RE: LED at 60 HZ? (was RE: Radio Shack Strobes)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 07:59 AM 3/2/2004 -0700, you wrote:
>Original poster: "Ian McLean" <ianmm-at-optusnet-dot-com.au>
>Hi Terry, Dave
>
>As an experiment, I built this simple LED strobe to compare it to my xenon
>flash tube based strobe which I have already built.  The xenon strobe is
>built around a UJT based zero-crossing detector, an SCR and a trigger
>transformer.
>
>The reason I did the comparison is because of the inherent problems with
>xenon flash based strobes - i.e. short run times, about 10 seconds max.,
>before things start overheating and the strobe starts to flicker.  Both the
>tube, and the series load resistor on the xenon positive output gets very
>hot very quickly.

Ahh.. you're using the "camera flash" type design, not the "repetitive 
strobe" design.  Get yourself a copy of Edgerton's book (Strobe, Flash), or 
check the web.  Basically, you need a better way to charge the capacitor 
(for line frequency strobes, an off-line voltage doubler is great) than 
through a series resistor. For variable frequency, inductive charging is 
the way to go. And, you need to manage the tube current. (higher voltage, 
shorter flashes, for instance)



>The LED strobe works reasonably well, but there is some smearing of the
>image of the SRSG platter - about an inch or so at the platter electrodes in
>my case.  The xenon strobe leaves the platter image rock steady stationary.
>
>Is the smearing really caused by LED persistence, or is it something to do
>with the type of LED I was using (a water-clear ultra-bright 5mm red LED)?

Probably more likely that the "flash duration" for the LED is much longer 
than that on the xenon flash lamp.


>Regards
>Ian