Display Electronics Relay Selection

RELAY SELECTION 5 to12 Volt

Tech Note

Relays and contactors are electro mechanical devices (contactors are bigger relays used for higher currents & voltages) and are very useful. They are typically used for switching bigger loads from smaller loads. For example a PIC or microprocessor output could not directly switch a device which drew more than approximately 20 mA. By using relays PIC’s and microprosseors can drive very large loads, only limited by the contact rating of the relay. Being electro mechanical objects, relays can often sustain short overloads and spikes, whereas semiconductor type devices would be damaged. Relays and contactors also offer excellent electrical isolation, guaranteeing noise immunity and in many cases added electrical safety.

When selecting a relay there are 2 main parameters to consider, the coil operating voltage & current and the contact rating. The voltage ratings for the relay contacts, unless specified must be derated when switching DC. Typically a relay able to switch 230 V AC at 1 Amp may only be able to switch upto 30V DC for the same current.