UPS stands for Uninterruptible Power System, which is applied to protect your computer or equipment when there is a power failure. Without UPS, for instance, once a blackout happens, your computer data will be lost because of power interruption. While if you installed a UPS, it will take over the city power and supply electricity power to your computer during a blackout.
It is similar to the function of emergency lights, but the technology is more advanced, the transferring is much faster, and the application is more widely.
As mentioned above, we know what it would cost if our computers were shut down immediately once our city power failed suddenly. The data you just keyed in would be lost, or the whole database you are running would be damaged; while in some situations, your hardware might be damaged too. Although hardware can be repaired or repurchased, it is costly! As for those lost data, it could not be even reinstalled; and which might cost more or might be priceless! If it happened in a hospital, can you imagine how bad it would be if a surgery operation was interrupted because of power failure?
Besides the above functions, UPS can also protect your equipment from spike, surge, sag, and noise. Meantime, most of UPS are made with AVR function (Auto Voltage Regulation), which is able to protect your equipment from the voltage vibration of city power.
UPS is required for most equipment which can not be interrupted accidentally when they are in operation, such as computers, medical equipment, fire-fighting equipment, security system, and military equipment, etc. However, some equipment is not suitable for applying a UPS. For those inductive loads, such as motors, air-conditioners, & fans, and those equipments with high start-up current, such as copiers & laser printers, are not good for applying a UPS.
To know how a UPS functions, we have to know three main categories of UPS, which are on-line, off line, line interactive. The following is a brief introduction of the three types of UPS:
1, On-line UPS:
In the early stage, almost UPS are on-line type, which structure is the most reliable. The basic concept is to separate the input and output of UPS, in which no matter if the city power is stable or even during a blackout, the output is always maintained in a stable status, which is transferred from battery energy. The operation of this type of UPS is more like that of water bank. The supply of water is always going on no matter if there is water entering to the water bank. While when it rains, the water bank can save water from the rain. As you can see, the supply of water would be very stable, and the supply can be stopped only when the water gate is closed.
As above, the water gate is similar to the power switch of UPS; and the battery of UPS is similar to the water bank. Whenever you need a stable power, just turn on the power switch. No matter what the quality of city power would be, the quality of output is always good since it is transferred from battery directly, even it is limited if the battery is not charged at the same time. Meantime, the waveform of on-line UPS is always sine wave, the same as that of city power.
2, Off-line UPS:
Basically, the supply of output power is from city power at the normal situation. But, the city power is always detected at real time by the detection circuit. Once a blackout happened, the supply of output power would be transferred immediately from city power to battery, which energy would be applied to produce AC power for the protected equipment?
However, most off-line UPS do not function only for blackouts; when the voltage of city power is not stable, it will be regulated by AVR function; while if the voltage is too low or too high, UPS will also transfer to battery mode. Besides, the UPS can also protect your equipment from spike, surge, sag, and noise of city power.
As mentioned above, there is a transferring between city power and battery power. For the related description, please refer to the point 5. Meantime, the waveform of off-line UPS is much different from on-line one's. Please refer to the point 6 for the details.
3, Line-interactive UPS:
The working axiom of line-interactive UPS is similar to off-line one. The difference is that line-interactive UPS integrates charging circuit and inverter into a two-way transferring circuit. It will detect city power and decide whether it is in a normal range or not. If there is any deviation at input power, the inverter will provide power transferred from battery bank, and then maintains the power output.
On the contrary, when it is in a normal situation of city power, the charging circuit will charge the battery bank in a short time. Meanwhile, sine-wave output is another advantage of line-interactive UPS. This revolutionary UPS technology makes line-interactive UPS can enjoy the benefits of low price, high reliability, and high cost-benefit returns.
As description above, if the applied UPS are off-line or line-interactive type, there is a transferring between city power and battery when the city power voltage is too low or there is a blackout. However, it won't happen in an on-line UPS since battery power will take over the city power once the UPS is turned on.
