How to choose relays according to requirements?

Update:31-03-2021
How to choose a relay:
1. First understand the necessary conditions  
①The power supply voltage of the control circuit, the maximum current that can be provided;   
②Voltage and current in the controlled circuit;   
③How many sets and types of contacts are needed for the controlled circuit. When selecting a relay, the power supply voltage of the general control circuit can be used as the basis for selection. The control circuit should be able to provide enough working current to the relay, otherwise the relay will be unstable when it is closed.   
2. After consulting the relevant information to determine the conditions of use, you can search for the relevant information to find out the model and specification number of the required relay. If you have a relay in hand, you can check whether it can be used based on the data. Finally, consider whether the size is appropriate.   
3. Pay attention to the volume of the equipment. If it is used for general electrical appliances, in addition to the cabinet volume, small relays mainly consider the circuit board installation layout. For small electrical appliances, such as toys and remote control devices, ultra-small relay products should be used.