Relay Buying Guide
A relay is an electrical control device, which is an electrical appliance that makes a predetermined step change of the controlled quantity in the electrical output circuit when the change of the input quantity meets the specified requirements. It has the interactive relationship between the control system and the controlled system. 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.
Relays are widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment, and are one of the most important control components. Relays generally have induction mechanisms that can reflect certain input variables, such as current, voltage, power, impedance, frequency, temperature, pressure, speed, light, etc., and can implement "on" and "off" control of the controlled circuit. Between the input part and the output part of the relay, there is an intermediate mechanism that couples and isolates the input quantity, processes the function and drives the output part.
Different types of ATO relays
Electromagnetic relay (EMR) consists of electromagnetic system, contact system and release spring. Since the relay is used in the control circuit, the current flowing through the contact is relatively small (generally below 5A), so an arc extinguishing device is not required. ATO provides compact-size electromagnetic relays with common coil voltages of 12V/24V/110V/220V for your choice. How to select the right one?
- Select the power supply voltage of the electromagnetic relay coil: When choosing an electromagnetic relay, firstly, you should choose whether the power supply voltage of the relay coil is AC or DC. The rated I working voltage of the relay should be less than or equal to the working voltage of its control circuit.
- Select the rated working current of the electromagnetic relay coil: For a DC electromagnetic relay driven by a transistor or an integrated circuit, the rated working current of the coil (2 times the pull-in current) should be within the output current range of the drive circuit.
- Select the contact type and contact load of the electromagnetic relay: electromagnetic relays include: single group contact, double group contact, multiple group contact, normally open contact, normally closed contact, etc., should choose the contact type suitable for the application circuit. The contact load of the selected relay should be higher than the maximum voltage and maximum current of the circuit controlled by its contact, otherwise the relay contact will be burned.
- Select the appropriate volume of the electromagnetic relay: The size of the relay is usually related to the size of the relay contact load, and the size of the relay should be determined according to the application circuit.
The solid state relay (SSR) is a four-terminal device with two terminals as the input terminal and the other two terminals as the output terminal, and an isolation device is used in the middle to realize the electrical isolation of the input and output. Solid state relays can be divided into AC type and DC type according to the type of load power supply. According to the switch type, it can be divided into normally open type and normally closed type. According to the isolation type, it can be divided into hybrid type, transformer isolation type and optoelectronic isolation type, with optoelectronic isolation type being the most. Solid state relays are made of semiconductor devices instead of traditional coils, and do not need to rely on the movement of mechanical parts to control the opening and closing of switches, which effectively improves reliability and service life. Since coils are no longer used, problems such as electromagnetic interference and contact "sparks" are not encountered, and safety has also been greatly improved. ATO provides single phase and three phase solid state relays, including DC-AC and AC-AC, with load current from 10A to 120A.
Thermal Overload Relay
Thermal relays are mainly used for overload protection of motors, and are usually selected according to the type of motor, working environment, starting conditions and load properties.
- When the motor windings are connected, the thermal overload relay of two-phase structure can be selected. If the grid voltage is seriously unbalanced and the working environment is bad, the thermal relay of three-phase structure can be selected; when the motor winding is connected by △, it should be Choose a three-phase structure thermal relay with a phase failure protection device.
- For a motor that operates normally for a long time, the rated current of the thermal element of the thermal relay is taken as 0.95-1.05 times the rated current of the motor; for a motor with poor overload capacity, the rated current of the thermal element of the thermal relay is taken as 0.6-0.8 times of the rated current of the motor. For motors that start infrequently, it is necessary to ensure that the thermal relay does not malfunction during the starting process of the motor. If the starting current of the motor is 6 times its rated current and the starting time does not exceed 6s, it can be selected according to the rated current of the motor. For the motor with repeated short-time duty system, the allowable operating frequency of the thermal relay must be determined first, which can be selected according to the starting parameters of the motor (starting time, starting current, etc.) and the energization duration rate.
There are many types of timer relays, ATO offers analog time delay relays, digital timer relays and programmable timer relays for your different applications. The following aspects should be considered when selecting:
- Current and voltage level. For magnetic damping and air damping time relays, the current and voltage level of their coils should be the same as those of the control circuit. Motor type and transistor type time relays, the current type and voltage of their power supply. The rating should be the same as that of the control circuit.
- Delay mode. The delay mode is selected according to the requirements of the control circuit, namely power-on delay type and power-off delay type.
- Contact type and quantity. Select the contact type (delayed closing or delayed opening) and quantity according to the requirements of the control circuit.
- Delay accuracy. Electromagnetic damping time relays are suitable for occasions with low precision requirements, and motor-type or electronic time relays are suitable for occasions with high delay
- The operating frequency should not be too high, otherwise it will affect the electrical life and even cause the delay action to be out of tune.
Signal relays are commonly used devices in automatic control systems. They are used to connect and disconnect circuits to issue control commands and reflect equipment status to form automatic control and remote control circuits. All fields of automatic control use relays. ATO signal relays are available from 1.5V ~ 24V. Signal relays play an important role no matter as the core part of the relay signal system or as the interface part of the electronic or computer signal system. The reliability of the action of the relay directly affects the reliability and safety of the signal system.
How to select a relay?
When selecting a relay, factors such as the type of power supply, the rated voltage and rated current of the contacts, the rated voltage or rated current of the coil, the combination and number of contacts, the pull-in time and the release time should be mainly considered.
- Understand the necessary conditions, for example, the power supply voltage of the control circuit and the maximum current that can be provided; the voltage and current in the controlled circuit; how many groups and what form of contacts does the controlled circuit need? When choosing a relay, the power supply voltage of the general control circuit can be used as the basis for selection. The control circuit should provide enough working current to the relay, otherwise the relay pull-in is unstable.
- After checking the relevant information to determine the conditions of use, you can find out the model and specification number of the relay you need. If you already have a relay on hand, you can check whether it can be used according to the data. Finally, consider whether the size is appropriate.
- Pay attention to the volume of the equipment. If it is used for general electrical appliances, in addition to considering the chassis volume, the small relay mainly considers the circuit board installation layout. For small electrical appliances, such as toys and remote control devices, ultra-small relay products should be used.
As a control device, ATO relay has the following functions:
- Expand the control range: For example, when the control signal of a multi-contact relay reaches a certain value, it can switch, break, and connect multiple circuits at the same time according to different forms of contact groups.
- Amplification: For example, sensitive relays, intermediate relays, etc., with a very small amount of control, can control circuits with high power.
- Integrated signal: For example, when multiple control signals are input to the multi-winding relay in a specified form, the predetermined control effect is achieved after comparison and synthesis.
- Automatic, remote control, monitoring: For example, the relay on the automatic device can form a program control circuit together with other electrical appliances to realize automatic operation.