Notes on stroboscopes

Stobe dangers

1 in 4000 of the population has photosensitive epileptics, so this can be an important problem when working with stroboscopes. At a rate of 4 flashes per second about 3% of the photosensitive population are sensitive, the figure then increase, at 25 fps it has risen to 75%, falling to 4% at 65 fps.

Various countries have different rules on what kind of flashing is allowed and how long it is allowed to be used.

Notes on building xenon flash circuits

From: [email protected] (Ruben)
Subject: Re: BIG PhotoFlash design!  250 Watt-Seconds
Newsgroups: sci.electronics.design
Date: Sun, 19 May 1996 00:34:37 GMT
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On Fri, 17 May 1996 21:28:18 GMT, [email protected] (Wyatt Earp) wrote:

>250 Watt-Seconds is a lot of power, most of the cheapest flash units I
>rip out of cameras use a small flash tube and about a 300uF cap. If we
>assume 330 Volts DC charge...
>
>C=2469uF !!!
>
I used to design stage-effects, and played some time with strobes. Build a number, from 750 J at high rates to 22500 J single flash. Philips makes Xenon-lamps, designed for photographic use, but they are not flash-tubes, but burn continually, so using them as flash tube shortens their life-span, assuming you increase power. They are expensive, from $250 for the smallest to $1100 for the biggest.

For caps I used a huge array of MKT motor-caps. 10 uF at 630V is cheap, a few dollars, and building an array of these is not to hard. These caps are screw-mount, and you can just fill a board with them, and switch them in parallel. Keeps the ESR low, which is a requirement.

All problems I had related to heat. The 750 and 1500 Joules models had a habbit of melting their main wire. On typical stages one uses a lot of extension-wires, and its power consumption could be high enough to heat the extension to the point the insulation came dripping off, without blwong a fuse. Had to lower the amount of energy per flash at higher rates. The protective window in front was another problem area. Poly-carbonate covers work fine, but a single fingerprint absorbes enough IR to melt a hole in the cover. Glass won't melt, but shatters if dirty. Don't allow anything near it. Colored paper will catch fire within seconds, at max rate. Always use it to flash at a wall, never let the public look into such a bright flash.

The biggest used four larger tubes, flashing two by two, but charge-times were too long to make it useable as a real strobe. It was used to flash the ceiling of a large stadium. I considered it to be useless. I never solved the problems it had, like eating its eight, expensive, diodes (>$40 each) for lunch. It sucked dips in the mains, big enough to cause digital equipment to fail. Imagine all the effects of the audio-boys resseting after each flash. I kept it running for a few months, but when the edges of the window chaught fire I scrapped it. I modified one off the triggers for the small strobe (750 and 1500) to allow multiple units. 

---

Ruben

From: [email protected] (Sam Goldwasser)
Subject: Re: BIG PhotoFlash design!  250 Watt-Seconds
Newsgroups: sci.electronics.design
Date: 18 May 1996 18:11:50 GMT
Organization: Multiverse
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In-reply-to: [email protected]'s message of Fri, 17 May 1996 21:28:18 GMT

In article <[email protected]> [email protected] (Wyatt Earp) writes:

>   After reading Sam Goldwasser's tech notes on photostrobes
>	http://www.paranoia.com/~filipg/HTML/REPAIR/F_Camer_Flash.html
>   and ripping out the flash circuits of a few cheap camera's to play
>   around with, I would like to build a real big, bright strobe light
>   that will emit some serious photons!  Mouser lists a flash tube rated
>   at 250 WS (watt seconds) at 450 Volts.

>   250 Watt-Seconds is a lot of power, most of the cheapest flash units I
>   rip out of cameras use a small flash tube and about a 300uF cap. If we
>   assume 330 Volts DC charge...

<snip>

>   C=2469uF !!! got 250 W-s at 450 V.
For high power xenon tubes, you may also need to carefully calculate the value of a low resistance series inductor which will control the current pulse (as noted in the FAQ as well). This must be tailored for each combination of W-s, V, C, and xenon lamp model. The current pulse should be somewhere around critically damped - no undershoot (which damages the tube electrodes).

(Another response to this questions noted this as well). 

>   I checked the mouser catalog under caps for a 2500uF cap rated for 450
>   volts, I was not surprised to find they did not list one that big!
>   They do list a 1100uF @ 450V, but they are $38.55 each!  And it would
>   take 2 to get even close to the 250WS power I crave.

