How to choose the appropriate PCB relay
What should I pay attention to when choosing PCB relays? Here are four aspects to explain how to choose the appropriate PCB relay:
Electrical parameters
Load current and voltage
Clearly define the load current size and voltage range in the application scenario, ensuring that the contact load capacity of the selected PCB relay can meet the requirements and has a certain margin. For example, when controlling low-power LED light circuits, small current/voltage relays can be used, while in high-power devices such as motors, relays must be used to control high current and voltage. The specifications of general relays usually indicate the rated current and voltage of the contacts, such as common specifications such as 5A/250VAC, 10A/120VDC, etc.
Consider the following types of loads: resistive loads, such as resistive heating wires; Inductive loads, such as motors and transformers; And capacitive loads, such as capacitor banks. Inductive and capacitive loads can generate significant surge currents during on/off times, and relays that can withstand such surges should be selected. Usually, the current margin of a relay must be appropriately increased according to the type of load.
Coil voltage
Next, determine the type of AC or DC power supply provided by the control circuit and the amount of power supply voltage, and then select the matching relay coil voltage. For example, if the power supply used on the control circuit is 12V DC, a PCB relay with a 12V DC coil voltage needs to be selected.
Pay attention to the voltage stability in the control circuit. If the voltage fluctuation is very large, you can consider choosing a relay that allows a wide range of coil voltages, or taking voltage stabilization measures to ensure that the relay works properly.
Switching frequency
Understand the switching frequency that relays must withstand in application scenarios, including the amount of time relay contacts can be turned on and off per unit of time. If the switching frequency is high, longer mechanical and electrical lifespan should be considered to ensure reliability even in long-term high-frequency switching. In specific control circuits on automated production lines, relays may switch frequently;
Therefore, it is necessary to pay attention to the lifespan indication of the relay. At low switching frequencies, although the requirement for lifespan may be relatively low, the stability of the relay over a long period of time cannot be ignored to avoid performance issues such as contact oxidation caused by prolonged stagnation.
Physical parameters
Size and installation method
Choose PCB relays of appropriate size while keeping in mind the space limitations imposed by the application. If the space of the PCB board is compact, it is necessary to choose miniaturized relays, such as surface mount relays. If there is enough space, large-sized relays such as needle relays can be chosen, which can have relatively good heat dissipation performance. The length and width of common small PCB relays may only be a few millimeters, while large PCB relays may exceed ten millimeters or even larger.
Installation method on PCB board: For example, plug-in type, which means inserting pins into sockets on the PCB board; Surface mount, which is directly soldered onto the surface of the PCB board; Or other special installation methods. Ensure that the installation method of the selected relay complies with the design and process of the PCB board, making it easy to install and solder.
Number and arrangement of pins
According to the control circuit requirements of the application, verify how many pins are needed for the relay: for example, a simple switch control may only require a set of normally open or normally closed contacts, resulting in fewer pins. Complex logic control or control of multiple loads may require multiple contact combinations, thus requiring relays with more pins.
Pay attention to the distribution of pins, which should correspond to the circuit distribution on the PCB board to avoid issues such as pin crossing and interference, which can further facilitate wiring and soldering.
Environmental parameters
Temperature and humidity
When the application scenario is in a high-temperature environment, or when the internal heat dissipation is poor and the temperature is very high, a high-temperature resistant PCB relay must be selected. Besides, because the current-carrying capability is lowered and the life is shortened in the high-temperature environment, the performance change of relays under high temperature should also be taken into consideration. Meanwhile, it is important to ensure in parallel that the plastic casing of the relay and other materials will not be deformed or aged at high temperatures.
In case of high humidity, such as in damp basements or in electronic devices by the sea, relays that feature good moisture resistance should be used to avoid water vapor from entering the relay and thus causing contact corrosion or degradation in insulation performance along with other failures. The level of protection or the IP rating of the relay can be consulted to assess the level of moisture resistance.
Vibration and impact
If equipment is subject to vibration and impact during operation, such as in vehicle electronic devices and industrial machinery, etc., anti-vibration and anti-impact PCB relays should be selected. This includes the structural design of relays that can withstand a certain degree of vibration and impact and the internal contacts and connections being stable to avoid poor contact or disconnection of contacts as a result of vibration and impact.
In addition, special installation methods or shock-absorbing measures can also be considered for special vibration and impact environments in order to further protect the relay.
Electromagnetic Interference
If there are large motors, frequency converters, communication equipment, and other strong electromagnetic interference sources around the application scenario, it's necessary to choose PCB relays with superior EMC so that external electromagnetic interference will not influence the normal operations of the relays and cause misoperation or distortion of signals. You can check the EMC-related indicators and certifications of the relay.
Meanwhile, the electromagnetic radiation of the relay to the outside should be estimated in order not to interfere with other sensitive electronic devices. During the design of the PCB boards, reasonable wiring and shielding can be considered to reduce the effect of electromagnetic interference.
Performance and Quality
Brand and reputation
The well-known brand and good reputation of PCB relay manufacturers ensure better performance, quality, and reliability of their products. QIANJI is a supplier engaged in the production and manufacturing of relays for more than 20 years, with strong core strength and guaranteed relay quality. The relays produced usually undergo strict quality testing and verification processes, and the consistency, stability, and durability of their product performance reduce the probability of failure during use
Quality certification
QIANJI's products have relevant quality certifications, such as IEC, UL, Ce and other national or regional certifications. These certifications mean that the product has reached a certain level of safety, performance, and quality, which can provide great reference in the selection process.
For example, some application areas, such as medical equipment and industrial control systems, require high security. The use of relays should pass relevant safety certifications to ensure the safety of personnel and equipment.
For example, some application areas, such as medical equipment and industrial control systems, require high security. The use of relays should pass relevant safety certifications to ensure the safety of personnel and equipment.
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