How to choose the relay

How to choose the relay

Relays are widely used in schemes of management and automatic devices as allow to operate big capacities at the exit at entrance signals of low power, to carry out switching of chains, to fix deviation of characteristics concerning the required level. When choosing the relay for the device of the specific electric circuit it is necessary to be guided by some practical recommendations taking into account characteristics of the device.


1. Define the characteristics of the relay demanded to you. First of all, decide on the necessary size of operation. It represents value of input parameter at which the relay works. The second important characteristic of the relay – is minimum the power brought to operating part which is required for the translation of the relay from initial in operating condition.

2. Find out what operated power is required for the relay in your situation. On the power of management distinguish the relay of chains of low power (no more than 25 W), average power (to 100 W) and the increased power (power relays).

3. Specify the necessary response time of the relay, that is period from the moment of giving of signal prior to impact on the control circuit. On this characteristic of the relay also time relays differ on high-speed, slowed down.

4. When choosing specific design of the relay pay attention to the characteristics relating to device shortcomings: work speed, size of electric and mechanical resource, availability and size of hindrances at disconnection and short circuit of contacts.

5. Evaluate the operating voltage and current intensity in relay winding – they have to be in limits of the permissible values specified in technical documentation. If current in winding decreases, it leads to decrease in reliability of formation of contact. The increased current leads to heating of winding and decrease in reliability of the relay at the maximum allowed temperature.

6. Choose the relay with a little increased characteristics of operating voltage in comparison with demanded. Otherwise at short-term giving on winding of the increased tension can lead to mechanical overstrain in magnetic conductor and contact unit. And the electric overstrain of winding at disconnection of chain can cause insulation breakdown.

7. When choosing the mode of contact units of the relay consider value of the switched current, the nature of expected loading, total number and frequency of switching in chain.

Author: «MirrorInfo» Dream Team