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Author Topic: UPS recommendations  (Read 1734 times)

Weaver

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UPS recommendations
« on: March 13, 2017, 04:06:31 AM »

Any recommendations for a cheap really fat (long runtime) UPS? Maximum runtime or is it J, or C, per £. Not going for max current delivery. Basic, no shutdown notification i/f required as it isn't for a server.

I'm sure I've asked about this before but just I can't find the thread. I was asked to try and evaluate the current draw, on which I failed. It will be three dsl modems, one low-power Firebrick router, one HP 24-port switch, one or two WAPs. Iirc we might have tried to do some guesswork.

Second issue: I'm wondering if I should partition the whole lot into two groups supplied by two UPSs. Instinct says 'no' because of unequal usage of the UPS. But I'm the other hand I could keep the modems alive longer than everything else so as to avoid upsetting DLM by letting the modems go offline. (If you believe in last-gasp awareness, then this is a non-issue.) Having multiple UPSs might be a desperate way of getting more runtime, but again it represents uneven usage. Also I don't know how the runtime vs current works, nor how the J / C / runtime vs £ economics work, whether getting twice as much runtime costs you more or less than twice as much money when purchasing a fatter UPS.

A really stupid idea (rule out, sanity-check). Would it make any sense at all to have one UPS driving two or more UPSs in turn? This daft cascade idea gets rid of the unequal usage thing but presumably the wastage due to double power conversion inefficiencies is stupid and just wastes the root UPS, or even worse, completely overloads it.
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jelv

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Re: UPS recommendations
« Reply #1 on: March 13, 2017, 08:49:42 AM »

I can remember the previous discussion but can't find it. I'm sure for devices which run on 12V DC we suggested running them direct from 12V leisure batteries (which can have over 100Amp/hour capacity) to avoid the conversion loss.

Increasing run time would be just adding more batteries in parallel (making sure the state of charge was equal before coupling them for the first time).

For non-12V devices you'd need an inverter to be able to plug their bricks in.
« Last Edit: March 13, 2017, 08:53:34 AM by jelv »
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Weaver

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Re: UPS recommendations
« Reply #2 on: March 13, 2017, 10:08:12 AM »

I'd be a bit nervous about putting batteries in parallel in case for some unknown reason they discharge at different rates - does that even make sense / is that even possible though in this configuration? After all you did say to equalise them to begin with.

And indeed, apart from the modems, the other kit needs mains, so there's nothing I can do about that. And Iím not up to diy as a healthy enthusiast might be. By power conversion I meant the generation of mains twice if we feed one ups from the output of another.

Can anyone give me any tips for models? And how to choose commercial UPS kit for maximum runtime per £.
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nallar

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Re: UPS recommendations
« Reply #3 on: March 13, 2017, 10:32:50 AM »

Parallel batteries have to stay at the same voltage (since they're in parallel...), so it's safe to put in parallel any batteries of the same chemistry even if they're of different capacities.

Series batteries have balancing problems, however for lead acid batteries in a UPS this isn't typically a problem as they spend most of their time at a "float charge" which will tend to even out the cell voltages. Lead acid cells can tolerate a slight overvoltage MUCH better than lithium ion/polymer, which will tend to vent and/or explode.

By default APC 3000VA UPSs come with four 12V lead acid batteries in series, each of which is composed of multiple cells already in series.
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Weaver

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Re: UPS recommendations
« Reply #4 on: March 13, 2017, 11:21:55 AM »

Thank god someone knows what they're talking about.
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Chunkers

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Re: UPS recommendations
« Reply #5 on: March 13, 2017, 01:02:17 PM »

I always used to buy APC UPSes but they are expensive so I bought a CyberPower one cheap in a sale a couple of years ago and its been fine.

I don't really use all the intelligent features anyway, its just to keep things alive for 5 mins when the power fails.  In my view the enterprise devices are overpriced for home users so I would go with a cheap one, but I guess it depends on what you are after ....

Chunks

Formatting of link corrected - roseway
« Last Edit: March 13, 2017, 01:16:58 PM by roseway »
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Weaver

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Re: UPS recommendations
« Reply #6 on: March 13, 2017, 01:14:01 PM »

In this case, I'm not using the shutdown interface at all, as  I mentioned earlier, because it's only for infrastructure equipment. So all I need is lots of run-time for cheap money, and decent build quality / reliability too. Helpful tip duly noted. Thanks. Any one else have any recommendations?
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Ronski

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Re: UPS recommendations
« Reply #7 on: March 13, 2017, 01:27:40 PM »

I have an APC1500 at home,  also one here which now the server has gone is just  powering the network and cctv gear.  For my works computer I have a Cyberpower one which  I've had no problems with.
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nallar

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Re: UPS recommendations
« Reply #8 on: March 13, 2017, 01:31:47 PM »

It helps if you know local sysadmins who will have gear being replaced. Can pick up good quality UPSs which have been in use for a few years and only need new batteries, as some businesses will aggressively replace old equipment much earlier than necessary.

