Uninterruptible Power Supplies - Brief Overview
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While we are building more advanced and safer nuclear power plants near the already-existing water- and wind-powered ones, the chance of a total power failure still exists. Plus, the quality of the incoming power can vary.
The fast evolution within the IT&C fields has brought us some quality devices that deliver astonishing performance, but are quite sensitive to the quality of the electricity. These devices also tend to be expensive. If you have a high-end system, you probably want to protect your investment with a UPS, just in case.
The role of a UPS is twofold. First, it will protect you from bad incoming power quality, and second, when blackouts happen, it will give you enough time to save the data on which you're working. That is, if and when the blackout persists, it can deliver the power you need for a limited time, so you won't even observe that something ever went wrong (such as voltage spikes for fractions of seconds and other issues).
You never know when lightning will strike and cause an over-voltage in your electrical circuit. Such a strike can ruin a computer in which you've invested thousands of dollars. Nowadays the more costly PSUs have been "trained" for such situations; however, the same can't be said for the motherboard, HDD, or the CPU.
It is at one of these times that you're most likely to understand the necessity of a UPS and its potential to be a true "life saver." Nevertheless, we all know that smart people learn from the pain of others. Be smart; at first it may seem quite expensive to get a UPS, but quality and security do cost money. If working on the computer is your main source of income, you'll probably observe that your investment will pay for itself in just a few blackouts.
When the voltage drops under a critical level, the PSU will fail to deliver necessary power to the parts inside the system, and even if this is just for a very short period (2-3 ms), the system will stop working in a flash. Restarting the computer and resetting your working environment will drain valuable seconds -- to say nothing of the stress of losing the most recent thing on which you were working or developing.
You've probably seen a UPS at a local company in a server room or workstation backup storage environment, where the entire place was full of wires and electrical device boxes. A UPS is, from an external perspective, a black box that eliminates any chance of failure due to a blip in the power delivered by the power plant.
(An example of a UPS)
However, any PSU can be divided into three main parts: the power supply, the inverter, and the battery. Obviously you cannot store AC in the battery, so before it is used during, for example, a blackout, conversion must happen from DC to AC. The inverter accomplishes this task. When these conversions happen there is a slight amount of power loss, but the overall efficiency of the PSU depends on the quality of the inverter.
The battery is the most important part in term of minutes/hours you have "remaining" when a blackout occurs before you need to shut down the system. A battery that has a large capacity is able to store and supply energy for long periods of time; however, this comes with a higher cost of producing that device. For this reason most of the batteries used in everyday UPSes can hold out for about 10-15 minutes at the given power level (that is expressed in watts).
The batteries used in UPSes are sealed lead acid (SLA) batteries as these offer a reasonable back-up time for their price. If you want longer times, however, something with "wet" lead-acid batteries with ordinary liquid sulfuric acid electrolyte are the solution. Just use them with care; oh, and they do tend to be heavier.
The power supply is responsible for charging the battery whenever it's needed, nothing more and nothing less. Naturally, a little power is again lost when this happens, but nothing is ideal or perfect in this world. Efficiency is all that matters.
With this knowledge, you could create a so-called homemade UPS yourself. Explaining how to do this in detail is way beyond this article's scope and objective. If you're truly interested in this subject, I advise you to read more deeply in the details presented in this article if you ever want to attempt such a task.
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