Te rahi UPS me te wā mahi pākahiko

How this is calculated#

A UPS has two sizes that matter: the power its inverter can deliver, and the energy its battery holds. This tool works both from a list of what the UPS supplies, then the current it draws from the supply.

You list each load with how many there are, the real power each draws in watts and its power factor. The tool adds the watts, and it adds each load's apparent power. With your headroom for growth on top, the UPS needs at least that many kVA, and its kW rating, its kVA times its output power factor, must cover the watts. The larger of the two is the rating. The tool also names the next typical size up; the sizes are common ratings, not a standard's list.

The battery must hold the load's watts for the run time, divided by the inverter's efficiency, times an ageing factor so it still lasts when old. Divided by the bus voltage that gives Ah, but at the run time's rate: a battery gives far less than its 10 or 20 hour Ah over a short run, so the maker's discharge table decides the battery.

The input is the load through the UPS's efficiency plus the power to recharge the battery in the time you set. AmpSize does not hold AS 62040, so the headroom, efficiencies and ageing factor are your assumptions. The result names the AS/NZS 3000 rules for converters.

Worked examples#

• An office rack: two servers, three switches and storage, 15 min needs 1.86 kVA, so a 2 kVA unit, with 4.7 Ah at 96 V.
• The same rack for an hour still needs 1.86 kVA and a 2 kVA unit, but the battery holds 1,821 Wh.
• A comms rack and security system, 30 min on a 192 V battery needs 4.17 kVA, a 5 kVA unit, with 10.6 Ah at the bus.
• A small data hall of forty 1.2 kW racks, 10 min, three‑phase needs 61.86 kVA, an 80 kVA unit, drawing 76.6 A a phase.
• A home office PC and router, 10 min needs 0.51 kVA, so a 1 kVA unit.

Limits#

The battery figure is the energy and Ah at the run time's rate. It does not pick cells: read the maker's constant-power discharge table at your end voltage and temperature. The tool does not model a UPS in parallel, redundancy such as N+1, the bypass supply, or a generator behind the UPS; for that, size the generator for the UPS's input.

See also: Generator sizing, Battery and Cable size.