HOW FLASHES WORK:
The way a flash works is simple, a large charge of electricity is released through a tube filled with gas producing a bright light. This actually works in two stages.
1) The capacitor is charging by the power supply.
2) During this time (the delay between shots) the gas comes out of ionization.
3) When charging the voltage cannot overcome the resistance of the gas locked in the flash tube.
4) The charging is usually indicative with a slight whine and then a “ready-light” comes on”.
5) But when charged fully and released by the camera shutter either direct or through a relay, the “trigger voltage” will cause the gas to be ionized and it will conduct the main charge to create a brief flash of light.
6) You press the shutter release, the camera will trigger the flash in synchronization with the curtains or mirror and exposure will take place either on film or digitally saved.
7) Since flashes have different power potentials how do we know the right amount of light was released?
8) We don’t, but the flash knows if we imputed the right data.
9) It's really quite slick, nothing too complex and the main components are capacitors to store energy, an energy source like a battery pack and a flash tube. The energy from the battery charges the capacitor. This is the “recycle time” from dead to peak in milliseconds, seconds and minutes, which seems like hours when you have a prancing diva coming down the aisle.
The main capacitor discharges rapidly through the gas at nominal voltages usually around 320-330 volts. In older units (285 HV Vivitar from Japan) this voltage was usually triggered by the shutter contacts in the camera. In the pre-digital days these contacts were heavy metal able to handle 250-300V internal to the camera.
The point here is very important because digital cameras have electronic circuits very sensitive to high voltage. To guard the camera, the problem is solved by the use of a relay in line in the flash which isolates and handles the stronger current. The camera contacts are isolated from the high voltage because the relay is triggered by as little as six volts on contact
The knowledge base is important here because similar looking flashes even with similar sounding names will have catastrophic effects if used wrong. Several devices made by Wein Corporation are offered to isolate the high current and drop the voltage to a comfortable six to eight volts.
They look like an additional hot shoe and fit between the synch cord and the hot shoe thus they will not allow anything but the simplest PC and hot shoe tasks. No I-ttl or D-ttl or E-ttl capability.
Be safe, there is a safety list located at www.botzilla.com/photo/strobeVolts.html This website provides what individual owners have tested on their personal flashes. I further caution some may be accurate and some owners might not of known what they are doing. I still give this site a fairly high rating as to accuracy. Call me if you are puzzled.