What is an inverter and how do I use it?

What is an electrical inverter?

Definition and operating principle

An inverter is an electronic device that maintains the power supply to your equipment in the event of a power cut. Its principle is based on the conversion of energy stored in batteries into alternating current that can be used by your appliances. Unlike a simple standby generator, the inverter intervenes instantly, with no perceptible interruption to service.

The operation of an inverter hinges on several key components. The rectifier converts AC mains current into DC to charge the batteries. The inverter, the central element of the system, then transforms the direct current from the batteries into alternating current when the main power supply fails. An intelligent control system constantly monitors the quality of the power supply and triggers battery switchover as soon as an anomaly is detected.

The differences between inverters and gensets

Although UPS and gensets both provide emergency power, their operating modes differ considerably. The generator produces electricity using an internal combustion engine, and requires a start-up time of several seconds or even minutes. This interruption, however brief, can be fatal for sensitive IT equipment.

The inverter, on the other hand, guarantees a totally seamless transition, with a switchover time of less than 10 milliseconds for the most efficient models. This absolute continuity preserves data integrity and avoids sudden system shutdowns. What's more, the inverter offers permanent protection against electrical disturbances such as overvoltage, undervoltage or interference, even when the grid is operating normally.

The different types of inverters

The off-line or stand-by inverter

The off-line inverter, also known as the standby inverter, is the most economical solution on the market. In this type of device, the mains current feeds directly into the connected equipment under normal circumstances. The inverter only intervenes in the event of an outage or significant voltage variation, with a switchover time generally between 2 and 10 milliseconds.

This configuration is ideally suited to low-critical home applications, such as protecting a personal computer, an Internet box or a family NAS. Off-line inverters offer autonomy generally limited to a few minutes, enough to save your work in progress and shut down your equipment properly. Their main asset is their excellent value for money, with entry-level models available from 50 to 80 euros for power ratings from 300 to 600 VA.

The line-interactive inverter

The line-interactive inverter represents an intelligent compromise between performance and cost. This type of device incorporates an automatic voltage regulator (AVR) that corrects voltage variations without straining the batteries. When grid voltage fluctuates within an acceptable range, typically between -25% and +15%, the inverter automatically adjusts the output voltage using a multi-tap transformer.

This technology is particularly well-suited to environments where micro-interruptions and voltage variations are frequent. Line-interactive UPS are mainly used in small businesses, professional workstations and medium-sized IT installations. Their battery switchover time, typically less than 4 milliseconds, guarantees effective data protection. Line-interactive models range in price from 150 to 500 euros, depending on power and features.

Online or double conversion inverters

The online UPS represents the ultimate in electrical protection. Its double conversion principle ensures total isolation between the input network and the protected equipment. Alternating current from the grid is first converted to direct current to charge the batteries and power an inverter, which then produces a perfectly sinusoidal, stable alternating current.

This architecture guarantees a power supply of impeccable quality, totally immunized against all electrical network disturbances: overvoltage, undervoltage, interference, harmonics, or frequency variations. The battery changeover time is strictly zero, as the equipment operates permanently on the inverter. Online UPS are a must in critical environments: server rooms, data centers, medical facilities, sensitive industrial equipment or telecommunications systems.

The main drawback of this technology is its high cost, with prices generally starting at around 500 euros for entry-level models, and rising to several thousand euros for professional installations. Energy efficiency is also slightly lower than with other technologies, as double conversion generates energy loss in the form of heat.

Inverter selection criteria

Calculate power requirements

Determining the power required is the fundamental step in choosing an inverter. This power is expressed in volt-amperes (VA) or watts (W), with a power factor (usually 0.6 to 0.8) linking the two units. To correctly size your UPS, you need to add up the power consumption of all the equipment you wish to protect.

Let's take a concrete example: if you want to protect a desktop computer (350W), two monitors (80W each), a router (15W) and a NAS (65W), the total power required is 570W. A safety margin of around 20 to 30% should be added to allow for peak consumption at start-up and for the future development of your installation. In this example, a 750W to 850W inverter (i.e. around 1000 to 1200 VA) would be appropriate.

Manufacturers usually indicate the VA power rating on their inverters, but it's crucial to check the wattage rating too, as this is what will really limit your charging capacity. A 1000 VA inverter with a power factor of 0.6 can only deliver a maximum of 600W.

Battery life and capacity

The autonomy of a UPS determines how long your equipment will be able to run on batteries in the event of a power cut. This autonomy varies considerably according to the load connected: the more you load the inverter, the shorter the autonomy. Manufacturers generally advertise full and half-charge ranges.

