VDA 355 Module Integration: Mounting, Swelling & Busbars
Short answer: VDA 355 module integration requires secure mechanical mounting, controlled compression to manage prismatic cell swelling over service life, correctly torqued busbar connections taken from the module datasheet, and adequate electrical isolation including creepage distances. The standardised 355 × 151 × 108 mm envelope means the same housing, cooling plate and fixture can be reused if the module changes.
Mechanical integration of a VDA 355 module is one of the first engineering decisions a pack builder makes, and one of the most consequential. Get the mounting, compression and electrical connections right and the module will perform to its datasheet for its full service life. Get them wrong and the consequences range from premature capacity fade to a structural failure under vibration. This article covers every mechanical interface a pack builder must resolve.
What the VDA 355 envelope gives you
A VDA 355 module measures approximately 355 × 151 × 108 mm (length × width × height). Those dimensions are standardised through the VDA — the German automotive industry association — so that modules from different cell suppliers share the same mechanical envelope. The direct consequence for a pack builder is that the housing, cooling interface and fixture remain unchanged when the module source changes. You design the pack once around the envelope; you do not redesign it around a specific supplier.
This decoupling is one of the principal advantages of the VDA 355 format and the reason the format has been adopted well beyond its automotive origins.
Mounting and structural attachment
Prismatic modules are typically bottom-mounted or side-mounted to a structural baseplate or frame. In either case the mount must:
- Restrain the module in all six degrees of freedom against the vibration and shock loads defined in the application standard (automotive packs reference UN ECE R100 for road vehicles; stationary packs reference IEC 62619, published by the International Electrotechnical Commission).
- Allow controlled thermal expansion of the module casing without introducing bending loads into the cell stack.
- Not over-constrain the module in the swelling direction (see below).
Bolt patterns, bracket geometries and torque values for any mounting hardware associated with the module itself are specified per product; consult the module datasheet rather than applying generic values.
Prismatic cell swelling: why the housing must accommodate it
Prismatic lithium cells — whether LFP or NCM — expand slightly as they cycle. This is a normal electrochemical effect: lithium ions intercalate into and de-intercalate from the electrode material, and the electrode stack grows and contracts with each charge–discharge cycle. Over the full service life, a residual thickness increase accumulates on top of the reversible per-cycle movement.
The module manufacturer addresses this at the cell level with end plates and banding (metal straps or side plates) that apply a defined preload to the cell stack. This preload serves two purposes: it maintains uniform contact pressure across the electrode area, which is important for resistance uniformity, and it limits the free expansion that would otherwise cause delamination.
For the pack builder the implication is twofold:
- Do not over-constrain the module. If the housing applies an additional compressive load on top of the module's own banding, the combined force can exceed what the end plates are designed for.
- Provide expansion clearance or a compliant layer. Over the module's service life — 1,500 to 2,000 cycles for the VDA 355 modules in the Avantis Energy catalogue — the overall module height and width will have changed slightly from their as-new values. The housing must accommodate this without generating contact between adjacent modules or between a module and an adjacent structure.
The magnitude of swelling, and the preload applied by the end plates, are specified per product on the module datasheet. No generic value should be applied across products.
Vibration and shock resistance
Automotive applications require the pack to survive the vibration spectrum of the vehicle body, typically characterised by a power spectral density profile and a number of shock half-sine pulses. The module-to-housing attachment must prevent any relative movement between module and structure throughout this envelope.
Rubber-bonded or elastomeric mounts are sometimes used to isolate the module from high-frequency vibration, but they introduce compliance that must be factored into the swelling management strategy. A fully rigid mount simplifies swelling management but transmits the full vibration load into the module casing.
Stationary applications have lower vibration requirements but must consider seismic loading in some jurisdictions.
Busbar connections and tightening torques
The positive and negative terminals of a VDA 355 module are typically connected with bolted busbars; confirm the terminal type per product. The connection hardware — busbar material (typically aluminium or copper), contact area, bolt size and tightening torque — must be taken from the module datasheet for the specific product. No generic torque figure applies across all modules; applying the wrong torque either under-clamps the joint (high contact resistance, heat generation) or damages the terminal insert.
