# What happens when a capacitor is over voltage?

1. Sep 20, 2010

### Wetmelon

I see voltage ratings on capacitors, but I don't know what they mean. Does the cap break down above the voltage?

In application, I have a pair of .047uF caps rated for 5.5V. They are connected to DTR and GND on a D-SUB9 connector for programming a uC. I'm not sure what voltage that pin has, though.

2. Sep 20, 2010

### vk6kro

Voltage ratings on capacitors give the lowest voltage that may destroy the capacitor. This means that the capacitor is permanently destroyed as a capacitor, even if the voltage is removed. It may test as a short circuit, or it may break down at a lower voltage next time the capacitor is used.

Air spaced capacitors are usually not destroyed by high voltage but will arc over if the voltage is high enough. Removal of the voltage is sufficient to restore the capacitor to full capability.

A 5.5 volt capacitor would be unusual. The DTR line from a computer's serial port may carry up to +15 Volts or -15 volts, so the capacitor should be rated at at least 25 volts. This depends on the circuit, of course, and it may already have measures to make a low voltage capacitor safe.

3. Sep 21, 2010

### Wetmelon

Ok. Makes sense. The caps aren't soldered into anything, they are simply in a solderless breadboard. The circuit is attached. They seem to be "BC 473" (ceramic?) caps, yellow case. I did a quick google and I saw 5.5V ratings...

I guess I should get what I really need, huh?

Circuit here. D-sub9 is the pinout in the top left.

4. Sep 21, 2010

### vk6kro

Yes, a higher voltage capacitor will cost a bit more but nothing compared with the grief of having one fail.

A dud capacitor can cause many  worth of destruction of other components.