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We have a school computer lab with 40 identical PCs with the following specs:

  • Lenovo H530
  • Intel® Pentium™ G3220 (3.00 GHz Dual-Core) processor
  • 2 GB RAM
  • 500 GB HDD (7200 rpm)
  • 15.6 inch TFT
  • Standard Mouse and Keyboard

How much is the power consumption of one PC?

I need to install an online UPS for the lab and don't know if I should go for a 6kVA UPS or a more expensive 10kVA UPS. Any help would be appreciated.

Giacomo1968
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    Power consumption varies depending on system load. If you want to know how much power your computers use you will have to measure it under various conditions, like when a class full of students are using it. Otherwise it is nothing more than a guess. There are many online power estimators / calculators to give you a rough estimate based on your specs which can do a better job than we can. Please do some research, that is not something we have to do for you. Whatever you come up with, shoot for at least 50% larger than you calculated. – Appleoddity Dec 01 '18 at 05:25
  • You are, I suspect, asking the wrong questions, and theone you asked can't be answered accurately without more info and/or measuring equipment. Some relevant points are What is the purpose of the YPS here? (Protection or runtime), how many PC's will be on at once, will they all start together what make and model screens? – davidgo Dec 01 '18 at 05:30
  • These computers have, I believe 280 watt power supplies (which excludes monitor). While 280 watts defines the maximum draw, and this is not realistic, 200 watts average including a monitor per system while running is a reasonable guess. You also need to know that watts is significantly more then kVA so would expect even the 10KVa unit would be marginal to support all these systems. – davidgo Dec 01 '18 at 05:38
  • "How much is the power consumption of one PC?" -- Measure the power consumed under load with a power meter such as a Kill-a-Watt. The power rating of the PSU is poorly correlated to the actual consumption, as well as power calculators. Don't be surprised if the numbers are no more than 120 watts and 240VA. A UPS with a 10kVA rating (and fully charged, fresh battery) would only supply power for about 5 minutes of runtime at such a load of 40 systems . – sawdust Dec 01 '18 at 08:04
  • Are you possibly asking for a hardware recommendation for a measrunign device,? Or a software recommendation for an app to measure? – Mawg says reinstate Monica Dec 01 '18 at 08:46
  • Why are you looking for UPS protection? From a hardware pov the equipment is worth less then a decent large ups. You may be better off with no UPS or multiple consumer grade UPS's (2-4 PCs to a UPS) – davidgo Dec 01 '18 at 19:55

2 Answers2

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I used the online Cooler Master: Power Supply Calculator to calculate, as closely as I could follow your specs, the power consumption of one computer.

At 50% CPU utilization I got 130 W, while at 90% I got 166 W, which does not include the power drawn by the monitor.

I don't think that your students will be using their computers very intensively during a power blackout, or at all. But if they do, let's say they each use 150 W, which gives over 40 computers the total of 6000 W.

I have tried to compare this with (only for example and not advocating it at all) this UPS, costing about $6000. Even such a costly UPS is only able to supply 7,000 Watts for just 9 Minutes on internal batteries.

At further expense, this can be driven up to the maximum of 1 Hour 39 minutes for this UPS by adding external batteries.

I therefore don't see the point in an expensive 10kVA UPS, which will only solve the problem for a short time. A 6kVA UPS, whose main function should be to let the course gracefully terminate, should be enough.

If you wish more than that, you should invest in an emergency generator running on fuel. The UPS should only last the time required to start up the generator.

harrymc
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  • There are a number of reasons for going with the larger UPS. A big one is strain.As a rule, The larger the UPS, the better the componentary - and you are talking about very high current draws here. Similarly, a Watt is significantly more then a VA(how much depends on the equipment, but up to 40% on small systems). Also, in this configuration you can't ignore monitor usage as most likely whole circuits will be wired in. Monitor usage could be anything from an additional 15 -45 watts per unit. – davidgo Dec 01 '18 at 19:31
  • are you aware the link to the example UPS you used was a 10kva unit? You might want to clarify that you are not advocating for the cheap ups as your answer implied to me. – davidgo Dec 01 '18 at 19:34
  • @davidgo: Thanks for the above information. I have corrected the answer to show I'm NOT advocating this costly beastie, – harrymc Dec 01 '18 at 19:41
  • $10k is not costly for a decent UPS, but you raise a very valid point. At $250 per computer it's protecting it would be cheap for servers, but for 4-5 year old PC's (presumably without valuable data) you are probably better off taking some risks. – davidgo Dec 01 '18 at 19:51
  • @davidgo -- "watts is significantly more then kVA" & "Watt is significantly more then a VA" -- Stop repeating this nonsense. You have it backwards. Read https://superuser.com/questions/348103/pc-watts-usage-comparison/348104#348104 – sawdust Dec 01 '18 at 20:39
  • @sawdust - I wonder if there is some confusion in the way we are communicating. (I do have a fair idea of power factor correction, voltage/current draw being out of phase, which is what this is actually about) My point is that if you calculate the computer output in watts, you can't say that a computer which uses 700 watts will work ok with a UPS which is rated 700va, because that UPS will probably only be rated at about 450 watts - eg https://www.amazon.com/APC-Back-UPS-Battery-Protector-BR700G/dp/B002RCNX8K – davidgo Dec 01 '18 at 21:29
  • @davidgo -- You seem confused, since what you claim to explain is not what you originally posted. "My point is that if you calculate the computer output in watts,..." -- No, the power consumption should be measured in VA and watts for accurate sizing with a UPS. "that UPS will probably only be rated at about 450 watts" -- A misleading comment, since that depends on the UPS. There's a conservative convention of using a power factor of 0.6 for the worst case situation and/or an uninformed user. Study https://www.apc.com/salestools/SADE-5TNQYF/SADE-5TNQYF_R1_EN.pdf – sawdust Dec 01 '18 at 23:26
  • @sawdust - IMHO this thread is reaching an end so I don't expect to respond again. My final comments are - I've yet to see computer PSU rated in VA. Cheap power meters like kill-a-watts and multimeters units measure power in watts, not VA. The (biased) article you linked does not seem to me to support your assertions - it advises that power supplies on PC's are typically capacitor based and power factor ranges from 0.55 to 0.75.It advises slightly oversizing the UPS so as to ensure PFC issues don't cause it to overload. – davidgo Dec 02 '18 at 02:19
  • (I assert its biased, because while it is absolutely correct, it neglects to mention the fact that circumvents this whole problem - ie if you buy a UPS on its wattage and not VA rating you won't have a problem. It is my strong belief that the VA rating on UPS equipment is there primarily to legitimise bigger numbers making UPS's sound more impressive to the uninitiated) – davidgo Dec 02 '18 at 02:21
  • @davidgo - "I've yet to see computer PSU rated in VA." -- Irrelevant; it's the measured conumption that's salient in this case, not the capacity or maximum. "Cheap power meters like kill-a-watts ... measure power in watts, not VA." -- I don't know every power meter, but I do know that you are definitely wrong regarding the Kill-a-Watt. – sawdust Dec 05 '18 at 06:15
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Buy a power measuring device like a Kill-A-Watt, or similar device. Plug all the devices you want powered by the UPS into a power strip and plug it into the meter. Then run the computer under a heavy load. You can use a variety of stress testing software. A simple but effective one is stress for Linux. You should see the maximum power draw on the meter. Based on that reading, you can multiply by 40. I would add 50% minimum on top of that for safefy. You might add more computers, computers get upgraded, perhaps you add a printer, etc...

Keltari
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