When working with relays, one of the vital things to understand is the voltage and current requirements of the electromagnetic coil. The coil is the current-driven element that activates the relay when powered. It generates a induced field that actuates the armature, thereby controlling the connected load. If you use mismatched voltage or power to the coil, the relay may fail to activate, or it could be destroyed.

Relay coils are designed to operate at specific voltage levels. Common coil voltages include 5V, 12V DC, 24V, and 120V, available in both DC and alternating current. It is critical to align the input voltage to the relay's specified operating voltage. Using a over-voltage than specified can cause the coil to become thermally overloaded and fail catastrophically. Using a lower voltage may not generate adequate pull-in strength to actuate the armature, resulting in intermittent operation or complete non-response.

Current draw is another key factor. The amount of current the coil draws depends on its ohmic value and the applied voltage, following Ohm’s law. For example, a 12 volt relay with a 240-ohm coil will draw 50 milliamps. Always review the technical specifications for the exact coil current or power rating. If your control circuit cannot supply enough current, the relay may fail to engage consistently. In such cases, you might need a MOSFET or driver circuit to boost the current from a microcontroller or low-power switch.

It is also important to consider whether the relay coil is DC-compatible or AC-rated. DC coils have a steady-state current, while AC actuators are optimized for the alternating direction and 60Hz of AC power. Using a DC relay with AC voltage or AC coil on DC power can lead to thermal stress, audible vibration, or coil burnout. Some relays are multi-voltage capable, but you should always verify the specifications.

Additionally, when de-energizing a DC actuator, a voltage spike can occur due to the collapse of the magnetic field. This inductive surge can damage sensitive electronics like IGBTs or microcontrollers. To prevent this, use a snubber diode across the coil terminals. This diode offers a discharge route for the current to dissipate when the circuit is deactivated.

Always review the product datasheet before connecting a relay. Pay attention to the operating voltage, current draw, energy consumption, and whether it is AC or DC compatible. Never rely on intuition — even small mismatches can lead to unreliable operation or component destruction. Properly matching the coil requirements ensures your relay performs optimally, without risk, and for its complete service life.