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Testing UPS Output Waveforms

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Re: Testing UPS Output Waveforms

#91

Post by rdbl27 »

scottlamb wrote: post #50
Aurornis wrote: post #38

Earlier quoted context omitted.

This is called an online UPS and it's still a thing. It's not a good option for home use because it's always sending power through an inefficient path. The devices we use have power supplies that can handle transients and fluctuations.

Where is it a good option? I'd expect datacenters to be more focused on efficiency, not less.

Datacenters are focused on "never letting the equipment go down for any reason."

If they can do that efficiently, that's great.

If they have to choose between efficiency and outage risk, they always drop efficiency. That's why they use exclusively online UPS.

Re: Testing UPS Output Waveforms

#92

Post by scottlamb »

rdbl27 wrote: post #91
scottlamb wrote: post #50

Earlier quoted context omitted.

Where is it a good option? I'd expect datacenters to be more focused on efficiency, not less.

Datacenters are focused on "never letting the equipment go down for any reason." If they can do that efficiently, that's great. If they have to choose between efficiency and outage risk, they always drop efficiency. That's why they use exclusively online UPS.

> Datacenters are focused on "never letting the equipment go down for any reason."

Disagree. I'm most familiar with Google. For a long time at least their UPSs were built in to each machine and not super reliable. They built entire datacenters without cooling with the understanding that for a few days a year it may be too hot for human access. The reliability is from failing over to other equipment—machine, cluster, even region.

Small/on-prem/co-location datacenters may make totally different choices, but I think the major cloud/AI providers would be similar to Google in this respect.

The sibling comment about other industries was enlightening to me though.

Re: Testing UPS Output Waveforms

#93

Post by SigmundA »

labcomputer wrote: post #89
SigmundA wrote: post #64

Earlier quoted context omitted.

I understand what a differential probe does, what I don't understand is why they are so expensive. Again one can get a whole USB differential scope for the same price or less. Seems like just a differential probe should be relatively inexpensive well under a $100. The Tiepie software actually works very well even though it's Windows only, they do have Linux library, just no GUI on Linux. Its not single purpose its a…

The thing you posted isn't the same thing as a differential probe. It's a single input low bandwidth scope that floats at the common mode voltage, with an optically-isolated data output. Now, let's say you want to probe two things at the same time (triggered by a common signal source). You can't. And the reason you can't is because the producer took the expedient of floating the entire scope, and there's no trigger i…

>Now, let's say you want to probe two things at the same time (triggered by a common signal source). You can't. And the reason you can't is because the producer took the expedient of floating the entire scope, and there's no trigger input.

Yes this is very inexpensive single input scope, they make more expensive multi input scopes you can stack as many as you want and have them synced:

https://www.tiepie.com/en/usb-oscilloscope/handyscope-hs6-di...

The difference in price between their single ended and differential scope is not the much so it seems the actual differential part is not the expensive part, back to my original point.

>Related to that, this thing doesn't appear to have a step attenuator, which is why the effective resolution depends on the volts/div setting of the input.

They sell differential step attenuators: https://www.tiepie.com/en/usb-oscilloscope/accessories/diffe...

>Also, they don't specify the CMRR, which is one the main figures of merit people look for on differential probes.

CMMR 60db from thier spec sheet: https://download.tiepie.com/Documents/Datasheets/Datasheet-H...

>This is not to say the product you linked shouldn't or can't be used for anything, but it is a niche product. That's probably why it is advertised as a "power quality monitor" and not an "oscilloscope".

From their spec page: "The tables below show detailed specifications of the Handyscope TP450 high voltage oscilloscope."

and

"The Handyscope TP450 is delivered with the versatile Multi Channel oscilloscope software, which transforms the Handyscope TP450 into an oscilloscope, spectrum analyzer, data logger, multimeter and protocol analyzer."

They make quite a few differential scopes, that just happens to be a inexpensive one physically deigned for power quality analysis.

Re: Testing UPS Output Waveforms

#94

Post by Dylan16807 »

cwillu wrote: post #87
Dylan16807 wrote: post #67

Earlier quoted context omitted.

> If you get dips in voltage below the range that the PSU can handle, it will kill the PSU. How does that happen? Let's say it's running and I drop the input to 80 volts. Why do I get any behavior that isn't "runs at reduced capacity" or "shuts off"? And what part of the circuit is failing? Are we assuming a combination of missing current limiting and a heavy load? If I'm just watching youtube then it shouldn't overl…

Low voltage requires higher current to maintain a given output power.

Yeah but that's what the shutoffs are for.

Re: Testing UPS Output Waveforms

#95

Post by SigmundA »

Aurornis wrote: post #65
SigmundA wrote: post #64

Earlier quoted context omitted.

