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Use a transformer as switch (relay) ?

Posted: Mon Jan 01, 2018 3:34 pm
by Lenp
I am building a simple device, to operate a solenoid air valve with a small micro switch. Because I want small flexible wires to the switch, and the switch will be in the operator's hand, for safety I want low voltage on the switch circuit. Unfortunately, line voltage valves are all I have in stock. Yes, a transformer and relay does come to mind, but consider that the relay is not really needed. Just put the transformer line voltage primary in series with the solenoid coil. The primary winding's high impedance does not allow the coil to energize. When the transformer low voltage secondary is shorted, by the switch, the primary impedance will go down and the solenoid energizes. Almost any transformer with a 120 volt primary will work since the solenoid valve draws only parts of an amp, and the switch is isolated by the transformer's windings!

Now you can put that big barrel of salvaged transformers to a clever new use!
For the techie's among us.... ... -a-switch/