UPS Systems buying guide

What’s the definition of UPS?
An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery runtime of most uninterruptible power sources is relatively short (only a few minutes) but sufficient to start a standby power source or properly shut down the protected equipment.
A UPS is typically used to protect hardware such as computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 volt-ampere rating) to large units powering entire data centers or buildings.

Why we should need UPS?
1. ups will supply power to the load when the utility is in failure (power cut or abnormal).
2.ups will supply stable and high quality power to the load, it improve the work efficiency also prolong the service life of the equipment.
A UPS contains a battery that "kicks in" when the device senses a loss of power from the primary source. If you are using the computer when the UPS notifies you of the power loss, you have time to save any data you are working on and exit gracefully before the secondary power source (the battery) runs out. When all power runs out, any data in your computer's random access memory (RAM) is erased. When power surges occur, a UPS intercepts the surge so that it doesn't damage the computer.

What are the different types of UPSs and how do they differ?
The three general categories of modern ups systems are on-line, line-interactive or standby.
Offline/Standby
Offline/Standby UPS. Typical protection time: 0–20 minutes. Capacity expansion: Usually not available
The offline/standby UPS (SPS) offers only the most basic features, providing surge protection and battery backup. The protected equipment is normally connected directly to incoming utility power. When the incoming voltage falls below or rises above a predetermined level the SPS turns on its internal DC-AC inverter circuitry, which is powered from an internal storage battery. The UPS then mechanically switches the connected equipment on to its DC-AC inverter output. The switchover time can be as long as 25 milliseconds depending on the amount of time it takes the standby UPS to detect the lost utility voltage. The UPS will be designed to power certain equipment, such as a personal computer, without any objectionable dip or brownout to that device.
Line-interactive: 
Just like the standby units, line-interactive upss provide protection from spikes and surges, as well as supplying auxiliary power if a voltage sag or a blackout occurs. Unlike the standby units, line-interactive upss provide automatic voltage boost when the power dips, without accessing the batteries. This feature provides continuous lined conditioning, promotes longer battery life, and eliminates electronic "noise" that can cause minor application errors and loss of data.
Online/double-conversion
The basic technology of the online UPS is the same as in a standby or line-interactive UPS. However it typically costs much more, due to it having a much greater current AC-to-DC battery-charger/rectifier, and with the rectifier and inverter designed to run continuously with improved cooling systems. It is called a double-conversion UPS due to the rectifier directly driving the inverter, even when powered from normal AC current.
In an online UPS, the batteries are always connected to the inverter, so that no power transfer switches are necessary. When power loss occurs, the rectifier simply drops out of the circuit and the batteries keep the power steady and unchanged. When power is restored, the rectifier resumes carrying most of the load and begins charging the batteries, though the charging current may be limited to prevent the high-power rectifier from overheating the batteries and boiling off the electrolyte. The main advantage of an on-line UPS is its ability to provide an "electrical firewall" between the incoming utility power and sensitive electronic equipment.


How long can equipment keep running on a UPS?
There is no standard answer. There are ups solutions available to support almost any application anywhere from five minutes to two days, the solution just depends on your application. Typically, you should plan on enough run time to allow you to save any open files and safely shutdown the system.

How to calculate the capacity of a UPS?
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 (of) between 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.


What are the precautions for using UPS?
1.The use of ups requires a clean environment with good ventilation.
2.The output socket of the ups should be clearly marked. Do no apply unrelated loads or cause short circuit.
3.Do not use inductive load, such as money-counting machine, daylight lamp and air conditioner to avoid damage.
4.Make sure the generator's output power is two times more than the ups rated power, if the user uses the generator during the power fail. ups must be connected after the generator is operating stably.
5.When turning on the ups loads, start from the heaviest in duty, and then the ones in the order of duty.
6.The ups output load should be controlled at about 60%, where the reliability will be the best.


What kinds of equipment should I use with the UPS? Is there any limit for it?
Normally, the ups is used for PC, high technical equipment & medical appliances. Most ups are designed for PC, so not all the equipment could be connected with it, especially, conducting loads just like cooling fans, refrigerators that have the motors. These kinds of equipment will damage the ups. Moreover, copy machine and laser printers that have huge starting current also could not be used with ups. The huge starting current will impact the capacity of ups.

what factors should be consider when we buy the UPS?
In general, users should consider three factors: the technical performance, service assurance and product price.
Step 1: make sure your needed type of UPS
Step2: make sure your needed power (VA) value of UPS
Step 3: determine the required standby time of load
step 4: choose a good brand of UPS is very important