New UPS power quality assessment - Page 1
Forum section: electronics / beginners

author: Bloodred
author_rank: Contributor
timestamp: October 08, 2023, 04:04:38 pm
content: Hello!I'm new around here and I'm hoping to share in some electronics / power quality wisdom that I still lack on my own.I've debated for quite a while whether this post should go in the Computer category, or the Power category or right here. Ultimately I decided to post here since I'm certainly a beginner in this field and I imagine this is basic stuff for somebody who knows what they're doing, I hope it's not considered off-topic.Long story short(er), I recently bought a new UPS that I would like to use with a few computers and associated peripherals (some monitors, networking equipment and a DAC / headphone amp). What I bought is aFSP / Fortron Eufo 3k, a line-interactive UPS rated for 3000VA and with sinewave output. The load I'd expect should be about 1.5kW at most, likely a lot lower in most practical situations since I don't really have all computers at full load at the same time.Since the computers I want this UPS to power are fairly expensive, I decided to test it and have a look at it before connecting all my gear. After confirming that basic functionality was fine, I wanted to see the actual output waveform the UPS is producing. I only have a cheapo Owon VDS1022I USB oscilloscope available and it cannot handle 230V AC, nor do I have a high voltage probe to use, so instead I decided to measure through a transformer instead (rated 230V to 15V).Using this transformer I took the attached measurements. The first one is just the wall AC I get, I used this as a sanity test to confirm that my measurement setup produces reasonable results (seems like it does). The other 2 shots are the UPS output when running on battery, as you can see it does look sinusoidal but not quite clean. The waveform my scope gets at 5ms/div is a bit chaotic, but at 200us/div I think it more accurately captures what's going on, it looks like there's some sort of periodic ringing, especially near the peaks of the sinewave. Note that I took these measurements at about 400W load on the UPS, ~300W from an older computer I have running a stress test and another ~100W from an incandescent light bulb.Now after all that introduction, my question is just whether this waveform is adequate for powering computers and computer peripherals. Like I said, I already tested with an older computer and it worked perfectly fine, but could this cause issues in the longer term, or is there no cause for concern?I tried to do my homework and research UPS outputs, I've seen cleaner sinewave outputs but also some really terrible looking squarewaves on lower-end units and as far as I can tell even those don't kill computer PSUs, so my own conclusion for now isit's fine.I would appreciate some input from somebody more qualified and experienced in the field than me, if need be Icanstill return the UPS free of charge for another 2-3 weeks.Thanks!

author: bdunham7
author_rank: Super Contributor
timestamp: October 08, 2023, 04:25:18 pm
content: Try running it with only resistive loads like the lightbulb. That noise you see is switching noise, but it may be from the UPS or from the computer PSU that is loading it. The UPS will have a higher source impedance, so no matter how clean its output is, load noise will be magnfied compared to operation directly from the mains. In any case, it looks good enough.

author: wraper
author_rank: Unknown
timestamp: October 08, 2023, 04:26:17 pm
content: As long as it's more or less sine, it's fine for anything. Computer power supplies are not some precision devices and often mains voltage is distorted way more than that. Cheap UPS do not even output sine and still work fine for most of things.

author: Bloodred
author_rank: Contributor
timestamp: October 08, 2023, 04:54:57 pm
content: Quote from: bdunham7 on October 08, 2023, 04:25:18 pmI have actually tried that already, though I did not save images of those tests. I first tried it out with no load, then with just the light bulb and the output looks effectively the same in all situations. There is a small difference I observed, namely that with lower load the noise is mostly "focused" around the peak of the sinewave and with greater power draw from the UPS it spreads out a bit more around the peaks, but it's fundamentally the same and its amplitude didn't really seem to change. I'm glad to know that this seems fine!Quote from: wraper on October 08, 2023, 04:26:17 pmYeah, that's basically what I had concluded as well but it's nice to hear some confirmation. The noise doesn't look to bad and I didn't imagine power supplies would be so sensitive and designed with such tight tolerances that this would be a problem, but I haven't really seen any information about this anywhere so I figured it's safer to ask before risking stuff that's several times the cost of the UPS.In any case, thank you both for your quick answers!

