High-voltage tractive accumulator.

Start with the inspection envelope, not the cell count.

A Formula SAE accumulator is simultaneously a structural enclosure, a high-voltage assembly, a low-voltage controls package, and a serviceable competition component. The design process began by translating rules and vehicle needs into three primary objectives: reduce enclosure mass and center-of-gravity height, clean up controls packaging for manufacturing and service, and produce a rules-compliant battery capable of passing technical inspection.

As Energy Storage Lead, Muhammad worked across those boundaries rather than treating them as separate projects. Mechanical choices changed insulation and wiring space. Segment voltage affected service procedures. Board placement affected harness length and lid clearance. The report was structured to keep those interfaces visible and give later teams a reference for design, fabrication, and validation.

Use structure to solve mass, sealing, and service access together.

The shell houses the cells, controls boards, protection devices, and five internal walls that create six segments. The team selected 6061 aluminum for strength, weldability, and mass reduction. Relative to the outgoing steel container, the report estimated the aluminum shell alone at roughly 30% lighter.

Low-profile mounting tabs reduced footprint while being designed around 40g lateral and 20g normal load cases. The enclosure exterior was simplified by removing unnecessary wall perforations. Above it, a matching aluminum lid followed the approximately 7.8-degree slope of the container so water would not collect on its surface.

Fourteen #6-32 fasteners were placed around bends and edges to compress a quarter-inch, 60-durometer polyurethane gasket. This was not decorative closure hardware: fastener spacing, lid stiffness, and gasket compression worked together to make the seal consistent.

Translate the CAD into datums, welds, and repeatable internal geometry.

Fabrication established the accuracy of every system that followed. The shell panels, internal walls, mounting tabs, and lid interface had to retain alignment through cutting, fixturing, and welding. Distortion at this stage would accumulate later as misaligned segment guides, uneven gasket compression, and maintenance-plug tolerance.

The build sequence therefore moved from the external shell to the five internal partitions and guide features before electrical hardware was installed. Fit checks kept the segment channels square and preserved working clearance along the low-voltage region.

Keep the pack serviceable before it ever becomes high voltage.

Nomex 410 lined the conductive shell and lid. Overlap and edge treatment mattered because a nominally insulated panel can still expose metal at a seam, corner, or fastener. Above the segment stack, interlocking FR-4 sheets formed a secondary plane between the high-voltage cells and low-voltage controls.

Eighty-four Energus Li2x4p25RT packs were divided into six series segments of fourteen packs each. Before the maintenance plug was installed, each segment remained limited to 58.8 volts maximum. Once connected, the complete pack reached 302.4 volts nominal and 352.8 volts maximum.

Copper busbars joined each segment. M8.8 fasteners were tightened to the report’s 10 N·m requirement, and double-tab washers provided positive locking against vibration. The pack choice also brought factory cell-level fusing, integrated sensing, protected cells, threaded copper-plated terminals, and a compact 2×4 format suited to a single-layer enclosure.

Make the pack’s safety state visible and controllable.

The low-voltage system determined whether the battery could operate safely. Custom Battery Monitoring System and Voltage Monitoring System boards fed a central accumulator PCB alongside the precharge, shutdown, DC-DC, 60-volt trigger, and Accumulator Indicator Light functions. External Deutsch connectors linked that local controls package to the vehicle’s master harness.

Consolidating those functions on a central board reduced point-to-point wiring, shortened signal paths, and gave troubleshooting a clear physical reference. It also kept high-voltage switching logic, indicator behavior, and BMS communication packaged above the isolated cell plane instead of distributed around the enclosure.

Use a physical interface to define the energized state.

The maintenance plug bridges the six isolated segments into the full 352.8-volt series pack. Removed, the highest available segment voltage is 58.8 volts; installed, its copper links complete the tractive-system path. That made the plug a safety boundary, not just a connector.

A one-piece bar would have inherited the accumulated positional error across all six segment interfaces. The design instead used independent capsules held by a common handle. Each capsule carried a solid copper link with press-fit female Amphenol connectors, allowing local movement to absorb tolerance stack while maintaining a single operator action.

Unique extrusions and matching cutouts keyed the assembly against incorrect orientation. Once the lid was fastened, it physically retained the handle, providing positive locking against loosening in service.

Design the equipment around the battery, too.

The team also developed a dedicated charge cart so the accumulator could be handled, serviced, and charged outside the chassis. A commercial 2,000-pound flat cart provided the base; a welded, hip-height work surface improved access, while a shelf and drawer kept electrical tools and supplies with the pack.

The electrical system combined the charger, auxiliary power, grounding, protected inlets, and covered outlets into a transportable setup. The report documents a later 220-volt charging option added to reduce turnaround between test cycles. A mechanical dead-man brake used opposing wheel chocks, springs, and bicycle-brake controls so the cart’s default unattended state was stopped.

Build an inspectable system, not a sealed mystery.

Final integration joined the enclosure, insulation, segments, maintenance plug, contactors, fuse, controls boards, indicator light, external connectors, and lid into a single inspectable assembly. The documentation preserved design intent, key hardware values, manufacturing sequence, and the questions an inspector or future subsystem lead would need answered.

The most important external result was concrete: the accumulator passed structural inspection, the first successful pass in team history. That outcome validated the work as more than a design report—it showed that a first-generation high-voltage system could be manufactured, presented, and accepted against competition requirements.