Electronic – Can Radial Electrolytic capacitors blow up from AC

accapacitor

I'm into model railroading, and I was modifying one of the cars to have extra LEDs.

There are 2 wires going through this car that connects to the tracks to receive power. I cut the red and black wires, connected everything correctly to the right polarity for the LED and the capacitor. So I apply full power to the car, 18 volts. The capacitor can take up to 50V (220uf).

All seemed fine, I cut the power to the train and the LED stayed lit for a few seconds as it's supposed to. So I decided to give it full power again and leave it so it can charge the capacitor. All of sudden I started hearing noises then BOOM!!!! The capacitor exploded around my face and burst into flames nearly killing me and destroying my house.

Here's how it looks like.

The film is completely out. I asked one of my friends and he said it's because the power going through the wires is AC and it can feed negative polarity to the positive wire.

Regardless, next time I must use a diode to keep the flow only "+" to the "+" leg. So my question is Why has this happened?

I'm now traumatized of ever using capacitors again.

Best Answer

Electrolytic caps are polarized, they can indeed blow up if you get polarization wrong or apply a higher than rated voltage to them. Same goes for tantalum capacitors, these can be even more dangerous.

If you look at the capacitor, there is a + and a - sign on it, they're there for a reason.

Depending on what you are trying to accomplish, a series diode or a diode bridge may be a solution, but it is hard to tell without a full circuit diagram of your set up.