Nickel Strip Sizing Guide for E-Bike Battery Packs

Choosing the right nickel strip size for your e-bike battery is critical for both performance and safety. Your choice must be based on the continuous current draw of your motor and controller.

A strip that is too thin will dangerously overheat, reduce performance, and create a fire risk. Conversely, an overly thick strip is expensive and difficult to weld. This guide will teach you how to calculate your e-bike's current requirements and read ampacity charts to select the proper nickel strip, ensuring your battery pack is both powerful and reliable.

The Critical Role of Nickel Strips in Battery Performance and Safety

Properly sizing the nickel strips for a custom e-bike battery pack is a foundational step that dictates the pack's safety, efficiency, and overall lifespan. These metallic strips are the conductive pathways that connect individual lithium-ion cells, creating the electrical network that powers your ride.

The dimensions of these strips—their thickness and width—are not minor details; they are critical engineering parameters. An incorrectly sized strip can compromise the entire system, turning a high-performance battery into an inefficient and hazardous component.

The consequences of using undersized nickel strips are significant and multifaceted. First, an undersized strip introduces unnecessary electrical resistance into the circuit. As high current flows through this resistance, energy is converted into heat instead of being delivered to the motor. This phenomenon means that wasted energy increases exponentially with the current. This wasted power directly translates to reduced range and sluggish performance.

Second, this excess heat is transferred directly to the battery cells, raising their temperature beyond safe operating limits. Sustained exposure to high temperatures accelerates the chemical degradation of lithium-ion cells, permanently reducing their capacity and drastically shortening the battery pack's service life.   

Most importantly, undersized nickel strips pose a severe safety risk. The heat generated can be intense enough to melt the strip itself, damage the insulation of surrounding components, or harm the Battery Management System (BMS). In a worst-case scenario, this extreme heat can trigger a thermal runaway event in one or more cells, leading to catastrophic failure, including fire or explosion.

Therefore, understanding how to select and size nickel strips is not just about maximizing performance; it is a non-negotiable aspect of building a safe, reliable, and long-lasting e-bike battery.   

SEE ALSO How to Build a DIY Ebike Battery Pack Safely

Material Science: Pure Nickel vs. Nickel-Plated Steel

When selecting material for battery connections, the choice is between pure nickel and nickel-plated steel. While they may appear identical to the naked eye, their properties are vastly different, and for any serious e-bike battery build, only one is acceptable: pure nickel. The decision to use pure nickel is grounded in the fundamental principles of electrical conductivity, corrosion resistance, and long-term reliability.

Pure nickel, specifically grades like Ni200 or N6 which are over 99.6% pure, offers low electrical resistance, making it an excellent conductor for the high currents found in e-bike applications.

Nickel-plated steel, conversely, is a steel strip with a very thin coating of nickel. Steel has significantly higher electrical resistance—pure nickel is approximately twice as conductive, and depending on the steel alloy, its resistance can be up to ten times higher than pure nickel. This higher resistance means that for the same amount of current, a steel strip will generate substantially more waste heat, leading to the performance and safety issues discussed previously.   

Corrosion resistance is another critical differentiator. Pure nickel is highly resistant to rust and oxidation. Nickel-plated steel relies on its thin plating for protection. However, the moment the strip is cut to length or spot-welded to a cell, the underlying steel is exposed.

In the presence of humidity, this exposed steel will inevitably rust. Rust is not just a cosmetic issue; it degrades the electrical connection, increases resistance further, and creates dangerous "hot spots" that can lead to pack failure over time.   

The primary reason nickel-plated steel exists in the DIY market is its lower cost. Unscrupulous vendors often market it simply as "nickel strip," exploiting its visual similarity to deceive buyers.

However, the small upfront savings are a poor trade-off for the immense risks. The higher cost of pure nickel should be considered a necessary investment in the safety, performance, and longevity of the battery pack.   

Practical Guide: How to Verify Pure Nickel

Given the prevalence of deceptively labeled nickel-plated steel, it is essential for any battery builder to verify their material. Two simple and definitive tests can be performed.

The Spark Test: This is the quickest method. Using a Dremel, grinding wheel, or other rotary tool, lightly grind the surface of the strip. If you see a shower of bright sparks, the strip is steel. The abrasive wheel quickly cuts through the thin nickel plating and hits the steel core, which sparks. Pure nickel will not produce these sparks when ground.   

The Saltwater Test: If a grinder is unavailable, this method is equally effective. First, aggressively scuff or scratch the surface of the strip with sandpaper or a file to ensure the underlying metal is exposed. Then, submerge the strip in a cup of saltwater. Check it after 24 hours. If any rust has formed, it is nickel-plated steel. Pure nickel is highly corrosion-resistant and will show no signs of rust.   

Performing one of these tests is a mandatory step before building a pack. Trusting a vendor's label is not enough when safety is on the line.

Calculating Your E-Bike's Current Demand (Amperage)

Before selecting a nickel strip size, the first step is to determine the maximum continuous current your e-bike system will draw. This value, measured in amperes (A), is the single most important factor in sizing all conductive components in your battery pack's main circuit. It is crucial to design for the continuous current draw, not the momentary peak current.

