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[OM] "Forming" the capacitors in OM flashes?

Subject: [OM] "Forming" the capacitors in OM flashes?
From: nrky@xxxxxxxx
Date: Thu, 19 Jul 2001 22:35:36 -0500
Hi All,

I have to agree with Dirk, but not for all of the reasons he specified,
caps can't be specified for bandwidth, although you can't get 10Hz
through a 1pF cap
no matter how hard you try, nor for distortion (well that can depend...
caps do have an internal resistance that should be taken into
consideration when
designing audio circuits but isn't/wasn't a lot of the time)
They can be spec'ed out for varience in C over a temp range, and for a
production
range (I'm speaking mostly for electrolytics - which are the
sloppiest/leakiest
of the ones available AFAIK) and internal resistance, and that's about
it.  
There are high-tolerance mylar, ceramic and tantalum caps out there that
are also used 
in digital and audio, but the bandwidth is still determined by the R/C
time constant, and the charge-holding capacity (capacitance-duh!) is for
them is a lot less than what can be gotten with electrolytics*
*body size vs. capacitance being the governing factor in this case.

Re-forming on electolytics is really not needed...exercising them once in
a while
definately wouldn't hurt though...the damn things dry out after awhile.

Just to muddy the waters some...but they are different animals.

Bill  >; P
"Life unfolds on a great sheet called Time (film)*,
and once finished (developed)* is gone(here)* forever..."
*provided ya have a good archival system in place.


Date: Thu, 19 Jul 2001 10:26:31 +0000
From: Dirk Wright <wright@xxxxxxxxxxxx>
Subject: Re: [OM] "Forming" the capacitors in OM flashes?

Chris Charlton wrote:

> 
> Thinking back to my electronic engineering course at
> uni, electrolytic caps need to be conditioned before
> use to work when new, they do degrade with time,
> rather quickly, if I remember they exhibit more
> leakage and a lower overall "power" capacity. If you
> weren't afraid of opening up your flash guns, very
> high quality audio grade capacitors are available that
> would give a more consistent output and last longer,
> they also have less leakage which means while your
> flash is charged but idle, it will consume less
> battery power. Have a look for:-
> 
> Elna Cerafine/Silmic
> Sanyo caps

I agree that electrolytics need to go through a forming process when
they are new. I don't believe that they need occasional "re-forming"
however. 

Do Not use audio hifi capacitors in your flash. Electrolytics designed
for photoflash use are specially designed to have very low discharge
resistance, so that they don't heat up as much on a full charge dump.
Audio capacitors are designed to have low distortion and a wide and
uniform bandwidth. They are different animals. 

- -- 
"I have a dragon and I'm not afraid to use it!"

Dirk Wright



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