Rack power and UPS fundamentals

Power in the datacenter

Electricity is the most critical resource in any server room. Even a one-second outage can corrupt data and take services down for hours. That is why power is designed in layers, each one covering for the previous.

Typical power chain

Utility grid → Transformer → ATS → UPS → PDU → Equipment
                              │
                         Generator
                          (backup)

• ATS (Automatic Transfer Switch): switches between grid and generator automatically.
• UPS: bridges the gap during the transfer (seconds to minutes).
• Generator: keeps the room running through long outages.

UPS: Uninterruptible Power Supplies

In server rooms, always use online double-conversion UPS units. Zero transfer time, and they filter every power anomaly: spikes, sags, noise and frequency drift.

UPS runtime

Runtime depends on battery capacity and connected load. A datacenter UPS typically gives 5 to 15 minutes — enough for the diesel generator to start, not enough to ride out a long outage on its own.

PDUs: Power Distribution Units

PDUs distribute power inside the rack. They range from a dumb power strip to a remotely controlled, per-outlet metered device:

Recommendation: metered PDUs at minimum. Per-outlet metering tells you which device draws the most — invaluable for capacity planning.

Power redundancy

Feed A / Feed B

In a 2N setup, each rack gets two independent power paths, each with its own UPS and PDU:

Feed A ── UPS A ── PDU A ──┐
                            ├── Server (dual PSU)
Feed B ── UPS B ── PDU B ──┘

Servers with redundant power supplies plug into both PDUs. If one entire path fails, the other keeps the server up.

Watts vs VA

• VA (volt-amperes): apparent power — what the UPS is rated to deliver.
• W (watts): real power — what the equipment actually consumes.
• Power factor: the W/VA ratio, typically ~0.9 on modern UPS units and PSUs.

Example: a 10,000 VA UPS with a 0.9 power factor delivers 9,000 W of real power. Always size against watts, not VA.

Capacity planning

1. Inventory each device’s draw (nameplate, vendor spec, or a real measurement — nameplate values are usually pessimistic).
2. Add up the watts per rack.
3. Keep headroom: stay under 80% of the PDU’s rated capacity.
4. Balance phases if your feed is three-phase.
5. Project growth: reserve capacity for the next equipment you will install.

Power in CreaRack

Each rack in the Rack Editor has a Power Cons. field (in kWh) where you record the rack’s consumption, so the figure lives next to the rack layout instead of in a forgotten spreadsheet. For the UPS side, UPS Monitor tracks your uninterruptible power supplies via SNMP — battery charge, load and runtime — and [[crearack—ups—add-ups-devices]] explains how to discover and add them.

Related

• [[crearack—ups—add-ups-devices]] — add your UPS units to UPS Monitor
• [[crearack—monitoring—que-es-ups]] — what UPS Monitor does
• [[crearack—redes-infra—refrigeracion]] — every watt consumed becomes heat
• [[crearack—redes-infra—cableado]] — physical cabling of the rack
• [[crearack—redes-infra—monitorizacion]] — monitoring the whole infrastructure
• [[crearack-tech—guides—capacity-planning]] — technical capacity planning guide

Véase también

• [[crearack—redes-infra—refrigeracion]]
• [[crearack—redes-infra—cableado]]
• [[crearack—redes-infra—monitorizacion]]
• [[crearack—monitoring—que-es-ups]]
• [[crearack—ups—add-ups-devices]]
• [[crearack-tech—guides—capacity-planning]]