Network & Power
UPS sizing
Load, power factor and runtime → minimum and recommended UPS VA and W, plus battery Wh.
List the rack loads or enter a total, set the power factor, runtime target and headroom, and get the VA and W floors a UPS must clear, the recommended rating with headroom, and the battery energy the runtime needs. Enter a candidate UPS's nameplate VA and W to see whether it passes both.
load
Enter load as
Use measured or typical draw, not the nameplate maximum — a 750 W PSU in a media PC usually pulls 150 W. Amplifiers: use 1/8 of rated output for music.
Minimum UPS rating
389 VA
350 W real power · PF 0.90
The floors. A UPS must meet both — a unit can pass VA and still overload on W.
Recommended (with 25% headroom)
486 VA
438 W · buy the next stock size up
Keeps the load at 80% of rating.
Battery energy for 15 min
97Wh
≈ 5 Ah at 24 V (80% depth of discharge)
W × min ÷ 60 ÷ 0.9 inverter efficiency. Cross-check the manufacturer's runtime chart at your load — lead-acid delivers less Ah at high discharge rates.
check a specific UPS (optional)
Enter both figures from the datasheet — e.g. 1500 VA / 900 W. The W figure is the one that bites.
- ▸ Load a UPS to 50–80%. Runtime vs load is steeply non-linear: half the load gives well over twice the minutes.
- ▸ Online / double-conversion: zero transfer time and regenerated, clean output — the right choice for DSP cores and switches that reboot on a 10 ms dip. Line-interactive is cheaper and fine for less sensitive loads.
- ▸ Batteries lose capacity from year one and typically need replacing at 3–5 years. Headroom does not fix that — schedule the swap.
- ▸ Add a network management card for shutdown signalling to PCs / NAS, and put the UPS on the monitoring VLAN.
Need this math wired into a real system? We do that for a living.
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