How big of a capacitor would I need to release 5 amps for 0.2 seconds? Just what the title says, 5 amps for 0.2 seconds. Please bear in mind that I have absolutely no grasp on electrical wiring, so I would appreciate simple terms.
What I need to do is release a burst of electricity for a short time. Not sure about Voltage, but the current should average around 5.2 amps. A 0.3 farad capacitor would be a bit large for my purposes, but if that's what I need, that's what I need.
 A: When a capacitor of capacitance C is charged to a voltage V, and discharged through a resistor R, then the current will decay exponentially:
$$I = I_0 e^{-t/RC}$$
The voltage on the capacitor will follow the same exponential decay,
$$V = V_0 e^{-t/RC}$$
To answer your question one would have to make some assumptions. You will have to do the calculation with your own numbers to get a solution to your problem.
Assume we charge the capacitor to 10 V, and it must not drop below 5 V. Assume further that you want the current to be "no less than" 5 A - so we need 5A at the end of 0.2 seconds.
We can compute the resistor: R = 5V / 5A = 1 Ohm.
We next compute the time constant: dropping the voltage by 50% in 0.2 seconds means that
$$e^{-0.2/RC}=0.5\\
RC = -\frac{0.2}{\log 0.5}=\frac{0.2}{\log 2}$$
With a resistance of 1 Ohm, it follows we need a capacitance of 0.3 F (Farad). That's a pretty big capacitor. You can see them at this link - they are about 10 cm long and 6 cm diameter.
Be warned: such a capacitor is quite a dangerous thing. You have to respect their polarity: if you wire it up the wrong way, it will literally explode and spew electrolyte (=acid). Also, if you charge it up and short circuit the terminals, the energy comes out very quickly - generating a potentially strong spark. I used to make those with a capacitor that was only 0.001 F. I worry about the possibilities with one this size. Note also that the stored energy is $\frac12 C V^2$, so when it is charged to 10V, it stores 15 J. All that energy in a spark can be quite bright. Watch your eyes.
