Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
I have a question, how can i chargw up my capacitor to full? I tried simply connecting it to a battery and that didn't work because I think it only charged to the battery's power level, when it should go to 400 v. Do I have to put a resistor in series when charging or what?
A capacitor will only charge to the voltage of the battery you connect it to. The voltage rating - 400 volts in your case - indicates the maximum safe voltage you can charge your capacitor to. If you try to charge it to a higher voltage, the capacitor may be damaged.
With large-valued capacitors and batteries with high current capability, you should put a resistor in series to limit the peak current. Otherwise, you can get arcing and accompanying hot metal splatter.