Camera flash

Revision as of 16:24, 25 February 2006 by GalFisk (talk | contribs) (+info, typos, etc)
Camera flash circuit

A camera flash can be used for spudgun ignition in several ways, either by itself or by feeding the high voltage from the flash capacitor through a step-up transformer (commonly an ignition coil, flyback transformer or a mains transformer in reverse). The main advantage of camera flash-based ignitions is that it can be built using cheap, readily available components. The spark is more powerful than that of a piezoelectric ignitor. A camera flash is usually powered by one or two AAA or AA cells. Disadvantages include several seconds of recharge time before the ignition can be triggered again, and significant shock hazard from the storage capacitor if built improperly. The camera flash is most easily obtained from a disposable camera, many places that develop films from these will give the discarded camera shell away for free if asked. The flash capacitor can store charge for a long time, and should be discharged before handling the circuit.

The ignition that requires the least modification of the camera consists of cutting one of the main leads to the flash tube, and connecting a step-up transformer in between. Triggering the flash will produce a spark from the output of the transformer. The advantage to using the flash tube itself to switch the main discharge, is that almost any small switch can be used to trigger the circuit. If the trigger switch is replaced by a thyristor (SCR), the ignition can be triggered by an electronic circuit. The flash tube can also be replaced by a heavy duty switch for triggering, though if the switch is too weak welding may occur and ruin the switch. This switch will also be carrying the full voltage of the capacitor, and must be properly insulated to reduce the risk of electric shock.

Another ignition method that does not require an external step-up transformer, consists of removing the flash tube, and taking out the trigger lead as well as the two main leads. These are then connected to three electrodes, which are placed together to form a spark gap of a millimeter or less. Triggering the flash will ionize the air in the gap and discharge the main capacitor. This produces a more intense spark than the first method, but it requires a more complex park gap. The electrodes can also erode over time, requiring readjustment.

A camera flash can also be used to trigger sprinkler valve solenoids built for mains voltage, however the opening time will be brief since the flash capacitor is drained quickly.