1. Selection of rated working voltage of relay
Rated working voltage of relay is the most important technical parameter of relay. When using the relay, the working voltage of the circuit (i.e. the circuit where the relay coil is located) should be considered first, and the rated working voltage of the relay should be equal to the working voltage of the circuit. Generally, the working voltage of the circuit is 0.86 of the rated working voltage of the relay. Do not burn out the rated voltage of the relay. In addition, some integrated circuits, such as NE555 circuit, can directly drive the relay to work, while some integrated circuits, such as COMS circuit, have a small output current and need to add a transistor amplifier circuit to drive the relay. Therefore, it should be considered that the output current of the transistor should be greater than the rated working current of the relay.
2. Selection of contact load
Contact load refers to the bearing capacity of the contact. The contacts of the relay can withstand a certain voltage and current when switching. Therefore, when using the relay, the voltage added to the contact and the current passing through the contact should not exceed the contact load capacity of the relay. For example, the contact load of a relay is 28V (DC) × 10a, which indicates that the relay contact can only work on the circuit with DC voltage of 28V. If the contact current is 10a, if it exceeds 28V or 10a, it will affect the normal use of the relay and even burn the contact.
3. Selection of power supply for relay coil
This refers to whether the relay coil is using direct current (DC) or alternating current (AC). Usually, beginners in the electronic production activities, are using electronic circuits, and electronic circuits often use DC power supply, so must be the use of the coil is the DC voltage relay.