When the relay is used correctly, the following three aspects are essential.
(1) the rated working voltage of the relay
The rated working voltage of the relay is one of the most important technical parameters of the relay. When using relay, we should first consider the working voltage of the circuit (i.e. the circuit of the relay coil), and the rated working voltage of the relay should be equal to the working voltage of the location circuit. In general, the working voltage of the circuit is the rated working voltage of the relay. 0.86. note that the voltage of the circuit in the circuit must not exceed the rated working voltage of the relay, otherwise the relay coil will burn easily. In addition, some integrated circuits, such as the NE555 circuit can directly drive the relay to work, and some integrated circuits, for example, a COMS circuit output current is small, need to add a level of transistor amplifier circuit can drive the relay, it should consider the rated working current transistor output current should be greater than the relay.
(2) contact load
The contact load refers to the bearing capacity of the contact. The contact of the relay can withstand a certain voltage and current when it is converted. So when using a relay, the voltage that is added to the contact and the current passing through the contact should not exceed the contact load capacity of the relay. For example, there is a relay contact load of 28V (DC) * 10A, indicating that the relay contacts can only work on a circuit with a DC voltage of 28V, and the contact current is 10A, which exceeds 28V or 10A, which will affect the normal operation of the relay, or even burn the contacts.
(3) relay coil power supply
This refers to the use of relay coils for direct current (DC) or alternating current (AC). Usually, beginners in the electronic production activities are electronic circuits, and electronic circuits often use DC power supply, so we must use the coil is a DC voltage relay.

Relay is an automatic switch element with isolation function. When the change of excitation volume reaches the specified value in the input circuit, the automatic circuit control device that can control the electric quantity in the output loop will have a step change. It has an induction mechanism that can respond to some external excitation quantity (electricity or non electricity), an actuating mechanism that controls and controls the controlled circuit, and an intermediate comparison mechanism that can compare, judge and transform the size of the excitation volume. Relay is widely used in remote control, telemetry, communication, automatic control, mechatronics and aerospace technology. It plays the role of controlling, protecting, regulating and transmitting information.
The relay generally reflects the input variables (such as current, voltage, power, frequency, impedance, temperature, pressure, speed and light) of the induction mechanism (input); to the controlled circuit on and off control actuator (output) between the input part; and the output part of the relay, and are coupled to the input isolation function, treatment and mechanism of the middle part of the output (driver).
As a control element, the relay has several functions as follows:
(1) expand the control range: for example, when the control point of a multi contact relay reaches a certain value, it can be changed according to different forms of contact groups, and at the same time, switching, breaking and connecting multiple circuits.
(2) magnification: for example, sensitive relays, intermediate relays, and so on, with a very small control amount that can control a large power circuit.
(3) integrated signal: for example, when multiple control signals enter the multi winding relay according to the prescribed form, it will achieve a predetermined control effect after comparison.
(4) automatic, remote control and monitoring: for example, the relay on the automatic device can be programmed together with other electrical appliances to realize automatic operation.

The relay is called relay. It is an electrical control device. It is an electrical apparatus that causes the controlled variable to have a step change in the electrical output circuit when the change of input volume (excitation volume) meets the specified requirements. It has an interactive relationship between the control system (also called the input circuit) and the controlled system (also known as the output circuit). Usually used in automatic control circuits, it is actually a "automatic switch" that uses a small current to control the operation of large current. So in the circuit, it plays the role of automatic regulation, safety protection, conversion circuit and so on.