Question UPS Doesn't Last Long With Desktop Computer In Sleep Mode

[Crag_Hack]

I'm just curious how my battery backup UPS only provides a very short time to provide charge to my desktop computer while it's in sleep mode. If it can do ~20 minutes at ~120 watts how come it can't do much at all when the computer is sleeping at ~5 watts or so. A laptop can sleep for quite some time...
Thanks!

 

[Darkbreeze]

Are you SURE it is still able to do 20 minutes while it's actually running? How old is this UPS?

Sounds to me like maybe the battery needs to be replaced. And why would you need to be running on UPS power while the unit is "sleeping" anyhow? While sleeping or hibernating a laptop shouldn't even NEED to be running on UPS backup in the first place unless the laptop battery was already nearly dead. Not even really sure WHY you would even connect a laptop to a UPS in the first place when it already HAS it's own battery?

UPS is for desktop systems that DON'T have a battery, so that you can safely shut down without losing anything you've been working on.

 

[Crag_Hack]

I am aware of these things. Sometimes the power goes out at night when my desktop is sleeping and by the morning it has depleted the UPS charge and the computer is off. I have an APC backup and the Powerchute app for it tells me there is about ~20 minutes of charge at ~120 watts for my desktop computer. It runs self-tests every several weeks so I'm trusting the app stats. A laptop can easily sleep over night without losing charge thus the comparison. I'm guessing the UPS is designed for high watt usage only and something about efficiency complicates things.

 

[USAFRet]

it tells me there is about ~20 minutes of charge at ~120 watts for my desktop computer

Have you ever tested that "20 minutes"?

 

[Darkbreeze]

Have you ever tested that "20 minutes"?

Right. That was my first question too.

I did however misunderstand that it's WITH the desktop that he's thinking he has issues while sleeping. I misunderstood it to be the laptop, but doesn't really change the equation. Rather than trusting any "app" to be accurate, I'd want to actually see how long it can remain powered, both actively and sleeping, in real time.

Also, what is the EXACT model of your desktop power supply and the exact model of your APC UPS?

 

[bill001g]

There is some overhead just having the UPS running on battery. The overhead is small but it is a higher percentage being wasted compared to when it running at higher levels of output. On one of my UPS it has a option to not turn off when nothing is drawing power. With that option on the UPS will actually drain the battery just from running its fans and display after a few hours even though there is nothing plugged into it.

But as other have suggested your batteries likely do not actually last 20 minutes any more. Once they get over 3 years old you start to see most have degraded performance. At 5 years many barely hold a couple minutes. I know mine look perfectly ok on the self tests but then at some point the UPS will attempt to go to battery and shut off almost immediately.
I have started to replace them at 3 years even if they seem good.

Newer UPS have started to use lithium rather than lead acid but these units cost 2 to 3 times as much.

 

[Darkbreeze]

Exactly.

 

[Crag_Hack]

Perhaps I place too much trust in APC's app... actually not perhaps but almost certainly ha... I did find this efficiency graph I wonder how bad things get at ~5 watts or so. If things were linear though and I indeed did get 20 minutes at 120 watts then at 5 watts we'd get 8 hours which still doesn't last the whole night assuming APC's app is accurate. And as the efficiency drops off the total backup time should lessen correct? This is mine:

APC Back-UPS 850VA, 120V, 2 USB charging ports - BE850M2 | APC USA

BE850M2 - APC Back-UPS 850VA, 120V, 2 USB charging ports | APC USA

www.apc.com

 

[USAFRet]

Perhaps I place too much trust in APC's app... actually not perhaps but almost certainly ha... I did find this efficiency graph I wonder how bad things get at ~5 watts or so. If things were linear though and I indeed did get 20 minutes at 120 watts then at 5 watts we'd get 8 hours which still doesn't last the whole night assuming APC's app is accurate. And as the efficiency drops off the total backup time should lessen correct?

Things are NOT linear!

UPS's are not meant to last all night.
They exist to give you enough time to shut down gracefully.

 

[Crag_Hack]

What I mean to say is things not linear and thus are much worse than linear given the efficiency dropoff.

 

[bill001g]

Lets say there is a fan that takes 10watts of power when it runs on battery. If you run a 100 watt load that is 10% overhead. If you run 5watts it is 200% overhead....the fan eat more power than the load.

That is over simplifying it though. In some ways the battery can run longer if you pull the power slower. If you drain the power quickly a lot of the power is going into heat. When you draw slower there is less waste to heat. If everything was 12 volt dc then it would be simpler to figure out. The conversion to 120 volt ac is not real efficient so that is likely where most the issue is.

A commercial UPS I saw a spec sheet on said to run the most efficiently above 20% load but below 75%. Who knows what a consumer UPS will do. I suspect though you are in the case where there is some fixed amount of overhead no matter how much power you use so running very low loads will not be very efficient.

 

[Darkbreeze]

If you live someplace where the power is regularly going out at night, your UPS isn't the problem, well, not the main one anyhow, and you should simply be shutting things down before you go to bed so you don't have to worry about it. If it's a power grid issue because you live in a region where the power grid sucks and it's just unavoidable, then just power off every night. But if that isn't the problem, then you definitely need to either get your home electrical or the leg from the source correctly repaired or give that UPS some love. Or replace it.

In any event, like I said from the start and was repeated here, those UPS systems aren't meant to be used as an ongoing source of power anyhow. They are only meant to give you time to save your work and shut down so you don't lose anything. Using hardware in the way in which it was meant to be used tends to afford it the ability to last a lot longer and function properly while it does.

 

[Crag_Hack]

Thanks guys. It just occurred to me to run the math, if I get 20 minutes @120 watts, I should get 8 hours at 5 watts if the relationship was linear, which it obviously is not. I sleep 10 hours lol so there's part of the answer.

 

[Karadjgne]

Can also depend what else is plugged in, to which ports, Windows settings etc. UPC's generally only have a couple of battery ports, the rest are just protected ports, but if the monitor is also on a battery port, and not set to sleep or the windows timers are set with stuff like 'wake on Lan' etc, you'd be using a lot more juice during 'sleep' than just low power C6 state, and possibly hitting C0 (On) state instead.

Waking a pc from sleep isn't a gradual buildup, like waking up on a lazy sleep-in Sunday morning, it's closer to Christmas morning at 5am with a 5yr old suddenly bouncing on the bed, and the resultant adrenaline rush. A PC waking up on a UPC several times, not going to last that long.