72V Triangle
Battery

The application had a triangular cavity and a hard requirement for 72 volts. Every commercial pack is a rectangle — so the choice was to compromise the design around a box, or build the battery the shape needs to be.

The challenge: pack enough 18650-class cells into a triangular cross-section to hit 72V nominal, while keeping it safe, balanced, and serviceable.

Constraints: this is energy that doesn't forgive mistakes — thermal runaway, cell imbalance and short circuits are all real failure modes. The geometry could be unconventional; the safety could not.

I designed the pack around the triangle from the first sketch instead of forcing a rectangle to fit. Cells are arranged in a triangular nest (a 4-3-2-1 stack), wired into a series string to reach 72V, with a custom BMS handling the part that actually keeps it alive.

• Geometry-led layout — cell placement follows the triangular envelope, maximizing capacity in the available volume.
• Bespoke BMS — per-group monitoring, balancing, and protection against over-voltage, over-current and thermal events.
• Serviceable build — terminals, sense leads and the LED status indicator are all accessible without tearing the pack down.

Why these choices: in hardware the constraints are physics, not preference. Designing around the real envelope produced a denser, cleaner pack than any adapted off-the-shelf option could.

Finished pack, process shots, and detail close-ups. Replace the placeholders with the hero photo, assembly/iteration process shots, and GIFs of the LED indicators, charging cycle and installation.

72V nominal off a Li-ion series string is a question of how many cells you put in series. The arithmetic that drove the whole layout:

// series count for a target pack voltage
const CELL_NOMINAL = 3.6;   // V per Li-ion cell
const TARGET = 72;        // V nominal
const seriesCount = Math.round(TARGET / CELL_NOMINAL); // → 20S
const packNominal = seriesCount * CELL_NOMINAL;        // 72.0 V
const packMax     = seriesCount * 4.2;                 // 84.0 V full charge

Hardest challenge: balancing and thermal management inside a shape with no symmetry to lean on. The triangular nest concentrates cells at the base, so sense-lead routing and heat paths had to be planned around the geometry, not bolted on after.

What I learned: hardware punishes hand-waving. A bug in software throws an error; a bug here is heat. That changes how carefully you design every single decision.

What I'd do differently: build the thermal model before the mechanical one — the geometry I committed to early made cooling harder than it had to be.