I am often asked by ProAV installers why they should use a UPS and which type to use.
In many cases, there is the misconception that UPS systems are to provide enough backup power to let you finish your telepresence meeting or to let you finish watching your Netflix movie when there is a power cut. In fact, the primary functions of a UPS are to protect the equipment connected to it from brown outs and black outs, provide enough time for the equipment to shut down safely without data loss, or to give enough time for a back-up generator to start up.
The protection of AV systems in particular, is very important, as brown outs can cause serious damage to sensitive AV equipment.
Types of UPS Systems
There are two basic types of UPS system, line interactive and online-double conversion. There are also offline systems, but these are technically not UPS’s, as ‘UPS’ is an acronym for ‘Uninterruptible Power Supply’ and a power cut with an offline system will cause an interruption.
Below is a brief explanation of the differences.
Standby/Offline battery Back-up
Picture 1:Offline battery Back-up
The offline ‘UPS’ is simply a battery providing limited back up power, which sometimes includes power conditioning for brown outs. The cheapest standby/offline units will only turn on the batteries when the primary power source fails. Some more expensive units may also offer some surge protection. An offline ‘UPS’ can take up to 45 milliseconds to switch over to battery power. This delay can cause damage to sensitive AV equipment.
Line Interactive UPS
Picture 2: Line Interactive UPS
The line interactive UPS does filter out some peaks in power, but is not fully regulating the output current. Fluctuations in the output current are still passed through. These units will offer a quicker response time (up to 10 milliseconds) and have some basic automatic voltage regulation (AVR) and surge suppression. Lower-priced units will put out a simulated or modified sine wave and higher-priced units will produce a pure sine wave. Sometimes, these higher end units will revert to battery backup in a brown-out situation (to boost the voltage) and in an over-voltage situation (to lower or “buck” the voltage).
Since the line interactive UPS still has a delay of several milliseconds before the batteries kick in after a power cut, there is still a risk of causing damage to AV equipment.
Further, and probably most relevant to the ProAV industry, the Line interactive UPS has only limited ability to filter out fluctuations from the input AC-power. These small fluctuations can be amplified in AV installs (by amplifiers for instance) and manifest themselves as ‘noise’ or ‘snow’ on screens, or as humming noises from speakers. A line interactive UPS for AV, although commonly used, is not advisable.
Picture 3: Online UPS
The highest level of UPS protection is online. Online units take the incoming current (AC), rectify it to the battery voltage of the UPS (DC), filter it, invert it and convert it to the appropriate output voltage for the unit (AC). Consequently, the output voltage is always perfectly steady and the sine wave is always pure. None of the small fluctuations are passed by an online UPS. Only clean power out!
Additionally, there is no delay from power cut to battery power, since current flows across the batteries at all times. Further benefit to this comes in the form of battery life expectancy. Since the batteries are constantly ‘online’, typical lifespan of these batteries is improved by a year or two over other types of UPS.