Re: nonresonant cap = imcomplete charge ?

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Larry,

On 21 Oct 2002, at 11:42, Tesla list wrote:

> Original poster: "Laurence Davis by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>
> 
> Call me thick headed, but...
> I understand how a less than resonant cap
> (i.e. xfmr req 27.5nf and tank cap is say 12nf or some number below 27.5) 
> does not use all of the power of the xfmr energy.
> 
> with a LTR cap, the energy from the xfmr charges the cap, and then
> there is still time left in the cycle that is not charging the cap.
> this equals less energy per bang.
> 
> but I've heard that (or maybe misunderstood) a GTR cap (as above xfmr
> req 27.5, tank is greater than 27.5, say 35nf)....
> so I've heard that a GTR cap is not as efficient as a resonant cap.
> it was stated that less energy is stored than a resonant cap.
> 
> is it the impedance of charging of the capacitor? the charge rate of the 
> capacitor is not a straight line.  so it would then follow that if the 
> charge rate is not a line, that if a GTR cap contains less energy than a 
> resonant cap, then the average charging rate should be less than a resonant 
> cap compared to a GTR cap.
> 
> am i on track or completely lost?
> thanks,
> larry.

I had occasion to ponder this last night in the process of designing 
a coil for the competition. I'll address that in another on-topic 
post. Basically, a lossless resonant charging scheme can charge the 
cap to twice the peak voltage of the transformer in a half cycle. 
Given that it is unwise to set the gap wider than the peak 
transformer voltage, that extra possible voltage cannot be taken 
advantage of but the energy can be used by multiple cap charges per 
cycle. Also remember that E is proportional to C but also 
proportional to V^2. You can take advantage of the extra available 
energy by using a larger cap and still hitting Vpk of the transformer 
to get a bigger bang but just one per half cycle. Increasing C beyond 
a certain point starts lowering the peak cap voltage below the 
transformer peak voltage with a marked decrease in stored energy so 
there is a happy medium.

Regards,
Malcolm