The envelope is shared; what flows through the terminals is not. The three VDA 355 modules in the Avantis Energy catalogue, all NMC, show how much the electrical load on a busbar joint can differ inside the same footprint:
| Configuration | Nominal voltage | Capacity | Max. continuous discharge | Weight |
|---|---|---|---|---|
| 1P4S | 14.64 V | 177 Ah | 348 A | 11.85 kg |
| 2P6S | 22.02 V | 116 Ah | 332 A | 12.2 kg |
| 3P4S | 14.68 V | 174 Ah | 348 A | 12.2 kg |
Size the busbar cross-section on the continuous current of the module you actually use, not on the footprint. The 1P4S is catalogued under the name 174 Ah while its specification line reads 177 Ah; confirm against the datasheet. Always use the module datasheet as the primary source. For a detailed breakdown of how chemistry affects module output, see the comparison of LFP and NMC in the VDA 355 format.
Electrical isolation and creepage distances
The module terminals and any exposed conductive surfaces of the casing must be isolated from the housing and from adjacent modules. The relevant design parameters are:
- Clearance: the shortest air-path distance between two conductors at different potentials.
- Creepage distance: the shortest path along an insulating surface between two conductors.
Minimum values follow from the working voltage, the pollution degree and the insulation-coordination rules the system standard refers to, with IEC 60664-1 as the usual basis. The system standard itself depends on the application: IEC 62619 for industrial and stationary battery systems, UN ECE Regulation 100 for road vehicles.
In practice, pack builders use pre-formed insulating sheets (aramid paper, PET film or similar) between modules and between modules and the housing. Any gap or cut in the insulation that reduces the effective creepage distance below the standard minimum is a non-conformance.
Module-level isolation requirements — including any voltage withstand test the module has been subjected to — are stated in the product documentation. For further context on how safety requirements apply to the VDA 355 format, see the safety overview for VDA 355 modules.
The format advantage in practice
The standardised envelope of the VDA 355 module means that a pack housing designed around the 355 × 151 × 108 mm footprint, with its cooling plate geometry and busbar routing, can accept modules from different sources without structural redesign. That is the core argument for the format: a second source does not require a new mechanical design.
The VDA and MEB battery modules available from Avantis Energy are built to this standardised envelope. Ask for the datasheet of the module you shortlist: mounting, terminal and swelling data are specified per product.
Frequently asked questions
What are the dimensions of a VDA 355 module for housing design purposes?
A VDA 355 module measures approximately 355 × 151 × 108 mm (length × width × height). These are the nominal as-new dimensions; the housing design should account for manufacturing tolerances on the module and for the small dimensional change that accumulates over the module's service life due to prismatic cell swelling.
How much do prismatic cells in a VDA 355 module swell over their service life?
The magnitude of swelling depends on cell chemistry, electrode design and the preload applied by the module's end plates and banding. No single figure applies across all products. The module datasheet specifies the expected dimensional change; use that figure, not a generic assumption, when sizing the housing clearances.
What tightening torque should I use for the busbar bolts on a VDA 355 module?
Tightening torque is specified per product in the module datasheet. Applying a generic torque value risks either under-clamping the joint — leading to elevated contact resistance and localised heating — or damaging the terminal insert. Always use the value stated in the documentation for the specific module you are integrating.
Do I need to apply external compression to a VDA 355 module inside the pack housing?
Usually not. A VDA 355 module normally arrives with its cell stack already under preload, applied by its own end plates and banding; confirm this on the datasheet of the specific module. The housing should not add compressive load beyond what is needed for secure mechanical attachment. Over-constraining the module in the swelling direction can exceed the structural limits of the end plates.
Which electrical isolation standards apply to a VDA 355 module pack?
The applicable standard depends on the application. IEC 62619, published by the International Electrotechnical Commission, covers industrial and stationary lithium battery systems; road-vehicle packs fall under UN ECE Regulation 100. Creepage and clearance minimums follow from the working voltage and the insulation-coordination rules those standards refer to, usually IEC 60664-1. In both cases, minimum isolation distances must be maintained across the full service temperature range and after any dimensional change due to swelling.
Discuss your integration requirements
If you are specifying a pack around the VDA 355 format and need module documentation or application support, contact Avantis Energy to discuss your pack requirements.