U.P.S. is NOT a "set it and forget it" device, it requires maintenance periodically!
When the battery light or LED comes on a Uninterruptible Power Supply it means that one or more of the batteries has failed or is failing.
Now you ask: "How does the Uninterruptible Power Supply know this?"
Answer: There is a separate circuit that takes a single battery off line and does a test on the battery, how often and how low it drains the battery will depend on the manufacture and the number of batteries.
The Uninterruptible Power Supply I am most familiar with is the APC family of Uninterruptible
Power Supply. They range from 1000 Watt to over 10,000 Watt. Now you have to consider the wattage to know how long a
Uninterruptible Power Supply can keep a computer or bank of computers running once there is a power failure.
Your computer has a 600 Watt Power Supply, that means the maximum output from the PS is 600 Watts, you also have your monitor plugged in to your
U.P.S. (Uninterruptible Power Supply). Your Uninterruptible Power Supply is a 1000 Watt output so you should be able to
power your computer from 35 to 45 minutes on the
Uninterruptible Power Supply batteries, not advisable but possible. If you have a
Uninterruptible Power Supply and are using the computer when the power fails it is advisable to save your work and power down your computer as soon as possible.
Another factor in this is the type of battery, the best is a sealed Lead Acid battery which is what APC uses the most, although they make a few with the Li-Ion batteries.
When a battery drops below a certain capacity then the Uninterruptible Power
Supply processor turns on the LED to tell you "Hey! Over here! One of the batteries is failing to retain a full charge or doesn't discharge for the specified time at the specified voltage/amperage! Change it out!"
Now how do you know which battery has failed? With out a special tester you don't. For a small to medium APC
U.P.S. you would change all the batteries, any where from three to nine.
Note: If you happen to change a Uninterruptible Power Supply battery or series of batteries please keep in mind these batteries require special handling for disposal, do not under any circumstance throw them in the local trash! (Besides the lead and other metals are of value).
Why is there an urgency in changing the battery, that is why have a circuit that tests then turns on a light when a battery fails?
If your Uninterruptible Power Supply had a bad battery and the power went off where you needed to be able to get to a computer and shut it down gracefully and the
Uninterruptible Power Supply batteries died before you managed to shut the computer down gracefully (i.e.: the start button) then there is a chance that the hard drive controller could have been in a write sequence, that data would be lost, there is a high probability that the drive could become corrupt, thus losing all the data on the drive.
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This would be a disaster for a business if it was a server, especially if it was a mission critical server.
Some larger Uninterruptible Power Supplies have a maintenance schedule where you change out a bank of batteries periodically, six months to a year.
Now you know why the Uninterruptible Power Supply will turn on the LED and beep every so often, change the batteries!
A U.P.S. makes an excellent surge suppressor and will make up the difference in voltage during a "brown out".
04/24/2013 - Come on people!
A Uninterruptible Power Supply is an expensive device, read the
documentation that comes with it! If you can't find the documentation then go to
the manufactures web site and download it. If you don't take care of your device
it surly will not take care of your computers and peripherals that are connected
to it. A dead Uninterruptible Power Supply is a poor insurance policy for sure!