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    Specifications to Consider for Selecting UPS Systems

    An uninterrupted power system or UPS provides battery backup and protects your equipment during power outages. In order to buy the best UPS system for your needs, it is important to check specific ratings to make sure the system works for you. Some of the important output ratings you should consider are explained below.

    Power Factor – This measures the maximum load the UPS can tolerate. A perfect power factor of 1 means that all of the power is being used by the UPS system without any wastage. In practice however, most devices don’t have a perfect power factor, and some of the power is wasted. For example, a UPS may be rated at 10,000 VA for 30 minutes; this means that the UPS should take loads up to 10,000 VA and continue to run for 30 full minutes. However, if the power factor for the same UPS is given as 0.6, then the UPS can only take 0.6 x 10,000 VA or 6000 VA at specified runtime. It is typical to have a power factor of 0.6 – 0.8 for most UPS systems.

    Crest Factor – complex devices such as computers often require a peak current that is higher than simpler devices such as lightbulbs. A UPS device must be able to provide this peak current demanded by your devices. The crest factor measures the ratio of the peak current to the average current. A crest factor of 1.414 means that the waveform is perfectly sinusoidal and a “good” waveform. A low crest factor signifies that the UPS is unable to produce the peak current demanded by your devices, and this will cause your device to malfunction. You should first check your devices to see if they exhibit a crest factor greater than 1.4. If they do, then your UPS must be capable of matching their needs. A low crest factor signifies that the UPS is unable to produce the peak current demanded by your devices. If the crest factor supplied by the UPS is not the correct load, it may cause the output voltage waveform of the UPS to be distorted and may cause malfunction of your connected equipment.

    Total Harmonic Distortion – This measures any distortion in the smooth sinusoidal waveforms of an electric device. When a waveform is distorted, it means that the current not only includes the normal 60Hz frequencies, but also other distorted frequencies that can cause excessive heating and damage your devices. This can cause a distortion in the current waveform labelled THDi (where ‘i’ stands for current) or in the voltage waveform (where ‘v’ stands for voltage). Most UPS devices will include a filter to reduce the THDi and THDv. The lower the rating, the lesser is the distortion in the current. Therefore, while selecting your UPS device, a lower THDi and THDv rating will ensure your devices are better protected.

    Transfer Time – The definition of transfer time, sometimes also called switchover time, says it is the amount of time a UPS will take to switch from utility to battery supply during a mains failure, or from battery to mains when normal power is restored. What this means is that when the main power supply fails, the UPS will need to switch to a battery mode to provide sufficient power and ensure smooth running of the attached equipment. The transfer time duration differs, depending upon the UPS system attached. It should, however, always be shorter than your equipment’s hold up time. Hold up time is the amount of time your equipment is able to maintain consistent output voltage during a mains power shortage.

    Backup Time (UPS Runtime) – That depends on what you intend to backup with your UPS. Runtime refers to the amount of time a UPS will be able to power its attached equipment in the event of a power disruption. The more equipment you have plugged in to your UPS, the less runtime you will have, so it’s important to make sure your UPS is only providing backup power to your most critical equipment.

    Advanced Battery Management – Maximizes battery performance, life, and reliability through intelligent, precision charging. A three-stage charging technique that automatically tests battery health. Provides advance notification when preventive maintenance is needed, allowing ample time to hot-swap batteries without ever having to shut down connected equipment significantly extending the life of your UPS's battery (and, quite possibly, your contract).

    Overload Capacity – Overloads are temporary requests from users that exceed absorption in continuous operation. They are caused by current peaks which may occur when one or more appliances are switched on. If the overload exceeds the admissible limits, the UPS guarantees the energy supply via the automatic bypass line. In the event of an “online” UPS, the transfer is affected without any break in power (transfer time = 0 ms). The by-pass is a safety device with protection and its own auxiliary power supply and therefore it supplies the load with its own circuit that is independent from the rest of the UPS.

    Voltage Regulation – Line-interactive UPS systems use automatic voltage regulation (AVR) to correct abnormal voltages without switching to battery. (Regulating voltage by switching to battery drains your backup power and can cause batteries to wear out prematurely.) The UPS detects when voltage crosses a preset low or high threshold value and uses transformers to boost or lower the voltage by a set amount to return it to the acceptable range. Online UPS systems use a more precise method of voltage regulation: they continuously convert incoming AC power to DC power and then convert the DC power to ideal AC output power. This continuous double-conversion operation isolates connected equipment from problems on the AC line, including blackouts, brownouts, over voltages, surges, line noise, harmonic distortion, electrical impulses and frequency variations.

    When calculating the voltage regulation, it is “the ratio of UPS output voltage drops from no load to the full load”. The formula for voltage regulation is: (Vnl – Vfl) / Vnl * 100% Here Vnl is the no load voltage and Vfl is the full load voltage.

    ECO Mode Operation – Advanced online network/server UPS systems may support economy mode operation to save energy and reduce operating costs. While input power quality is good, the UPS operates with maximum efficiency. If input power quality worsens, the UPS uses double conversion to provide maximum protection. Online UPS systems operating in economy mode can increase efficiency by as much 10% compared to traditional on-line UPS systems.

    Emergency Power Off – Network/server UPS systems typically include provisions for connecting to your facility’s Emergency Power Off (EPO) circuit. During an emergency, activating the EPO switch will immediately de-energize all the equipment connected to the EPO circuit.

    Efficiency – The ratio of output to input power. Generally measured at full-load and nominal line conditions. If the power efficiency of a device is 90 percent, you get back 90 watts for every 100 you put in, and the rest is mainly dissipated as heat from the filtration process.

    Maintenance Bypass – An external wiring path to which the load can be transferred to upgrade or perform service on the UPS without powering down the load.

    Parallel Operation – The ability of UPSs to be connected so the current from corresponding outputs can be combined into a single load.

    Redundancy – The ability to connect units in parallel so if one fails the other(s) will provide continual power to the load. This mode is used in systems when power failure can’t be tolerated.

    About Maruson
    Maruson designs and manufacturers uninterruptible power supply (UPS) systems, power distribution units (PDU), automatic voltage regulators (AVR), energy storage systems (ESS), inverters, and other power management products. Founded in 2003 in California with additional offices and factory worldwide, the company offers decades of problem solving experience to the power management market that help people, businesses, institutions, and agencies protect their critical electronics from power disturbances or to power whole homes, offices, and stores. To learn more, visit www.MarusonUSA.com.

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