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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
wumpus, that 'sizzling' sound is a warning. Carefully examine the capacitor operating in the dark each tiny blue light is corona slowly eating away at the insulation....... May be an interresting photographic subject!
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
I also bought some caps from and had them shipped to germany, they seem to be good quality, shipping is fast and cheap, absolutely reccomended.
Are you sure that only a spark in air gives you a short enough flash? I image if you discharge the same capacitor through a xenon flash lamp, the duration will be about the same, but the light output will me much more.
Registered Member #325
Joined: Fri Mar 17 2006, 12:42AM
Location: Turku, Finland
Posts: 55
joe doh wrote ...
Are you sure that only a spark in air gives you a short enough flash? I image if you discharge the same capacitor through a xenon flash lamp, the duration will be about the same, but the light output will me much more.
I've been considering this idea and I did play around with xenon flash tubes a bit. Basically higher voltage means shorter duration pulse and higher peak light intensity for the same energy level. They tubes seem to fail easily when abused like this, and can be dangerous if they explode.
I might still try connecting together a string of disposable camera flash tubes (any idea how many would be ideal?) and fire them at 20kV at a few tens of Joules just to try it out.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
What kind of flash tube are you using? A tiny camera flash one? I think if you get a biggish laser flashtube (which you can easily find on eBay), you are not going to have any problems, as they are designed to take several kJ, whereas your capacitor can only supply about 100J. Bu honestly, I don't think you need that much power, you should be able to get away with a much smaller capacitor (e.g. 50nF at that voltage) so you can safely use your camera flash tube. Have a look at Thomas is using 50nF on a normal camera flash and he is doing some semi-high speed stuff with it.
Registered Member #116
Joined: Fri Feb 10 2006, 03:19AM
Location: Erie Pa, USA
Posts: 29
Toner is definately a non-conductor. The developer (the magnetic material) is also a non-conductor, as it is mainly ferrite- I've pondered its use in a thermite reaction. I have yet to try it untill I get aluminum powder. Try polypropylene sheet instead of the OH transparencys. Rich
Registered Member #325
Joined: Fri Mar 17 2006, 12:42AM
Location: Turku, Finland
Posts: 55
Based on empirical observations, I am pretty sure the toner on my is slides does not cause problems:
The flashovers patterns seems random and do not always occur along areas with toner
I built a small capacitor (just a few nF) using completely blank transparencies, flashover still occured.
I tried moving two electrodes connected to a flyback quickly around a transparency to see how the arc behaves around areas with toner. I did not observe that the toner would affect the behavior of the arc. Only when the plastic melted and started carbonizing did I notice conductivity.
* I have had similar (but not as severe) problems with new, untouched PP sheets.
Registered Member #325
Joined: Fri Mar 17 2006, 12:42AM
Location: Turku, Finland
Posts: 55
joe doh wrote ...
What kind of flash tube are you using? A tiny camera flash one? I think if you get a biggish laser flashtube (which you can easily find on eBay), you are not going to have any problems, as they are designed to take several kJ, whereas your capacitor can only supply about 100J. Bu honestly, I don't think you need that much power, you should be able to get away with a much smaller capacitor (e.g. 50nF at that voltage) so you can safely use your camera flash tube. Have a look at Thomas is using 50nF on a normal camera flash and he is doing some semi-high speed stuff with it.
Thanks for suggestion and link! Very useful . I will definitely consider laser flash tube if I can find one.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
If you find the link usefull but cannot make sense of it I would be happy to translate it for you.
If you have trouble locating a suitable laser flashtube I could possilby sell you one, since I have a couple ranging in size from 5mm x 10cm up to 20mm x 20cm or so. I have not used them in ages, so I might aswell part with one.
By the way, I have now constructed an identical capacitor of OHP transparencies and kitchen Al-foil, which measures 180nF. I have also found the transparencies to be able to stand off quite a lot of voltage - more than I can readily generate anyway. When I have the time I will conduct some tests if I get the same flashover problems.
Registered Member #325
Joined: Fri Mar 17 2006, 12:42AM
Location: Turku, Finland
Posts: 55
joe doh wrote ...
If you find the link usefull but cannot make sense of it I would be happy to translate it for you.
babelfish and some rudimentary German worked out well, thanks for the offer though.
joe doh wrote ...
If you have trouble locating a suitable laser flashtube I could possilby sell you one, since I have a couple ranging in size from 5mm x 10cm up to 20mm x 20cm or so. I have not used them in ages, so I might aswell part with one.
I'll get back to you in a PM on that.
joe doh wrote ...
By the way, I have now constructed an identical capacitor of OHP transparencies and kitchen Al-foil, which measures 180nF. I have also found the transparencies to be able to stand off quite a lot of voltage - more than I can readily generate anyway. When I have the time I will conduct some tests if I get the same flashover problems.
Nice, please let us know your results. This could be a rather efficient way of building capacitors (a few nF per layer) if one can find a reliable way to circumvent the surface tracking problem. Cheap too, at least for people working in teaching institutions, where used OH transparencies are abdundant. The capacitors may not be ideal for resonant applications such as Tesla coils (the dielectric could be lossy), but might do ok for energy discharge applications. My plan is to build a 1uF capacitor able to withstand at least 25 kV in this way.
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Homemade plate stack capacitor, surface tracking problem
. I will definitely consider laser flash tube if I can find one.