Barry's Coilguns

RLC Circuit Simulation

This is a Java simulation of a classic RLC (resistor - inductor - capacitor) circuit. You should see an applet (below) with slider controls to adjust the parameters, which controls a graph of inductor current during its initial response.

About the RLC Simulation

Schematic of series resistor, inductor, capacitor This simulates a RLC circuit alone, without the projectile. This coil has constant (fixed) inductance throughout the simulation. This is a "simple" circuit to let you play with various component values and see what happens.

Your goal in this little game is to find a combination of values which result in maximum peak coil current, and which also dies away to near zero in about the time it takes the projectile to pass the mid-point of your coil. Good luck!

So you probably need to estimate first how much time is needed. Look at a crude timing estimate for one approach to get some ballpark figures.

The program will auto-scale the vertical axis to show multiples of 4 and 10 amps. Also, it will auto-scale the horizontal axis based on the natural frequency of the tuned LC circuit. It will display enough time for at least 2 complete cycles, and as many as 8 cycles. Be sure to read the axis labels carefully to understand the scales.

This is the same RLC circuit which is typically analyzed in standard introductory engineering courses. It is a well-understood circuit, and you can find books and equations to describe its characteristics on the web. Please see my analysis on my next web page for some general comments about how this is adapted to coilguns.


Are you having a problem running the applet? This program requires Java Runtime Environment (JRE) 1.4 or above. The current recommended JRE is Version 7 Update 17 as of March 2013.

You can download the latest Java executables from Oracle at Then look through their list for your operating system and click the desired file to download.

If my applet still doesn't work, try to open your Java Console window in your web browser. The console icon will usually look like a steaming coffee-cup. Copy and paste its contents into a message and e-mail it to me for trouble-shooting.

About the Program

This program solves a first-order linear differential equation, by numerically computing the change in voltage and current in each small increment of time. It uses a fourth order Runge-Kutta solution for improved accuracy.

The program was written with IntelliJ ( using Swing classes. My Java source code is open and freely available in (20KB).

I want to keep the Internet clean so please report bugs, request features, send me compliments and make suggestions about the simulator.

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