When I recommend a battery backup for the first time on a site, I generally ask questions about whether or not the lights tend to flicker on the site. Does the power go off often? Do you have to replace light bulbs more often than at other places you are familiar with? These questions give me an idea of the quality of the power at the site. I tell the customer about both, the better online battery backup, as well as, the lesser offline battery backup. If the answers to my earlier questions indicate questionable power, I strongly urge the customer to purchase the better battery backup.
Because the idea of affordable online battery backups for smaller sites is a relatively new one, older sites that I service, were likely not ever told about online battery backups. When problems lead me to suspect power issues, I recommend the purchase of an online battery backup. In every case where an online battery backup has been installed, there have been no power related equipment failures. In most cases, unusual unexplained problems have been eliminated.
Battery backups have to have a rectifier that converts AC power from the wall to DC power to charge the batteries. They have to have an inverter that converts the DC power from the batteries to AC power that the connected equipment can use.
From there, they function in two distinctly different ways:
The offline uninterruptible power supply 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 a predetermined level the uninterruptible power supply turns on its internal DC-AC inverter circuitry, which is powered from an internal storage battery. The uninterruptible power supply 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 uninterruptible power supply to detect the lost utility voltage. The uninterruptible power supply will be designed to power certain equipment, such as a personal computer, without any objectionable dip or brownout to that device.
The online uninterruptible power supply is ideal for environments where electrical isolation is necessary or for equipment that is very sensitive to power fluctuations. The initial cost of the online uninterruptible power supply may be slightly higher, but its total cost of ownership is generally lower due to longer battery life. The online uninterruptible power supply may be necessary when the power environment is "noisy", when utility power sags, outages and other anomalies are frequent, when protection of sensitive IT equipment loads is required, or when operation from an extended-run backup generator is necessary.
The basic technology of the online uninterruptible power supply is the same as in a off line uninterruptible power supply. However it typically costs much more, due to it having a much greater current AC-to-DC battery-charger/rectifier. The rectifier and inverter must be designed to run continuously and requires an improved cooling system.
In an online uninterruptible power supply, 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.
The main advantage to the on-line uninterruptible power supply is its ability to provide an electrical firewall between the incoming utility power and sensitive electronic equipment. While the standby and line-interactive uninterruptible power supply merely filter the input utility power, the double-conversion uninterruptible power supply provides a layer of insulation from power quality problems. It allows control of output voltage and frequency regardless of input voltage and frequency.
Although, in a few cases the strange problems that lead to the suggestion of a higher end battery backup were not solved by the battery backup, the equipment is undoubtedly better protected from power incidents. Being better protected leads to being more reliable and lasting longer.
On one site we service, the online battery backup system sounded an alarm . We were called in to check it out and found that the utility power was running at 137 volts. The UPS was sending a steady 120 volts to the server and network equipment. It took a couple days for the utility company to correct this problem. All the while our system just continued to hum along, completely isolated from this voltage increase.
Please keep in mind that Ontario’s electrical power supply system is aging and being asked to supply more and more power as it gets older. This will lead to our electrical supply being more and more unreliable and erratic. I think, unless major changes happen, in the near future it will be necessary to run all sensitive equipment such as computers with online battery backups.