Discussion on the Test of Crimping Voltage Drop of Automobile Harness Terminal

With the rapid development of science and technology, the functions of automotive electrical appliances are increasing, and the electrical system is becoming more and more complex. From engine control to transmission control, from driving, braking and steering control to safety assurance system and instrument alarm system, from power management to various efforts to improve comfort, the automotive electrical system forms a complex large system, which is connected by automotive neural network-wiring harness system, which requires the technical requirements of wire harness design, process control, manufacturing and assembly.

As an important control index of wiring loom production, the voltage drop of terminal crimping in automotive wiring harness will affect the attenuation and distortion of signal transmission, as well as the service life, reliability and temperature rise of connector. In severe cases, it will lead to ablation and melting of connector. Therefore, the voltage drop of terminal crimping is controlled as an important index in national standards and major OEMs and wiring harness parts factories. The common test methods and judgment standards of the main engine and wiring harness factory are often not uniform, which restricts the development of wiring harness.

Automotive Wiring Harness Terminal Pressure Drop Causes

Terminal crimping relies on the contact between copper wire and terminal to realize electrical conduction. From the microscopic physical point of view, any solid surface with smooth appearance is rough and uneven. Therefore, the copper wire and the terminal are not in surface contact, but in point contact, and the actual contact area is larger than the visual contact area.

Generally, the surface of metal is covered with oxide films and other kinds of films. In the actual contact range, only some of the broken films or places with voltage breakdown can form direct metal-to-metal contact, while most of them are in contact with each other through films. In fact, current can only pass through these contact points called "conductive spots". When the current is conducted through the copper wire and the terminal, the current will concentrate on those tiny conductive spots, and the current beam will contract near the conductive spots. As the current beam shrinks near the conductive spot, the path through which the current flows increases, and the effective conductive area decreases, so a local additional resistance appears, which is called "shrinkage resistance" or "concentrated resistance" and is denoted by R1.

The voltage drop of terminal crimping is mainly composed of the following parts: R=RI+R2+R3

R1 is the shrinkage resistance. When the copper wire and the terminal are in contact with each other, their surfaces can't be completely contacted, but it is point-to-point contact on the microscopic level. When the current flows from one contact to another, the current line is contracted to produce resistance, and the resulting resistance is called contraction resistance.

R2 is the conductor resistance, which is the sum of ohmic resistance of the terminal and the copper wire. Its size depends on the conductivity, cross-sectional area and length of the materials selected for the terminal and the copper wire, and it is also related to temperature.

R3 is the film resistance, which is the resistance produced by the adhesive film and thin film on the surface of copper wire and terminal.

The Automotive Wiring Harness Terminal Pressure Drop Test Method and Judgment Standard

2.1 Test method and judgment standard of terminal crimping voltage drop in QC/T29106-2004 technical conditions of automobile low-voltage wire harness

2.1.1 Terminal Voltage Drop Test Method

Measure between two points from the middle of the terminal to the 75mm-long wire. After deducting the 75mm-long wire voltage drop, it is the voltage drop at the terminal to the wire crimp. When one terminal connects two or more wires at the same time, current is applied to each wire to measure the voltage drop.

2.2 Test Method and Judgment Standard of Terminal Crimping Voltage Drop in MES67010d Wire Harness

2.2.1 Terminal Voltage Drop Test Method

After the wire is electrified, the minimum, intermediate and maximum value of terminal pressure height (C/H) should be distinguished when measuring. The measured power supply should have a maximum voltage of 50mV when it is open and a maximum current of 100.5mA when it is energized.

2.2.2 Criteria for Judging Electrical Drop

The maximum voltage drop of terminal crimping should be 2mV/A, and the maximum voltage drop of terminal should be 3mV/A ..

2.3 Test method and judgment standard of terminal crimping voltage drop in 24352NDS00N Terminal Pressure Parts Specification

2.3.1 Terminal Voltage Drop Test Method

(1) During crimping, the conductor compression ratio of copper wire is below 80%, which is defined as follows:

(2) Set the terminal pressure height (C/W) to be constant, and take the terminal pressure height (C/W) of the same part as the lower limit value, the middle value and the upper limit value to measure the voltage drop between the crimping part and the wire, and subtract the resistance of the wire part to calculate the contact resistance of the crimping part. When tested, the open circuit voltage is 20±5mV and the short circuit current is 100.5 mA.

