Can the tab barrier be machined down to 1 mm?

A: No. A 1 mm rib drifts 0.4 mm over a 355 mm cavity, and after 200 insertions the top is rounded enough to scratch the tab root. The thin option is a milled insert in 1.5 mm glass-epoxy, bonded in, at double the part cost.

Do four 20 mm ports let dust into the cavity?

A: The grommet fills 14 mm and leaves a 3 mm annulus, so dust has to turn two corners. Eight hours under IP54 dust conditions deposits 0.3 g/m² inside. A 0.2 mm breather membrane cuts that airflow by 15%.

Why not use a 10^6 Ω dissipative liner?

A: Because the module is already bonded to the fixture. A dissipative layer adds a parallel path to earth and its leakage shows up in the sense leads. Insulating foam removes it.

How is the fifteen-second lid rule verified?

A: With a timer on the hinge switch and a scope on the loop. The roller opens at 8°, the contactor releases in 0.2 s, and the bleed resistor needs 11 s to reach 5 V. Three runs at 25 ℃ and three at 5 ℃ stay under 14.5 s.

Can a battery module case double as a shipping case?

A: Mechanically yes, commercially no. Shipping wants wall thickness and cushioning, testing wants ports and sight lines. One shell serving both grows from four ports to seven, each needing a plug. Two shells cost less than one compromise.

Battery Module Case: Battery Module Test Case

Quick answer: A battery module case does two jobs on the bench: 2 mm barriers between tab centres 18 mm apart, and four 20 mm ports that carry probes outside.

Why the Tab Barrier Is Fixed at 2 mm
Where the Four Sensing Ports Land
An Insulating Liner at 10^12 Ohms, on Purpose
Cable Ports and the Fifteen-Second Lid Rule
Keeping the Internal Rise Under 5 K
FAQ

1. Why the Tab Barrier Is Fixed at 2 mm

A 355 × 150 × 108 mm module sits in the cavity with its tabs standing 12 mm proud of the end face, the two centres 18 mm apart. Across that distance one loose lead falling on the pair is a dead short.

The barrier is 2 mm thick, and three limits squeeze that number. At 1 mm the rib top wanders 0.4 mm after the mould cools and scrapes the tab root on the way in. At 3 mm the rib eats 3 mm of an 18 mm centre distance, leaving a 7.5 mm slot per side for a 30 mm tab that needs room to move, so the module jams halfway down. Two millimetres with 1.5 mm clearance per side lets the tab float without touching.

Height runs 16 mm, four above the tab, with 3 mm of free space to the lid foam that closes as the lid lands. Cut it to 12 mm and the module shifts 2 mm vertically, walking the tab root out from behind the barrier. Past 20 mm the module has to be lifted 8 mm further at changeover, which ends one-handed handling.

Tab centre distance	Rib thickness	Rib top to tab	Slot per side	Module length served
14 mm	2 mm	3 mm	6 mm	280–320 mm
18 mm	2 mm	4 mm	8 mm	330–380 mm
22 mm	2.5 mm	5 mm	9.7 mm	380–420 mm
26 mm	3 mm	6 mm	11.5 mm	420–480 mm

2. Where the Four Sensing Ports Land

Two points sit at the tab roots, one on the top face, one in the centre of the base. The first pair answers whether the joint is heating; the second whether heat is even or piling up in a corner.

Battery module case, black shell open on a pale wood table, empty compartment with ribbed lid and two red-tipped latches in front

All four ports run through the long side wall at 20 mm, hole centre 8 mm off the tab root. Shrink to 16 mm and the 15 mm grommet has half a millimetre left, rolling its lip after three insertions. Open to 25 mm and the 5 mm annulus becomes a convection path worth 2 K of internal rise.

Position holds within ±3 mm. A probe seated 6 mm deep reads 2 mm off the tab; drift 6 mm and it touches the can, so the two points flatten into one shell reading.

The base point is the one people delete. An 8 mm pocket of still air traps heat, and after 2 h the base runs 4 K above the top face.

Sensing point	From tab root	Port diameter	Depth	What it reads
Positive tab root	8 mm	20 mm	6 mm	Joint heating at the busbar
Negative tab root	8 mm	20 mm	6 mm	Symmetry against the positive side
Top face, mid-length	90 mm	20 mm	4 mm	Mean can temperature
Base centre	150 mm	20 mm	4 mm	Trapped heat under the module

3. An Insulating Liner at 10^12 Ohms, on Purpose

Most enclosures chase a conductive liner. This one goes the other way, because the bench is already bonded and a second path to earth is a liability. Strapped to a grounded fixture, a dissipative layer would sit in parallel with the tab and push stray current through the sense leads.

The foam is cross-linked polyethylene: 5 × 10^13 Ω surface resistance, 10^14 Ω·cm volume resistivity, 8 mm thick, 45 kg/m³. Fifty insertions leave the cavity below 200 V on a static meter, where plain EVA under the same handling reaches 1.8 kV.

Humidity breaks the figure quietly. At 80% RH an adsorbed film drops it to 8 × 10^11 Ω, still the same order; water uptake under 1% brings it back to 3 × 10^13 Ω after 72 h in a damp chamber.

Conductive foam suits a shipping case and hurts this one.

4. Cable Ports and the Fifteen-Second Lid Rule

Cable ports are drilled apart from sensing ports though both are 20 mm. Six conductors pass: two at 4 mm² for the main loop, four at 0.5 mm² for signals, bundled to 14 mm. A 2 mm silicone grommet leaves a 3 mm annulus.

Battery module case photographed at an angle on grey, egg-crate foam in the lid, foam dividers below, small keypad instrument at lower left

A roller microswitch on the hinge side does the interlocking. At 8° of lid travel the roller releases, the contactor drops out in 0.2 s, and a 100 Ω bleed resistor pulls the loop from 60 V to 5 V in 11 s. That is 14.2 s against a 15 s allowance.

The harness gets a 30 mm service loop each side and a tie-down every 150 mm. After 5000 lid cycles the grommet has stretched under 1 mm and the bundle has moved under 2 mm.

5. Keeping the Internal Rise Under 5 K

The 5 K figure is module surface against ambient: 30 ℃ inside after 2 h in a 25 ℃ room. Three paths share the load.

A 4 mm solid modified-PP wall at 0.22 W/(m·K) runs 3 K above ambient outside and passes heat to the room, about 55% of the load. The 8 mm liner takes about a tenth and saturates after 2 h. The rest leaves through the ports and the 10 mm still-air gap under the lid.

A thicker liner works backwards. The same duty cycle in a 15 mm liner stabilises at 7 K, because the foam keeps heat inside instead of letting the wall do its job.

Conclusion

A battery module case earns its place on the bench with four details: a 2 mm barrier, four 20 mm ports that carry thermocouples outside, a liner above 10^12 Ω, and a lid switch that clears the loop under 15 s. Get all four right and the internal rise settles at 5 K. Anything beyond that belongs to the fixture, not the shell.