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Line Interactive UPS Systems

A range of line interactive uninterruptible power supplies including desktop, tower and rack mount uninterruptible power supplies suitable for a wide variety of applications including CCTV, security panels, EPOS terminals, IT servers and networks accessories. Line interactive UPS tend to be single phase output systems and can provide longer runtimes by oversizing the UPS or adding external battery cabinets where the UPS design provides this option.

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What Is A Line Interactive Uninterruptible Power Supply?

A line interactive UPS is an uninterruptible power supply which is classed under IEC EN62040-3 as Voltage Independent (VI). The inverter section of the UPS system is energised but only supports the load when the mains power supply fluctuates or fails completely.

This type of UPS technology is best suited to uninterruptible power supplies up to 3kVA and allows for a compact UPS design with an internal battery and a relatively low cost. Some UPS manufacturers supply larger line interactive models up to 10kVA but all are limited to a single phase input and output supply.

The UPS tends to have a built-in automatic voltage stabiliser (AVS) which under normal conditions (when the mains power supply is present) protects the connected load from mains power problems including sags, surges and brownouts.

The AVS can be transformer based and sometimes referred to as a buck/boost transformer. When the input voltage is high, the transformer ‘bucks’ to reduce the output voltage and when it is high the transformer ‘boosts’ the output supply voltage. The ‘buck/boost’ transformer uses a series of transformer taps to adjust the output voltage. An AVS can also be referred to as an automatic voltage regulator (AVR). A small battery charger is built into the UPS and charges the battery set. The UPS also has a built-in EMC/filtering circuit to provide protection from mains borne interference in the form of electrical noise, spikes and transients.

If the mains supply voltage falls outside the input voltage window or the input frequency window of the AVS or AVR, the inverter section connects to the load supply line and powers the connected load. The inverter section draws on the DC (direct current) of the built-in battery set and inverts this into an AC waveform to power the load.

When the inverter section picks up the load or disconnects there is typically a 2-4mS break in electrical supply. This is well within the capacitance level of the switch mode power supply (SMPS) within a computer or server which can hold capacitance up to 15-20mS or longer.

The output waveform from inverter can be a pure sinewave or square wave. A square wave output is sometimes referred to as a Pseudo sinewave. The inverter section may also be rated for long running periods at 80-100% load allowing additional battery extension packs to be connected to a rear panel connector (if available). The loads are generally connected using IEC320 sockets.

Lead Acid UPS Batteries

The standard battery for a line interactive uninterruptible power supply is a valve-regulated lead acid (VRLA) battery with a 5year design life. The battery will require replacement during years 3-4 depending upon the number of charge/discharge cycles it has under gone and the ambient temperature of the room or server rack the UPS system is operating within. The recommended ambient temperature of a UPS lead acid battery is 20-25˚C. If the temperature is above this range the battery life will degrade. For every 1˚C rise above 30˚C the battery design life of 5 years will halve.

Lithium-ion UPS Batteries

Lithium batteries are starting to become available for some line interactive uninterruptible power supplies. Lithium UPS batteries can withstand a far larger number of charge/discharge cycles. Lithium batteries are more suited more rapid cycling, unlike the standby preferred mode for lead acid batteries. Lithium batteries tend to have a 10 year design life.

An uninterruptible power supply with lithium batteries will have a charging and battery management circuit specially for a lithium-ion battery. Lead acid and lithium batteries are not interchangeable.

Replacement UPS Batteries

Replacement UPS battery sets tend to be available for line interactive uninterruptible power supplies. These UPS may have a ‘hot swap’ or user-changeable battery option, allowing the battery set to be easily swapped out. The replaced batteries can then be returned for recycling in line with WEEE/RoHS directives and local recycling regulations.

UPS Warranty Periods

The warranty period on line interactive uninterruptible power supplies is typically 24-36months (2-3 years) as standard including the battery set if used within the UK. Longer warranty periods up to 48months (5 years) may be available through the purchase of an extended warranty or offered as by the UPS manufacturer.

Outside the UK the warranty period may only cover the electronics and provide the UPS battery with a 12months warranty. Please refer to the individual uninterruptible power supplies for more specific information.

UPS Trade-in Service

Server Room Environments may be able to offer a trade-in rebate for your existing line interactive system or battery set if you are thinking of a system upgrade. This is dependent upon the brand of UPS system, its age and amount of time since its last inspection.

UPS Monitoring Software and Adapter Cards

UPS monitoring software is supplied as a downlink or on a CD-ROM dependent on the UPS brand and type. A range of plug-in adapter cards and external communications devices is available for remove monitoring including SNMP (Simple Network Management Protocol), MODBUS, JBUS and volt-free signal contacts.