1. Core physical background: Why nickel?
Before comparing current values, let's make it clear that pure nickel and nickel-plated steel strip are two very different things.
Pure nickel (N6/Ni200/Ni201): Resistivity is 9.6×10⁻⁸ Ω・m. It has good electrical conductivity, corrosion resistance, and weldability.
Nickel-plated steel strip: Its resistivity is about 2.5 to 3 times that of pure nickel. Although the cost is low and the spot welding strength is high, the heat generation is particularly serious under high current, which can easily cause thermal runaway.
Industry guidelines: Pure nickel strips must be used for power batteries (electric vehicles, power tools).
2. Calculation logic of nickel strip current carrying capacity
How much current the nickel strip can withstand depends essentially on the Temperature Rise (Temperature Rise).
Joule heat is generated when an electric current flows through a conductor: Q = I 2×R t
If the heat dissipates less quickly than it is produced, the temperature of the nickel strip will rise. Inside the battery pack, we usually do not want the temperature rise of the nickel strip to exceed 15 °C-30 °C to prevent heat from being transferred to the battery core and affecting the life.
3. Four key factors affecting current carrying capacity
It is not enough to simply look at the specification table. In actual engineering applications, the following factors will significantly change the "ceiling" of nickel strips:
Heat dissipation conditions (closed vs open)
The same 0.15 mm thick nickel strip can run 10A on the air circulation test bench, but if it is wrapped in thick brackets, highland barley paper, and heat-shrinkable film, heat accumulation will cause it to reach a dangerous temperature at 7A.
Series-parallel structure
In a multi-parallel (P) battery pack, the main bus (Main Busbar) withstands the total current. For example, for a 10A output 10P battery pack, the nickel strip of the main output pole must be very thick, or the current must be shared by multiple layers.
Spot welding quality
Contact Resistance is an invisible killer. If the spot welding is not strong or there are too few solder joints, the current will generate great local heat when passing through the solder joints. Typically, at least 4 solder joints are required for each connection.
Length effect
While current capacity is related to cross-sectional area, resistance increases with length. Excessively long nickel strips will produce significant Voltage Drop (Voltage Drop), which will not only generate heat but also lead to unbalanced voltage between cells.
4. Advanced industry solutions: How to break through the bottleneck of nickel strip?
When your design current is greater than 30A, the single-layer pure nickel strip will highlight its own disadvantages. It is too thick to pass through the spot welder, and it is too wide to fit the bracket. So there are the following alternatives:
Nickel-copper composite tape (Ni-Cu-Ni): This is currently the mainstream solution for high-performance battery packs (such as Tesla, high-performance electric motorcycles). Copper in the middle (excellent conductivity), nickel plated on both sides (convenient spot welding). Under the same cross-sectional area, its current-carrying capacity is 2-3 times that of pure nickel.
Multi-layer superposition: by spot welding a layer of nickel strip first, and then covering the second layer above and spot welding. This method can effectively increase the cross-sectional area and solve the problem of single-layer, too-thick welding impenetrability.
Copper nose thickened wire: At the outlet of the main positive and negative electrodes, nickel strips are no longer relied on, but copper terminals or silicone wires are directly welded to the current collector.
5. Summary and Suggestions
When choosing a nickel strip current, don't get stuck in the "fuse current", but stare at the "temperature rise index".
DIY players: It is recommended to reserve a 50% margin. If the calculated current is 10A, please configure it according to the specification of 15A or 20A.
Industrial design: Temperature rise test must be carried out. Nickel ribbon temperature should not exceed 60 °C after 30 minutes of full load operation.
Pit avoidance guide: You can try it with a magnet! True pure nickel is very magnetic, and the section will not rust. If the magnetic force is very strong, it is likely to be a nickel-plated steel strip, so you must use it with a 60% derating or abandon it directly.
Lisa
Sales Manager
Phone Number/WhatsApp
(86)-18291772322
Ta-Nb@titanmsgp.com