author: alligatorblues
author_rank: Regular Contributor
timestamp: October 09, 2023, 12:45:05 am
content: Line interactive UPSs work by a transformer that has 5 or 6 windings, 15-20 V apart in output, when powered by the mains. If the line voltage drops, the UPS opens one relay and closes the one one voltage step up. That raises the output voltage, making it somewhat more stable. But the sine wave is not corrected until utility power is lost, and the UPS is on an inverter power by the batteries.Full inversion UPSs convert the mains power to DC and then back to AC.. The inverter uses IGBTs and massive filtering+mcu control to create a perfect sine wave from scratch. This type of UPS is much more difficult to manufacture and test, because the performance is +-1V output, +-1hz, 98% power factor, processor-generated sine wave, .01% failure rate over 20 years.So you should never connect dirty loads, like anything with a heater (laser printers, incandescent light bulbs, or motorized devices.The full inversion type UPS vs line interactive is like a gun vs a knife! Full inversion is cleaning power 24/7. Line interactive cleans power only when it loses utility power. Otherwise it just switches coils on a toroid transformer to keep the output within a range of ~10VAC from 120 mains.I use the Liebert GXT4-3000RT-120. But that requires a 30A circuit, and therefore a 30A outlet, which is completely different from typical residential wall receptacles. So, you have to have that wired. But I have never experienced damage from dirty AC mains power. But I have a lot of expensive equipment, some of which requires continuous power.Those go for about $4,000 + $500 for an external battery cabinet, for more reserve power. I got the whole package new and sealed from eBay for $600. And they last about 20 years. My uncle is a service rep for Liebert, now owned by Vertiv.Line interactive units are manufactured only in smaller sizes, up to ~3kVA, aimed at the soho market. If it was me, I'd switch to a full inversion type UPS, because it offers more protection, and eliminates pesky problems, like ram DIMMs that go bad. Even a direct lightning strike will not pass through a 3KVA full inversion UPS.

author: jonpaul
author_rank: Super Contributor
timestamp: October 09, 2023, 06:43:10 am
content: Besides waveform, noise, THD, a UPS eval should have1/ Transient protection2/ Line dropout time > one mains cycle3/ High quality batteries4/ Reliable invereter and cutover circuitsWe buy APC not chinese junkj

author: Jeroen3
author_rank: Super Contributor
timestamp: October 09, 2023, 07:32:45 am
content: The skewed sine peaks show this ups is not dual conversion and passes mains.If you want clean power you need a dual conversion.This is just mains noise, worsened with some high frequency swithcing noise behind the lower impedance of the cables and plugs.

author: Bloodred
author_rank: Contributor
timestamp: October 09, 2023, 07:57:05 am
content: Quote from: alligatorblues on October 09, 2023, 12:45:05 amYeah, I've looked into line-interactive and online / double-conversion units, unfortunately every online unit I looked at seemed to have rather loud (going by their spec sheets) fans that seemed to run all the time and since I use this at home that was just a no-go from the start. I had to pick a line-interactive model since these are 100% silent when operating off mains, as they just connect the output to the power input. I can accept some fan noise when the UPS is on battery, but not all the time because the double conversion is always running.Quote from: Jeroen3 on October 09, 2023, 07:32:45 amI'm not sure I understand what you mean. Only the first image shows mains and that has no real noise. The peaks are a bit 'flattened' on mains but from what I gather this isn't necessarily abnormal. The other 2 images are on battery, which means the UPS was disconnected from mains when I took those measurements, those are the noisy ones. How can that be mains noise when mains was physically disconnected?

author: wraper
author_rank: Unknown
timestamp: October 09, 2023, 09:31:51 am
content: Quote from: jonpaul on October 09, 2023, 06:43:10 amAPC is the worst you can get for premium price. I have no experience with FSP UPS but knowing their computer PSUs I'd buy it any day over APC junk which builds even their $5K UPS with cheap Chinese Nantong Jianghai capacitors and Kung Long batteries. Not to say there are well known Eaton and Riello who make good reliable stuff that does not overcharge and kill batteries in 2 years.

author: BeBuLamar
author_rank: Super Contributor
timestamp: October 09, 2023, 10:35:32 am
content: Well perhaps you can make the same measurement without the UPS directly from the outlet. I wonder if it's better than the UPS.

author: Bloodred
author_rank: Contributor
timestamp: October 09, 2023, 12:42:09 pm
content: Maybe I wasn't clear, the 2nd and 3rd images are taken with the UPSnot connectedto the outlet. Only the first is with it connected to the wall and I only really used that to confirm that I was getting a reasonable-looking result from the transformer and scope I was using to test.Quote from: wraper on October 09, 2023, 09:31:51 amI used to have a cheapo APC unit a while back (~500W), that one failed in some rather nasty way in which it 'leaked' like half (~115V AC) onto the ground on its outputs. I found out when I got a shock by touching an HDMI cable that was plugged into a monitor that was powered through the UPS. It was a mild shock, fortunately. Still, this is a really bad failure mode for a UPS in my eyes, it kind of put me off APC. I get that the unit was cheap, but failing in such a way that it turns into a safety hazard is still a big no-no.

