300 kW Modular Load Bank — 6-Layer PCB

Factory and site acceptance tests of datacenter UPS systems need real loads: up to 300 kW on 400–480 V three-phase, derated for 208 V and single-phase 230 V operation, with a hard physical ceiling of 500 A per phase. The board has to be modular — caster-mounted units that combine — and survive the currents involved.

My first layout attempt on 4 layers hit a physical wall: there simply wasn't enough copper real estate to route power and control cleanly without carving up the ground plane. That board had to be abandoned.

I restarted as a 6-layer KiCad design: dedicated power planes, ESP32-based control firmware, I2C and VREF critical routing first, then differential Ethernet, then power, then the rest.

For autorouting I ran extensive experiments with FreeRouting 2.1.0 in batch mode on a portable Java 21 runtime. Along the way I learned that the batch loop never terminates on its own and ignores pass-count settings — the fix is passing --routerSettings.stop_pass_no via reflection, which makes runs bounded and reproducible.

The workflow gates every iteration on ERC/DRC plus visual review before anything gets committed or sent anywhere near a fab.

The project is honestly still in progress: the best autorouting runs got down to a handful of unrouted nets, and DRC is not clean yet — the board is NOT orderable, and I won't claim otherwise.

What it has already produced is a repeatable hardware workflow: bounded FreeRouting runs with deterministic exit, a disciplined layer stack-up decision, and review gates that catch regressions. When the DRC goes green, the design files will be ready for manufacturing review.