The ASI (Alimentation Sans Interruption), or UPS (Uninterruptible Power Supply) in international terms, is a crucial piece of equipment. It ensures a continuous power supply to your IT systems (computers, monitors, peripherals, servers) in the event of a cut in the main electricity supply.
This device gives you a safety window to take the necessary actions: save your work, shut the computer down safely, or switch on a secondary power system.
A UPS generally contains one or more batteries. When the mains power fails, these batteries immediately deliver the current needed by the equipment connected to the unit.
Types of uninterruptible power supplies
The market is divided into three main UPS families, each with a different operating mode:
Standby (offline) UPS
This is the most basic model. Under normal conditions, it passes electricity from the mains straight through to the devices. When there is an outage, the equipment instantly switches to battery power. This changeover is very fast (a few milliseconds) and usually causes no noticeable disturbance. These UPS units are small and are ideal for home or personal use.
- Advantages
- Low initial cost.
- Compact design.
- Easy to use.
- Disadvantages
- The electricity supplied to the devices is not filtered from mains disturbances.
- There is a brief delay when switching from mains to battery power.
- The charging circuit can affect battery lifespan and extend charging time.
Line-interactive UPS
This model is based on offline architecture, but with a technical improvement: the battery is kept on charge permanently. In the event of a power cut, converting the battery voltage into AC power is faster, which shortens the switching period. This transition time between the two sources is therefore minimised. The charging system is optimised, improving overall efficiency.
- Advantages
- Competitive cost (similar to standby models).
- Shorter switchover time when the power changes source.
- Ability to regulate and filter the voltage.
- Disadvantages
- Room for improvement in terms of equipment protection.
- The switchover between power sources still exists.
- Internal protection components are subject to wear and tear over time.
Online double-conversion UPS
With this type, the equipment is always powered by the battery. The battery is constantly running through a charge and discharge cycle. The major advantage is the total elimination of switchover time between the external power and the battery. These systems are the most reliable and are therefore preferred for powering servers or computers where shutdown is unacceptable.
- Advantages
- Complete removal of any switching process between power sources.
- Maximum protection of equipment against any electrical anomaly, as the power supply is completely independent from the incoming mains.
- Disadvantages
- Less energy-efficient due to continuous battery charging.
- Higher initial purchase cost.
UPS with additional external battery
While most UPS systems include internal batteries, some situations call for much longer runtime. It is possible to use a UPS with an external battery housed separately from the main unit. This option allows you to keep systems running for several extra hours.
What are the different uses for a UPS?
An uninterruptible power supply is an essential tool in many environments. It is widely used at home, in offices and in industry (for example, data centres), where a power cut can have serious consequences or lead to the loss of vital data.
UPS systems are commonly used for:
- In the home, UPS units are most often used for:
- Powering a desktop PC (particularly popular with gamers).
- Keeping circulation pumps for boilers or central heating running.
- Pellet burners.
- Solar-powered water heaters.
- In the office, their main use is:
- Powering workstations and IT peripherals.
- In industry, UPS units are used mainly for:
- Powering server systems.
How to estimate the runtime of your UPS
The runtime of a UPS is determined by the capacity of its battery and the power consumption of the devices connected to it. To calculate the approximate time the UPS will operate autonomously in the event of a power cut, you can use the following formula:
- $T = \frac{A \cdot U}{P}$
- $T$ : runtime expressed in hours.
- $A$ : battery capacity in ampere-hours (Ah).
- $U$ : battery voltage in volts (V).
- $P$ : total power consumption of all devices (in watts W).
Numerical example: a device (P) has a power of 300W, the battery (A) is 100Ah and its voltage (U) is 12V.
$T = \frac{100 \cdot 12}{300} = 4$
The battery can therefore support this load for 4 hours.
How to define the power rating of the UPS you need
The required power rating of your UPS depends on where and how it will be used, and what you want it to do. Before choosing, you must determine how many devices you want to protect and how much power they require. It is always advisable to choose a unit that is slightly more powerful than you currently need, leaving headroom to add more equipment later.
What are the benefits of using a UPS?
- Improved protection: voltage fluctuations and sudden surges can damage vital components in your equipment. The UPS acts as an effective barrier to keep your systems safe. It also gives you time to back up your data and shut devices down without risking a crash.
- Longer equipment lifespan: an unstable power supply can speed up component wear and cause faults. A quality UPS delivers the stable voltage required, helping to extend the lifespan of all connected devices.
- Service continuity during outages: in areas where cuts are frequent, and if your heating depends on electricity, the UPS guarantees essential minimum operation. It reduces the risk of damage to the heating system and keeps your circulation pump running for a safety period.