For conventional domestic use, an autonomy of 5 to 15 minutes is generally sufficient to save your work and perform a clean shutdown of your equipment. Professional environments may require longer autonomies, from 30 minutes to several hours, obtained either by using higher-capacity batteries or by adding external battery modules.

Battery technology also plays a crucial role. Lead-acid batteries (VRLA) are used in the majority of inverters on the market and offer good value for money, with a lifespan of 3 to 5 years. The more expensive lithium-ion batteries have the advantage of a longer service life (8 to 10 years), a smaller footprint and shorter recharging times.

Additional functions

Modern inverters incorporate numerous features that enhance their usefulness and ease of use. The LCD display shows essential information in real time: charge, remaining autonomy, input and output voltage, or battery status. This interface enables instant monitoring of your installation without the need for additional equipment.

Network connectivity via Ethernet or Wi-Fi turns your UPS into an intelligent piece of equipment that can be remotely supervised. The management software supplied enables you to program automatic actions such as sequenced shutdown of your equipment, email notification in the event of an incident, or detailed reports on consumption and electrical events.

Lightning protection sockets and RJ45 or coaxial protection ports also protect your telecom equipment from lightning-induced power surges. Some models offer "sacrificial" sockets without backup power, useful for less critical peripherals such as printers or speakers.

How to install and use an inverter

Physical installation of the inverter

The location of your inverter deserves special attention. Choose a dry, ventilated location away from direct sunlight. The ideal ambient temperature is between 15 and 25°C, as batteries are sensitive to extreme temperature variations. An excessively hot environment significantly reduces their service life, while excessive cold reduces their capacity.

Make sure you leave enough space around the inverter to allow air circulation and facilitate heat dissipation. Medium and high-power models generate considerable heat and generally require 10-15 cm of clearance on the sides and rear. Avoid installing the UPS in a closed cupboard or under a desk without adequate ventilation.

The electrical connection must comply with certain basic rules. Always connect the inverter directly to an earthed wall socket, never to a power strip or extension cord, which could create parasitic resistance and limit the available current. Check that your electrical installation is properly grounded to ensure safety and proper operation.

Commissioning and configuration

Before using your UPS for the first time, it is essential to fully charge the batteries. This initial charge may take 8 to 12 hours, depending on the model. Some manufacturers even recommend leaving the UPS charging for 24 hours before connecting equipment, to optimize battery capacity and longevity.

Then connect your equipment, starting with the most critical. Prioritize your devices according to their importance: servers, network equipment, primary workstations, then secondary devices. Never overload the inverter beyond 80% of its rated capacity, to maintain a safety margin and optimize its energy efficiency.

Installing the management software supplied by the manufacturer allows you to fully exploit the capabilities of your UPS. These applications, generally compatible with Windows, macOS and Linux, ensure communication between the UPS and your computers via USB, serial or network. Configure automatic shutdown settings so that your systems shut down cleanly when the remaining autonomy reaches a critical threshold, typically 5 to 10% of charge.

Good usage practices

Regular maintenance of your inverter guarantees its reliability and extends its service life. Test battery operation every month by disconnecting the UPS from the mains for a few minutes. This test allows you to check actual autonomy and detect any battery degradation before it becomes critical.

Keep an eye on your UPS's audible alarms and visual indicators. An occasional beep during a power failure is normal, but repeated or continuous alarms usually signal a problem requiring your attention: overload, battery failure, or excessive temperature. Refer to the user manual for correct interpretation of the various alarm codes.

Battery replacement is an essential part of maintenance. Even with optimum use, lead-acid batteries gradually lose their capacity and need to be replaced every 3 to 5 years. Signs of an end-of-life battery include reduced autonomy, more frequent charging, or low-battery alarms. Don't wait for a complete failure to anticipate this replacement.

Inverter applications in practice

Protecting IT equipment

Home and office computing are the most common applications for UPS. Your computers, NAS servers and network equipment contain valuable data, the loss of which could have serious consequences. A sudden shutdown due to a power cut can corrupt system files, damage databases, or result in the loss of unsaved documents.

The UPS protects not only your data, but also the physical integrity of your equipment. Repeated power cuts and voltage variations place excessive stress on electronic components, reducing their lifespan. Mechanical hard disks are particularly vulnerable to sudden stops, which can lead to read head crashes and bad sectors.

For a typical workstation with a computer, two monitors and a few peripherals, a 600 to 800 VA UPS is more than sufficient. More complex installations including servers, disk arrays or professional network equipment require higher power ratings, from 1500 to 3000 VA depending on the configuration.

