With the rapid development of electric vehicle, the safety of high-voltage battery system has become the focus of industry and users. In the process of daily use and maintenance, how to effectively guarantee the safety of technicians and the surrounding environment of vehicles is a challenge that can not be ignored.

It is in this context that the manual maintenance switch (MSD), as an important "safety door" in the battery pack, has gradually entered the vision of engineers and maintenance personnel. Although it looks like a simple structure, it plays a vital role in the management of high-voltage circuits.

This article will take you to understand the function, design standards and selection points of MSD, and help you fully understand this key component to protect the safety of electric vehicles.

In order to ensure the safety of electric vehicle maintenance in high voltage environment, the battery pack is usually equipped with a manual maintenance switch MSD, which can disconnect the high voltage circuit, put the maintenance work in a safe state, and quickly disconnect the high voltage circuit in case of short circuit.

Although MSD is only a small component in Pack, it is critical to product safety, so its design and selection are particularly important.

Manual Service Disconnect (MSD) - A critical safety component in electric vehicle battery systems

The basic working principle of MSD is that it is installed in the main circuit, with built-in high-voltage fuse and high-voltage interlock function.

When an external short circuit occurs, the fuse will be blown to cut off the high-voltage circuit; When the high voltage needs to be disconnected manually, the high voltage interlock will be disconnected first and then the high voltage circuit will be disconnected.

In addition, some types of MSDs, such as the MSD700 and Mini-MSD, offer a secondary unlocking feature, as well as features such as seals, manual disconnect handles, high pressure warning signs, and housing and retaining structures.

First, the MSD must be designed so that it can be easily disconnected manually, and the connection must be durable for at least 50 cycles, which may be higher in actual use. After the installation is completed, the protection level of IPXXD must be met, which needs to be ensured by the battery pack enterprise and the MSD supplier. When disconnected, the protection level of IPXXB shall be reached, which is the requirement of MSD itself and can not be ignored. Otherwise, fingers may come into contact with high-voltage dangerous parts, which has serious potential safety hazards.

Secondly, the MSD is usually mounted on the lid of the battery pack, so it must be IP67 or IP6k9k airtight. This shall be considered as an important parameter in the selection and the supplier shall be required to provide the corresponding verification report.

In addition, to ensure the reliability and safety of the PACK throughout its life cycle, it is recommended that MSD components be subjected to vibration testing and IP67 or 48Kpa tightness testing prior to selection. It is also necessary to consider environmental aging factors, such as the high temperature aging test at 125 C or 140 C for 1008 hours. After the test, MSD still needs to meet the air tightness requirement of 28Kpa to ensure its IP reliability.

In addition, the material of MSD is basically plastic except Fuse and HVIL connectors. These materials must meet the fire resistance rating of UL94 V0 to pass the fire test of the battery pack.

If the fire resistance rating of the MSD is insufficient, an external fire source may enter the battery pack from the MSD, causing serious consequences. Therefore, it is important to carefully check the key characteristics with the supplier when selecting an MSD.

In practical applications, the design requirements of MSD are far more than those mentioned above, including functional requirements such as temperature range, on-load cut-off capacity, chemical corrosion resistance, mechanical strength and reliability. In particular, reliability is particularly important in the process of vehicle operation.

In the past, we have found many faults caused by MSD, such as MSD buckle loosening after long-term use, resulting in occasional high-voltage circuit break during driving, which brings great difficulties to diagnosis. Therefore, when choosing MSD, the product and technical strength of the supplier must be strictly considered.

With the gradual platformization of products in the industry, the classification of MSD tends to be stable, mainly based on the two parameters of maximum voltage and maximum current, which not only simplifies the selection process of engineers, but also helps to reduce costs.

Of course, although platform-based MSD products can meet most of the needs, for some specific application scenarios, it may also require customized development by host factories or battery pack companies and MSD suppliers.

Although MSD is small, it has great responsibilities. It is not only one of the core guarantees for the safe operation of the high-voltage system of electric vehicle, but also directly related to the safety of maintenance personnel and vehicle users.

With the continuous iteration of battery technology and the standardization of vehicle platform, the product design and selection of MSD need to be more rigorous and systematic. It is suggested that relevant enterprises should cooperate with reliable suppliers in the early stage of product development to control the quality and performance of MSD from testing and verification, material selection to life management. Only by putting every detail into practice can we truly build a solid high-voltage security line and promote electric transportation to a safer and more reliable future.