As a leading UK supplier of UPS Systems we offer a number of different types of UPS, manufacturers and their associated options and peripherals. Sometimes it can be quite daunting when first faced with the prospect of choosing the right UPS and level of power protection for your application. We have therefore put together this brief guide on how to choose a small UPS system and by this we mean a single phase UPS with output sockets.
UPS Loads and Connections
The first thing to identify is all the loads to be protected. Ideally you should only UPS protect the critical power loads. These are those mission critical (to the organization or yourself) IT components, systems and peripherals that must be kept powered when the mains fails or fluctuates.
You may also identify essential loads. These are loads that require power protection but normally only when the mains is present. Surge and spike protection can be ideal for these. To protect essential loads you may decide to add them to the critical power loads or protect them separately.
You may also identify non-essential loads, systems and peripherals that do not need to be UPS protected such as lighting and alarm/security systems. The latter may well already have their own built-in battery backup.
When listing the loads you may be able to identify the Watts or Amperage (Amps) drawn. You should also know the mains voltage and phases in the supply. Typically in the UK a single phase supply is 230Vac 50Hz and a three phase supply 400Vac 50Hz. If in doubt, contact the Eco Power Projects Team who can guide you through how to make the final calculations to arrive at a total load size and build in an expansion factor for the future.
Finally when listing the loads, remember to record the socket type required. Different loads can have different plug types be these UK square pin (with or without a built-in transformer) or IEC-IEC lead connected. With this you can select a single phase UPS system with the right number of sockets or a combination of an uninterruptible power supply with an appropriate power distribution unit (PDU).
Once you have a UPS size in mind it is important to decide on the backup power time you want the uninterruptible power supply to run for when the mains power supply fails. This may be a short time, just long enough to ride through short power breaks and activate connected any connected shutdown software or longer up to several hours. Choosing the right runtime is important not just to cover power breaks but also when selecting the UPS format as the longer the backup time the larger the overall size and weight of the UPS will be.
There are several formats available including desktop, tower and rackmount. Desktop a small systems designed to sit beside the protected equipment. Tower systems tend to be tall and narrow in design to side beside a file server. Rackmount systems are designed for installation inside a server cabinet (19inch) and may be up to 500mm or 800mm or even 10000mm deep. The larger the UPS system, the greater the weight to be supported by any rails. If additional battery extension packs are installed, these will add to the overall physical size, weight and potentially input supplies. Most battery extension packs simply connect to the UPS and draw a charging current from it. Others may have their own built-in charger and need a separate mains connection point.
There are three types of UPS design available: standby, line interactive and on-line. Each provides a varying degree of protection. Standby UPS are the cheapest and provide low-grade power protection. This is basically some spike and filter suppression when the mains is present and possibly some correction of mains surges, brownouts and sags. The inverter is normally off and there is a break in output supply (approximately 4mS) when the inverter/battery section activates. Modern PC and server power supplies can copy with this length of break and though the output wave form from the inverter is not a perfect sinewave (more like a square-wave) it is still suitable.
Line interactive provide medium-grade power protection. The inverter may still be considered off-line but is generally energized and ready for action so the switch on time may be shorter (2-4mS). The inverter will generally provide a sinewave output and when mains power is present an automatic voltage stabilizer (AVS) provides a fairly stable source of power free from brownouts, sags and surges with additional EMI filtering for spikes and electrical noise.
On-line UPS provide premium-grade power protection. The inverter is always connected to the load and powered, providing a digitally generated sinewave output. The output supply is not only ‘clean’ but also stable and tightly regulated in terms of voltage and frequency. The additional benefits of an online UPS are that the inverter is generally rated for continuous running for long periods so adding additional battery extension packs up to 7hours or more is not normally an issue. The on-line UPS design also incorporates an automatic bypass to protect the load if the UPS has a fault condition or is overloaded.
External UPS Bypass and Service
It may be necessary to server or swap-out your UPS during its working life. Adding an external maintenance bypass allows this without disruption to the connected load.
UPS Shutdown Software and Communications
Most UPS today have a USB port and some an additional RS232 port. These are used to communicate with the UPS manufacturers UPS monitoring and control software. The UPS may also have a card slot into which an SNMP adapter may be installed to give the UPS an IP-address for communication over Ethernet networks. In more industrial environments it may be important to have volt-free signal contacts or MOD-BUS communications for building management system (BMS) reporting. Not all UPS can provide these additional communication modes.
This is a simply guide to single phase UPS protection and if you have more questions or would like a section added please let the Eco Power Projects team know.