Back when I was prototyping the wiring for the Marsarium, I got snagged on a bit of a problem. Whenever one of the gas valves closed, everything would wig out a little. I would loose connection with the the relay boards that were controlling all the 12 volt stuff.

Flyback diodes mounted on the marsarium.

When I was describing the problem to my friend Kurt Schoenhoff, he figured it out straight away:

“It sounds like you need some flyback diodes.”

The gas valves used 12 volt solenoids for starting and shutting off the gas flow. Apply 12 volts, and the valve would open. But while the magnetic field inside the solenoid collapsed and the valve closed, it would briefly run in reverse and generate 12 volts. This feedback current ran back into the relay controllers and threw everything out of whack.

Basic flyback diode schematic.

The flyback diode acted as a ‘shunt’, diverting this feedback current away from harm. It channeled it back into the solenoid valve, where it got eaten up by resistance in the wire coil inside. Leaving the relay controllers happy and stable.

I used 1N4004 diodes, which was total overkill. The main difference between the 1N400x diode series is their supported voltage.

The 1N4001 can block up to 50V of reverse voltage, while all the way up at the other end the 1N4007 can block up to 1000V. The 1N4004 blocks up to 400V of reverse voltage, can handle 1A and will have about about 0.7V drop.

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