UPS Overview

UPS's provide AC power when the main source of AC power is removed.
Most can shut down a computer after a certain period after a power failure. Some really small or cheap UPS's don't have this feature, making them virtually useless for computer use. Perhaps useful for powering a VCR or network gear...
Most have some way of monitoring the internal workings of the UPS. The better ones have more monitoring abilities.
Most have some way of putting out an alarm when the main power goes away, or when the battery(s) need replacing.
I learned that UPS's are rated in 'VA', which means Volt * Amps. They are also rated in Watts, which is the only useful measure. Though one would think there is a direct conversion between VA and Watts, it seems each company makes up their own conversion.

The cheapest UPS's make pure square waves, which is simple, but tough on AC loads. The waveform looks like this (where the dotted line is 0 volts):

|-------|       |-------|       |-------|
|       |       |       |       |       |
        |       |       |       |       |       |
        |-------|       |-------|       |-------|

The next improvement is has several names including 'modified sine wave', as it more closely resembles a sine wave, and it looks like this (where the dotted line is 0 volts):

|---|           |---|           |---|
|   |           |   |           |   |
        |   |           |   |       |   |
        |---|           |---|       |---|

The next improvement is sometimes called a "stepped sine wave", or "synthesized sine wave", or "pure sine wave", and depending on the number of steps, can be very very close to a real sine wave. The waveform looks something like this (where the dotted line is 0 volts) (also note this isn't a triangle wave, it just looks similar to one due to my poor ascii-art):

  --        --        --
 -  -      -  -      -  -
      -  -      -  -      -  -
       --        --        --

APC Smart UPS 1000

After having great success with the 3000va version of the APC Smart UPS, I decided to buy two of the 1000va units on ebay. The black one had USB in addition to a db-9 serial port. It also came with a set of batteries that were 1/2 regular size (and 1/2 regular capacity). The white one has the correct batteries, but the serial port didn't work for some reason. Perhaps it had something to do with the two units being shipped in a cardboard box with absolutely no padding of any kind, and a serial cable being plugged into the broken serial port... Not too smart considering the two units weighed over 70lbs, and both units showed visible damage.

A word to the wise, if you buy a UPS on ebay, pick it up locally or make sure it is shipped with proper padding. As for the small batteries, when you picked up the unit, they shifted around. It is always a bad sign when you pick up a substantial piece of electronics and feel something heavy inside shifting around...

I came to a reasonable agreement with the seller, and have ordered (from elsewhere) a dual serial port adapter that plugs into the smart-slot that comes with all APC smart ups's. Hopefully I will be able to communicate with the ups with the adapter.

APC Smart UPS 1500

The APC Smart UPS 1500 comes in several form factors. Mine is like a brick rather than a tower. It has served me well. Today, I replaced the batteries. The batteries attach to the UPS with an Anderson PowerPole connector. This is a really nice connector. I didn't have it pushed down close enough to the battery and it hit a small transformer on the circuit board above the battery. I cleverly tore off 2 pins of the transformer. This made the unit not power up. I opened up one of my APC Smart UPS 1000, and it has a very similar circuit board and transformer. The difference is that the battery and cables is much further from the circuit board. It is likely impossible to mush the circuit board with the 1000 and pretty likely with the 1500. This is a 10 year old design. Hopefully APC has improved it, and made it more difficult to break off parts on the circuit board when changing batteries.

APC Smart UPS 3000 RM3U

As far as I am concerned, APC makes two types of UPS's. The first type is consumer junk. Their Conext brand is an example of this. APC Back-UPS is another example of this (though I haven't tested their newer, USB communication versions). The other type of UPS they make is a serious UPS suitable for office, or other professional use. All of the APC Smart UPS's are serious UPS's. I bought mine on ebay for $62. (The seller couldn't test it because it had a 30a plug. I build an adapter for it.) The batteries worked, which is the major potential expense with buying used UPS's.

The Smart UPS 3000 came with a network card that enabled it to talk to a network. This is very handy if you want to shut down more than one machine when the power fails. If all you have is a serial port, or a USB port, it can only be hooked up to one machine, and tell it to shut down. With a network port, you can tell lots of computers to shut down. The network card is configured via the serial port on the UPS. You can configure the IP address of the card this way. The UPS has a web interface that tells you everything you ever wanted to know about the condition of the ups. Voltages, loads, temperatures, logging info, and the like are easily accessable.

