirrel cage motors nobly relabeled as "self  
>> excited
>> induction generators") so they would prime themselves and start
>> generating. If it works with cyclic asynchronous motor it should work
>> with a linear one too, shouldn't?
>
> In what way is it self-priming?  Given a large enough, flat plate
> dynamo, I'm sure one could exploit the Earth's natural magnetic field.
> But, a small dynamo the size of which is suitable for a bike would
> never have sufficient surface area for electrical generation, no
> matter how fast it's made to spin.
>
> Remember that energy is neither created nor destroyed -- if it's
> self-generating, it has to draw energy from somewhere.  Traditional
> alternators draw this energy from shaft rotation.  Where is the
> self-excited generator drawing its energy from?

Dynamos convert mechanical energy into electromagnetic energy. In a  
dynamo, there is positive magnetic feedback, so any tiny seed field  
will build up until it reaches a saturation level determined by the  
structure and operating conditions of the dynamo. The seed field  
magnitude doesn't matter. But dynamo design is tricky: you really  
have to understand and use Maxwell's equations. The network theory we  
use for circuit design won't get you there.

John Doty              Noqsi Aerospace, Ltd.
jpd at wispertel.net