Nickel Strips

Note - this page is now outdated and requires updating for Rev 6.

Use:

Nickel strips are used in the battery modules to connect the battery cells to the busbars. They will be spot-welded to both parts.

Pure nickel (not nickel plated steel which is also commonly available) must be used for its higher conductivity and thus lower power loss. Ideally, we would use the highest conductivity material available, however this is not possible due to the nature of spot welding. The resistivity of nickel allows enough heat to be generated during the welding pulse.

There will be styles of nickel strips in the battery modules. One will be a Long Nickel Strip which goes on the bottom of the battery module. The other is a Short Nickel Strip which will be on the top of the module.

Relevant Specifications:

Width - 7 or 8 mm (design works with both, 8mm is ideal due to lower resistance)

Thickness - 0.1 to 0.127mm (either will work, thinner will allow for quicker spot welding - depends on availability)

Material - 99%+ pure nickel (NOT nickel plated steel). There exist multiple checks for verifying this. One such test is a vinegar bath - if rust appears on the modules, they are nickel plated steel, if not, they are pure nickel. Another test is to take a grinding wheel to the strips, if the strips have steel, they will spark.

Amount Required:

Initial Information

Assumptions / Simplifications

The bent radii of the nickel strips can be ignored

OTHER ASSUMPTIONS?

Calculations

SHORT NICKEL STRIP

Length of strip = 75mm

Depth of bent areas = 1.25mm

Number of bent areas = 4

Length Required per strip = length of strip + (number of bent areas * depth of bent areas * 2) = 75 + (4 * 1.25 * 2) = 85mm

Length for short strips = 85mm * 360 strips = 30.6m

We need half as many long nickel strips as short nickel strips, but the long nickel strips are twice as long (following the same pattern). So just double the amount required from the short nickel strips.

Total length required = 30.6m * 2 = 61.2m

Add a safety factor of 1.5 or 2x

We should get around 100m of nickel strip

Weight of material:

Volume = 10000cm * 0.0127cm * 0.8cm = 101.6cm³

Nickel Density = 7.81g/cm³

Mass = 101.6cm³ * 7.81g/cm³ = 800g

Results

800g minimum should be ordered.

Source For Material:

We will likely source the material from Aliexpress due to its abundance. Care must be taken to ensure that the supplier is selling pure nickel, and not nickel plated steel. Endless Sphere Forums is a good place to look for official links.

Alternate sources are 18650shrink.com (a US based DIY powerwall store), Sunstone Welders.

Ordered from here on Nov. 22, 2019:

https://www.aliexpress.com/item/32335859025.html?spm=a2g0s.9042311.0.0.24d84c4dVq3UMy

Manufacturing:

The nickel strips will come on a roll. They need to be cut and formed into the shapes required.

Jigs for both should be created to increase manufacturing speed. It may just be one jig that serves both functions.