capacitor bank

[username]

i am going to build a 34kJ capacitor bank using 6 400vdc 12000uf capacitors in series to make a total of 2400vdc but wanted to know if it can explode or fail somehow, can it overload from the voltage?the caps are rated for 400 but the surge is 450. will the 2400 volts be distributed evenly or what? also i bouth one cap to test it out, and noted that they are EXTREAMLY loud when discharged, and just one has a 960 joule energy so i cant realy fathom 34,000, can the sound kill you? i know that the electricity will kill you no mater what but wanted to know about other things so i can be prepared or rethink the design.

[StarKannon]

It can easily blow up if you get back emf. What you should do is isolate each capacitor with diodes so this does not happen. The voltages and amperage you will be playing with are very very very high one screw up and you are done. So you are gonna need to observe some safety rules, always fully discharge your power supply when not in use and store it with a wire in between your output anode and cathode to keep it from building a charge due to free air. (Last one is a little over kill for yours but it is a good habit to get into if you want to make larger). Sound, it will be loud depending on what you hook it up to so I would not worry.

*Memorize these* It will keep you alive
http://www.repairfaq.org/sam/safety.htm

[powerlabs]

At those voltages, the capacitors we are talking about here are most definitely electrolytic. They will not blow up from back EMF, what happens is that the dielectric absorbs the back EMF by electrolyzing a small amount of the Hydroxide solution it is bathed on; a tiny amount of Hydrogen gas is produced, which dissolves back into the electrolyte. At worse case scenario multiple discharges would result in the capacitor venting a little bit of Hydrogen gas.
And no, the sound won't kill you (it will cause hearing damage though). But if you dead short them they will eventually get damaged.

[StarKannon]

I respectfully disagree my professor blew a capacitor with back emf it was depending on the voltages sheer overload will cause them to blow. It is always good and safe practice to isolate the capacitors with a diode.

Though I must admit I am a huge admirer of your work I am trying to build one of the Electro-thermal guns that you demonstrated with a few improvements of my own I have already built rail and coil guns and now I wanna try one of those. Is there any ratio for bore size to ionization of a material? Or any formulas I should be aware of to do with ionization. Thanks,

[powerlabs]

You can blow regular dielectric capacitors from back EMF. And you can certainly ruin 'Lytics very quickly from reverse charging, or overvolting. But back EMF will not blow electrolytics.

You can figure out a good ballpark number as to how much energy is needed to ionize something by doing a simple heat capacity calculation to a temperature where the material becomes a plasma...

[StarKannon]

Perhaps I may be mistaken, still my proff was adamant about it to the point of he would fail that lab if you did not take the proper precautions maybe it was more a lesson in good form more than anything else.

Where would I find the ionization temperature I assumed that and I googled it, but could not turn anything up. Is there a specific site I could read up on the subject more thoroughly or a book title you would recommend?

[powerlabs]

It is not a hard set number because as the temperature goes up more of the material dissociates. A quick google search yields the following:

"
According to Nernst 1864-1941, at the pressure of 1 atm at 1700ºC, about 0.6%, at 2200ºC, about 4 % of all water molecules are dissociated. Following kinetic gas theory, we imagine dissociationto be the following process: When a molecule impacts on another one or the wall of the vessel, it is fragmented into its atoms. The higher the temperature of a gas, the more molecules will attain the kinetic energy required for fragmentation. This is in agreement with the fact that dissociation rises with rising temperature. Individualmolecules can also reach at comparatively low temperatures such large velocities , the required kinetic energy and thereby fragmentation; in fact, the really occurring kinetic energy of single molecules obeys the laws of chance, only the mean value of the kinetic energies of allmolecules is determined uniquely by the temperature. At the temperature t and the pressure p, a definite fraction of n molecules is always dissociated. For example, in steam, under those conditions, nx molecules of n molecules are dissociated, that is, only n - nx = n(1 - x) molecules H2O are present as well as nx molecules H2 and nx atoms O, which form immediately n/2·x molecules O2. Hence there exist after dissociation instead of the initial n molecules n(1 - x) + nx + n/2·x = n(1 + x/2) molecules. The quantity x is called the degree of dissociation. However, after there has been installed a certain degree of dissociation in the mixture of the gases H2O, H2 and O2 , the chemical conversions do not at all finish. Also then every water molecule fragments at a sufficiently strong impact into its atoms. However, simultaneously, if two water molecules and one oxygen molecule impact with sufficient strength, they combine into water. In the equilibrium state as manymolecules fragment as form anew."

[username]

thanks for all the answers!!!