RE: Capacitor plate eddy currents -- was: wiring for functionality or design

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Hi David:

The proximity to the primary and the differing top/bottom airflow are
both likely explanations.  I don't have any experience with coils the
size of yours, but I wouldn't expect the cap to generate that much heat,
so I would suspect eddy currents more.  Others with big-coil experience
may know better.

I did an experiment several years ago to investigate primary
proximity-related losses, by scoping differences in primary ringdown
times as a function of stuff brought near the primary coil.  The losses
were mapped to an equivalent ESR in the primary coil and I never made
any attempt to determine just how significant such losses were to
operation.  The only take-home message is that incremental losses were
measurable with NST's roughly a foot below the primary.
http://www.pupman.com/listarchives/2000/November/msg00359.html

Regards, Gary Lau
MA, USA


> Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
>
> Hi Gary,
>
> Hmm, that's strange that you mention eddy current losses
> in the cap plates as this may explain an affect that I've no-
> ticed while firing my big coil, which can be seen @:
> http://dawntreader.net/hvgroup/david/gm.html
> In photos #2,7, and 8 the turquoise green exterior metal
> can of the primary cap and its relative position to the pri-
> mary coil above can clearly be seen. Anywho, I've noticed that after
> firing the coil, the top side (the side nearest to the primary coil)
> often does have noticable exterior warmth that is no-
> ticably above ambient temperature, but the bottom side seems to
> remain cool. The top side doesn't seem to get
> dangerously overheated but does definitely feel noticably
> warmer than ambient temperature even after only 1 minute
> or so of firing. Do you think the eddy current issue could
> possibly address this observation? Thanks for any com-
> ments or suggestions. BTW, the exterior tank of this cap
> is obviously composed of ferrous metal as it has a strong
> attraction to a magnet and I know that iron does indeed
> experience notable eddy current losses, hence the fine
> lamination of transformer cores.
>
> David Rieben
>
> PS-- Maybe the fact that the bottom side of the cap also acts
> as one of the "walls" of the fan chamber for cooling the stationary
> SG electrodes also contributes to its "cooler" surface?
>
> ----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Wednesday, January 25, 2006 1:20 PM
> Subject: RE: wiring for functionality or design
>
>
> >Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
> >Short, direct interconnects are always better - losses are lower and
it
> >just looks better.  But there is such thing as too close to the
primary.
> >Exactly when that occurs is unclear, but I'd keep things at least
6-8"
> >below the primary, to avoid eddy current losses in cap plates.
> >Regards, Gary Lau
> >MA, USA
>
>
>