Silicon Controlled Rectifier

The SCR is the high-current solid-state switch. Its requirements are defined by the maximum capacitor voltage, and the maximum expected current.

Silicon Controlled Rectifier

For this coilgun, the PIV (peak inverse voltage) is limited by this capacitor's specifications to 250v.

The peak current is found from the equations for RLC circuits, or from my RLC Simulator applet.

Assuming: C = 12,000 TF, L = 200 TH, V = 200vdc, R = 10 milliohm

Estimated peak current I_peak = 670 A, as shown in the screen capture below:

Therefore, we will choose an SCR with a short-duration (5 ms) rating of more than 670A. Or, we will find an SCR with a sustained current rating of 67 A or more, since SCRs can typically handle a 10x over-current for very brief periods.

The chosen SCR is a stud-type GE C158N, rated for 110A and 800v.

This SCR is a relatively inexpensive device, purchased on eBay for $4.50 USD each. A photograph is shown below.

Last update June 25, 2007 by Barry Hansen ©2007