UPS: which power to choose (VA and watts)

This article was machine-translated from French and is being reviewed. Prices are in Algerian dinars excl. VAT.

To know which UPS power to choose, add in watts the consumption of what you want to protect, divide the total by 0.8, then choose a model whose wattage (not just VA) covers the result. VA and watts are linked by power factor: watts = VA × power factor. The six EAST UPS models in the asloitech.com store all show a factor of 0.6: 650 VA equals 390 W. Models from 650 to 1,500 VA are in stock. All prices in this guide are in DA HT.

Why a UPS in the office

A sudden outage can:

• corrupt open files, especially if the disk is writing;
• lose unsaved documents;
• damage the system or a server’s database that could not shut down properly;
• cut the router, switch and IP phones, thus losing internet and calls.

The UPS takes over on its battery during a outage. This time is used to finish current work and shut down devices in order. In Algiers, brief outages and voltage dips are risks to consider for a server, recorder or telephone exchange.

Calculate power: watts, VA and power factor

The watt (W) measures the actual power consumed. The volt‑ampere (VA) measures apparent power, i.e. voltage multiplied by current. The power factor links the two and is at most 1:

• watts = VA × power factor;
• VA = watts ÷ power factor.

A UPS datasheet gives two values. Your load must stay below both limits, but it is almost always the watts that decide. Here’s the method.

1. List the devices to protect and note each one's power in watts. A wattmeter plugged into the outlet gives the actual consumption. The nameplate shows a maximum, often higher than what the device normally consumes.
2. Add up the watts.
3. Divide the total by 0.8. The UPS should not run continuously at its limit: the margin preserves the battery, absorbs startup peaks and leaves room for a device added later. Many manufacturers advise not to exceed about 80 % of the wattage.
4. Choose a model whose watts exceed that result. If you want the equivalent in VA for a UPS with a 0.6 factor, divide again by 0.6.

This last division only applies to UPS models that list a factor of 0.6. A recent double‑conversion UPS is often given with a factor of 0.9 to 1: 1,000 VA then gives 900 to 1,000 W. Always compare the watts on the datasheet, never just the VA.

Calculation examples

The loads below are example values to illustrate the calculation. Replace them with your measurements.

Check edge cases. For 450 W, the EA285 Pro (510 W) is unsuitable: 450 ÷ 510 gives 88 % load, above the margin. For 600 W, the EA2120P (720 W) would run at 83 %: too close. For 1,000 W, the EA2200 (2,000 VA, 1,200 W) is out of stock and its 1,200 W remains below the required 1,250 W.

What type of UPS: offline, line‑interactive or online?

The power is insufficient: the UPS type determines the quality of the supplied current.

The model names in the store do not specify their type or battery waveform. Only the EA285 Pro mentions an AVR. Read the manufacturer’s data sheet before buying a server.

The waveform deserves verification. On battery, many entry‑level UPSs provide a simulated sine wave, in steps. Some PC and server supplies with active power factor correction (PFC) handle it poorly and may shut down during the switchover. For a server, request a pure sine wave on battery, or test the switchover before commissioning.

UPSs from the asloitech.com shop

Prices from asloitech.com on 06/11/2026, excl. VAT, subject to availability. The recommended maximum load is 80 % of the watts (390 × 0,8 = 312, for example).

The price does not follow the power. The EA2120P (1,200 VA) costs 19,500 − 16,000 = 3,500 DA HT less than the EA2100 Pro (1,000 VA) and delivers 120 W more. Compare the datasheets before choosing: number of sockets (4 for the EA2120P, 3 for the EA2100 Pro), battery, UPS type. The MC 650 VA costs 15,500 − 10,500 = 5,000 DA HT more than the EA265 Pro, with 8 outputs instead of 3. For a network rack, the rack format of the EA2150R is designed to fit: see how to organize a network rack.

Autonomy: how long does an UPS last?

The store does not indicate battery capacity or autonomy of its models. To know the duration, ask the manufacturer for the autonomy curve versus load.

Keep two principles in mind. First, stored energy is read in watt‑hours: a 12 V, 7 Ah battery holds 12 × 7 = 84 Wh (example reading from a datasheet, not the battery of a shop model). You therefore need at least 300 Wh usable to run for one hour at 300 W, i.e. 300 ÷ 84 ≈ 3.6 batteries of this size, before UPS losses. Second, duration does not vary proportionally with load: on a lead‑acid battery, doubling the load cuts autonomy by more than two.

A desktop UPS therefore supplies only a few minutes at full load. That is enough for a clean shutdown, not to keep working. For several hours you need external batteries, an online UPS with a battery cabinet, or a generator: sizing on the quote.

To make the shutdown truly clean, connect the UPS to the server if the model offers a USB or network link with an automatic shutdown software (check the datasheet). Without that, no one shuts down the server when the outage hits at night.

Batteries and maintenance

Small desktop UPSs generally use sealed lead‑acid batteries. Lithium models exist, lighter and supporting more charge cycles, but are pricier to buy: the datasheet indicates the type.

The lifespan of a battery depends on heat, the number of cycles it has endured, and its age. The manufacturer provides an indication on the datasheet. Place the UPS in a ventilated room, out of direct sunlight and away from heat sources: in Algiers, summer quickly degrades a battery kept in a closet.

Test the UPS at regular intervals, outside working hours and after a backup. Use the autotest function if available, or unplug the mains cord and observe the switchover and how long it lasts. Replace the battery as soon as its autonomy drops significantly or the UPS reports a fault. The store record from 06/11/2026 does not include a spare battery: price on quote.

What to plug into the UPS, and what to leave on mains

Plug in: the server or NAS, the switch, the router or box, the IP phone, the CCTV recorder and its camera power supplies. A switch or router left on mains cuts access to the server, even if the server remains powered by the UPS.

Leave on mains: the laser printer, whose heating draws a high current that UPS manufacturers generally advise against plugging in, as well as radiators, air‑conditioners, kettles and coffee machines. Motors (pump, gate) also draw a high starting current. For CCTV, see our guide on the UPS for cameras and our CCTV solution.

What a UPS does not protect

• Devices not plugged into it: a printer, a router left on mains.
• Direct or nearby lightning: a UPS does not replace the surge protector on the panel nor a good grounding. A voltage spike can also enter via a network or telephone cable leaving the building.
• A long outage: empty battery, the output stops.
• A failed disk, accidental deletion or ransomware: only a backup protects. See the 3‑2‑1 backup rule.
• A theft or fire.

Frequently asked questions

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