Flash lamp question.

[Daedronus]

Suppose I have 2 flash lamps connected in series. I know how to compute the explosion energy for each alone, but, how do they behave connected in series respectively how do you compute the total energy for the 2 series connected flash lamps?

[Doc]

I think that you'll have balance problems due to the different striking voltages and current draw characteristics.

STEVE!!

[krazer]

This is a pretty common arrangement used in high power yags (and is certainly better than having them in parallel!), so it should work find as long as you design the PFN right.

I am not 100% sure on this last comment, but to the best of my knowledge a lamp can be modeled as a resistor with some amount of negative resistance, so putting the two in parallel should result in the voltage being shared equally between each one, and since by definition current will be equal, the explosion energy for the assembly should be 2x the explosion energy from before.

[Daedronus]

Suppose they are not the same type of flash lamps, would they balance by themselves?
The explosion energy will be the sum of the energy for each of them?

[mixedgas]

Suppose I have 2 flash lamps connected in series. I know how to compute the explosion energy for each alone, but, how do they behave connected in series respectively how do you compute the total energy for the 2 series connected flash lamps?

It doesn't work that way. One lamp will always explode long before the other because of differences in impedance.

This is why they are almost never mounted in series unless somewhat underdriven or simmered. You need to calculate Ko and there is a on line calculator for that. Lamps are only ran near their explosion energy if you wish to have a short lamp lifetime.

Download the Perkin Elmer flash handbook from their web site. Most lamps, except for the Russian family of lamps, are P.E. designs at one time or another and are thus world standards, as PE bought EG&G that was founded by Dr Edgerton, who developed the xenon strobe. So if you find dimensions that are close to a PE lamp, you have some very similar numbers.

Then Go to Don's strobe FAQ. http://members.misty.com/don/donflash.html

Steve

[mixedgas]

Suppose they are not the same type of flash lamps, would they balance by themselves?
The explosion energy will be the sum of the energy for each of them?

NO. It does not sum. In series, the lamp with the least explosion energy should explode first. And in parallel some circuit means must be installed to balance them, usually a small resistance in series with each lamp.

Lets make sure we are on the correct page of the book,
You understand that the term "explosion energy" means the peak energy that would destroy the lamp 50% of the time correct?



Steve

[Daedronus]

Well, if I want to run them at 20% of the explosion energy I need to figure that out in the first place
And yes, I know about the calculator.

What it wasn't clear was what happens if you have more then one connected in series.

[mixedgas]

Well, if I want to run them at 20% of the explosion energy I need to figure that out in the first place
And yes, I know about the calculator.

What it wasn't clear was what happens if you have more then one connected in series.

Equal sized lamps in series will try to balance, different arc lengths/diameters will not. The if things are equal, the lower voltage lamp, or the lamp with a better cathode, may be a few percent different. It is strongly dependent on age as well. Really long ones go from a reverse slope to a long positive column, ie.. resistive, at some point in the discharge. Since they are in series, Iflash is Iflash, but V tube determines the balance. You can, once the energy peak is past, model them as two series resistors.
Worse case would be a old, depleted lamp, in series with a new lamp.

You will now have two cathode falls, need to form two emissive spots, and may need more then normal boost, simmer voltages, if you are using boost or simmer before starting. That takes a lot of energy, probably considerably more then double the single lamp energy. For sure, you need twice the open circuit voltage of a single lamp.

External triggering may be a real mess unless you can use the same transformer to drive both tubes. Series triggering would be prefered.
If one ionizes early and the other is late, you may not have enough emissivity to transition from Townsend Discharge into Glow and then Arc for both tubes and you'd get a weak flash or no flash.


You are using series triggering?

Steve

[Daedronus]

Yes, I'm using series triggering with no simmer. It's a self built driver and I can probably build one for each lamp, but that will mean a bit more trouble then just strapping them in series.

Also I'm not sure how consistent is my driver, so synchronizing two triggers might prove to be difficult.

[LesioQ]

GentleLase by Candela runs two big lamps from single PFN in series, no simmer, side triggered.
With 30% lamp load (relative to explosion energy) they can withstand up to 1-2millions shots, just have to replace them as a pair. And the laser does 60J at 755nm, 3ms.

Piotr.K