For regular UPS, the transferring time will be 2-10ms; while a regular computer can stand the power interruption for 16-20ms without any data loss. Therefore, any type of UPS, on-line, line-interactive, or off-line, is suitable for PC use.
Sine wave is the standard waveform of our city power. And, on-line & line-interactive UPS provide the same waveform for output, too. However, for the cost consideration, there is another type of waveform coming out, such as square & step wave. The step wave is better than the square one since it looks more like sine wave. That's why the step wave is also called the modified sine wave.
However, the step or square wave is not proper for some appliances. To explain this, we have to know that there are three categories of loads, resistive load (such as bulb lamps), capacitive load (such as computers), & inductive load (such as fans & motors). For sine wave, it is fine for all types of load. On the other hand, the step or square wave is not good for inductive load because the damage would be deadly serious.
However, it's usually not recommended to apply a UPS for inductive load, even it's sine-wave output, since the starting current would be very large, and which would decrease the life span of those components on board.
In the markets, the capacity is usually rated by VA value, in which the "V" means voltage, and "A" means current; while VA value is the score of "V" by "A". However, the VA value is not a real power rating; in fact, the real power rating is "W" (Wattage), which is usually measured by power meter. Generally, the real power rating, the W value, is always equal to or less than the VA value, which means that there is a power factor (pf) between the the W & VA values, and it is always equal to or less than "1".
In the best condition, the power factor is equal to 1. But, it's not common since the load type also influences it. As for UPS, on-line type is usually over 0.8 and 0.6 - 0.7 for line interactive & off-line UPS.
Generally, the battery type used for small-medium UPS is sealed maintenance free, lead-acid battery. The type of battery can be installed in any direction. As for our model SI-500, the battery is Ni-MH type, which is usually applied for notebook computer use. With such battery, the space used for battery is only half of that of lead-acid type, while the backup time is more than double, and so is the cost.
Battery will be aged as time going by; even it is stored in stock. On the other hand, if the battery is in use with a correct usage, the battery can have even longer life span. According to experience, the regular battery life is 2-3 years. As each battery life cannot be known before it is dead, it would be risky when a blackout happens while the battery energy is not left so much for computer use. Therefore, it would be necessary to replace battery periodically.
Although the applied battery is maintenance-free type, it would be still necessary to have the battery used with a correct usage. The correct usage is that the battery energy should not be used up usually when a blackout happens, and more, always put the battery in charging right after discharging. If you are not going to replace battery periodically, you may make self-test by pushing the test button for the purpose, or by pulling out power cord for simulating a blackout; then you'll find that if the battery energy is left enough for your computer use. Once the left energy is not able to provide the required backup time, the battery has to be replaced.
The backup time is limited to the battery energy; of course, the load you connected also influences it. Generally, the backup time with full load is about 5 minutes. In other words, for a stand-by UPS with capacity around 500VA, the backup time is around 10-20 minutes, according to the battery capacity.
As to extend the backup time, you may apply a larger capacity of UPS, or apply a long backup UPS. The larger UPS is designed for using with more computers, and you can apply it with fewer computers for a longer backup time too. However, to apply a long backup UPS would be more cost efficient. Besides cost consideration, our long backup UPS is also designed with an extra large charger, which is not usually included in a regular UPS, for charging larger external battery. The most advantage is that the backup time is no limit, just can provide backup time as long as your external battery can afford.
To have UPS with more functions, it would be necessary to apply monitoring software. For using with the two different monitoring soft wares, there are two types of interfaces, dry contact & RS-232. With the dry contact one, the software can provide information, such as if city power is normal & if battery is in a low level, on your monitor screen; and functions include auto data saving & auto shut down of your computer.
While the RS-232 one can provide more information. Besides the mentioned above, the information includes input/output voltage, current, frequency, temperature, and loading. The additional functions include auto on/off of your computer with pre-set time, remote control by phone or by LAN, and many more. All the information to be displayed & monitoring functions is based on the software capability.
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