While peak currents last for only a few seconds (e.g., during hard acceleration), it is the sustained, continuous current that generates significant heat and poses the greatest thermal risk to the nickel strips.   

The fundamental relationship between power, voltage, and current provides a straightforward way to estimate this value. The formula is: Continuous Current (A)= Battery Voltage (V)/Motor Power (W). This calculation should use the motor's nominal power rating and the battery's nominal voltage. For example:

High-Power E-Bike: A system with a 1000W motor and a 48V battery.

Current = 1000W/48V=20.8A.   

Mid-Range E-Bike: A system with a 750W motor and a 52V battery.

Current = 750W/52V=14.4A.   

Standard Commuter E-Bike: A system with a 500W motor and a 48V battery.

Current = 500W/48V=10.4A.   

While this formula provides an excellent estimate, the definitive value for the maximum continuous current is set by the pack's Battery Management System (BMS). The BMS is the safety circuit that protects the battery cells from over-discharge, and it has a specific continuous discharge rating. If your BMS is rated for 40A continuous discharge, then your nickel strips must be sized to handle 40A, even if your motor calculation is lower.

The BMS rating is the absolute ceiling for continuous current, and all series connections must be built to withstand it. It is a sound engineering practice to add a safety margin of at least 20% to your calculations, ensuring the system operates well within its thermal limits. Therefore, if your BMS is rated for 40A, you should size your strips for 40A, not a lower calculated value. This ensures the pack remains safe even if the motor or controller is upgraded later.   

SEE ALSO What Do Amp Hours Tell You About an Electric Bike Battery

Understanding and Calculating Nickel Strip Ampacity

"Ampacity," a portmanteau of ampere capacity, refers to the maximum current a conductor can carry continuously under specific conditions without exceeding its temperature rating.

For nickel strips in a battery pack, this means handling the e-bike's current demand without getting hot enough to damage the battery cells or create a fire hazard. It is not a fixed, universal value for a given strip size; it is a sliding scale of heat and risk. Pushing more current through a strip generates more heat, and at a certain point, that heat becomes unacceptable and dangerous.   

The physics behind this is governed by two key principles. First is electrical resistance. The resistance of a strip is determined by the material's intrinsic resistivity (ρ), its length (L), and its cross-sectional area (A). The formula is R=ρL/A. This shows that resistance decreases as the cross-sectional area (thickness × width) increases. A wider or thicker strip provides more pathways for electrons to flow, reducing resistance.   

The second principle is Joule heating, which describes how electrical energy is converted into heat. The formula for power loss as heat is P=I ² R, where P is power (heat) in watts, I is current in amps, and R is resistance in ohms. This equation is critically important because it shows that heat generation is proportional to the square of the current.

Doubling the current through a strip does not double the heat; it quadruples it. This is why a small increase in motor power or a poorly sized strip can lead to a dramatic and dangerous increase in temperature.

Online charts for nickel strip ampacity are abundant but often conflicting. Some vendors provide optimistic ratings, while test conditions like ambient temperature and strip length are rarely specified. For safety, it is essential to use conservative, well-vetted data. The following table consolidates information from multiple sources to provide a reliable, safety-focused reference for DIY builders.

Advanced Techniques for High-Current Applications

For e-bike systems demanding more than 15-20A, a single nickel strip is often insufficient. Two techniques are used to increase ampacity:

Stacking/Layering Strips: The most common method is to spot-weld multiple layers of nickel strip on top of each other. This effectively increases the total cross-sectional area, lowering resistance and increasing current capacity.

For example, to handle a 35A load using 0.15mm x 8mm strips (rated at 7A each), you would need five layers (5×7A=35A). As a conservative rule of thumb, some builders assume a slight loss of efficiency with each layer due to imperfect contact, but for practical purposes, the ampacity is additive. This method is essential for builders with spot welders that cannot handle thicker nickel.   

The Copper/Nickel Sandwich: For very high-current paths, such as the main series connections on a powerful pack, a superior method is the copper/nickel sandwich. This involves placing a strip of highly conductive copper against the battery cells and then placing a nickel strip on top of the copper. The spot welder then welds through the nickel to the cell.

The nickel's higher resistance allows it to heat up and create a strong weld, effectively clamping the copper strip in place. The copper, with its much lower resistance, carries the vast majority of the current with minimal heat generation. This is the gold standard for high-performance builds.   

Matching Nickel Strips to Your Battery Architecture

Applying the principles of current demand and ampacity to the physical layout of a battery pack requires understanding the different roles of series and parallel connections. A typical e-bike battery is a series/parallel configuration, denoted as "xSyP," where 'x' is the number of cell groups in series and 'y' is the number of cells in parallel within each group.   

Series Connections: Connecting cell groups in series (positive of one group to the negative of the next) adds their voltages together to reach the system's target voltage (e.g., 13 groups of 3.7V cells in series, or 13S, creates a 48V pack). The capacity (in Amp-hours) remains that of a single parallel group.   

Parallel Connections: Connecting cells in parallel (all positive terminals together, all negative terminals together) adds their capacities together to increase the pack's range. The voltage remains that of a single cell.   

