Does Power supply run through the UPS

[pallab]

Suppose my computer draws 900W at full load, and I have a 850 watts UPS. I know if there is a blackout, and I am at full load, my computer will shut down.
What I want to know is this:
When there is NO blackout and I am at full load, can my computer actually draw 900 W or is it like the power supply can only draw upto the UPS specification?
Like If I have a 1000W power supply and 850 watt UPS connected to my computer, can It never draw more than 850 watts?
I mean does the power supply get power only from the UPS, not from the wall?

 

[IntelUser2000]

If the 850W is the AC output limit, then when the load is over that, its simply going to trip a breaker or something to protect it.

Though I guess its possible to make a UPS where it would power it directly so an 850W rated UPS can power a 1000W equipment, in practice maybe its not a good idea.

The reason is UPS does the double duty of not just smoothing out power spikes, but also to provide temporary power for safe shutdown of important equipment.

It would simply be a bad user experience to allow 1000W normally, but only 850W when the battery backup is active. So the AC power limit being equal to DC power limit seems like the correct way to design the UPS.

 

[UsandThem]

If your computer is plugged into the UPS, then yes it provides the power.

As far as can you pull more wattage from the UPS than it's rated for, that depends on the unit. Some units might allow short periods above its rated output (like many quality power supplies can do before shutting down to prevent damage), but I imagine it would be hard on the UPS, and you really should avoid doing it. If you need a larger UPS because of the wattage of your PC needs it, buy one.

However, just because you have a 850w power supply, it does not mean you are always pulling that amount. The power supply pulls what it needs depending on the use and the hardware (plus a little bit of loss due to the efficiency).

 

[pallab]

Thanks guys, this was really helpful.
How much do you think this will draw:
3900x+rtx 2080 super on a beefy mobo like the crosshair viii, if I overclock the cpu and gpu to an extreme limit?
i already have the rm1000x, so it would require a 1200W UPS with some overhead to supply the 1000. But I may draw less power I guess. A 1200W psu in India costs 4 times the power supply here in India.

 

[UsandThem]

Probably no more than 500w peak.

The new Ryzen CPUs don't appear to have much headroom to overclock, so right now it seems like it's best to just let them do their automatic boosting. The GPU will let you overclock more, but unless you want to it to have a short life, I would back off from the "extreme limit", and maybe just go more of moderate overclock.

 

[mindless1]

Depends on the type of UPS
(online vs offline)

 

[VirtualLarry]

My experience with a variety of consumer UPSes is, if you connect equipment to the battery-backup sockets, and it draws more wattage than the UPS is specced to handle, it will alarm. Even if it's on AC power. Because that's not a "safe" condition, should the power go out, the inverter will be overloaded, and it will suddenly shut off, and might be damaged as a result.

It is possible to "bypass" that, by plugging the PC into the "Surge-protected Only" outlets, but then, you don't get the benefit of the battery-backup.

Lastly, don't think that because you bought a 1200W PSU, that you need a 1200W UPS. Only if your PC is going to be running at full-load, near it's maximum capacity, which is not a wise idea, UPS or not. Don't forget the additional load of the monitor, USB3.0 powered hub, network switch, (inkjet) printer, or other peripherals. (DON'T put a laser printer on a UPS, ever.)

I have my PC on a 650W EVGA 80Plus Gold PSU, I draw maybe 400W max at the wall according to my K-A-W, and I have it connected, along with a 40" 4K UHD TV/monitor (100W by itself) to a 1300VA+ APC UPS. I'm not sure of the wattage capacity, but I haven't exceeded it yet. I think it's around 800-900W.

 

[Red Squirrel]

Most consumer UPSes that you buy at a store are standby units which mean it's running 100% off normal shore power when it's available and only switches over to inverter if power goes out. HOWEVER some may still measure the current to make sure that it's within spec if it does have to switch to battery so it may still alarm or even shut down. Some may also do a self test at some random time, and then fail and shut down if the draw is too high.

I usually try to buy a UPS much larger than what I anticipate putting on it, as that will give a bit better run time. When you load a UPS to it's max capacity you are lucky to get even 1 minute of run time, don't listen to what it says on the box.