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[OM] Re: Lighting an airship? was Re: Re: Flash for E500

Subject: [OM] Re: Lighting an airship? was Re: Re: Flash for E500
From: Tim Hughes <timhughes@xxxxxxxx>
Date: Fri, 16 Nov 2007 22:49:58 -0800 (PST)
The nominal Joules are calculated from 1/2CV^2 as you indicated. 

Sometimes there are clever marketing claims inflating the Joules because "their 
sytem has better
conversion efficiency" etc, but basic comparison is almost always from 1/2CV^2. 
  It should
ideally  be actually delivered Joules to tube (but never is ). The capacitor is 
never completely
discharged at end of full dump, so it should actually be : 1/2CVmax^2 
-1/2CVquench^2 - thyristor
losses -Inductor losses. (where Vquench is about typ 60V or so ) Because of 
squared operation the
60V energy left is not a massive reduction (~5%). The thyristor losses are more 
maybe as much as
10% and inductor losses a few %. Large Studio units do not have auto, so don't 
suffer thyristor
losses.   Ideally you should compare integrated light energy delivered, and 
some studio vendors do
quote that, but since you can mix and match heads from different vendors the 
stored energy is
still a basic useful comparison.

As a generalization most portable higher power flashes like Sunpak 622 or Metz 
CT1/4,Metzct45,oly
T45 ,Qflash etc fall in the 70 to 200J range. With 4 AA cells they are usually 
70J max and with 6
AA cells typically ~100+J or so. It is mainly the issue of the recharge times 
would get too long,
if they were much more powerful for a given battery size. If you did a modern 
design using latest
high rate rechargeables you could do a lot better. I converted a MetzCT60 to 
modern rechargeable
batteries with a large reduction in weight, over the original Lead Acid battery.

Tim Hughes

 
--- Jeff Keller <jeffreyrkeller@xxxxxxxxx> wrote:

> 
> Tim,
> 
> Is that 1/2  x  C  x   V**2  or some other measure? Do you have any
> idea what "marketing" does to get the watt-second ratings of the
> studio flash?
> 
> -jeff
> 
> On 11/16/07, Tim Hughes <timhughes@xxxxxxxx> wrote:
> >
> > Chuck,
> >        The T32's are actually 70J.
> > Studio units tend to waste the light produced a bit more (reflectors less 
> > effective) and also
> with
> > larger tubes the lamp conversion efficiency is a little lower.
> >
> > Tim Hughes
> 
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