Capacitor Questions

[Sublime]

I'm pretty new to this, and I've just been constantly studying and watching videos on everything about electricity and soldering and components. I've been watching EEVBlog for quite a while, as well as quite a few other people, and I've recently been tearing down my own things to further understand things on a hands on level. Well, one question I have is this: I've heard Dave and a few others mention to be careful with 200V capacitors and that they could really hurt and shock you, even if unplugged. Can someone expand on this? How can one be shocked by a capacitor? Touch the metal prongs? Or is it only if your skin is charged? What is a safe way to discharge a 200V Capacitor? I saw one comment say they were shocked after a week of leaving their device unplugged. How long do I have to wait?

[Stonent]

Well capacitors are somewhat like small rechargeable batteries that can put almost all their power behind a discharge.  The capacity is rated in Farads, or usually MicroFarads (uF), NanoFarads (nF) and PicoFarads (pF).

I doubt nF and pF will hold anything long enough to hurt you if the device has been off for a while.

If you're in doubt, usually a screwdriver across the terminals is a good way to discharge.  Be warned though that sometimes a capacitor will cause the screwdriver to stick because capacitors can put a lot of Amps behind their discharge. The more farads, the longer they will hold a charge and the more energy will be behind the discharge.

Whenever working with higher voltage, do not put yourself in a situation were electricity could go through one arm and out the other. That's how you can get killed, so keep an arm behind your back.

In this video a 2.7 volt 2600 Farad capacitor is used to do some welding.

[Stonent]

I'd also recommend this video:

[Sublime]

Thank you!!! That is much appreciated!