Disposable camera flash

A somewhat common "disposable camera" flash arrangement has a xenon flashtube with impedance characteristic (Ko) of about 11-12 ohms-amps^.5. I take this to mean resistance of 1 ohm at 121-144 volts, and .5 ohm at

The energy storage capacitor is typically charged to 300-330 volts. I have a bit of experience suggesting that its impedance is a tenth or two of an ohm, and that this flashlamp's arc at that voltage can take 50 microseconds or more to "get nice and warmed up and cooking" with the available voltage and energy storage capacitor.

This makes me think that the flashlamp's current peaks with voltage across it maybe around 225-250 volts with its resistance around .6-.7 ohm, which means peak current around 300-400 amps. I would like to say closer to 300 or low-300's than 400, after considering effects of resistance and inductance of wiring from the energy storage capacitor to the flashlamp.

I do remember some bit of some rule of thumb that peak current through the flashlamp in smaller camera flash units is close to initial energy storage capacitor voltage divided by 1 ohm.

This applies more when the flashlamp is is a compact linear one like the ones used in most "disposable camera" flash units, as well as when the flashlamp is the small most-popular U-shaped one used in many cheap "party strobes".

I have a few web pages touching onto this:

- Don Klipstein ( snipped-for-privacy@misty.com)

"Don Klipstein"

The electro used in a typical disposable camera flash is 160 uF, charged to

So from: E = 0.5CVsquared - the energy stored is about 7 joules.

The duration of the flash is close to 1 mS, after which most of the energy is lost from the cap.

So, 6 joules goes west in 1 mS.

Makes the peak power about 6kW.

..... Phil

Ya know, I measured a bunch of caps shorted with a xenon (t_r =3D 5us, kinda slow, but not a bad >1kA switch), but of all the things I tried, I didn't have a photoflash on hand to test.

If you know the capacitor's specs, it's easy to calculate. It's pretty damn close to the short circuit RLC with Vc(0) =3D 300V or so. If ESR > 0.1 ohm, it's more like RL.

Snap-ins are pretty damn nice, BTW. Full discharge in 10us, 1.6kA peak current. Regular aluminum cans stink, usually with ohms of ESR

-- the flash tube hardly pops when you dump one of those things into it.

Tim

That would be average power

You asinine question has no exact answer.

.... Phil

Perhaps if you assume it's an audio question you'll feel confident enough to answer it exactly.

More like average around 6 kW, with peak significantlty greater, over this millisecond.

- Don Klipstein ( snipped-for-privacy@misty.com)

Maybe a bit optimistic. Typical IGBTs for flash service are rated at ~150A peak collector current.

Best regards, Spehro Pefhany

So ballpark figures are 10J and 50kW?

Sounds reasonable (ballpark) -- looks like it is more like 160uF tops in those wimpy disposable camera flashes.

Here's a charging schematic:

Neat little circuit. Thanks

ote:

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I do know that those caps can hold their charge for months..many months.

Handle them as such.

TMT