A Tabletop Demonstration Railgun

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The large current pulse needed is usually produced with a bank of capacitors, connected in parallel to the rails. The magnitude and length of the current pulse depend on the resistance and inductance of the wires, rails, and the projectile itself. After a limited amount of trying to calculate/simulate what kind of pulse we would get a more experimental route was taken. The initial power source was a 1.5 mF capacitor at 300 V, yielding the following energy:

E = ½ C V2 = ½ * 1.5 mF * (300V)2 = 67.5 J

This was followed by two capacitors at the same voltage (135 J) and then four (270 J).

Figure : The 1.5 mF caps

After this, new capacitors rated at a higher voltage were used, starting with one 100 mF capacitor at 1 kV (50 J). The voltage was then raised and more capacitors were added, ending with six capacitors at 3 kV, storing 2.7 kJ. This gave a large enough current pulse to easily see the acceleration in the projectile.

Figure : The final capacitor bank

Figure : Closeup of one of the capacitor's specs