Flashlamp Video

[planters]

They usually do have a preferred direction. At high pressures the valve usually leaks less when the higher pressure side is not against the packing. For vacuum to atmospheric this should not be important. There may be less turbulence in the direction that gives you better flow, but as long as the adjustment is continuous ie predictable, then you should be OK.

[Draco]

ok, tubing is now ordered, all i need to do is machine the electrodes and i have every thing i need to start experimenting with home made lamps, even thorated rods, thorium allways has a warm place in my heart (not literally of course metaphorically)

[Draco]

I now have all the parts to start machining and i have been working on the timer control for the trigger, the two options i currently have is to use the timer to turn on and off the whole 555 circuit
or use it to just directly to control the fet while leaving the 555 running, or just cycle the power to the whole driver board, what would be the preferred method? There are not bug caps on this that would need current to charge and interrupting power to the 555 is easier, i was wondering which would be best for this situation?

[Draco]

well just as a feared the emi killed the timer module, i think i need to shield the hell of of it now so time controll take 2

[planters]

Remember what I said about the Lasorbs? I killed a few Chinese 555 timers the same as you did before these were installed in parallel with the timer power supply and the timer modulation output. I did not do anything else and, knock on wood, no problems so far. I have a pulse generator, on-and-off toggle on the front of the big laser. When I turn it on, it repetitively pulses at its set frequency, but if I want a single shot I simply switch the power on to the module and as soon as it fires I switch it off again. This is not very sophisticated, but it works well.

[Draco]

I ordered this lasorbs this morning and dug out some high speed diodes as well. Now does all your gear use the same ground buss, i was considering a separate power source for the timer board, like a wall wart or something like that, right now i am making a small shield as well for the timer. only it was just the timer that failed, the 555 on the driver board is still happily working

[planters]

Same ground buss. Heavy gauge, short and tightly clamped. Then, Lasorbs wherever I am in doubt. I also do a run through whenever I add a component and check potentials. I have made a few stupid wiring mistakes and this saved me. I am an advocate of non conductive hardware. My optical "bench" where the head and the optics sit is fiberglass and the screws are nylon. 20kJ can sit inches below!

[Draco]

yeah that's a great practice, when i went with a base for my capacitor bank i went with a plastic one even though it cost more, that voltage multiplier has all nylon hardware as well, i think we both have had similar experiences when we found that somthing that should have not been conductive or connected to ground was conductive and/or grounded, i used to work on a non conductive platform when i had to stand on cement, heck even with shoes on i found out the hard way that they form a capacitive coupling to ground. I am glad i made these learning mistakes on lower current stuff.
I made a few changes to the trigger supply, i added a few chokes with capacitors in hopes to filter out anything going to my power supply and till i get the lasorbs i put diodes across the input to my spare timer and shielded it the best i can.
here is the base schematic i used for this device

[planters]

I am using an automobile, trigger transformer for the step up and so I actually switch several hundred volts from a few uF snubber cap into the primary winding of the transformer. You are doing the more classical "dump" of the 12V in the primary winding, using the transformer's inductance to store the energy. How long are the sparks?

Regarding your previous question, based on this drawing, I would probably place a switch to interrupt the coil dump so that once you have dialed in a particular rate, you could "fire when ready". I have another concern that I don't have the knowledge to answer. If the high voltage will be used to capacitively couple to the low pressure gas in the flash lamp, I think you will have some ringing in the high voltage coil. This might induce some stray voltages into your transistor. I don't know how significant this might be.

[Draco]

With the current set up i am getting about 1cm to 1.5cm of arc length, and it indeed does ring, I am measuring a peak around the range of 200-400 volts with a duration of around 50-200us when i am drawing an arc, when it's left open i can't seem to measure any ring at the input to the driver, with a .5mh choke in series with the timer and zener diodes at the time i knock it down to 40 volts.
it does fire my largest commercial lamp that has a gap of 125mm.
One thing the schematic does not show is the FET, the IRF640 has an internal fly back diode, i think that is what it's called, it's shown as a zener diode with the cathode connected to the drain and anode to the source, my idea was the same as yours, i was going to ground the gate with the relay on the timer, i dont believe that would damage the either device. the diodes i put on the timer seem to be working like they should but i am diffidently open to other suggestions, the ignition coil you use though is out of my price range. i also ordered the lasorbs.