so this is just a hypothetical to all you Engineers out there.

is there some kind of limit on capacitors? could you in theory build a capacitor to handle any amount of load?

are there physical limits? those huge lasers and particle accelerators have to have some kind of stored energy to power them, right?

6/17/2006 1:19:30 AM

yes there are physical limits

6/17/2006 2:14:48 AM

Total stored charge = Capacitance * Voltage.

6/17/2006 2:15:50 AM

Are you talking about a single capacitor? Most particle accelerators and things use capacitor banks instead of a single, large capacitor.

6/17/2006 9:19:37 AM

There are real limits relating to the material and geometry used in constructing your capacitor. This is somewhat of an oversimplification but here goes. The dialectric (non-conductive material inserted between the conducting charged surfaces) used as well as the geometry for the most part give you the maximum voltage before dialectric breakdown (the capacitor becomes a short.) The material, size, and geometry are all also involved in the capacitance. Within certain ranges you can basically scale a capcitor along certain dimensions and proportionally increase its capacitance. For example, a cylindrical capacitor could have it's length doubled and its capacitance would follow. If you changed the distance between positive and negative surfaces though, you'd change more than just the capacitance.

This would seem to suggest that as long as you had enough material and enough space you could build a capacitor that would handle any load. The material problem you run into is that at extremely high voltages you'll start to run out of things you can use as a dialectric that won't become conductive eventually as voltage increases. You could of course always use vaccum but vaccum capacitors are much less efficient.

Size also could eventually become a problem too as a large enough capacitor would suffer from large internal resistances. This would also decrease the efficiency and simplicity of the capacitor. You can also see that since we can not nescesarily scale in all 3 dimensions and simply increase capacitance, large capacitors will have complex geometries if they are to also be space-efficient. The computation of electric and magnetic fields within the capacitor during and after charging/discharge may yield other problems (instability during charging/discharge, "hot" spots where voltage can spike and result in shorting, etc.)

^And yeah, they use banks of capacitors rather than a single one. A single large capacitor faces all the challenges I mentioned above as well as being impractical. If a single soda can sized capacitor blew or failed, it'd be a simple thing to replace. If a 60 ton monster failed, it'd be a huge construction project just to replace it let alone buy a new one.



[Edited on June 17, 2006 at 11:47 AM. Reason : ]

6/17/2006 11:30:24 AM

word. i figured as much but i thought i'd ask the experts.

6/18/2006 3:31:32 PM