Re: [Phys-l] entropy and electric motors

[Bernard Cleyet <bernardcleyet@redshift.com>]

I was taught, long time ago, that design optimum was for equal copper  
and iron (hysteresis & eddy current?) loss, at least in transformers.

Was I miss-taught?

bc thinks his


On 2008, May 23, , at 09:10, John Denker wrote:

> > Do you happen to know where the loss comes from in real electric  
> > engines?
>
> Mainly from "I^2 R" loss in the windings.
>
> Engineering is generally a multivariate optimization process, with
> lots of tradeoffs between the various variables.  If all you cared
> about was efficiency, you would use more wires and fatter wires in
> the windings ... but you also want to optimize the power-to-weight
> ratio and the power-to-capital-cost ratio, which argues for fewer
> and thinner wires.
>
> Keep in mind that this I^2 R loss is a nuisance loss, not required
> by thermodynamics.  It is like friction in your heat engine, which
> is not required by thermodynamics.  It causes an inefficiency in
> _addition_ to whatever inefficiency is required by Carnot.