author: wraper
author_rank: Unknown
timestamp: October 09, 2023, 01:45:33 pm
content: Quote from: Bloodred on October 09, 2023, 12:42:09 pmVery unlikely it was failure. Most likely just normal current leakage to earth through Y safety capacitors and UPS connected to mains voltage with no earth connection.

author: Bloodred
author_rank: Contributor
timestamp: October 09, 2023, 03:53:05 pm
content: Can't say I understand what was going on with that UPS, but what I can say for certain is that the outlet it was plugged into was properly grounded since the first thing I did afterwards was to check.

author: wraper
author_rank: Unknown
timestamp: October 09, 2023, 04:32:46 pm
content: Quote from: Bloodred on October 09, 2023, 03:53:05 pmIf monitor had only 2 prong plug and no earth connection, then this had nothing to do with UPS at all. As of UPS itself, as long as mains socket is earthed, it won't be able to put any potential on earth wire. Not to say people complaining about half of mains voltage on enclosure/connectors is very common. And most of the time it's just double insulated devices working as intended or lack of earth connection in the socked. As of claim that socket is properly earthed, house wiring done improperly is very common and you cannot be sure unless actually verify it. My previous apartment had no earth on like one third of the sockets due to electrician failing to properly insert wires into a few of the sockets so wires coming to next sockets in the chain had no earth either. My current house is better, buy I'm not thrilled about wiring quality either.

author: Bloodred
author_rank: Contributor
timestamp: October 09, 2023, 05:29:29 pm
content: I measured the voltage on the UPS's outlets, it had ~115V between earth and live and about ~90V between earth and neutral IIRC.I measured the same things at the wall outlet and I got ~230V between earth and live and I think 0-1V between earth and neutral there. I'm not an expert but I do not believe the measurements I got through the UPS are normal, while what I got at the wall outlet looked correct.Later I also bought one of those plug-in outlet testers and it indicated that the outlet was grounded correctly, while plugging it into the UPS indicated a fault. I did actually verify the outlet. I'm not just saying the outlet is grounded because I believe it is, I've verified it in all ways I knew how to verify and everything indicated that it was, in fact, grounded.As for the monitor, it has a grounded 3-pin power cable going into a plug pack which then connects to the monitor with a barrel jack. I assume the earth ground goes through to the barrel jack. Even if it doesn't, the monitor was connected to another PC on the same UPS both with a USB cable (it has a built-in hub) and with a DP cable, both of those are also grounded on the PC side as far as I know, so the monitor was almost certainly grounded.

author: bdunham7
author_rank: Super Contributor
timestamp: October 09, 2023, 05:47:06 pm
content: Quote from: Bloodred on October 09, 2023, 05:29:29 pmIn every design I'm aware of for a consumer or commercial UPS (I'm US-based, so consider that) the ground should be passed through uninterrupted. However, if you use a plug-in socket tester, it will indicate normal operation if the UPS is in the line mode (dormant) but in the off-line mode (active) it will show an open ground fault. This is not because the ground is open, but rather because the line and neutral are floating and no longer ground referenced. Nothing about this should cause the ground line itself from having any appreciable potential to actual earth under any circumstances, but theneutralmay float up in off-line operation whereas it would be tied closely to ground by the building wiring in the on-line mode. I've no idea what was going on in your case, but it isn't too hard to imagine a scenario where a floating neutral would result in voltage appearing where you don't want it--but not on the ground of course.So, did this problem occur (the shocking and the socket tester showing a fault) in the on-line or off-line mode?

author: Bloodred
author_rank: Contributor
timestamp: October 09, 2023, 07:02:38 pm
content: Both the shock and the tester showing a fault occurred with the UPS in line mode, so with completely normal mains AC available and the UPS plugged into an outlet which didnotshow any faults. I would haveassumedthat the earth ground is connected straight through as well, so I also found this very strange and like I said, I don't understand what was going on.

author: bdunham7
author_rank: Super Contributor
timestamp: October 09, 2023, 07:04:49 pm
content: Quote from: Bloodred on October 09, 2023, 07:02:38 pmThat's a fail, at least in systems I'm familiar with.

author: bdunham7
author_rank: Super Contributor
timestamp: October 09, 2023, 07:09:45 pm
content: Quote from: wraper on October 09, 2023, 09:31:51 amI love APC mid-sized (1-1.5kVA) LF sine-wave units because I can buy them dirt cheap and fix their flaws. Those super-low-ESR capacitors don't really seem to be an issue, but they do blow up their batteries trying to meet their specs. If I'd paid the full price for a new one, I'd be less thrilled. Still, I have a small army of various-sized APC UPS units that are 10-25 years old and still going. I haven't looked at their newer stuff but I'd guess that they are worse.

