Data centers are transitioning from AC to DC

Original Article ↗ Hacker News Discussion ↗

High‑power data centers are increasingly looking at high‑voltage DC (around 800 V) distribution instead of traditional AC, aiming to cut conversion losses, simplify UPS architectures, and better match the DC nature of servers, batteries, and AI racks. Commenters note that DC power is not new—telco and some hyperscale facilities have used -48 V or other DC schemes for decades—but advances in wide‑bandgap semiconductors (SiC, GaN) and megawatt‑scale loads are making HVDC more attractive and practical. The shift raises serious engineering questions around safety, breakers, hot‑swappable 800 V racks, and equipment availability, and prompts parallel debates on where DC makes sense in homes and grids versus where AC remains cheaper and safer.

DC vs AC in Data Centers

  • Many commenters say DC distribution in data centers (and telco) is not new; 48V DC has been common in telecom for decades, and some data centers have used DC since at least the 2000s.
  • Hyperscale AI data centers are pushing 800V DC rack-level buses to cut conversion stages, wiring losses, and UPS complexity. Wide‑bandgap (SiC/GaN) converters at ~95%+ efficiency and solid-state DC breakers are cited as enablers.
  • Others argue that 3‑phase 400 Hz AC with rectification can be similarly efficient, leveraging mature aerospace‑grade components and small transformers.

Safety and Engineering Challenges

  • 800V DC with hot‑pluggable racks raises concerns: persistent DC arcs, MOSFETs that can fail “on,” and the need for complex hot‑swap controls, shutters, and PPE.
  • Multiple anecdotes highlight how DC arcs can vaporize probes, tools, and cables; several note DC breakers and switches must be specifically rated, not re‑used AC parts.
  • There is debate over skin effect at 400 Hz: some claim it’s “significant” for busbars; others say it’s modest (skin depth ~3 mm in copper) but acknowledge it matters at very high currents.

HVDC vs AC on the Grid

  • HVDC transmission is described as more efficient than AC at a given voltage and useful for long distances and interconnecting unsynchronized AC grids.
  • Key tradeoff: AC makes voltage conversion cheap and easy; DC has lower ongoing transmission losses, but conversion equipment is costlier and complex, though improving.

Home and Low‑Voltage DC Ideas

  • Several people want DC in homes to avoid many small AC‑DC bricks (for LEDs, electronics). Others counter:
    • Appliances need high power, making low‑voltage DC impractical due to massive cable sizes and losses.
    • Different devices need many different DC voltages, so DC‑DC converters would still be everywhere.
    • DC arcs and code/safety issues make residential DC unlikely beyond niches (PoE, USB‑PD, RV/solar).

Historical Framing (Tesla vs Edison)

  • Multiple commenters criticize the “Edison’s revenge” headline as clickbait and historically misleading.
  • Consensus view: past AC vs DC arguments were about transformer technology limits, not deep ideological stakes; with modern power electronics, DC is just another tool where it’s economically and technically advantageous.