FAQs - UPS Sizes - 3kVA
Typical questions clients ask before buying a 3kVA UPS (3000VA uninterruptible power supply) to protect their computers, server rooms and IT networks. A 3kVA UPS may also be refered to as a 3kW UPS (3000W) if the UPS is rated at unity power factor.
A 3kVA rack mount UPS is designed for installation inside a server cabinet. A Tower unit is a free standing unit that normally sits on the floor. A combination Rack/Tower or Tower/Rack 3kVA UPS is dual form factor UPS designed to be installed as a 19inch rack mount UPS or a floor standing tower.
Online UPS provide a superior output than line interactive and have an automatic bypass. Online 3kVA UPS provide a break free supply whether running on mains power or inverter power. The transfer is seamless and the load sees a continuous sinewave output. With a line interactive 3kVA UPS, the main power is conditioned by a built-in automatic voltage stabiliser. When the mains power fails or fluctuates, the inverter section provides power to the critical load from the battery supply. The transfer from and to inverter and battery power can see a small disruption in the output waveform which is covered by the capacitance inherent within a critical load’s switch mode power supply.
The recharge time for a 3kVA UPS lead acid battery set should be up to 6hours but will be dependent upon the size of the battery (measured in Ah) and the size of the charger (measured in Amps). The longer the runtime, the larger the battery set installed and potentially the longer the recharge time. A rule of thumb is to achieve 80% within 24hours (formula Ah/A=recharge time). Charging in non-linear and so the last 20% can take several hours longer. For extended runtime packs connected to the UPS, the charging capacity can be increased to reduce the recharge time by using a larger charger. This may be installed inside the UPS itself or in the battery extension pack. Note that each externally battery charger will require its own AC power source. Lithium-ion batteries can recharge far quicker and reach 80-100% capacity within 2hours.
A 3kVA uninterruptible power supply will have a built-in battery pack and the amount of runtime the UPS can provide when there is a mains power outage is dependent on the load connected. At 80% load a typical 3kVA/3kW UPS can provide 5-10 minutes of battery runtime. This can be extended by adding plug-in battery packs if the UPS has this facility or oversizing the uninterruptible power supply. For long runtimes, in excess of 7hours, standby power generators can be more cost-effective than a large battery set.
Online 3kVA UPS are also referred to as double-conversion or even triple-conversion UPS systems. This refers to the AC-DC-AC or AC-DC-DC-AC operation of the UPS as it converts the mains AC (alternating current) into DC direct current via the rectifier charger assembly and then converts the DC back to AC via the online inverter. The inverter generates a digital sinewave without a break in supply whether powered from the mains power supply or battery set. In a line interactive UPS an automatic voltage regulator (AVR) powers the load when mains power is present and an inverter ‘cuts-in’ during a power outage. The break in supply is minimal (2-4milliseconds) and most modern switch mode power supplies (SMPS) – used to power electronics, computers, servers and network devices – can work with a line interactive UPS. The principle benefit of an on-line UPS, aside from its superior waveform and no-break supply, is a built-in automatic bypass. If the UPS has an internal fault or is overloaded the connected load is automatically transferred to the mains power supply without a break in supply.
Most 3kVA/1kW UPS use a valve regulated lead acid (VRLA) maintenance free battery with a 5year design life. Some 3kVA UPS are available with lithium-ion batteries with a 10year design life. Lead acid batteries are the most commonly used as a lead acid battery is the most suitable for standby operation, as required by uninterruptible power supplies. Lithium-ion batteries provide greater energy storage density, faster cycling and are less susceptible to heat and can therefore be used in warmer operating environments. For some server rooms and data centres, the use of lithium-ion UPS batteries allows savings to be made in air conditioning and cooling systems.
How long UPS batteries will last is dependent upon several factors including their design life, type, the number of charge/discharge cycles they are put through and the ambient temperature of the room they are working within.
Lead acid VRLA UPS batteries can be of the 5year or 10year design life type. These will require replacement within 3-4 or 7-8 years respectively. In terms of room ambient, the recommendation for lead acid UPS batteries is 20-25°C. For each 1degree rise above 30°C the design life halves. Lithium-ion UPS batteries have a longer design life from 10years or longer but have a higher cost than lead acid types.
When you purchase a 3kVA UPS, the product warranty will generally include the batteries for the warranty period. Some UPS manufacturers limit the warranty to that provided by their battery supplier, and this may be on a pro-rata basis i.e. 100% warranty cover in year 1, 80% in year so and so on. Some UPS companies will offer extended battery warranties and battery cover including testing and replacement as part of their UPS maintenance contracts.
A single phase 3kVA or 3kW UPS designed to connect to a single-phase electrical supply. It is sometimes called a single-phase UPS for a 1/1 (single phase in and single phase out) installation. The UK electrical supply voltage is 230Vac 50Hz and a 3000VA UPS will be supplied with a power cord with a BS1363 3-square pin plug to plug into a wall socket. Power from the UPS is provided typically by IEC320 C13 outlet sockets on the rear of the UPS or via a UPS maintenance bypass or a a power distribution unit (PDU) if either of these are also installed.