Re: Joules - Vrms or Vp (fwd)

To: tesla-at-pupman-dot-com
Subject: Re: Joules - Vrms or Vp (fwd)
From: Tesla List <mod1-at-pupman-dot-com>
Date: Sun, 2 Aug 1998 22:03:31 -0600 (MDT)
Approved: mod1-at-pupman-dot-com


---------- Forwarded message ----------
Date: Mon, 3 Aug 1998 09:00:31 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Joules - Vrms or Vp (fwd)

Hi Bart, 
           Since you asked :) ............

> Date: Wed, 29 Jul 1998 23:27:57 -0500
> From: "Barton B. Anderson" <mopar-at-uswest-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Joules - Vrms or Vp (fwd)
> 
> Tesla List wrote: Subject: Re: Joules - Vrms or Vp (fwd)
> 
> > > Regarding the calculation for Joules..... J = 1/2 x C x V^2.
> > > Should V = Vp or should V = Vrms? Why? (if you know).
> > V = Vpeak, since that is the energy when the gap fires.
> 
> First, thanks to all who responded. I was *patient* to not reply
> until I heard from quite a few on the list on this matter. The
> question was derived from Terry's Coil data for my coil where Vp
> was used to calculate 12.4J vs. what I originally calculated to
> 6J. The difference was of course, I was using Vrms instead of Vp.
> Hence, "ask the List".
> 
> It is very apparent, that the joules we calculate for TC's is
> dependent on our reference of time and energy. We could measure
> voltage across the cap when the gap fires initially, or we could
> view it as the energy available across the cap "prior" to the
> firing, and still yet, we could view it in terms of energy
> available minus losses after the bang.
> 
> I personally like Robert's and others expression that the energy
> available at the time of firing is what should be determined. If
> our gaps are not synched to peak firing, or our losses are
> extensive, we should term these differently. It appears that the
> V^2 is Vp^2 for all practical purposes. Possibly a separate energy
> delivered rating is needed to separate efficiencies and losses
> into the equation. Jsec.?
> 
> Thanks again to Greg, Richard, Stone, Dale, Antonio, Shaun,
> Robert, and Terry for your responses and related responses. John,
> Malcolm, and Bert, I would still be interested in your respected
> thoughts on this subject either on or off the list. I know
> efficiencies have played a major role in discussions in the past.

I have always used 0.5CpVp^2 as a measure of instantaneous energy 
available to charge the secondary capacitance (and ignored losses) to 
calc an absolute best case figure for Vs to assist in choosing Hs.
I have measured a transfer efficiency approaching 90% in a small coil.
Xp for that coil was around 26 Ohms.  Then I have taken BPS and 
multiplied it by Ep to get a true primary power figure. This assumes 
Ep is constant with each bang (pretty well is with sync and static 
gaps). From there, wallplug power measurement - E*BPS gives a loss 
figure for the charging circuits. Things are not so easy for async 
gaps unfortunately. I have found these methods very useful in 
determining what might be done at various power levels. The most 
useful indicator I have found concerns matching sshot spark lengths 
with theoretical Vs which IMHO bears out lumped theory rather well.

Malcolm