Securing home automation systems

Modern home automation relies on a permanent electronic infrastructure: home automation boxes, Zigbee or Z-Wave gateways, surveillance cameras, connected alarms or smart thermostats. This equipment provides critical functions such as home security, temperature control and remote monitoring. A power cut instantly paralyzes your entire installation.

The UPS keeps your home automation systems operational during power cuts, guaranteeing the continuity of your security and surveillance systems. Your alarm system remains active, your cameras continue to record, and your Internet connection remains functional if your box and router are also protected. This protection is particularly important in areas prone to frequent cuts.

A 300 to 600 VA inverter is generally sufficient to protect all the equipment in a standard home automation installation, as each device consumes very little energy. Autonomy can reach several hours on such a low charge, enabling you to maintain your essential systems during extended outages.

Professional and industrial applications

In the service sector, UPS systems secure workstations, servers, network equipment and IP telephony systems. Data loss or service interruptions can have considerable financial consequences, not to mention the impact on productivity and customer satisfaction. Call centers, bank branches or medical practices depend on a stable, uninterrupted power supply.

Industry uses inverters to protect programmable controllers, variable speed drives, supervision systems, or sensitive measuring equipment. A micro-cut can be enough to disrupt a manufacturing process, resulting in scrap, costly downtime or equipment malfunctions. Industrial UPS systems, often of high power (5 to 500 kVA), ensure the continuity of critical processes.

The medical sector is probably the area where power supply reliability is of greatest importance. Diagnostic equipment, patient monitoring systems and life-support systems cannot tolerate any interruptions. Medical UPS meet strict standards and offer redundancy levels to ensure maximum availability.

Inverter advantages and limitations

The benefits of an inverter

Protection against data loss is the most immediate and obvious benefit of a UPS. Whether you're working on an important document, a complex spreadsheet, or a creative project, a power cut at the wrong time can wipe out hours of work. The UPS gives you the time you need to back up your files and shut down your systems properly.

Preserving equipment represents a significant economic benefit. Voltage variations and repeated power cuts accelerate the ageing of electronic components and can lead to premature failure. Investing in a quality UPS is often less expensive than frequently replacing equipment damaged by electrical problems.

The continuity of service offered by a UPS enhances your productivity and comfort of use. No more untimely restarts, lost documents or interrupted downloads. For professionals, this constant availability can mean the difference between meeting a crucial deadline and losing a customer. The peace of mind provided by an inverter is priceless, especially in regions where power cuts are frequent.

Constraints and drawbacks

The initial cost of acquiring an inverter can seem a significant investment, especially for high-quality professional models. Prices range from 50 euros for an entry-level UPS protecting a single computer, to several thousand euros for professional installations. Added to this cost is the periodic replacement of batteries, usually every 3 to 5 years.

Space and weight are other constraints to consider. A medium-power UPS can weigh 8 to 15 kg and occupy a volume comparable to a computer CPU. High-power models for professional applications are more like small cabinets, and sometimes require a dedicated installation with forced ventilation.

Operating noise is also worth mentioning. Powerful UPS cooling fans can generate annoying noise levels in a quiet office environment. Some models activate their fans continuously, while others only trigger them in the event of a high load or excessive temperature. Off-line and line-interactive inverters are generally silent in normal operation, with noise only occurring in the event of battery switchover.

Conclusion

Today's UPS is an essential piece of equipment for anyone wishing to effectively protect their sensitive electronic devices from the vagaries of the power supply. Beyond the simple function of providing back-up in the event of an outage, it ensures permanent protection against all electrical network disturbances: overvoltage, undervoltage, interference or frequency variations.

Choosing the right UPS is based on a precise analysis of your needs: power requirements, desired autonomy, type of equipment to be protected and available budget. Off-line inverters are ideal for simple domestic applications, while line-interactive models offer an excellent compromise for small businesses. Online double-conversion inverters are reserved for critical environments requiring impeccable power quality.

Installing and using an inverter presents no particular difficulties, provided you observe a few basic rules: ventilated location, initial battery charging, correct power sizing, and regular maintenance. The investment in a quality UPS quickly pays for itself in savings on the replacement of damaged equipment and the peace of mind it brings.

Whether you're an individual looking to protect your household equipment, or a professional needing to guarantee the continuity of your critical activities, the UPS represents valuable insurance against the sometimes disastrous consequences of a faulty power supply. In an increasingly digital world, where our data and equipment are of considerable value, neglecting this protection would be taking an unnecessary risk.