High-current system design

One chain

The battery-to-inverter path is a chain: cells/BMS -> terminal -> fuse -> switch -> busbar -> cable/lugs -> inverter. Every item must carry continuous and surge current and survive the fault environment.

Connections make heat

Resistance at lugs and studs causes I²R heating. At 300 A, 0.001 ohm makes 90 W at one connection. Correct conductor preparation, die, compression, stud size, flat mating surface and torque are safety features.

Lugs and crimping

Use closed-barrel copper lugs matched to conductor and stud. Use a quality hex or indent crimper that produces the lug maker's specified crimp. Pull-test samples and seal with adhesive heat shrink where appropriate.

Torque

Use a calibrated torque tool and the component's published value. More torque is not safer: it can strip threads, crack devices or deform lugs. Mark completed fasteners with torque seal as an inspection aid, not proof.

Thermal validation

Run the system at a sustained high load, then inspect with an IR camera or thermometer. Compare like connections; a local hot spot suggests resistance. Do not touch exposed energized conductors.

Rule of thumb

If you cannot state the expected current, full conductor length, protection rating and manufacturer limit for a circuit, the circuit is not ready to build.

CHAPTER CHECK

• I can explain the purpose of every component covered here. • I can identify the exact manufacturer limit that controls my design. • I have added the decision, rating or measurement to my schematic/worksheet.