Data centers are transitioning from AC to DC

Original Article ↗ Hacker News Discussion ↗

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.