3. Analysis of Test Conditions for Voltage Drop of Automotive Wiring Harness Terminal Crimping

3.1 The Difference Between Wires

3.1.1 Difference of Wire Diameter

Due to the different wire standards quoted by QC/T29106MES67010 and 24352NDS0O, the regulations on conductor structure (diameter of single copper wire and number of copper wires) are different, and the nominal diameter of the wire is also different. For example, the wire diameter of the lead sample in QC/T includes 0.75mm, but does not include 0.85mm; And MES standard includes 0.85 mm, but does not include 0.75mm.

3.1.2 Difference of Maximum Wire Diameter of Electric Wire

Because the maximum sizes of conductors are different in QC/T, MES and NDS standards. The maximum nominal diameter in QC/T29106 reaches 70mm².

3.2 Difference of Test Conditions

According to the pressure gauge (requirements for crimping width and crimping height), both MES67010 and 24352NDS00 require that the samples with the maximum, middle and minimum crimping height should be tested under the condition of a certain crimping width. From the terminal crimping process, it can't be guaranteed that the pressure gauge of each crimped terminal is the same in mass production, but its value can be between the maximum value and the minimum value of the crimping height of the test sample, which meets the requirements of the pressure gauge. Therefore, according to MES and NDS standards, if the mass-produced parts meet the pressure gauge, it can be considered that the voltage drop is also qualified. As for QC/T29106, if the terminal voltage of the test sample is 12mm, the test voltage drop is qualified; if the terminal voltage is 11mm or 13mm in mass production, it is impossible to directly judge whether the voltage drop is qualified. Therefore, the requirements of MES67010 and 24352NDS00 on the pressure gauge of test samples are more reasonable.

The MES67010 and 24352NDS00 test currents are only 10±0.5mA QC/T29106, with the minimum current of 5A and the maximum current of 100A. When QC/T29106 is used for testing, when a large current passes through the test sample, the test sample will obviously heat up, and at the same time, the test sample will dissipate heat. It is necessary to obtain the real-time temperature of the test sample, and calculate the resistance of the test sample through the temperature correction coefficient, which makes the test and calculation more complicated. While the test current of MES67010 and 24352NDS00 is only 10±0.5mA, so the heating is very small, which has little influence on the calculation of voltage drop and can be ignored. Therefore, MES67010 and 24352NDS00 require more reasonable test current.

Calculation and Analysis of Voltage Drop of Automotive Wiring Harness Terminal Crimping

4.1 Difference of Deduction Length of Wire

MES67010 and 24352NDS00 wires have a deducted length of 100mm. Compared with QC/T29106, the whole hundred measurement and calculation are more convenient.

4.2 Calculation of Wire Voltage Drop

The voltage drop defined in QC/T 29106 MES 67010 and 24352NDS00 as the test minus the voltage drop of the wire is the terminal crimping voltage drop. However, the applied voltage drop of the wire is not clearly defined as the voltage drop specified in JB/T8139 or IASO D611 or the measured voltage drop. I think the measured voltage drop will be more accurate. JB/T8139 or JASOD611 only defines the maximum voltage drop of the wire at 20℃, and the actual value may be less than the specified value. The actual value is also affected by the temperature, which may cause the voltage drop of terminal crimping to be smaller than the actual value.

Automotive Wiring Harness Terminal Voltage Drop Criterion Analysis

In QC/T29106 test result judgment standard, according to the change of the nominal diameter of the conductor from 0.5 to 70 mm², the maximum voltage drop is 3 to 25 mV/a. MES67010 does not distinguish the wire diameter, the maximum voltage drop of terminal crimping should be 2mV/A, and the maximum voltage drop of terminal should be 3mV/A 24352NDS00, according to the change of the nominal diameter of the conductor from 0.3 to 125mm², the maximum voltage drop is 1.2 to 3mV/a. It can be seen from the table that QC/T29106 is the most lenient criterion. Among the diameters of 0.5mm², 0.85mm² and 1.25mm², 24352NDS00 is the strictest criterion. MES67010 is the strictest criterion among 0.3mm² wire diameters.

Conclusion

In this paper, the test method and judgment standard of terminal voltage drop in QC/T29106MES67010 and 24352NDS00 are introduced and compared. By comparing the difference between QC/T29106' s test method and judgment standard of terminal voltage drop and foreign OEMs, we can make more detailed requirements on terminal crimping and improve the judgment standard.