Re: Resonant charging (in the days of King Spark)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

>Weazle wrote:
> 
> The power transformers they used had a turns ratio of 1:300, whereas
> our NSTs and OBITs are 1:100, meaning they must have been getting a
> very high secondary voltage in a resonant condition.  I'm surprised
> that the plate glass caps that they where using in those days could
> stand that sort of strain.  

Unless they overdesigned the plate glass cap... Sure, the glass is lossy,
and the breakdown voltage characteristics not as desirable as modern
plastics, but, in 1920, what else did you have?  (Ruby Mica, I suppose)...
And, of course, this is for a ship or shore station, where weight isn't as
big an issue (you don't have to drag that ton of glass around).  I think
that they would have just used healthy design margins, both for dissipation
heating and for dielectric breakdown.

Assuming you can deal with the other breakdown related issues (corona,
e.g.), efficiencies are generally better with higher voltages (less IR
loss, for one). The typical hobby tesla coil works around 10-20 kV mostly
because the components that are readily available inexpensively are in that
voltage range (i.e. NSTs, MOTs, polepigs, etc.).  Start getting up above 30
kV, and HV design becomes a bit trickier.  Also, their transformers and
other components may have been lossier, so a 300:1 ratio was needed to keep
the voltage up.

On the other hand, if you are buying things new, for a specific purpose,
then you can pick your design point differently.  A 10 kVA transformer for
30kV costs about the same as a 10 kVA transformer for 10 kV, if you're
buying it brand new (as opposed to surplus, or mass market (pole pig)).