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Mar 25 '20 at 19:21 history migrated from electronics.stackexchange.com (revisions)
Mar 15 '20 at 17:07 comment added jonathanjo @DavidSchwartz thanks, added your comment to answer
Mar 15 '20 at 17:06 comment added jonathanjo @PeterCordes thanks, added your info to answer. I certainly agree that USB etc is much better (fewer things to fail) for a single server if wiring is convenient.
Mar 15 '20 at 17:05 comment added jonathanjo @grahamj42 thanks, added your info to answer.
Mar 14 '20 at 0:52 comment added Peter Cordes Many UPSes can report to the computer over USB (or serial for even older UPSes). You don't need a fancy ethernet-accessible UPS if you have one supported by apcupsd on one computer that other computers can talk to to find out when to shut down. Although for the UPS capacity the OP is looking at, ethernet is probably a minor factor.
Mar 13 '20 at 19:15 comment added grahamj42 Modern server power supplies have near-unity power factor (otherwise correction would be expensive for large data centres). HP quote 0.99 h20195.www2.hpe.com/v2/GetPDF.aspx/c04346217.pdf
Mar 13 '20 at 4:35 comment added jonathanjo I don't have any experience of the Tesla products, but they're certainly interesting. I note from wikipedia "As of October 2019, the Tesla Powerwall 2 costs $14,600 for the recommended two units (plus $2,500 to $4,500 for installation) in the US; this price does not include the cost of solar panels"
Mar 13 '20 at 2:56 comment added Harper - Reinstate Monica $7500 for a UPS that doesn't even have the runtime!? Why not just install a subpanel with a Tesla PowerWall then? It's cheaper, and is actually made for long-term running, also the battery will last a LOOOT longer. Not like a "10kw" UPS with 1h10 at 1000W, obviously the battery is sized for 5 minutes to drop connections, settle databases, flush cashes and shutdown.
Mar 13 '20 at 2:23 comment added jonathanjo @niran90 I hope it's been helpful for you
Mar 13 '20 at 1:32 comment added niran90 @jonathanjo Thanks. I see that only the top suppliers like APC and Eaton provide the runtime graphs, which give a clear picture of 1) how many backup battery packs we will need to ramp up to >4hrs and 2) how hideously costly the combination of the UPS and batteries is actually going to be. It's quite clear that I need to investigate alternate solutions.
Mar 13 '20 at 0:29 comment added jonathanjo @alex.forencich You're correct of course, thanks. fixed in answer.
Mar 13 '20 at 0:29 comment added jonathanjo @user20637 thank you for finding my second silly arithmetic error, fixed now.
Mar 12 '20 at 21:51 comment added alex.forencich @user20637 looks like the Wh figure was wrong earlier, and that error was propagated but not fixed when the first error was discovered. So yes, should be 8 car batteries worth of storage, not 2.
Mar 12 '20 at 20:00 comment added user20637 "you need 4,000 Wh. A typical car battery is approx 500 Wh (Wikipedia), so your basic needs are at least two car batteries worth of storage" Huh? Is that arithmetic correct?
Mar 12 '20 at 18:02 comment added jonathanjo @niran90 They don't normally quote watt-hours because of the non-linearities. The best way to estimate time is to look up your load (in watts) against the curve of a particular UPS. The graph in my answer is very typical of the shape of the curve, though of course the power and time vary according to the given UPS.
Mar 12 '20 at 17:59 comment added Justin @jonathanjo - No worries, I'll delete my comments now.
Mar 12 '20 at 17:58 comment added jonathanjo @Justin ... I'm sorry, it was a stupid error, and should have been 4,000 Wh. P watts for T hours = P * T watt hours. I have fixed the answer text.
Mar 12 '20 at 15:16 comment added niran90 @Justin That's right, I need a UPS with a 4kWh battery, but no specification I have seen so far has the kWh rating mentioned. The most that is mentioned is the "autonomous time" in mins under max. load. And typically I have seen 5min - 15min. The UPSs that I have looked at require additional battery packs in order to scale up to ~4hrs.
Mar 12 '20 at 11:56 comment added niran90 Oh wow! Thanks for your detailed response. It's a lot to take in, and I hadn't anticipated that looking for a UPS would be such a tedious task, haha. But I will re-read your post a few times to absorb the pertinent information that will inform my decision :)
Mar 12 '20 at 10:47 history answered jonathanjo CC BY-SA 4.0