(Almost) shot dead by my flash

[Leigh B]

I've repaired both my canon 540ez and 550ex multiple times. guess im lucky

Probably,

I was a warranty service station for Novatron studio strobes, and have a healthy respect for high-voltage circuitry.

In an earlier life, while I was going to night school, I worked for a company that serviced Sorensen commercial power supplies. When you work on one in that's rated 10 AMPS at 5,000 volts, carried in on a fork lift, you're reluctant to take chances.

- Leigh

[Discoman]

Something to note is that some of the older caps can still retain a hefty charge even after being 'drained'. After a few minutes, or hours, the residual charge can appear at the terminals, making for nasty surprises.

My advice as an extension to this: many caps that carry higher voltages can store their power for easily several weeks after being unplugged. High voltage caps can still pack a very nasty surprise a month later.
Unplug the device for a couple weeks, the use a resistor discharge.
I have a book somewhere that has some HV projects and it has how to properly discharge caps, and how to do so safely.

[albada]

As to the voltage rating on the capacitors...
The voltage rating is always higher than the actual voltage during operation, as a safety measure.
Good engineering practice requires a factor of 2 for most applications, i.e. a 400-volt rating for 200 volts applied.
- Leigh

I've done a number of repairs and modifications of flash units. Yes, those caps are dangerous! I always put a large bleeder resistor across them before doing anything to a flash unit.

Anyway, that 2x safety factor is *not* followed inside most flash units. If the cap is rated at 330V, then that's probably what the flash will charge it to with fresh batteries.

Mark Overton

[Leigh B]

I've done a number of repairs and modifications of flash units. Yes, those caps are dangerous! I always put a large bleeder resistor across them before doing anything to a flash unit.

Having serviced many studio flash systems, and I concur in the use of a bleeder resistor in all cases. Better bled than dead. (Sorry )

Anyway, that 2x safety factor is *not* followed inside most flash units. If the cap is rated at 330V, then that's probably what the flash will charge it to with fresh batteries.

The operating environment of a battery-powered flash is very different from that found in an AC-powered flash.
Battery-powered units are generally incapable of generating over-voltage conditions, while that problem is quite common in AC-powered units.

The other constraint on electrolytic capacitors is the products available on the market. Caps rated higher than 500 volts are quite uncommon, so it's difficult to meet the 2x goal, but it's quite common to find caps rated at voltages significantly higher than nominal operating voltage.

- Leigh

[JBrunner]

It's really very simple. All electronics run on magic smoke that the scientist guys put in them. I have verified this by repeated observation. Whenever the magic smoke gets out of one of my gadgets, it doesn't work anymore.

[Newt_on_Swings]

I had an Olympus F280 hi-speed sync flash explode and burn on me a day before halloween. I was using it to shoot for an hour or two at a haunted house we made, and then after work while I was at a bar it started to smoke, heat up super quickly, and deform. The flash was practically brand new, bought it used, but there wasnt a blemish on it and worked quite well that day until it decided to explode.

I had barley enough time to rip out the enloop batteries with my shirt sleeve, as the temp started to get so hot the battery casings started to melt, and the plastic started to lock in around the batteries.

Turned out the main capacitor exploded and burned, it melted the front "red eye" of the flash, as well as a gapping hold in the battery compartment, plus a sicking burning smell. It sucked to have to replace a brand new purchase. I had to buy a new one luckily for only ~$50

[jp498]

I was tinkering with a small flash once, just a little cheap low GN one. I had it apart and touched a high voltage pin or cap. It locked my arm and hand up solid and I couldn't let go. I ended up quickly swatting the flash away with something in my other hand. I don't recommend trying this. If you do have to poke around, I agree with the bleeding suggestion, and I'd also keep one hand in my pocket for electrical shock safety.

[guitstik]

Studies have shown that current induced by voltages as low as 42 volts can be fatal.

I would hate to be a part of that study group. "Ok, so now we know 41volts won't kill you, let's see what 42volts will do, hold still please".