How to Choose Battery Cable
Description
The size configuration of battery cable needs to take into account multiple factors, such as the magnitude of current and voltage,the following are some basic steps and key points:
1.Determine the current demand
First, it is necessary to clarify the maximum output current of the battery system or the maximum current required by the load,this can be determined by referring to the battery’s specification sheet, the power parameters of the load device, and the related circuit design,for example, given that the rated voltage of a battery pack is 48V and the maximum power of the load device is 2000W,according to the formula (P = UI)（P=Power,U=Voltage,I=Current),the maximum current can be calculated(I = P/U = 2000W/48V\=41.7A\).
2.Consider the length of the battery cable
The length of the cable has an impact on the resistance, which in turn affects the voltage drop and energy loss,longer cables will result in greater resistance, so larger-sized cables need to be selected to compensate for the voltage drop,generally speaking, for every additional meter in cable length, the resistance will increase by a certain value (depending on the material and specification of the cable),for example, for a certain specification of copper cable, the resistance per meter may be (0.01Omega),if the cable length is 10 meters, then the total resistance is (0.1Omega),under high current conditions, this may lead to a significant voltage drop.
3.Select the battery cable material
Common cable materials include copper and aluminium,copper has good electrical conductivity, low resistance and can withstand large currents, but its cost is relatively high. Aluminium is not as conductive as copper, but it is cheap and light in weight. In some situations where cost is a concern and the current requirements are not particularly high, the use of aluminum cables can be considered,however, when configuring battery cables, due to the high requirements for electrical conductivity, copper cables are usually preferred.
4.Select the cable specification based on the current and length
Generally speaking, the specifications of cables are determined by their cross-sectional area,common specifications include 1.5mm², 2.5mm², 4mm², 6mm², 10mm², etc. You can refer to the current carrying capacity table provided by the cable manufacturer to select the appropriate specification.
For example, for copper cable, a 1.5mm² cable can typically carry about 10-15A of current, a 2.5mm² cable can carry 16-25A of current, a 4mm² cable can carry 25-32A of current, and a 6mm² cable can carry 32-40A of current,a 10mm² cable can carry a current of 40 to 63A,based on the previously calculated current demand and cable length, the appropriate cable specification should be comprehensively considered and selected. If the calculated current is 41.7A and the cable length is relatively short (such as less than 5 meters), a 6mm² cable can be selected,however, if the cable length is relatively long (such as over 10 meters), to ensure that the voltage drop is within the allowable range, it may be necessary to select a 10mm² cable.
5.Consider environmental factors
The ambient temperature has an impact on the current-carrying capacity of the battery cable,in high-temperature environments, the heat dissipation conditions of cables deteriorate, and their current-carrying capacity will decline.
Therefore, if the battery cables are installed in an environment with poor ventilation or high temperatures, the current-carrying capacity of the cables should be appropriately reduced, or cables of larger specifications should be selected. For instance, when the ambient temperature is 40℃, the current-carrying capacity of the cable may decrease by 10% to 20% compared to that at normal temperature (25℃). In addition, if the cables need to be buried underground or laid through pipes, it will also affect their heat dissipation, and the cable specifications need to be adjusted accordingly.
6.Leave a certain margin for battery cable
To ensure the reliability and security of the system, a certain margin is generally left when choosing the size of the battery cable,it is usually recommended to select the current-carrying capacity of the cable at 1.2 to 1.5 times the calculated current demand,for instance, if the calculated maximum current is 41.7A, then based on a margin of 1.2 times, a cable capable of carrying at least (41.7A*1.2 = 50.04A) needs to be selected,at this point, a 10mm² copper cable would be a more suitable choice.