Battery back up 550 not providing backup!

[Anonymous user]

My apc battery back up has been sitting under my office desk for a year or so now, but over the last week or so we had problems with the electric (RCD kept tripping), while I would have expected the computer to stay on for a while, it turned off straight away on all occasions.

The RCD is sorted now, but I want to figure out why it isn't doing what it is supposed to do, what is the most likely cause(s)?

Also I have looked on YouTube etc and see the examples do not have the Master enable button which I have, I can also see no mention of it in the online manual, help!!

[Anonymous user · Accepted solution]

Please post the exact model number of your unit, and the serial number as well.

There are a couple of generally relevant possibilities:

1. Check the obvious thing first: is the load connected to the correct set of outlets on the UPS? Some models have outlets that are not battery-backed.

2. The UPS itself is faulty or it has a bad battery.

3. Your computer's power supply is incompatible with the UPS's output waveform. The lower cost Back-UPS models (and a few Smart-UPS units as well, such as the SC420/620) output a "modified sine wave" when their inverter is powering the load from the internal battery.

Some computer power supplies (usually labeled as having Active Power Factor Correction) will shut down if the characteristics of the incoming power waveform change, as they would when the UPS goes over to battery

There are only two ways to fix this problem, if it is indeed the problem you are having. Either replace the computer's power supply with another, or get a UPS with a true sine wave output. (APC's Smart UPS 750, 1000, 1500 and larger models all have true sine wave output inverters.)

To test the UPS, safely power down and disconnect the equipment it is currently protecting. Plug it into a few lamps (incandescent bulbs would be best, to ensure enough load for a meaningful test), turn it on and remove the plug from the wall outlet. If the UPS shuts down suddenly, this would indicate a worn out battery or an internal fault.