What are the main parameters of a UPS (Uninterruptible Power Supply)? ( Part 1)

In data center server rooms, hospitals, and banks, you may have seen this “computer case-like” device – a UPS (Uninterruptible Power Supply).

In reality, it acts as a “power guardian” for networks and devices. It will step in immediately if there’s a problem with the mains power, ensuring your devices experience orderly power outages and operate smoothly.

However, when it comes to UPS selection and parameters, many people’s first reaction is:

“Ah… the higher the power, the better, right? As long as it’s stable, that’s fine.”

In reality, UPS parameters are far more complex than you might imagine—power is just the tip of the iceberg. Choosing the wrong one could not only waste money but also create risks. Today, let’s have a “parameter clarification” session; reading this before you buy will reduce 90% of your doubts.

First, let’s quickly clarify the concept: UPS (Uninterruptible Power Supply) is a device that can provide continuous power when the mains power is abnormal or there is a power outage. It can also play a role in voltage stabilization, filtering, and surge protection.

It primarily addresses two pain points:

1. Power outage risk: Sudden power outages to servers, switches, and databases may result in data loss and hard drive damage.

2. Electrical quality issues: Voltage fluctuations, momentary drops, surges, harmonics, and other problems can shorten the lifespan of equipment.

A UPS is like your “power insurance,” saving your life in critical moments.

UPS main parameters :

Rated capacity (VA/kVA)

The capacity unit of a UPS is usually VA (volt-ampere) or kVA (kilovolt-ampere), which represents apparent power and not all of it is available.

Why not just use watt (W) directly?

Because UPS outputs AC power, power = voltage × current × power factor. Since the power factor is usually not 1, manufacturers use VA as a standard designation.

Selection method:

• First calculate the total power of the equipment (W).

• Divide by the UPS power factor (e.g., 0.8).

• Multiply by 1.2 to 1.3 (for redundancy)

Assuming your server and network equipment have a total power consumption of 800W and a UPS power factor of 0.8:

800 ÷ 0.8 = 1000 VA
1000 × 1.2 = 1200 VA

Then you need to choose a UPS with a capacity of at least 1.2 kVA.

Output power factor (PF)

Power factor = Effective power (W) ÷ Apparent power (VA).

The higher the power factor of a UPS, the larger the actual load it can handle with the same VA.

Industry changes:

• Older UPS models: PF=0.7~0.8

• New high-end UPS: PF=1.0 (e.g., 1kVA can support a 1kW load)

A UPS with a low power factor may appear to have a large capacity, but it can actually only power a few devices.

Rated output voltage

UPS output voltages generally come in two types:

• 220V/230V: Applicable to Chinese, European, and other standards

• 110V/120V: Compatible with US, Japanese, and other standards

Some high-end models support adjustable output, which can adapt to different national voltage standards.

Choosing the wrong voltage can cause equipment to malfunction or even burn out completely.

Rated frequency

• Commonly used frequencies are 50Hz (China, Europe) and 60Hz ( USA , Japan ).

• Some UPS systems support 50/60Hz adaptive switching.

• Frequency stability is crucial for servers and communication equipment, as frequency drift can lead to clock errors or even system crashes.

Backup time (backup duration)

The duration of continuous power supply from the start of a power outage until the battery is depleted by the UPS.

Influencing factors:

• Load size

• Battery capacity

• UPS Type (Standby/Online)

Selection Recommendations:

• Office computers: 5-10 minutes is sufficient to save files and shut down.

• Server room: 15-30 minutes, allowing time for switching to generator.

• Core system: >30 minutes or even several hours (external battery pack required)