I have a Masters in EE, a long  time ago but I don’t think volts and amps have changed much… I can not figure out how to properly size a backup battery / UPS. My PC with an Nvidia 4080 and a 850 watt PSU is plugged into my CyberPower 1000VA UPS. The only other things plugged into that UPS are a printer which is mostly hibernating, and a network external drive that is almost never accessed especially when flying. 
 

I would think 1000VA would be sufficient (although the battery also says 530 watts which doesn’t compute to 1000VA), but I keep getting a warning tone.  How do you size a Backup battery / UPS or do you just not use one. Thanks!
 

 

I use a 1,500 VA UPS for my sim desktop, and only have the PC connected to it. My printer is a Laserjet and it is not recommended to be connected to the UPS at the same time, so I put it directly on the wall.

 

I use a conservative power factor of 0.8 (Apparent power (VA) ~= Power (Watts)/Power Factor) where most good quality PSUs now are probably more like 0.9 or better.

So an 850W PSU would be sized at 850 / 0.8 = 1063VA, plus whatever additional margin you care to add.  I'd probably go with a 1200VA or higher unit in that case, assuming your PSU is sized appropriately for the system.  The risk of under-sizing a UPS is a disorderly shutdown and resulting potential data corruption.  If you are fastidious about system backups (I am), then it's reasonable to accept some risk here...a 1000VA unit would probably work, with an extra added measure of risk.

You can use an inexpensive Kill-a-Watt meter to get a reasonable estimate of both power in watts and apparent power in VA as well, but the reading you get does not account for transients and peaks, and you need to load up the computer using something that vigorously exercises the whole system to get a meaningful read on the system's high power demand.

My primary sim machines (13900KS+4090+1600W PSU and 10900K+4090+1000W PSU) both run on 1500VA units, based on power meter readings and a healthy added margin.

Then after sizing the UPS for power rating, there's battery capacity, which affects run time under load.  I look for at least 5 minutes (preferably 10-15 min) at rated load to give me time to get to all the computers and shut them down in a power outage.  And a user-replaceable battery is a must-have.

Last, there's the eternal debate over pure sine-wave or stepped sine-wave approximation on the UPS output power waveform.  On a high-end performance system I go with sine wave, on lesser machines stepped square-wave approximation is OK.

I run only the PC and external water cooling systems on the UPS' battery backup output--monitor and sound system run via the UPS's surge protected outlets.  I have a placard near each PC with the emergency SCRAM keyboard sequence (Win+X U U) so I can shut things down fast even without a monitor.

I've used both APC and CyberPower UPS units with good results.

The VA rating is not the same as the watts rating (go figure). The CyberPower 1000VA UPS I looked at has a 600W rating, so your PC has the ability to exceed its power delivery ability.

I picked up an inline wattage meter a while back that I plugged into my simming rig and got a maximum power rating that I used to spec out a UPS, which I added about 150W just to be safe.

Thanks @Bob Scott especially for that great reply. I fully followed your explanation and logic. I may take this 1000VA back tomorrow and go to at least a 1200 VA unit. Thanks agai!

I got kinda outraged when a black out ruined my flight and got a 3kVA UPS (I had small one at that time but only hold for like 2 minuets due to aging), that gives me more than 70min when running P3D on old system (3850+1080) and still 45min+ (and with 3 years of aging)on my new system (79x3D+4080), or 6 more hours in idle.

Since then I only had 1 blackout over a hour and that's when I'm not flying .

Edited July 28, 20232 yr by C2615