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Structure and protection requirements of car harness

Time:2018-04-10 14:49:26

  To protect the harness in the car, compared with the common protection scheme, the PPTC self compound circuit protector has the advantage over the traditional solution, which can be used to protect the car harness and prevent the damage caused by the overheating accident. They are also easy to design and achieve closer to the ideal tree structure.

  More and more automakers are beginning to realize that an increasingly efficient circuit protection scheme is important in preventing damage to electric windows, electric vehicles, power outlets, and many other functional devices due to large current failures. However, because the structure of the car wiring harness must continuously meet the increasing demand for electrical and electronic devices, it poses a challenge to the protection of the circuit. In response to this challenge, Ho Chi electronics has studied how to use a self compound polymer positive temperature coefficient (PPTC) circuit protector to protect the car harness to prevent possible overcurrent damage.

  The structure of the car harness

  The ideal scheme for car harness is a hierarchical tree structure. "Trunk" is the main power supply, and the main trunk is divided into smaller and smaller "branches", and over current protection is used on each node. When using this structure, we can use space saving thin conductor to reduce weight and reduce cost. When using this harness structure, we can also optimize the protection of the system, and at the same time, we can isolate the faults and ultimately improve the reliability.

  Although the car harness scheme has many advantages, the number of circuits used in the current car is so large that it is difficult to realize dozens of circuits introduced from the junction box in practice. It's almost impossible to arrange it in a convenient location for drivers.

  Therefore, there are some ways to use online beam design, but this will cause some designers' benefits, and then lose them, for example,

  First, because load is incorporated into one circuit, there will be losses in connection line size optimization and load fault isolation.

  Two, the location of the junction box in the car can only be approached and maintained by trained service personnel, thus increasing the cost.

  Three, we need to connect lines between various functional systems, which will increase the length, volume and cost of connection lines.

  Auto harness PPTC self compound circuit protector

  The use of self compound circuit protector, such as PPTC, does not require motorists to maintain. Designers have several ways to use this circuit protector, which can be used alone or combined. For example, as the fuse needs to be replaced, ordinary car doors, car locks, light emitting diodes, and reversing mirrors need to be powered separately, and separate fuses are needed to be protected in the junction box. If the PPTC circuit protector is used on the door module, only one power supply can be used, thus the connection line is saved, the cost is reduced, and the size of the junction box is reduced.

  The junction box installed on the dashboard can still be used, however, the PPTC self compound protector is not installed near the common fuse, and can be installed in the junction box or on the other side of the junction box to save the area of the dashboard, as shown in Figure 2B. Besides, they can be placed closer to the connector, so that the length of printed wiring on printed circuit boards can be reduced. Therefore, the size of the entire junction box can be reduced.

  There is another feasible plan to transform the junction box into smaller boxes, which are installed at all parts of the vehicle without considering maintenance. In addition, the use of self compound circuit protection - their reliability is as high as the relay - the module can switch to protect its own output load, without the need to consider the problem of maintenance by the user in the position of installation.

  In this way, after using PPTC protector, the electrical structure can be closer to the ideal tree structure, and the predicted benefits can be realized.

  The PPTC protector has a variety of shapes and sizes. The through-hole circuit protector and surface mount circuit protector are suitable for modules installed in fuse box or printed circuit board. The ribbon protector can be easily used in the lattice box.

  Besides, a new generation of blade like PPTC protector can be inserted into the junction box as a blade fuse or a bimetal breaker. These protectors are self duplex and do not require user maintenance. Because their shapes are designed to be blades, designers can use it to replace fuses or bimetal protectors and do not need to modify the existing junction box design.

  The PPTC protector has many kinds of rated current products. Compared with ordinary fuse, its rated current starts at a much lower value, and the increment is much smaller. Therefore, they are more suitable for protecting the functional circuit of issuing commands, and can be more flexible in design.

  Typical protection requirements for car harness

  The wiring harness must be protected to prevent serious heating accidents, such as damage caused by short circuit in connection lines. The circuit usually requires a current of 0.10A to 30A, and for the battery system of 12V, the system voltage is 14V (for most trucks and buses, using the 24V battery system, the system voltage is 28V).

Shenzhen totem Industrial Co., Ltd.
Mr. He:15770693022  Mr. Pan:15986631971   E-mail: ttsy@tt-sy.com
Address:Shenzhen city Longhua District Guanlan Street big head No. 279 2 five floor