Being used, my UPS didn't come with a serial cable. There are instructions on the internet (not at that explain how to wire your own APS smart-signalling serial cable. About $2 of parts, and some soldering, and mine worked. You can get all the information that the web interface produces through the serial cable. APC provides software to talk to the UPS for Windows as well as Linux.

Belkin F6H375-USB UPS

I bought a few Belkin UPS's because they were cheap. They produce modified sine wave output. What is surprising to me, they provide quite a lot of UPS monitoring information. They provide battery level, load, input and output voltage, input and output frequency, input and output current, battery voltage, temperature, logging, and lots of other stuff. It even works over the network. Really quite impressive. Unfortunately the software support only works with windows-xp or older operating systems. I spent far too long with belkin tech support, but though it has lifetime tech support that does not include drivers. I recommend sticking with APC. Even though their consumer UPS's have a lot less frills, at least they have software that supports their older heardware.

Opti-UPS by ViewSonic

My first UPS was an Opti-UPS, 650E. It is rated at 650VA. It is a line-interactive UPS. I bought in in 1999. I think it cost $300. UPS's were more expensive in the past, and it is a line-interactive UPS which is more complex than cheap UPS's.

It produces a 'sine-step' output (see UPS Overview). It has since needed a new battery, but it keeps on working. Opti-UPS keeps on suppling software for newer OS's. Very boring, which is a big plus in a UPS.

The software can shut down a computer, and shows internal temperature, load, and input and output voltage and frequency. It is a crude way to measure the power consumption of a computer.


I bought two Pulsar Desktop 220 UPS. I think MGE is a French company, and is not affiliated with the MGE that currently makes computer power supplies. They use Ni-Cad batteries and a high frequency inverter, making them very small. They work ok, except the batteries wore out on one, and as far as I can tell, are impossible to replace.


I bought two used 1000VA line-interactive UPS's. They claim to be sine-synthesizing, which means there are many steps and the output approaches a sine wave. The communication software I found never worked well with the UPS's. One has failed, due to reasons I cannot determine. They use 4 relatively small 12v gel-cells (48v is pretty standard in larger UPSs).


I bought a 900VA UPS (really 500W which is pretty small for 900VA) from Conext. Conext is the less expensive brand name for APC, which is a very well regarded UPS company. Although I bought in around Nov-20-2004, it was made around Mar-2001. (UPS's are typically shipped with the battery disconnected, and the user connects the battery). It seemed fine. Then the power failed. There was a really horrible noise coming from my computer room. I unplugged everything in the room. I removed all the UPS's from the room, one at a time. It turned out the source of the noise was the Conext UPS. No doubt it was a low battery alarm or something. There was nothing I could to silence the UPS. I suppose I could have removed the battery, but instead I moved the UPS to the garage. It would be nice if there was some way to turn off the alarm. Perhaps the inability to turn off the alarm is related to the complete failure of the UPS. It seemed dead. Nothing I could do would make it power up. I called the support line, and got a very smart tech right away. He had me reset it, to no avail. I mentioned the software was old and didn't support Windows XP. Their web site said to use the default Windows UPS software. The tech explained how to use the APC Power Chute Business software with the UPS. He agreed to cross ship me a replacement UPS as mine was less than two months old. He speculated that the UPS failed because the battery was old. It would be nice if it simply notified the user that the battery was old, instead of turning off completely, but I suppose it would get the users attention...

Raiongroup Max Life Battery SPS AG12120T2

Around Jan 2014, I bought 2 12v 12ah batteries for my APC Smart UPS 1000. I bought them on ebay from seller 'raiongroup'. After all 'Max Life' sounds good. The batteries had a one year warranty, though if you were to buy them today, they have no warranty. Rule 1: Do not buy batteries without a warranty. Rule 2: If you are paranoid, save a screen shot because the current warranty may not be the same as the warranty when you purchased it. The batteries are not a well known brand. Rune 3: Do not buy no-name batteries. The only good thing I did was buy them with an American Express card which gives an extra year warranty on electronic purchases. Unfortunately for me, the batteries failed after 19 months. Batteries for UPSs typically last 3 to 5 years depending on how they are used, ambient temperature and other stuff. 19 months in mild conditions means the batteries are not 'Max Life' but rather 'Crap Life'. See rule 1 , 2 and 3. I replaced them with Powersonic, which only cost about 6% more and they have a 1 year warranty, which is pretty much standard for UPS batteries.

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