# Powering a railgun

1. May 19, 2012

### StickNinja

For fun I wanted to make a railgun, but I am having trouble figuring out how to generate a high current.

I have a 400F capacitor (only one, but it is suitable for my purposes).
It is rated at 2.7V

So the amount of energy it can store is 1458J, so it should be able to run the gun for 1/29 of a second

The problem I am having, is how do I generate the 150A?
Will it just run at 150A if it is allowed to discharge over 0 gauge wire (no other resistance is involved) or will it run at about about 1.4 amps if I am using 20ft of wire (maintaining 2.7 V)?

Capacitors have always confused me in this regard, any help explaining this would be appreciated.

At 150A, estimated velocity of a .1 gram object is 62 meters a second for this poject

2. May 19, 2012

### the_emi_guy

StickNinja
The capacitor voltage and current will decay exponentially. Start with ohm's law: if you discharge 2.7V with .018 ohms, you will start off with 150A. Both V and I will then decay with a time constant of RC = 7.2sec.

Make sure to check dataheet of the supercap, particularly its ESR and max current spec.

3. May 20, 2012