On Fri, 3 Dec 2004, Brian Densmore wrote:
Well it depends on the type of capacitor. It would have to be a polarized capacitor. I remember when I used to test power supplies for a company I worked at. We would buy them for our products, but they needed to be tested before being installed in our equipment. Every once in a while a PS would have the capacitor in reverse polarity. Quite a show when a big capacitor blows. Less frequently the capacitor would take too much voltage with the same end result, explosion. why do you say it would have to be instantaneous? Although from the description of the event it was instantaneous.
I'm pretty sure its going to take a few moments of current to start melting the plastic like that. Capacitors release their energy too quick.
I haven't been able to make a capacitor uniformly melt a jacketed wire. The wires would quickly vaporize at one point, leaving the plastic intact except for a small hole. At my last job we used a capacitive discharge device called a "thumper" to locate bad cable sections. It would discharge up to 15 kilovolts from a 15uF capacitor and thump a hole in the bad section.
Just for kicks long ago, I hooked the thumper up to a 40 watt fluorescent light one time. The light appeared to lift off the ground before exploding into dust. That thing made a violent self cleaning bug zapper too.
Oh, did I mention that the wire was dancing? It was pretty cool...
I believe the seperate video inputs of his television use switching diodes to select what video is live. I believe the current shorted the diodes, so all the inputs stay on. If I remember right, these boards cost $50, but only cost $1.00 to fix. But we have a warranty in this case to keep us out of trouble.
I love post mortem troubleshooting. When things go bad, its fun to see what exactly went wrong and keep it from happening again. Sounds like they had a design flaw which they later corrected. So we may have a happy ending out of this.