Tesla shares 48V architecture with other automakers

Original Article ↗ Hacker News Discussion ↗

Automakers are reassessing the long‑standard 12‑volt electrical system as Tesla rolls out and publicly shares a 48‑volt architecture, first used in its Cybertruck. Commenters highlight how higher voltage cuts current, copper use, weight, and connector complexity, enabling more powerful accessories and cleaner wiring when combined with Ethernet‑based data networks, while staying below key safety thresholds. Others note that partial 48‑volt systems and high‑voltage traction batteries already exist, but argue that moving all low‑voltage loads to 48V is a meaningful architectural shift that legacy manufacturers have struggled to coordinate with suppliers.

Why 48V Instead of 12V in Cars

  • Higher voltage for the same power means lower current; that allows:
    • Thinner, cheaper, lighter wires and connectors.
    • Much less I²R heating and reduced risk of “unscheduled welding.”
  • One commenter claims 16× lower losses (from I²), others point out you then use thinner wire (higher R) so realistic improvement is closer to 4×, with the big win being harness weight and cost.
  • Modern cars have many high‑power loads beyond the starter: electric power steering, pumps and fans, AC/heat pumps, defrosters, seat motors, audio amps, large wipers, etc. EVs add more electrically driven accessories, strengthening the case for 48V.

Safety Limits and Voltage Choices

  • 48V (often ~55V actual) sits just below common regulatory “extra‑low voltage” thresholds (variously cited as 50–60V DC depending on standard).
  • It is described as “right at the edge” of human safety: shocks hurt, especially when wet, but lethal accidents are rare compared to higher voltages.
  • Several posts stress that current through the body and conditions (wet/dry skin, path) matter more than voltage alone.

Network Architecture: Ethernet, PoE, and CAN

  • Cybertruck reportedly pairs 48V with an Ethernet‑centric architecture, possibly using power‑over‑data (PoDL/PoE‑like) to combine power and comms and reduce harness complexity.
  • Traditional cars rely heavily on CAN and LIN buses plus many point‑to‑point power runs.
  • Some argue CAN is too slow and fragmented for modern high‑bandwidth sensors and cameras; others say CAN’s deterministic arbitration is superior for safety‑critical control and that Ethernet is inherently less predictable unless you add TSN‑style mechanisms.
  • There is debate over whether PoE‑style power distribution in a car is smart optimization or “stupid” over‑complexity.

Industry Context and Prior Art

  • 48V has long been used in telecom (-48V), data centers, some marine systems, and in mild‑hybrid and premium ICE cars (often as a second bus alongside 12V).
  • Commenters disagree on novelty: some call Tesla the first to go 48V‑only for accessories at scale; others note 48V automotive experiments and mild hybrids since the 1990s and say Tesla is mainly executing what was already known.
  • A recurring theme: Tesla’s vertical integration lets it force a full‑system transition, whereas legacy OEMs are tightly bound to a 12V‑centric supplier ecosystem.

Implementation Details and Open Questions

  • Several expect legacy 12V parts to linger behind local 48→12V DC‑DC converters even in “48V cars.”
  • Practical issues raised: fuse and relay voltage ratings (many automotive parts are only 32V‑rated), DC arcing at 48V vs 12V, and EMC from many high‑slew DC‑DC converters.
  • It’s unclear from the thread exactly how completely Tesla has eliminated 12V or how they handle high‑power HVAC loads relative to the main 400–800V traction system.

Reception of the Article and Broader Commentary

  • Many find the technical explanation in the linked article shallow; the HN thread itself provides far more detail on efficiency, safety limits, and wiring practice.
  • Some praise Tesla for publishing and “pushing” the industry; others criticize the hype, note that multiple automakers already use partial 48V systems, and stress that leadership/marketing is being mistaken for unique invention.
  • There is a parallel, heated side‑discussion about the CEO’s behavior and politics, separate from the technical merits of 48V.