What features do MSDs need to have in order to ensure the safety of the Power Battery Pack. The beginning of the MSD in the Power Battery System Pack gradually becomes standard from optional, this process is not too long, in order to more reliable use and maintenance of the safety performance, MSD in the selection, need to consider some of the following factors.
1.MSD brief description
MSD's full English name: ManualServiceDisconnect; Chinese name: Manual Maintenance Switch.
The main function of MSD: In order to protect the safety of technicians who repair electric vehicles in a high-voltage environment or to respond to unexpected events, the connection of high-voltage circuits can be quickly separated so that maintenance and other work out of a safer state, such as external short-circuit situation protection, maintenance needs to be disconnected from the high voltage.
The basic principle of MSD: the MSD is designed in the Pack main circuit, with a built-in high-voltage fuse, and high-voltage interlock function. In case of external short circuit, the fuse cuts off the high voltage circuit; when the high voltage needs to be manually disconnected, the high voltage interlock will be disconnected first, and then the high voltage circuit will be disconnected.
2. Functions that MSD needs to have
In actual application, the design requirements of MSD should also include the use of temperature range, the ability to cut off with load, chemical resistance, mechanical strength and reliability and other functional requirements.
3.Elements to be considered for the selection of MSD in Pack
a: design in the middle of the Pack's battery, such as 100 string battery Pack, the MSD needs to be designed in the middle of the 50 string, in order to ensure that when disconnected to play the function of lowering the total voltage, the total voltage cut off into several lower voltage, can reduce the possible safety risks.
b:Pack installation, MSD must be in the car, you can achieve the car passengers can be found in the safety hazards, in the car can quickly cut off the high-voltage circuit.
c:MSD selection, the following factors need to be considered.
(1) Rated voltage: If the maximum voltage of the PACK is above or below 400V, a gear greater than or equal to DC450V should be selected.
(2) Load duration current: the rated current of MSD should be greater than 2 times of the load duration current.
(3) peak load current: the peak load current capability of the MSD needs to be greater than the peak load current.
(4) Response time consideration: the fusing response time of MSD should be less than the sticking time of the relay.
Although the MSD is only a small part of the Pack, as this part involves the safety of the product, its selection is very important and needs our full consideration.
5. Example of MSD selection
The output power of a project battery pack requires a current of about 130A
a:Pack's Umax:420V,MSD's rated voltage needs to be greater than or equal to 450V.
b:Consider the load duration current: MSD optional 350A Fuse (350A>2*130A)
c:Consider the response time: i.e. Umax:420VDCR100mΩ,short-circuit current:Umax/DCR=4200A
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