I've also picked up used APC UPSs from ebay at good prices by offering to use my own courier for collection only listings.

Be careful with cheap UPS manufacturers which you haven't heard of - might be safety problems.

I purchased a "PowerWalker" UPS on Amazon and discovered that the output polarity was reversed, and when switched off the output live was still connected - the neutral was disconnected instead.
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burakkucat

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Re: UPS recommendations
« Reply #9 on: March 13, 2017, 04:54:30 PM »

I purchased a "PowerWalker" UPS on Amazon and discovered that the output polarity was reversed, and when switched off the output live was still connected - the neutral was disconnected instead.

I hope you sent it back to Amazon under a dual heading of "not fit for purpose"/"severe safety hazard - dangerous to use" and also notified Trading Standards of the rogue equipment.

Was it a Chinese import?  :-\
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Weaver

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Re: UPS recommendations
« Reply #10 on: March 13, 2017, 04:54:50 PM »

So that's two votes for CyberPower kit. I have some APC units here, just are not butch enough.

@nallar - how does it work wrt costs of buying a replacement battery vs purchasing a whole new unit?
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nallar

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Re: UPS recommendations
« Reply #11 on: March 13, 2017, 05:31:46 PM »

If you go with official APC replacement batteries you may spend more than the cost of an off-brand UPS.

If you buy your own lead-acid batteries and bodge them in, it's significantly cheaper. For a smaller UPS multiple Yuasa NP12-12 batteries will work well, and should last longer than the originals would. They're available on Farnell.

APC UPS also like to overcharge the batteries, reducing the lifespan, so maybe they're not a great idea if you don't want to fiddle around to correct it. https://www.youtube.com/watch?v=jeVqtc2dbbc

Regarding the powerwalker UPS, I spoke to the manufacturer and they acknowledged the fault, stating it would be corrected for future units. I didn't report them to trading standards. They didn't issue a recall. Don't know whether it's still an issue. I got one unit refunded. The one I had disassembled I repaired instead as sending back something which I've voided the warranty on by disassembly isn't great. It works okay other than the safety issue.
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Ronski

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Re: UPS recommendations
« Reply #12 on: March 13, 2017, 08:18:32 PM »

I purchased my own APC1500 in Feb 2011, and replaced the batteries in May last year with a pair of these. I think in the works one I've changed them twice, but I'm sure we've had it a lot longer. No need to bodge them in, they are a direct swap except they are not stuck together like the pair that come out.
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currytop

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Re: UPS recommendations
« Reply #13 on: March 17, 2017, 12:48:10 PM »

My own experience is only with a couple of APC SmartUPS 2200W models. One bought new and one used and cheap. They are over 20 years old now and still running fine on original batteries! The load is lower than originally because of newer, lower power equipment so despite the reduced capacity there remains plenty to initiate a shutdown on critical devices. I do use the serial port to trigger timed shutdowns.

Crikey, they are heavy though, no easy matter to shuffle around despite looking like a desktop PC. Internally they are 48v == 8x 6v lead acid batteries.

I think the suggestion of just using a 12v battery is a good one where practicable. But isn't there something else to maintain apart from your network? Or is everything else battery powered with existing backup?
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Weaver

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Re: UPS recommendations
« Reply #14 on: March 17, 2017, 01:56:17 PM »

> But isn't there something else to maintain apart from your network? Or is everything else battery powered with existing backup?

I've just chosen to segment the problem. I'm dealing with core network infrastructure  alone here in this particular thread, just to make it easier to discuss. (Servers and desktop PCs can have their own individual UPSs with shutdown i/fs each.)

One thing is keeping the modems alive to keep DLM happy. Another thing is keeping the LAN up, so that means: switch, WAPs and the router alive, the latter because of its DHCPv4 server role. Next thing is keeping the internet connection up, which means everything aforementioned.

I would like to keep all of this core network stuff going for a long enough period that we have time to get the generator up, and that could take a while. This is because I am out of action and Mrs Weaver finds it difficult going out in the foul weather plus the fact that she can't pull the generator start cord as her hands hurt too much. Do have to make a plan about swapping out the generator for a user-friendly one.
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