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[TCML] Building a pulse generator
I did have a longer response prepared but when I pressed send, Yahoo
lost my entire text and gave me the login screen then wouldn't let me
recover my message.
Briefly - 4KV is what a xenon flash tube triggers with.
A microflash is an air-gap flash the main charge of 15-30KV (Edgerton
used 16KV) doesn't flow between two contacts until a second charge of
45-50KV is applied, ionising the air.
I'd love to use a xenon flash but apparently it's almost impossible (as
Edgerton noted) to get below 1/100,000th of a second. For my purposes
that's way too long. A true microflash runs at 1/1,000,000th of a
second.
As an example, at 500fps an airgun pellet travels 0.06 of an inch which
is around half its length in 1/100,000th of a second. A .223 rifle
bullet travelling at 2,800 fps travels around 0.336 of an inch or
around half its length in 1/100,000th of a second.
Raising that by a factor of 10 means the airgun pellet is frozen and
perfectly sharp while the .223 rifle bullet has a mere 0.08 of a
centimeter or just under 1mm during the exposure. That's acceptably
sharp.
Now, I'm really getting confused by all the responses I'm getting about
my pulse generator. I'm thus looking around at 115v AC - 12v AC
transformers with the thought that I won't have to bother with AC
generators. Now that makes life a lot simpler as I can put the 12v
output straight into an ignition coil to produce 30KV. This goes into a
capacitor of around 5,000PF
I think I can do the same with a 55KV ignition coil - off the same transformer outputs.
I can then apply the switching to the low-voltage side of the 55KV coil
to switch the flash on/off. For that I think a relay may work or (it's
time critical so maybe an optical relay).
Diodes, I can either get some 80KV 0.2A diodes from ebay or a load of
microwave diodes and cobble them together. Honestly, I'm all for
simplicity so the $28 diodes from ebay sound better. I know it's
wasteful but I don't think I really need more than half-wave
rectification. Once ionised the 30KV should just continue going until
the capacitor is empty. A fraction of single pulse of 1/60th of a
second should be enough to dump the capacitor.
Rhys Sage
SagePhotoWorld.com
America's favorite photographer.
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