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How to Choose a Low Frequency Connector (Part 1)

-Electrical Parameters-

Rated voltage

The rated voltage, also known as the working voltage, mainly depends on the insulating material used in the connector and the distance between the contact pairs. Certain components or devices may not perform their intended function below their rated voltage. The rated voltage of the connector should in fact be understood as the maximum working voltage recommended by the manufacturer. In principle, the connector can work well below the rated voltage. Therefore, we need to select the rated voltage reasonably according to the withstand voltage (electric strength) index of the connector, the use environment and the safety level requirements.

Rated current

The rated current is also called the working current. As with the rated voltage, the connector generally works well below the rated current. In the design process of the connector, the rated current requirement is met through the thermal design of the connector, because when the contact pair has current flowing, the contact pair will heat up due to the conductor resistance and contact resistance. When its heat exceeds a certain limit, it will destroy the insulation of the connector and form a contact to soften the surface plating, resulting in failure. Therefore, to limit the rated current, in fact, limit the temperature rise inside the connector not to exceed the specified value of the design. The problem to pay attention to when choosing is: For multi-core connectors, the rated current must be derated. This should be paid more attention in the occasion of high current. For example, the rated current of φ3.5mm contact pair is generally 50A, but the rated current of 5 cores should be derated by 33%, that is, the rated current of each core is only 38A. The more, the greater the derating.

Contact resistance

Contact resistance refers to the resistance generated by two contact conductors at the contact part. Two problems should be paid attention to when selecting: First, the contact resistance index of the connector is actually the contact resistance, which includes the contact resistance and the contact resistance to the conductor. Usually the conductor resistance is small, so the contact pair resistance is called the contact resistance in many technical specifications. Second, in the circuit connecting small signals, it is necessary to pay attention to the conditions under which the given contact resistance index is tested, because the contact surface will adhere to the oxide layer, oil or other pollutants, and the surface of the two contacts will produce film resistance . When the thickness of the film increases, the resistance increases rapidly, making the film a poor conductor. However, the membrane layer will undergo mechanical breakdown under high contact pressure, or electrical breakdown under high voltage and high current.

Shielding (anti-interference)

In modern electrical and electronic equipment, the ever-increasing density of components and the related functions between them imposes strict limits on electromagnetic interference. Therefore, the connector is often closed with a metal shell to prevent internal electromagnetic energy radiation or interference from external electromagnetic fields. At low frequencies, only magnetic materials can significantly shield the magnetic field. At this time, there are certain regulations for the electrical continuity of the metal casing, that is, the contact resistance of the casing.

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