>   OK, so my question is, how should I go about storing the charge for
>   this big flash tube?  It would be nice to find some big caps inside
>   some old, cheap surplus junk.  Anybody got any ideas?  Could I use a
>   CRT from an old TV?  When I was very young I touched the terminals on
>   the back of one of those and found that those things can hold quite a
>   charge!
No, a CRT stores less energy than your little photoflash. You need electrolytics. I don't know of any practical way of constructing such caps. Try surplus stores and this group - there have been postings offering exactly the caps you need for a reasonable price. 
>   It seems there was a thread about building your own large caps on
>   sci.electronics a few years ago, does anybody have any info on this?
>   As I glance around the room I see some metal foil, some newspaper,
>   wire and duct tape!  Sounds like I have all the parts right here.  I
>   imagine attaching the wires to the foil would be the hard part.
I don't think these are appropriate. For what you need, they would be as big as a desk (wile ass guess). 
--- sam

>   I have no idea what the dielectric constant of newspaper is, or how
>   thick it needs to be to stand up to 450 volts, or how much surface I
>   need to get 2500uF.  I could build a prototype out of sheet metal
>   (easier to attach wires to than foil, but does not roll up easy)  That
>   is assuming 4x8 feet is enough area!

>   There has to be an easy way to store this many electrons at home, and
>   still allow the quick discharge I need for this photoflash
>   application!

>   Thanks for any help you can provide!

>   Wyatt

0, unseen,,
*** EOOH ***
From: [email protected] (Sam Goldwasser)
Subject: Re: BIG PhotoFlash design!  250 Watt-Seconds
Newsgroups: sci.electronics.design
Date: 19 May 1996 01:43:27 GMT
Organization: Multiverse
Path: nntp.hut.fi!news.csc.fi!news.eunet.fi!EU.net!newsfeed.internetmci.com!in1.uu.net!library.erc.clarkson.edu!multiverse!199.218.112.132!sam
Lines: 45
Message-ID: <[email protected]>
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	<[email protected]>
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In-reply-to: [email protected]'s message of Sun, 19 May 1996 00:34:37 GMT

What kind of capacitor bank did you use for the 22,500 joule blowout?

Your 630 V 10 uF caps are only about 2 J each.

--- sam

In article <[email protected]> [email protected] (Ruben) writes:

   I used to design stage-effects, and played some time with strobes. Build a
   number, from 750 J at high rates to 22500 J single flash. Philips makes
   Xenon-lamps, designed for photographic use, but they are not flash-tubes,
   but burn continually, so using them as flash tube shortens their life-span,
   assuming you increase power. They are expensive, from $250 for the smallest
   to $1100 for the biggest.

   For caps I used a huge array of MKT motor-caps. 10 uF at 630V is cheap, a
   few dollars, and building an array of these is not to hard. These caps are
   screw-mount, and you can just fill a board with them, and switch them in
   parallel. Keeps the ESR low, which is a requirement.

   All problems I had related to heat. The 750 and 1500 Joules models had a
   habbit of melting their main wire. On typical stages one uses a lot of
   extension-wires, and its power consumption could be high enough to heat the
   extension to the point the insulation came dripping off, without blwong a
   fuse. Had to lower the amount of energy per flash at higher rates. The
   protective window in front was another problem area. Poly-carbonate covers
   work fine, but a single fingerprint absorbes enough IR to melt a hole in
   the cover. Glass won't melt, but shatters if dirty. Don't allow anything
   near it. Colored paper will catch fire within seconds, at max rate. Always
   use it to flash at a wall, never let the public look into such a bright
   flash.

   The biggest used four larger tubes, flashing two by two, but charge-times
   were too long to make it useable as a real strobe. It was used to flash the
   ceiling of a large stadium. I considered it to be useless. I never solved
   the problems it had, like eating its eight, expensive, diodes (>$40 each)
   for lunch. It sucked dips in the mains, big enough to cause digital
   equipment to fail. Imagine all the effects of the audio-boys resseting
   after each flash. I kept it running for a few months, but when the edges of
   the window chaught fire I scrapped it. I modified one off the triggers for
   the small strobe (750 and 1500) to allow multiple units.

   ---

   Ruben

 
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