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Warning - compatibility issues possible
on 11 May 2012
This UPS is a high quality product, but there is a high chance that your computer's power supply unit (PSU) may have a compatibility issue.
That's the problem I had when I received the unit yesterday. The computer ran for a while with a load of abut 135W shown on the UPS's LCD, which is well under the 540W rating of the UPS. All looked good for a while and then the computer stopped responding. That is not normal for my machine and it happened a number of times when powered by the UPS. It was fine with a direct connection to the mains.
After doing some research on Google, I found that this is a well known issue. Google "APC application notes" and read "Proper UPS selection for servers with active PFC power supplies", which is note number 147. That note has useful details that should be read before buying this unit.
It is now normal for PSU's to be of a type called active PFC and these may not work properly with a UPS that does not deliver a sine wave output. Note that the same issue applies to any UPS that delivers a stepped sine wave output; it is not specific to APC units.
After some further research, I found that some active PFC PSUs work up to a certain load with this type of UPS (the numbers were in the range of 250 to 300W). My computer had a solid state main drive and three large hard drives for storage and backups. I tried removing these drives to reduce the load on the PSU, which let the computer run without crashing.
I am getting nearly an hour run time on battery and the unit is quiet in use.
It's not easy to be sure if your computer will work with this type of UPS.
If you want to avoid issues then you need one of the more expensive units with a pure sine wave output. Three stars awarded, because the product is good, but the description should point out the compatibility risk.