Would a 450V parallel plate capacitor made from copper or aluminum foil melt when discharged through a circuit of about 1 ohm?

Answer 1

There's no reason for the capacitor to heat up, because it's only storing energy,

not dissipating it. When you discharge the capacitor, the energy flows out and

through the external circuit, and that's where it dissipates. If anything is going to

melt or explode, it's going to be something outside of the capacitor, through which

you try to jam the energy.

Which brings us to the 1-ohm resistor . . .

You have said that you have a "450V" capacitor. The rating marked on a capacitor

isn't the voltage across it when it's charged ... that can be whatever you make it.

The marking is the maximum that the capacitor can hold without arcing across

between the plates ... the number is called the "maximum working voltage".

You can try to charge a capacitor to whatever voltage you want, but it won't

hold any more than the number marked on it.

In order to discuss the fate of that 1-ohm resistor, we have to know what the

initial charge is on the capacitor. The only number given in the question is 450V,

and even though that's more likely the "max working voltage" of the capacitor,

let's assume for the moment that the capacitor is actually charged up to 450 volts DC.

The charging is complete, the staff retreats behind their bullet-proof plexiglass

bunker, puts on their dark glasses, and prepares to push the button that will

remotely close the circuit and discharge the capacitor through the 1-ohm

resistor. The button is pushed, and here's what the high-speed camera reveals

after the smoke clears and the fire units have departed:

As the energy drains from the capacitor, the voltage on it steadily dwindles.

How fast it dwindles depends on the resistance of the external circuit, and on

the "capacitance" of the capacitor (which tells us how much energy it takes to

charge it up to any given voltage).

What we do know about this circuit is that the capacitor is charged initially to

450 volts, and that it discharges through 1 ohm. This is enough for us to

calculate the initial current at the instant the switch is closed ...

I = (450 volts)/(1 ohm) = 450 Amps.

We can also calculate the power dissipated by the resistor at that instant:

P = I2 R = (450)2 x 1 = 202.5 kilowatts ... roughly the power that would be

demanded of a car battery if it had to start 85 cars all at the same time!

Regardless of the capacitance, and how quickly the charge on the capacitor

dwindles down from 450 volts, it's likely that this initial surge through the

1-ohm resistor causes it to self-destruct like a pellet of plutonium on the

tower at White Sands.

To answer the question:

Your capacitor is safe from harm. But if you're going to discharge it through 1 ohm,

then please wear gloves, safety glasses, and a kevlar apron.