I understand what a differential probe does, what I don't understand is why they are so expensive. Again one can get a whole USB differential scope for the same price or less. Seems like just a differential probe should be relatively inexpensive well under a $100. The Tiepie software actually works very well even though it's Windows only, they do have Linux library, just no GUI on Linux. Its not single purpose its a…

A good differential probe has to use precision components combined with careful factory trimming and calibration to get good common mode rejection ratio. The CMRR of the Micsig I linked is pretty average, but it's a lot better than the TiePie at low frequencies. Micsig also specifies it at multiple points across the spectrum, while TiePie doesn't even say where they measured it. It's all the differences like this tha…

>The CMRR of the Micsig I linked is pretty average, but it's a lot better than the TiePie at low frequencies. Micsig also specifies it at multiple points across the spectrum, while TiePie doesn't even say where they measured it.

It worse at high frequencies and the same in the middle. Again this is a whole scope compared to a probe.

Not sure why you think Tiepies are toys, they are use professionally in Europe, popular for automotive. They have a lot more expensive scopes, and the price difference for the differential versions are not that much.

Re: Testing UPS Output Waveforms

#97

Post by quickthrowman »

mbesto wrote: post #6

Curious - what actual real life issues do real world people encounter with dirty AC waves? Like I always hear the proverbial "this could cause harm to electronics" but are there real world tests of electronics failing? Does it fail over time or because of a one time instance? Same thing with under/over voltage.

I had a weird situation with a 480V three-phase 250kW generator, it passed an 80% load bank test (the load is resistive heat) with flying colors, almost rock solid 60 hz frequency with smooth operation.

This generator is meant to back up a 400A electrical service that runs a 480V 200 HP three-phase water pump motor, which draws ~225A and is controlled by a VFD. This pump motor and drive run just fine on utility power, but when utility power was cut to let the generator drive the pump, the generator output frequency started jumping between 57-63 hz and a manometer placed on the generator showed the gas pressure fluctuating wildly.

Now, a 480V 250kW generator puts out (250000/480/1.732)=300.712 amps, which should be more than enough to run the pump. I asked the generator manufacturer what size generator they would recommend for this 200 HP pump, and they said for a basic 6-pulse VFD, it would need a 350kW generator with a 600kW alternator, but the existing generator could be used if a harmonic filter was added to the variable frequency drive.

I don’t really understand exactly what the issue was, but something with impedance and harmonics that could be corrected with a harmonic filter, and once that harmonic filter was added, the generator was able to run the water pump just fine.

Re: Testing UPS Output Waveforms

#98

Post by butvacuum »

tredre3 wrote: post #28
chimpontherun wrote: post #9

I've noticed that ALL the devices I plug into my UPSes have external power bricks. Most of them are either 5V, 12V, or 19V So, I replaced all my UPSes with LiFePO4 batteries supplied by Victron AC->12V chargers. Routed the battery contacts directly to all devices that consume 12V (WiFi AP, network hubs, SLA 3d printers). Used 12V -> 5V adapters to supply 5V / USB2 devices (R-Pi servers). For 19V, Drok DC-DC boost con…

> Evidently, AC waveform generation is extremely power-hungry I've tested a dozen models from APC. The inverter used in those devices uses roughly 15-20W with no load. Then for any load they have about 85% efficiency. Then you have further losses into any PSU connected there because they tolerate square waves but aren't optimized for it. So yes, in the end, less than 40% of the battery capacity in cheaper UPSes is ac…

it's even worse: SLA's can only discharge to ~half their nameplate capacity or so- and if you're pulling tons of amps, it's even less. LiFePo4 otoh you'll get the nameplate capacity.

Then theres trivialities like LFP's voltage being higher so there's less resistive losses, etc

Re: Testing UPS Output Waveforms

#99

Post by garaetjjte »

mikeyouse wrote: post #35
mbesto wrote: post #6

Curious - what actual real life issues do real world people encounter with dirty AC waves? Like I always hear the proverbial "this could cause harm to electronics" but are there real world tests of electronics failing? Does it fail over time or because of a one time instance? Same thing with under/over voltage.

Modern furnaces are weirdly sensitive to ‘clean’ AC power. Mine won’t work on bad non-inverter backup generators and interestingly to me, doesn’t work on non-bonded (ground-neutral) power from an inverter generator. Had to chop the cord off a drill and build a bonding plug last winter when I finally figured out why it wouldn’t run. https://rvelectricity.substack.com/p/diy-generator-bonding-p...

Could it be that it directly uses AC for flame rectification and gets confused with ugly waveform?

Re: Testing UPS Output Waveforms

#100

Post by cyberax »

exmadscientist wrote: post #73
cyberax wrote: post #71

Earlier quoted context omitted.

I'm worried about long-term thermal wear from uneven heating, so I switch the current direction once a day. Simply because that's the maximum time I can set on a time delay relay that controls it.

Don't bother. That's not how these things fail, and one day is so so far beyond the thermal time constants involved that it's not doing anything useful. You would have to switch on timescales of seconds to minutes to do anything meaningful, and that would kill your relay in short order. If you are truly close to the design failure point of the rectifier, it's not safe to run at all. (You are almost certainly not.) If…

I removed it to see what happens :)

The reason I added it in the first place is because I've seen failures from uneven PCB heating. It's not the components themselves fail, but radiators get unglued and PCBs can get damaged.

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