Electronic – For switching 220VAC, is a specific coil voltage and coil resistance better than another

component-selectionrelayvoltage

Is there any reason why I might choose an EM-relay rated at coil-voltage of 24V or 12V, over one rated at coil-voltage of 5V, all other specs like contact max. current, switching voltage, life etc being same. The only other difference in specs that I see are coil resistance, and contact material.

Most of the circuit schematics I found online, seem to use 12V relays, and very few use 5V relays. Given that low coil-voltage rated relays have lower coil-resistance, I'd only believe that one wastes lesser energy in switching and holding the relay, by using the 5V one, compared to the 12V one.

PS> By default I might order the 5V part, as I have quite a few 5V power supplies at hand, and none rated 12V. But if there's a good reason to use 12V EM-relay, I don't mind. Both parts (5V/12V) cost same.

Best Answer

Relays coils is a current-driven device. If you can apply the specified voltage across the coil, there will be sufficient current and the relay will click. Ohmic losses in the winding is about the only difference.

+5V, +12V, +24V are some of the common supply rail voltages. Of course, the makers of the relays want to make relays for various systems. That's the rationale behind having a family of similar relays with different coil voltages.

P.S. Don't forget the protection diode in parallel with the coil.