One is to "know the enemy", that is to say, firstly, the nature and characteristics of the controlled circuit and the requirements for the 12v DC relay must be carefully investigated and thoroughly understood.

Secondly, comprehensively grasp and carefully analyze the various characteristics of the relay itself, such as principles, operating conditions, technical parameters, structural and technological characteristics, specifications and models, etc.; , Availability and economy are comprehensively considered, so as to correctly select and use relays.
The criteria for the correct selection of relays should be:
(1) The main technical performance of the 12v DC relay, such as contact load, operating time parameters, mechanical and electrical life, etc., should meet the requirements of the whole system;
(2) The structure type (including installation method) and external dimensions of the 12v DC relay should be able to meet the needs of the conditions of use;
(3) Economical and reasonable.
Usually used in automatic control circuits, it is actually an "automatic switch" that uses a small current to control the operation of a large current. Therefore, it plays the role of automatic adjustment, safety protection, and conversion circuit in the circuit. The above three points are the general criteria for selecting general-purpose relays.