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Ability claim | Voltage drop test
Author.
LCS
Source:
Post time:
2024-10-09
Definition of Voltage Drop
When current passes through a circuit, factors such as the resistance of wires, the resistance generated by components and parts in the circuit, etc. can cause a voltage drop in the circuit, which is called voltage drop.
Measure the voltage at the starting point and the ending point of the power supply, and the difference between the two is the voltage drop.
Reasons for voltage drop during crimping of automotive wiring harness terminals
Terminal crimping relies on the mutual contact between copper wire and terminal to achieve electrical conduction. From a microphysical perspective, any solid surface with a smooth appearance is a rough and uneven surface. Therefore, copper wire and terminal are not in surface contact, but in point contact, and their actual contact area is relatively large compared to the visual contact area.
Metal surfaces are generally covered with oxide films and other types of film layers. Within the actual contact range, only partially crushed film layers or voltage breakdown areas can form direct contact between metals, and most of them are in contact with each other through film layers. Current can only pass through these contact points called "conductive spots". When current is conducted through copper wires and terminals, it will concentrate and flow through those extremely small conductive spots, causing the current beam to contract near the conductive spots. Due to the contraction of the current beam near the conductive spot, the path through which the current flows increases and the effective conductive area decreases, resulting in local additional resistance called "contraction resistance" or "concentrated resistance" represented by R1.
The voltage drop of terminal crimping is mainly composed of the following parts: R=RI+R2+R3
R1 is a contraction resistor, and when the copper wire and terminal are in contact with each other, their surfaces cannot be completely in contact. On a microscopic level, it is a point to point contact. When current flows from one contact to another, the current wire contracts and generates resistance, thus the resistance produced is called contraction resistance.
R2 is the conductor resistance, which is the sum of the Ohmic resistance of the terminal and copper wire. Its magnitude depends on the conductivity, cross-sectional area, and length of the materials used for the terminal and copper wire, as well as temperature.
R3 is the film resistance, which is the resistance generated by the adhesive film or thin film on the copper wire and terminal surface.
Why is voltage drop testing necessary?
Through voltage drop testing, voltage drop phenomena can be quickly detected and timely measures can be taken to repair them, thereby ensuring the normal operation of the electrical system.
01 Check if the circuit is working properly
Testing voltage drop can determine whether the circuit connection is secure, whether the various components in the circuit are working properly, and whether there are faults such as short circuits, open circuits, poor contacts, etc.
02 Prediction of Fault Occurrence
Testing voltage drop can predict the occurrence of faults and take timely measures to avoid losses.
Test method and judgment criteria for voltage drop of automotive wire harness terminal crimping
2.1 QC/T 29106-2014 Technical Conditions for Automotive Low Voltage Wire Bundles
2.1.1 Terminal voltage drop test method is shown in Figure 3. The measurement is taken between the middle position of the terminal and wire crimping point and two points on the 75mm long wire. After deducting the voltage drop of the 75mm long wire, the voltage drop at the terminal and wire crimping point is obtained. When a terminal is connected to two or more wires at the same time, apply current to each wire separately to measure the voltage drop.
2.1.2 Voltage drop determination criteria: The voltage drop at the connection between the terminal and the wire should not exceed the specifications in Table 1. Table 1 QC/T29106 Voltage Drop Determination Criteria
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