Using Solenoids with COBRA Firing Modules

When connecting solenoids (e.g., for flame projectors) to COBRA modules, you may see unexpected behavior such as:

• Another cue fires when the solenoid fires.
• The module reboots immediately after firing a solenoid.

This is typically caused by the inductive “flyback” current generated by the solenoid coil when power is removed. The guidance below explains why this occurs and how to resolve it.

What’s Happening

A solenoid is an inductor. When energized, it stores energy in a magnetic field. When power is cut, that field collapses and releases energy as a voltage spike (flyback). Without suppression, this spike can backfeed into the module and cause unintended cue firing or a reboot.

The Fix — Add a Flyback Diode Across the Solenoid

Install a flyback suppression diode directly across the solenoid’s two leads. The diode provides a safe path for the coil’s energy when the field collapses, preventing the spike from reaching the module.

Recommended Parts

• Diode rating: approximately 100 V / 1 A general-purpose rectifier.
• Use one diode per solenoid.

Wiring Overview

• Connection: Wire the diode in parallel with the solenoid (same two terminals as the solenoid).
• Orientation: The diode must be reverse-biased during normal firing:
  • Connect the diode cathode (marked end) to the cue’s positive terminal.
  • Connect the diode anode to the cue’s return/ground terminal.
• Think of this like adding a second device in parallel on the same cue; the diode only conducts during the reverse spike.

Step-by-Step

1. Disconnect power and ensure the cue is safe.
2. Identify the solenoid’s two leads at the 18M/6M cue output.
3. Attach the diode across those same two points:
   • Cathode → cue +
   • Anode → cue – / return
4. Secure connections (solder/heat-shrink or suitable field connectors). Avoid loose or exposed conductors.
5. Reconnect power and perform a controlled test.