How to pick a UPS (not PSU) with right capacity?

[Supersonicwolfe]

So I have a 650 W system (3600+ GTX970, eyeing a RTX3070 and 5600 in future) needs a UPS.

Now, do I need to match the wattage of the UPS with PSU? Or I should be fine as long as the VA capacity is sufficient?

E.g.

VA calculation (650W computer +50W monitor router)/0.8 = 875 VA

But APC 900VA UPS is only rated to 450W??

[it_dont_work]

8 minutes ago, Supersonicwolfe said:

But APC 900VA UPS is only rated to 450W??

This is because ups's rating is also considering the power factor 

[Enderman]

Get a cyberpower PFC LCD UPS, they are pure sinewave and affordable.

[Glenwing]

23 minutes ago, Supersonicwolfe said:

So I have a 650 W system (3600+ GTX970, eyeing a RTX3070 and 5600 in future) needs a UPS.

Now, do I need to match the wattage of the UPS with PSU? Or I should be fine as long as the VA capacity is sufficient?

They do not need to be matched. The UPS needs to have a high enough power rating to supply power to the load, just like any power supply, that's all. If the load is 600 W you should get a UPS that has maybe 800 W or more to allow enough headroom.

 

Apparent power rating (VA) is irrelevant here and should be ignored. It is much higher than the real power rating (W) to allow headroom for devices with low power factor, which put additional load on the UPS without drawing more average power. This is typically motorized devices which have inductive loads with lower power factor. PC power supplies have active power factor correction, so the apparent power is only a little higher than the real power. You just need to look at the Watt rating and make sure your computer and other components don't exceed that. If you had a large inductive motor you might also be worried about exceeding the VA rating, but it really doesn't matter for computers.

 

What's more important is to get a pure sine wave UPS not a "simulated sine wave" because they can cause issues with active PFC circuits in modern power supplies and may cause your computers to shut down unexpectedly when the UPS is on battery backup power, even if there is plenty of battery left.

Quote

VA calculation (650W computer +50W monitor router)/0.8 = 875 VA

The 0.8 needs to be replaced with the power factor of the load, it's not a constant value. For a PC it's probably closer to 0.95 or 0.9.

[metaleggman]

8 minutes ago, Glenwing said:

They do not need to be matched. The UPS needs to have a high enough power rating to supply power to the load, just like any power supply, that's all. If the load is 600 W you should get a UPS that has maybe 800 W or more to allow enough headroom.

 

Apparent power rating (VA) is irrelevant here and should be ignored. It is much higher than the real power rating (W) to allow headroom for devices with low power factor, which put additional load on the UPS without drawing more average power. This is typically motorized devices which have inductive loads with lower power factor. PC power supplies have active power factor correction, so the apparent power is only a little higher than the real power. You just need to look at the Watt rating and make sure your computer and other components don't exceed that. If you had a large inductive motor you might also be worried about exceeding the VA rating, but it really doesn't matter for computers.

Do you need a UPS that matches or exceeds the wattage per, say, the calculations from PSU manufacturer sites or PC part picker for your build?  Or is it reasonable to just get something for what the computer in question would use in idle or a light workload?  The reason I ask is that if I were to use a UPS, it would be mostly to allow a file to be saved properly or to shut the system down properly (like say my NAS), not to finish a simulation, or iono, finish playing a game lol.  Given that GPUs and CPUs don't pull much on idle these days, would it come down more to the application?  Or is UPS pricing such that it makes sense to simply buy something with a higher wattage just in case?

 

[Glenwing]

1 minute ago, metaleggman said:

Do you need a UPS that matches or exceeds the wattage per, say, the calculations from PSU manufacturer sites or PC part picker for your build?  Or is it reasonable to just get something for what the computer in question would use in idle or a light workload?  The reason I ask is that if I were to use a UPS, it would be mostly to allow a file to be saved properly or to shut the system down properly (like say my NAS), not to finish a simulation, or iono, finish playing a game lol.  Given that GPUs and CPUs don't pull much on idle these days, would it come down more to the application?  Or is UPS pricing such that it makes sense to simply buy something with a higher wattage just in case?

The power from the wall still passes through the UPS at all times, so you probably would want the UPS to be rated for the maximum power your system will need at any given time (even if it's not on battery power during those loads).

[metaleggman]

20 minutes ago, Glenwing said:

The power from the wall still passes through the UPS at all times, so you probably would want the UPS to be rated for the maximum power your system will need at any given time (even if it's not on battery power during those loads).

OHH that makes sense.

[Supersonicwolfe]

18 hours ago, Glenwing said:

They do not need to be matched. The UPS needs to have a high enough power rating to supply power to the load, just like any power supply, that's all. If the load is 600 W you should get a UPS that has maybe 800 W or more to allow enough headroom.

So by that metric, I don't need a 700W UPS, a smaller 500W should be fine?

I calculated my current setup using CoolerMaster's site ended up just  416 W (Newegg gave me 421W), plus small 1080P 23 inch monitor, one small external drive, and some head room maybe 500W is enough?

Edited May 3, 2021 by Supersonicwolfe
added Newegg estimate

[Glenwing]

2 minutes ago, Supersonicwolfe said:

So by that metric, I don't need a 700W UPS, a smaller 500W should be fine?

(I calculated my current setup using CoolerMaster's site ended up just  416 W, plus small 23 inch monitor, one small external drive, and  some head room maybe 500W is enough?)

You would probably want more headroom than that, maybe 600 W.

[Supersonicwolfe]

1 hour ago, Glenwing said:

You would probably want more headroom than that, maybe 600 W.

Thanks I will look one in the 500-600W range. 

 

I calculated my setup using Ryzen 5 1600 (Outer vision for some reason don't have 3600 as an option) and they suggested UPS rating is 800 VA (with a 449 W PSU)

(https://outervision.com/b/dENZf0)

 

I just need one to protect my main rig from circuit breaker tripping in the shitty dorm room … Somehow the dorm lender thought putting 5 rooms on a tiny 10A breaker circuit is a good idea (Grid is 220-230V so that is a mere 2300W, someone plug in a Vacuum or hair dryer and pop goes the breaker)

Edited May 3, 2021 by Supersonicwolfe
Added outervision calculation results