MS16 Cell Level Fusing

Approach	Pros	Cons

Approach	Pros	Cons
Plate	Better for thermal distribution: helps to dissipate heat evenly across the cells Stronger/ more physically reliable: provides more structural support and reduces the stress on connections Easier for us to use / implement ( ? ): When we decide on a design we can machine it in batches ? Lower resistance variation: More consistent electrical connections across the cells Lower resistance at the point of connection if spot-welded properly Is also easier to make consistently across hundreds of batteries Able to design the plates ourselves on CAD to suit whatever cell arrangement our specific module has	Harder to replace individual cells: if one fuse blows, 1. as all cells are connected you cant just removed that one cell alone, 2. you’d probably need to replace the entire plate at that point Design issues: if we’re designing it ourselves there's a lot of space for error, if it isn't made correctly there's possibility for uneven current distribution and some cells would end up with higher loads More material: considering the weight factor, these plates are definitely the heavier option Don’t know if this is significant given the metal used will probably be around 0.1mm thick Generally more expensive to make: requires laser cutting for the battery strips requires one strip per module + any backup modules, test strips, failed attempts testing will require extra stripes as well (can probably be offset by making smaller strips meant for testing, but this won’t simulate a full plate)
Wires	Easier cell replacement: since each fuse is individually attached. if a fuse blows only that specific wire needs to be replaced This assumes we’re replacing individual cells in a module as opposed to just replacing the module and protecting the other cells in said module More leeway with placement and design: we have more variety in choosing the fuses that are right for our cells compared to a harder search for the exact plate that fits all requirements of our cells Lighter weight: uses much less material Might be cheaper: this approach requires no custom machining, just spot welding we can do ourselves	More work to implement: since each fuse is individually attached it will take a lot more attention and time to carry out Easy to mess up joints when making hundreds, which might lead to some batteries becoming unusable Inconsistent resistance: subject to small variations in wire thickness or weld quality can create uneven current distribution (more room for human error to matter) Also, has generally higher resistance, as much as 10x at the joints, when comparing both methods Weaker stability: no structural reinforcement like the plate More points of failure: since each wire is kind of doing their own thing they all have their own chances of weakening or breaking over time.

Fusing currents for various wire dimensions: https://www.powerstream.com/wire-fusing-currents.htm

Plate design video to serve as a basis: Making Battery Strips W/ Cell Level Fusing

Thermal conductivity for various metals for plating/wires: https://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html

Testing procedure:

Plate approach
- Electrical performance (to ensure fuse plate allows desired current to flow)
  - measure resistance across multiple points on the plate (check uniform distribution)
  - apply increasing current to simulate overcurrent conditions to determine the actual blow current and compare to the design value
- Thermal behaviour (check how well it dissipates heat)
  - run a continuous discharge cycle and record temperature at different points on the plate
  - or use simulations to model the heat dissipation
- Stress tests (checking it can withstand vibrations)
- Failure tests
  - force a single cell failure (overcharge, external short, thermal runaway)
  - if blown fuse disconnects, verify adjacent cells status, (did they experience any electrical or thermal stress as a result of the blown fuse)
  - check how a blown fuse affects the overall module and by what percent the performance is lowered by
Wire appraoch
- Electrical performance
  - measure wire resistence to ensure uniformity across cells
  - slowly increase current to record at what point the wires melt
  - consistently check if some wires heat up more than others (checking for uneven conditions)
- Thermal behaviour
  - measure temperature in high-current conditions
  - check for hotspots in design if possible
  - test different wire materials to compare heat dissipation (research for wire materials to be written below)
    - Thermal conductivity: Cu (ETP) = ~390 > Al = ~237 > Ni = ~90
      - Sigmaclad: ranges from 52 to 317 depending on which version we have
      - https://www.emsclad.com/wp-content/uploads/sites/12/2023/02/SIGMACLAD-Datasheet.pdf
      - Note: not sure how much heat dissipation matters in individual wires actually matter
- Durability (strength tests)
  - perform vibration testing or use simulation to see if the expected force is enough to break the connections
- Failure tests
  - force a single cell failure (overcharge, external short, thermal runaway)
  - if blown fuse disconnects, verify adjacent cells status, (did they experience any electrical or thermal stress as a result of the blown fuse)
  - observe any unintended side effects ie thermal damage to nearby components or sparking
  - check how a blown fuse affects the overall module and by what percent the performance is lowered by

Hypothesis prior to testing

Test	Plate	Wire

Test	Plate	Wire
Design	Harder and time consuming	Easier and more flexible
Implementation	Easier	More time consuming
Electrical uniformity	more consistent across cells	variability in individual wires
thermal dissipation	spreads heat more evenly	potential for localized hotspots
repairs	hard to replace individual fuses	easier
vibration resistance	more robust	wires can loosen over time
failure isolation	works if designed properly	works if wire melts fully
cost	probably more expensive	probably cheaper

Mechanical

MS16 Cell Level Fusing

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