Can I use offline UPS for a PC? Will the delay affect my PC if it is running when the power goes out? im planning to set up an offline UPS at my home i need my PC running without any disruption but i was wondering whether i can run PC on an offline UPS without any interruption.Will the offline UPS delay from main supply to battery affect my pc when the power goes out?

  • \$\begingroup\$ This question is off topic - a specific challenge in designing a UPS could be on-topic, but applying an off-the-shelf one to off-the-shelf office equipment is not within the mission of this stack exchange site. \$\endgroup\$ – Chris Stratton May 27 '17 at 18:59
  • \$\begingroup\$ sorry im new to stack exchange.I thought it is platform where you could ask technical doubts too. so where do i ask if this site cant answer it or call it off topic? I've also asked this in other forums too but still havent received a clear answer.Why is stack exchange built in the first place if it calls something off topic since it dont deal with designing? \$\endgroup\$ – firefly May 27 '17 at 19:15
  • \$\begingroup\$ @firefly Its the users job write a good question. This is a forum for electrical design questions. Cross posting is generally discouraged across the internet don't do it. electronics.stackexchange.com/help/how-to-ask \$\endgroup\$ – Voltage Spike Jun 1 '17 at 16:19

If both the UPS and your power supply are commercial products carrying UL or CE or both there would be no problem. There are requirements for the power supply to continue working with full load for at least one half cycle (10ms for 50Hz) without mains. Also the requirements for the UPS say that it should start to supply power for less than one half cycle.

| improve this answer | |
  • \$\begingroup\$ what is the result of set-point hysteresis in a brownout , is it synchronous? do all PC PSU's reject line transients the same? They are most common because they are 25%cheaper. not better. So it depends on both UPS and PSU quality for reliability. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 27 '17 at 19:23
  • 1
    \$\begingroup\$ I am not goint to argue on this. All PSU's should be designed to withstand 10ms @ full load and all UPS shall fire up before 10ms. If the power supply is properly designed it will survuve this transient. This kind of UPS's are the most used in SOHO applications. Of course 'online' is the best, but this will do too, and that was the question. \$\endgroup\$ – Todor Simeonov May 27 '17 at 19:24
  • \$\begingroup\$ but if Vin is 100V/us during transfer after a dropout will,PSU reject it? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 27 '17 at 19:25
  • \$\begingroup\$ This can't happen beacuse the relay of the line-interractive UPS connects its low frequency transformer whinding (couple of dozens of mH) to the PSU's capacitor - hundreds of uF. \$\endgroup\$ – Todor Simeonov May 27 '17 at 19:29
  • \$\begingroup\$ That isn't much in terms of sqrt(LC). The question becomes how much energy remains before the 10ms transfer takes place and what is the ESR of all loads. This is critical to determine if there is adequate storage time while V is unstable. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 27 '17 at 19:52

PC PSU's only store energy for 1 cycle minimum at full load. Thus if offline switcher causes. large dropout, it will fault some PC's.

This is why online UPS is best.

Offline UPS is just a life preserver for most but not all loads like Laser printers. Whereas Online UPS is a better "generator" with low Z and better load regulation.


There are 3 types of UPS

  1. Offline ... good
  2. Offline interactive... better
  3. Online , dual converters.... best

There are 5 types of DCDC converters used in UPS each with different cost, loss, surge and impedance load regulation tradeoffs.

  • Forward Converter
  • Push-Pull Converter
  • Half-Bridge Converter
  • Full-Bridge Converter
  • Flyback Converter ... cheapest
| improve this answer | |
  • 2
    \$\begingroup\$ Most commonly used UPS for PC are exactly line-interactive or in other words offilne. See my answer below. \$\endgroup\$ – Todor Simeonov May 27 '17 at 19:10
  • \$\begingroup\$ yes but depends PSU supply regulation , % load and transfer glitch, so I stand by my opinion from my experience. (-1) Todor \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 27 '17 at 19:10
  • \$\begingroup\$ I read somewere that the delay in switching from main to battery is around 20-100ms .So when power goes out when im working on my PC will the delay cause my PC to shutdown? i know the online UPS are the bests but they cost much more than an offline.A single online UPS wont be enough for me since im planning to run a mining rig which will draw considerable amount of power a online UPS of that rating would expensive .We often have blackouts in the winter. \$\endgroup\$ – firefly May 27 '17 at 19:30
  • \$\begingroup\$ @firefly open a datasheet of whatever UPS and look for the parameter transfer time. \$\endgroup\$ – Todor Simeonov May 27 '17 at 19:35

Not the answer you're looking for? Browse other questions tagged or ask your own question.