I have a UPS with 600VA.

When I connect it to my small laptop and a monitor, the total wattage amounting to 40W approximately (to the higher side), the ups on backup runs for 40-50 minutes.

**But when I connect my PC instead of laptop but with the same monitor, it runs on AC perfectly but when the power goes off, the UPS makes overload sound and turns off in 2-5 seconds. **

Also, when connected to the PC, the UPS doesn’t cold start. It starts only when plug is connected to power.

The PC is not a powerful one.


  1. Motherboard: DH61HO
  2. Processor: i3 2120
  3. Graphics card: GT710 without fan
  4. 2 Rams DDR3 1333 (4gb and 2gb)
  5. 120gb ssd
  6. 1TB HDD 2.5 inch which i took from external hdd
  7. 450W SMPS
  8. Four 80inch fans.

The UPS is not used much on backup but it is 4 years old.

Is this problem because of faulty battery or some internals of the UPS? Or is it due to my PC’s SMPS being faulty?

The UPS was working fine for the PC for 3 years and I suspended using it for 1 year. Then I resumed using it and after 1 year of use and added a GT710 and 3 extra fans. Then this problem started shortly after fans added.

I am really thankful for the time you took to read this. Any ideas will be appreciated with thanks.

  • Any modern laptop will run for 40-50 minutes or more on its own internal battery, so quite likely what you're seeing is how long the UPS' battery will last while powering the monitor. It's possible that the battery needs replacement. Some UPS brands/models allow you to connect them to the PC with e.g. a USB cable and use the supplied software to monitor battery condition. In any case, it shouldn't be too difficult to find and install a replacement battery. Jul 6 at 15:29
  • @Steve Rindsberg The laptop was charging when I tested. I calculated using the output watt of 12.5 watts. If I replace the UPS battery and then if its problem with board, then the total price would cost a new ups price. So I have to be sure.
    – Robert
    Jul 6 at 17:47
  • Will your laptop run w/o its battery? If so, try running it that way from the UPS. Jul 7 at 14:15

It sounds like you might have an issue with power factor correction and be right on the edge of what the UPS can handle - or the 600VA rating of the UPS is "optimistic" or both. The reality is your setup is "on the edge".

600VA is not the same as 600 watts. They would be the same in a DC circuit, but a VA is less then a Watt - how much less depends - but it could be as low as 350 watts. Indeed, a power factor of 0.7 is not uncommon which means that a 450 watt power supply is more then a 600VA UPS may be designed to handle.

That said, although you have a 450 watt PSU, I would think that the actual draw of the power supply should be a lot lower in that system - certainly your component current draw don't add up to anything close to 450 watts. This likely implies a cheap UPS that is failing.

  • Thank you for the detailed answer. So, is it UPS failing or the battery failing? Actual power consumption would be around 200 watts.
    – Robert
    Jul 6 at 17:41
  • What do you think if APC UPS?
    – Robert
    Jul 6 at 17:47
  • @robert APC is just branding. Some are good ups's some junk. The 600va will be junk. If you have a BX600L-LM it has a pathetic watt ranking of 300 watts and that will be your problem. These UPS's may be ok for switches/routers/small wiring closets but not much else.
    – davidgo
    Jul 6 at 19:41
  • Now back to the question. This UPS was fine for 3 years. I suspended using it for 1 year and again started using it. If the UPS is fully charged for 12 plus hours, it will last about 10 seconds for the PC backup. For the laptop, which is about 25 watts to 40 watts, it will last 40-50 minutes. Is it failing UPS circuit or just the battery needs replacement?
    – Robert
    Jul 7 at 2:04
  • @robert not sure. My guess would be the battery.
    – davidgo
    Jul 7 at 2:25

There's no way a 600va UPS is going to power 90% of desktops.

You need to have 1000va or 1500va to even have a chance of it working.

  • I am no expert but 600VA means 300 watts approx. The actual draw is far less; maybe 200 watts on the higher side.
    – Robert
    Jul 6 at 17:39
  • @Robert 300 watts is wishful thinking. They limit it to less than that so it has a decent run time.
    – cybernard
    Jul 6 at 19:28
  • acybernard, Any evidence for this ? Im HIGHLY skeptical. The relationship between va and watts has to do with where in the (50/60hz) cycle most power is being drawn - and is a factor of the power supply and load - not the UPS. Limiting the wattage to less then stated wpuld be false advertising and unneccessary - they can - and do - somply quote runtime (which is a function of the battery) at a percentage of load/based on draw. A 300 watt load on a 600va ups should not cause an overload.
    – davidgo
    Jul 6 at 20:01
  • @davidgo a pile of UPS that made a bunch of dumb claims sitting on my dinning room floor waiting for disposal(plus another pile I have already disposed of). Some are even APC.
    – cybernard
    Jul 6 at 20:14
  • @cybernard which UPS do you suggest?
    – Robert
    Jul 7 at 1:53

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