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What is the Use of the Manual Service Disconnect (MSD)?

Time:2024-03-18   Author:As Beam   Browse:

A battery pack is a device for storing and releasing electrical energy, usually comprising multiple battery cells. It is extensively used in various electronic devices and vehicles, such as mobile phones, laptops, electric vehicles, etc. The primary function of a battery pack is to provide a portable power source, enabling devices to operate independently. The capacity, voltage, and other parameters of a battery pack vary according to different application requirements. Moreover, to ensure the battery's safety and stability, battery packs are usually equipped with protective circuits and temperature control systems. The development of battery packs also focuses on environmental protection and sustainability, with numerous studies aimed at increasing energy density, extending lifespan, and reducing environmental impact.

With the popularity of 800V platforms in electric vehicles, high-voltage safety has become increasingly important.


What is an MSD?

The Manual Service Disconnect (MSD) is a switch device used within battery packs or high-voltage distribution assemblies to disconnect high-voltage circuits. This ensures quick separation of high-voltage circuit connections during maintenance or in case of sudden short circuits, safeguarding technicians. Typically installed in the main circuit, MSDs are built with high-voltage fuses and designed with high-voltage interlock features. In case of an external short circuit, the fuse will melt, cutting off the high-voltage circuit; for manual disconnection of high-voltage, the high-voltage interlock is disconnected first, followed by the high-voltage circuit. The design and selection of MSDs are crucial, involving product safety.


For new energy passenger vehicles, it is generally placed outside the battery pack housing for direct high-voltage disconnection during maintenance.


The installation location of the Manual Service Disconnect in electric vehicles varies widely, including inside the central armrest box or rear armrest box of the cabin, in storage boxes, etc., above the power battery assembly. Depending on the model, the vehicle maintenance manual should be consulted for location.

The Manual Service Disconnect is known by different names:

Manual Service Disconnect (MSD)

Emergency Manual Service Disconnect (ESS)


There are typically two ways to arrange the Manual Service Disconnect:

The first method places the Manual Service Disconnect at the positive pole of the high-voltage source. The second method positions the Manual Service Disconnect in the middle of the power battery assembly. In this case, the Manual Service Disconnect is located at the positive pole of the power battery, with a segment of the circuit between it and the Manual Service Disconnect. If the second arrangement is chosen, it must ensure that this circuit is placed in an area unreachable by the human body, usually inside the power battery assembly.

According to GB/T 19751-2005 "Safety Requirements for Hybrid Electric Vehicles," if the high-voltage connector can be disconnected without tools, it must meet the IPXXB protection level when unmatched, i.e., preventing direct finger contact. Thus, the base socket of theManual Service Disconnect should be designed according to the IPXXB protection level.


Recommended Steps for Operating the Manual Service Disconnect:


First, turn off the ignition switch and remove the key from the smart key system detection range (it is recommended to place it in a separate box).

Disconnect the negative terminal of the low-voltage battery and protect it.

Ensure insulation gloves are airtight and correctly worn.

It is recommended to follow these steps when operating the Manual Service Disconnect:

After disconnecting the Manual Service Disconnect, keep it in a separately controlled place, preferably in a dedicated box.

For safety, wait at least 10 minutes or longer to allow the internal capacitors of the high-voltage component assembly to fully discharge.

After the discharge time, ensure the environment is safe and risk-free before proceeding with maintenance.

Note that there are currently no specific requirements for the configuration of Manual Service Disconnectes. They are functional parts equipped by car manufacturers as needed, and some new energy electric vehicles may not be equipped with this switch.

Moreover, as a key component of new energy vehicles, domestic research on Manual Service Disconnectes is still in the initial stage, and related regulations and standards are not yet perfected. Therefore, caution should be exercised when operating the Manual Service Disconnect, adhering to relevant safety standards.


Maintenance of the New Energy Vehicle Manual Service Disconnect:

The Manual Service Disconnect is a component of the vehicle's electrical system, consisting of two main parts: the plug and socket. The socket is usually fixed on the vehicle, either on the power battery assembly box or the high-voltage distribution box. The plug can be configured with a fuse or directly connected with a busbar. Manual Service Disconnectes with fuses also provide short-circuit protection, enhancing safety.


Manual Service Disconnect Exterior Inspection

Check for damage, deformation, impacts, etc., on the overall exterior of the Manual Service Disconnect.

Manual Service Disconnect Plug Inspection

Check for damage, deformation, impacts, discoloration, etc., on the waterproof glue, terminal posts, fuse, clips, locking pins, etc., of the Manual Service Disconnect plug.

Fuse Inspection

Ensure the fuse is in good condition and securely installed; test resistance value with a multimeter (should be within the normal working range).

High-Voltage Interlock Test

Check the high-voltage interlock of the Manual Service Disconnect plug to prevent damage and ensure the vehicle operates normally; measure connectivity reliability with a multimeter and perform insulation testing.

Manual Service Disconnect Socket Reliability Check

Ensure the reliability of the Manual Service Disconnect socket for normal use; test for looseness, damage, corrosion, and sealing of the Manual Service Disconnect socket, measure connectivity reliability with a multimeter, test the security of fixing bolts with insulated tools, and perform insulation testing.

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TAG:   Manual Service Disconnect