Electrolytic cap in high-discharge application

[Rich Grise]

Thanks for the suggestion, but will it work that way? The reason
why I wanted a powerful flash is that it has to be clearly
noticeable from a distance of 400m, in broad daylight by people
who are looking in the general direction but not concentrating on
the light. It's to signal a moment in a sporting event.

With a strobe, you don't need it to be blindingly bright to be
noticeable. Typical disco-type strobes (that go really really fast)
use a 1 uF polyester cap. The tradeoff is between the charge time
and how much energy you want to put through your flashtube.

But for 2 Hz, I wouldn't use anything anywhere near 200 uF! Do
you have a junque box? I'd try different value caps, starting
at about 1 uF, and going up in value until you're happy - the
thing to look for is the lowest possible ESR (equivalent series
resistance), so that the current can go through the flashtube
really quickly, and make a nice sharp strobe. I think it's the
fast rise and fall times that stimulate the rod cells of your
retina.

Good Luck!
Rich

 

[Michael Wieser]

I'm thinking of making a strobe light using a Xenon tube from an
old camera flashgun (tube type unknown). Tentative scheme:
The strobe will fire 4 or 5 times at ~2Hz and then given a rest
for a minute or so before the next cycle. It is to be used for a
few hours at that duty cycle, but only for one day, and then
stored for months until the next time.

I'm thinking of charging the storage cap (maybe 220uF) to perhaps
300-400V from a 12V car battery via a dc-dc converter. I don't
want to go to the trouble of getting some special super-duper
cap - unlikely I can get a specific type here anyway. My question
is: If I use a run-of-the-mill electrolytic, the kind that's used
as a main dc filter in consumer products such as a CRT TV, how is
it likely to fare under the said conditions?

Some Caps from not to old PC-Powersupplys will do that without
problems.
Don`t forget the voltagebalance-resistors if you connect theese caps
in series

btdt

Dischargecount for several buildt units stopped at 15,000 because the
unit (flash-trigger-transformer and sourounding pcb) we need to test
needs only survive 5,000 events...

hth

-
Michael Wieser
--

 

[Pimpom]

Some Caps from not to old PC-Powersupplys will do that without
problems.
Don`t forget the voltagebalance-resistors if you connect theese
caps
in series

btdt

Dischargecount for several buildt units stopped at 15,000
because the
unit (flash-trigger-transformer and sourounding pcb) we need to
test
needs only survive 5,000 events...

hth

Thanks. Nice to hear about an actual experience. As I explained
in reply to someone else, I doubt that my unit will ever need to
fire much more than 1000 times. It's a temporary solution that
will probably be replaced with a better one in a couple of years,
and used at roughly 10-20 sequences an hour, 3-5 hours a day, 1
or 2 days in a year. I'm already thinking about the replacement.

 

[Pimpom]

With a strobe, you don't need it to be blindingly bright to be
noticeable. Typical disco-type strobes (that go really really
fast)
use a 1 uF polyester cap. The tradeoff is between the charge
time
and how much energy you want to put through your flashtube.

But for 2 Hz, I wouldn't use anything anywhere near 200 uF! Do
you have a junque box? I'd try different value caps, starting
at about 1 uF, and going up in value until you're happy - the
thing to look for is the lowest possible ESR (equivalent series
resistance), so that the current can go through the flashtube
really quickly, and make a nice sharp strobe. I think it's the
fast rise and fall times that stimulate the rod cells of your
retina.

Good Luck!
Rich

Thanks. I've already experimented with a Chinese-built 12V strobe
meant as a car decoration light. It uses a 2uF cap and flashes at
roughly the same frequency, but the output is nowhere near bright
enough. Maybe it's restricted by the charging circuit which I
haven't analysed yet. I also tried out the idea with the flash of
my Panasonic FZ30 camera which is fairly powerful for a built-in
unit. It was barely acceptable.

The idea of starting out with a smaller cap is a good one. But I
think something like 10uF will be a better starting point.
Placing the flash in a shaded area should make a big difference,
but that's not practicable.