Sizing for Series Connections: The High-Current Superhighway

This is the most critical application of nickel strip sizing. The series connections form the main path for current to flow through the entire pack. Therefore, every series connection must be able to handle the full continuous current of the pack, as determined by the BMS rating.   

The calculation is direct: Required Series Ampacity = BMS Continuous Current Rating.

For example, consider a pack with a 40A BMS. The builder must construct each series connection to handle at least 40A. Using the conservative ampacity table from the previous section:

If using 0.2mm x 10mm strips (~12A capacity), you would need 40A/12A≈3.33, meaning four layers are required.

If using 0.15mm x 8mm strips (~7A capacity), you would need 40A/7A≈5.71, meaning six layers are required.   

Sizing for Parallel Connections

The current flowing between individual cells within a parallel group is very low. This current exists primarily to balance small voltage differences between the cells in that group. Under normal operation, the current is negligible. Therefore, a single, standard-sized nickel strip (e.g., 0.15mm x 8mm) is almost always sufficient for these connections. Overbuilding the parallel connections adds unnecessary weight and cost without providing a significant performance or safety benefit.   

Sizing for Main Terminals & Busbars

The main positive and negative terminals of the battery are the points where all the current from the pack is collected before exiting to the controller. These terminals, and any busbars that connect multiple series links, must also be sized to handle the full pack current. These are prime locations for using the copper/nickel sandwich technique or creating very wide busbars from multiple layers of nickel to ensure they do not become bottlenecks.   

Essential Safety Protocols & Tooling Considerations for Spot Welding

Building a lithium-ion battery is an advanced DIY project that carries inherent risks. The process of spot welding, where high currents are used to fuse metal, demands strict adherence to safety protocols.

Personal Protective Equipment (PPE)

Safety gear is not optional.

Eye Protection: Always wear wrap-around safety goggles. Standard safety glasses do not protect from sparks that can fly from the side. A spot-weld spark is a small piece of molten metal that can cause severe eye injury.   

Hand Protection: Wear heat-resistant leather or welding gloves. They protect against sparks and heat, and critically, they provide insulation that can prevent an accidental short circuit if your hands bridge two terminals.   

Clothing: Wear long-sleeved clothing made from a non-flammable material like cotton or leather to protect your arms from sparks.   

Workspace Preparation

A safe environment is crucial for preventing accidents.

Work Surface: Use a clean, clear, and non-conductive work surface like a wooden bench. Never work on a metal table.   

Ventilation: Ensure the workspace is well-ventilated to dissipate any fumes generated during welding.   

Fire Safety: Keep a Class ABC or, ideally, a Class D (for combustible metals) fire extinguisher within arm's reach at all times.   

Remove Hazards: Remove all metal objects from your person and the immediate work area. This includes rings, watches, bracelets, and loose tools or hardware like screws or paperclips that could fall onto the exposed battery terminals and cause a catastrophic short circuit.   

Spot Welder Limitations and Settings

The quality of your spot welder directly impacts the safety and reliability of your battery. Most budget-friendly, portable spot welders available to hobbyists (often powered by small internal batteries or supercapacitors) have limitations. They typically struggle to produce consistent, strong welds on pure nickel strips thicker than 0.15mm. This technical constraint often necessitates the layering strategy for thinner strips to achieve the required ampacity for series connections.   

Before welding on your actual battery pack, always test your welder's settings on scrap pieces of the same nickel strip. The goal is to find a setting that creates a strong, durable weld that cannot be peeled off by hand (the "tug test") without creating such a powerful pulse that it blows a hole through the strip or damages the battery cell can underneath.

A good weld will leave two small, neat indentations on the strip. If you pull the strip off with force, it should tear the nickel, leaving the weld nuggets still attached to the cell, indicating a weld stronger than the strip itself.

Conclusion

In conclusion, mastering nickel strip sizing is essential for building a safe, reliable, and high-performance e-bike battery. Move beyond guesswork by calculating your true current draw, using only pure nickel, and consulting an ampacity chart to select the correct strip for your needs. Properly sizing for both your parallel and critical series connections ensures your custom battery pack is powerful, safe, and built to last.

FAQs

What size nickel strip should I use for my e-bike battery?

The size depends entirely on your e-bike's continuous current draw, calculated as Amps = Watts / Volts. Consult a nickel strip ampacity chart for specific ratings. Since a standard strip may only handle 5-7A, you will likely need to stack multiple layers for your main connections to safely handle the high current of most e-bike systems.

Is it okay to use nickel-plated steel for my e-bike battery?

No. Only use pure nickel strips. Pure nickel has much lower resistance, meaning it runs cooler and provides better performance with less voltage sag. Nickel-plated steel strips can dangerously overheat, are prone to corrosion, and will compromise the safety and longevity of your battery pack.

How does my battery's configuration (series/parallel) affect the nickel strip size?

It's critical. Parallel connections (within a cell group) divide the current, so they can use smaller strips. However, series connections (linking the groups) must carry the entire current your motor draws. Therefore, your main series connection strips must be significantly thicker, wider, or layered to handle the high amperage safely.