1. Selecting Relay Electrical Service Life
Select the relay based on the load type. Standard electrical loads require a relay service life of over 100,000 cycles, whereas loads involving frequent starts-such as vacuum pumps-require a relay with an electrical durability of 800,000 cycles.
2. Selecting Relay Coil Voltage Type
Relay coils are available in 12VDC and 24VDC types; 12VDC is generally selected for automotive relays.
3. Selecting Relay Contact Configuration
Selection depends on the load and circuit design. Generally, a single-pole double-throw (changeover) configuration is chosen for wiper relays and motor forward/reverse applications, while a single-pole single-throw (normally open) configuration is used for other applications.
4. Selecting Relay Enclosure Type
Relays come in sealed (plastic-encapsulated/Type S) and dust-cover types. Sealed types offer superior water resistance, making them suitable for wet areas, whereas dust-cover types offer better heat dissipation.
5. Selecting Relay Contact Material
Relay contacts must possess properties such as resistance to welding, arc erosion, and oxidation. Depending on the load current and required durability, trace metal elements-such as indium-may be added to the contact material.
6. Selecting Relay Switching Current (Make/Break)
There are three types of relay loads: resistive loads (e.g., rear window defroster, cigarette lighter, standard loads), inductive loads (e.g., blower motor, fuel pump, electric motors), and lamp loads. Selection is based on the device type and electrical performance requirements; the relay's make/break current capacity must exceed the load's peak inrush current and steady-state operating current. Special signal-type relays should be used for low-current loads (less than 0.3A).
7. Coil Power
Coil power consumption indicates the requirements placed on the control circuit; the current-carrying capacity of the coil control pin must exceed the coil's power consumption requirements.
