Texas Steampunks

Texas Steampunks & Neo-Victorians

I've been playing with the flash circuit from a single-use camera, and after reverse engineering the circuit I've begun making some changes.

The standard design uses a blocking oscillator running on a 1.5 volt AAA battery to produce 300 volts across a large capacitor. The capacitor is then discharged through the itty-bitty flash tube in about 1/1000 second.

After some modification (removing the big capacitor, flash tube, and trigger circuit) and adding a Greinacher voltage doubler, I've got about a 600 volt output.

Next, I'll be connecting one of my large xenon flash tubes to see if 600 volts will trigger it.  If not, I'll start adding  Greinacher stages (adding 300 volts per stage) until the tubes light up.

The end goal is to produce a high voltage/low current output that will gently fire multiple xenon flastubes in series.  I'm  ultimately looking to produce an (apparently) continuous filament of white light through the flash tubes rather than a millisecond-long blinding blast of light.

It should be an interesting series of experiments.

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Comment by JJ Folderol on July 23, 2011 at 6:51am

Thermal buildup would be a major problem if the intent was to operate at continuous full power, but I'm trying to achieve a very low power pulsed operation.

Theoretically, the entire system should function as a relaxation oscillator wherein the voltage multiplier will charge to the firing point of the xenon tube and immediately drop to a much lower sustaining voltage.  When the voltage drops a bit further, the xenon conduction will stop and the cycle will repeat.

It should be much like the operation of a neon bulb relaxation oscillator in which a capacitor across the neon lamp slowly charges to the firing point of the neon (about 80 volts) and fires the lamp.  The lamp then lights (conducts) until the voltage across it reaches the cutoff voltage (about 50 volts) and then shuts off.  When the lamp shuts off, the capacitor voltage begins to rise again until it reaches the firing point again.

That's actually a fairly short duty cycle with most of the lighting cycle at a fraction of the power requred for the initial neon ionization.

With the relatively high oscillation rate of the blocking oscillator, I expect that the visual persistance of the human eye will give the series of short pulses the appearance of continuous lighting.

I've increased the voltage to 900 volts so  far with no firing, so this weekend I'll be setting up a new voltage multiplier to take the output to 1200 and then 1500 volts, at which point I'll probably need more parts.

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