Energy Sources

There are basically three distinct energy sources available for use in a coilgun. You can employ an electrochemical cell, a capacitor or an inductor. A brief outline of each source and its associated support components is given below.

Electrochemical Cell -

The most suitable types for a coilgun application are either lead-acid or nickel-cadmium batteries. In both cases the cells have a low internal resistance which is important since this places a limit on the maximum power transfer from the battery. A battery source will maintain a fairly constant voltage during a firing sequence so the energy transfer is not diminished as in the case of the capacitor and inductor sources. A battery is pretty much a stand alone source requiring minimal additional components, a heavy (100's amps) on/off circuit breaker is probably all that is necessary from a safety point of view. You will of course need a charger of some sort to top up the battery from time to time.

Capacitor -

This seems to be the most popular source used and it's not hard to see why. A small high voltage capacitor bank can store a very large amount of energy (several kilojoules) which can be released in a few milliseconds - an awesome power transfer capability. An important factor to consider is the ESR - effective series resistance of the capacitor. This is similar to the internal resistance of a battery and will place a limit on the maximum power which can be drawn from the capacitor. A capacitor bank will need some kind of charging circuit. There are many possibilities here but a simple voltage multiplier or DC-DC converter circuit will usually be sufficient.

Inductor -

An inductive storage system consists of two windings on a closed magnetic circuit - basically a transformer. The primary winding forms the 'charging' side and the secondary winding delivers the output. This is a much more bulky system compared to the capacitor bank. As well as this drawback, there is the need to supply current continually in order to keep the inductor 'charged'. On the up side, the windings can be configured to produce any desired output voltage and current combination (within the capabilities of the device). The output can also be controlled by the collapsing the primary winding current in a controlled manner. Inductor storage systems can be built using superconducting technology which removes the need to continually supply current to keep it 'charged' however it introduces a host of other problems.