Sine Wave and Square Wave Uninterruptable Power Supply (UPS)
Last time when I wrote about UPS, I left out one of the more technical but important aspect of UPS equipment. I guess I should fill in the blanks here in case some of you find it confusing why some UPS are significantly more expensive than the others even though the supposed functionalities are about the same. There is such a big difference in price because there are 2 classes of UPS and they are built with completely different technologies.
Some Background on AC Electricity
The power we get from the power outlet is called AC (alternating current). They are provided by the local electricity company. As we already know, the electricity coming from the power outlet can be problematic at times hence the need of surge protector and UPS. The electricity we get from the wall outlet is in a waveform called sine wave.
In case you wonder what the 50Hz and 60Hz rating on the power outlet means, that describe the sine wave frequency of the current available in your country.
Sine wave is a characteristics of AC power that many electronic equipment are built to depend on. Electricity flowing into these devices are best to be in sine wave. One of these devices is the transformer in your computer. These transformers change the AC power into DC power to support a computer. Higher end transformers needed to power computers with high-end processors and graphic cards must be supported by AC in sine wave.
Power From Battery Are Not In Sine Wave
The battery used in all UPS can only provide direct output of electricity. That means it is a constant flow of electricity in a straight line. This is fine if the battery is hook up to equipment expecting DC (direct current). But this does not work at all if we are talking about powering equipment that are supposedly to be powered by AC.
Solution to this problem leads to two distinct types of UPS.
Square Wave UPS
The cheapest way to emulate AC sine wave from a battery is to produce a square wave of same frequency. Very simple circuitry will do the job. As long as the equipment does not need true sine wave AC power, square wave will do the job. It is a quick and dirty solution.
UPS built to provide square wave output from the backup battery are cheaper because of this simpler design and hardware cost.
The problem is that sensitive electronic equipment overtime will be damaged by the square wave electricity even if they can function under the square wave current. It is like feeding your car with diesel but that your car engine is not built for that.
Long term damage includes shortened life span of your computer equipment.
Sine Wave UPS
The more expensive way to build UPS is that they can reverse the DC power into true AC first. Then feeding the AC to the equipment connected to the UPS. This way, the sensitive equipment would not be impacted at all due to the change in power source. In fact, the artificially generated AC power by a good UPS has cleaner sine wave AC for sensitive electronic equipment which can potentially prolong the life of the equipment themselves.
Since there is not much breakthrough in technologies related to AC power generation for many years, the components necessary for AC generation from DC power is still very costly. As a result, sine wave UPS are more expensive.
Backup power supply UPS are likely square wave. Online power supply are likely sine wave. To find out for sure, you can check the specification of the UPS to make sure. It becomes important if you are protecting high-end computer equipment.
As of 2013, most mid to low range computers do not require the high-end UPS as backup power. As long as a decent transformer is used within your computer, they can likely take the impact of square wave power during the occasional power outage. Those equipment depending on a small DC adaptor are also pretty safe with basic UPS.
I know computers with i7 (and higher end models) using the latest power hungry graphic cards do not function properly with square wave UPS. If you have these high-end computers, it is best you shop for a matching high-end UPS.
Put it nicely, these computers are "high-maintenance".