author: Bloodred
author_rank: Contributor
timestamp: October 09, 2023, 07:21:50 pm
content: Quote from: bdunham7 on October 09, 2023, 07:04:49 pmYup, my thoughts exactly.

author: MrAl
author_rank: Super Contributor
timestamp: October 10, 2023, 11:10:18 am
content: Quote from: Bloodred on October 08, 2023, 04:04:38 pmHello there,I can offer a few notes here.First, using a transformer to measure the output of the UPS and line voltage is not a bad idea, i've used that myself. The drawback is that it will eat some of the harmonics, if present.What else you could do, if your scope is free floating, is use a voltage divider. I guess you have a 230vac line where you are? If so, and your scope can only handle 50vac max, then you need to divide down by at least 5 times. Going down by 10 times is also a good idea though. That means an upper resistor of 9x and a lower resistor of 1x. That means if you use 10k for the lower resistor then you need to use 9 times that, 90k, for the upper resistor of the voltage divider. Because the voltage is so high (230vac) you will need to use 1 watt resistors however, 2 watt even better. You can use 180k for the upper resistor and 20k for the lower resistor and then you can get away with using 1/2 watt resistors.You do have to make absolutely sure your scope is not grounded however, because if it is something will blow, unless the lower resistor lower terminal is connected to ground and the scope ground is connected to the lower resistor terminal, but you have to test for that before you proceed.The best test of course is to use something in the actual application. You should run one computer for a couple weeks and see how it goes. You can then move to two computers, then three, etc.Just a couple of things you may want to try.Although power supplies are some of the simplest circuits in pure theory, in practice they are some of the most complex and important.

author: Bloodred
author_rank: Contributor
timestamp: October 10, 2023, 03:33:02 pm
content: Yeah, I get 230VAC here. The oscilloscope claims it's isolated and that it can take 400V peak to peak with 10x probes, so it can actually take 40V peak to peak. There is no continuity from the USB GND to the GND on the probes so itlooksisolated, but it's still effectively some cheap Chinesium so I can't say I quite trust it, especially with potentially lethal voltages.I know about voltage dividers, I went with the transformer because I had it on-hand (I'd have to order / buy appropriate resistors and wait for them to arrive) and honestly I didn't want to play with high voltage. We use Schuko plugs here and if you don't know those are also reversible, so there's no guarantee which one of the conductors is live and which is neutral, even if I made a voltage divider with the intention of measuring between neutral and the mid-point I could easily make a mistake and plug it in the other way, thus turning the assumed "neutral" into the live 230V. I'm not even sure whether all outlets are wired the same. I don't play around with high voltage much, so I just went for the safe option with the transformer.I will be running some more tests with real loads (computers), especially since I need to wrestle NUT (Linux UPS management tool) into obedience to make sure automatic shutdown works correctly across all my systems.

author: MrAl
author_rank: Super Contributor
timestamp: October 12, 2023, 12:30:16 pm
content: Quote from: Bloodred on October 10, 2023, 03:33:02 pmHello again,There are tests you can do to verify what will work and what will blow up. If you have a ground connection you can check which side is the neutral regardless how the outlet is wired, but it sounds like this could be a bit iffy too so maybe you should just go with what works unless you find a better way.There is a pretty much guaranteed way to do this but you need a scope that runs on batteries. You simply just do not plug it in with the charger. There are many scopes out there now that have rechargeable batteries so you can be sure they are not connected to the line voltage, either live or even the neutral wire. That may be the only way to be absolutely sure that nothing goes wrong. After all, one mistake could be very costly.I purchased an OWON scope recently and although it's not the best scope in the world, actually far from that, it works good enough for many tests under about 20MHz. It's fully isolated though because it runs on rechargeable batteries. I could also plug in the charger because it's fully isolated, but I don't even do that because any tests I do do not take very long to peform so it only needs a little battery power finish that.

author: alligatorblues
author_rank: Regular Contributor
timestamp: October 12, 2023, 03:51:14 pm
content: Quote from: BeBuLamar on October 09, 2023, 10:35:32 amUPSs require a groound for reference. You can't just unplug them. As far as the fans making noise, I've never heard mine..

author: Bloodred
author_rank: Contributor
timestamp: October 18, 2023, 06:28:44 pm
content: Quote from: MrAl on October 12, 2023, 12:30:16 pmOh, yeah that would've been a good idea. The scope is USB powered and I have a tablet I could've plugged it into thus making the whole contraption battery powered, that would've worked if I had bought some appropriate resistors to make a divider. Well, using the transformer also got the job done in the end I suppose.