Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Testing UPS Output Waveforms

lttlabs.com

Post reply on HN
Print view View original

21–30 of 102 posts

Re: Testing UPS Output Waveforms

#21

Post by Aurornis »

> This can be done safely with high voltage differential probes like the R&SRT-ZHD, but we don't have any.

Entry level differential probes are $300. Less if you shop around or buy used. Micsig makes a good starter probe that would be more than enough for 60Hz AC mains testing and it comes in a generic form that would have worked with this scope.

A lot of things can go wrong, some dangerously so, if you incorrectly probe high voltage lines.

I don't know why they got such an expensive oscilloscope and then proceed to cheap out on the most basic tools needed to use it properly.

Re: Testing UPS Output Waveforms

#22

Post by Aurornis »

hex4def6 wrote: post #11
teraflop wrote: post #4

Cool graphs. > Our previous reticence to measure UPSs was centered around the connection of our very nice $50,000 Rohde & Schwarz MXO58 oscilloscope directly to mains power. [...] What we do have is a Chroma 61507, a programmable AC power source, capable of generating its own isolated Alternating Current(AC) signal. The AC signal created by the Chroma 61507 is galvanically isolated from the "earth"/ground, providing…

Agreed. For such low frequency stuff, it feels way safer to just buy a cheap Also, float the DUT, not the scope... Sometimes that's not possible, and the temptation is there, but it's really not worth it. Just buy the right gear like a diff probe. You can get one for a few hundred bucks if you don't mind going downmarket. You can also use two probes and do CH2 - CH1. (Disconnect the GND clips!)

> For such low frequency stuff, it feels way safer to just buy a cheap They should have spent $300 on a differential probe.

The higher end scopes can have some nice power analysis packages.

Re: Testing UPS Output Waveforms

#23

Post by Aurornis »

LabsLucas wrote: post #2

Testing the output of some UPSs from around the office. Checking out the results and finding avenues for further exploration.

Please spend $300 on a differential probe https://www.micsig.com/DPA/

I hope nobody sees this article and tries to replicate the experiments as presented. You can get away with it when everything goes correctly, but a diff probe is good insurance.

Re: Testing UPS Output Waveforms

#24

Post by SigmundA »

Aurornis wrote: post #21

> This can be done safely with high voltage differential probes like the R&SRT-ZHD, but we don't have any. Entry level differential probes are $300. Less if you shop around or buy used. Micsig makes a good starter probe that would be more than enough for 60Hz AC mains testing and it comes in a generic form that would have worked with this scope. A lot of things can go wrong, some dangerously so, if you incorrectly pr…

Why are differential probes so expensive and why don't more scopes just have differential port built in?

For about $300 you can buy a Tiepie differential usb scope: https://www.tiepie.com/en/usb-oscilloscope/handyprobe-hp3

Re: Testing UPS Output Waveforms

#25

Post by dylan604 »

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.

If you get dips in voltage below the range that the PSU can handle, it will kill the PSU. If you get spikes higher than the range that the PSU can handle, it can kill not only the PSU but things attached to the PSU as well. Most people are familiar with spikes with things like surge protectors, but most are unaware of how damaging voltage dips can be as well.

Re: Testing UPS Output Waveforms

#26

Post by zorgmonkey »

LabsLucas wrote: post #2

Testing the output of some UPSs from around the office. Checking out the results and finding avenues for further exploration.

Please just buy a proper differential probe for stuff like this, you definitely don't need the R&SRT-ZHD mentioned in the article. Otherwise loved the article btw.

Re: Testing UPS Output Waveforms

#27

Post by toast0 »

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.

over voltage (beyond reasonable tolerances) has a tendency to let the smoke out of components directly.

under voltage can do lots of things. Browning out with partial functionality can cause lots of problems. Some devices will pull about the same watts regardless of input voltage, so lower voltage means more current, and significant under voltage may require much higher than rated current and can damage connectors, leading to thermal runaway (loosened connector has more resistance -> more current -> more heat -> connector loosens). Brown outs during control sequences can lead to controlled loads running for longer than intended and over current situations too.

Re: Testing UPS Output Waveforms

#28

Post by tredre3 »

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 actually usable.

The reason you're seeing 20x is because obviously you've also greatly increased your battery capacity (typical under-the-desk APC units have 70-150Wh capacity, less than half of which is usable as explained above).

> Overall power consumption with AC present dropped by about 40%.

I'm finding that part harder to understand. The UPS consumes almost nothing when AC is on, so that can't be that. You've replaced multiple PSUs by more efficient, bigger ones, sure that can explain part of your improvement. But 40% drop is wild!

Re: Testing UPS Output Waveforms

#29

Post by Aurornis »

SigmundA wrote: post #24
Aurornis wrote: post #21

> This can be done safely with high voltage differential probes like the R&SRT-ZHD, but we don't have any. Entry level differential probes are $300. Less if you shop around or buy used. Micsig makes a good starter probe that would be more than enough for 60Hz AC mains testing and it comes in a generic form that would have worked with this scope. A lot of things can go wrong, some dangerously so, if you incorrectly pr…

Why are differential probes so expensive and why don't more scopes just have differential port built in? For about $300 you can buy a Tiepie differential usb scope: https://www.tiepie.com/en/usb-oscilloscope/handyprobe-hp3

You can create a pseudo-differential input by combining two input channels on almost every scope. That's not the problem the differential probe is solving, though. The differential probe exists to provide a differential measurement between two voltages that may be isolated or significantly different than the ground voltage of your oscilloscope.

The ground lead on your probes is connected straight to the ground on the power cable. This gets new users in trouble when they're probing power circuits and they don't realize that connecting the ground part of the probe to something will cause a short to ground. If that ground clip pops off and brushes against the high voltage you're trying to probe, you get sparks and maybe a destroyed scope.

The differential probe provides isolation and rejects the common-mode (shared) voltage between the two probe points before it gets to the oscilloscope.

I don't know about that USB probe, but I prefer not to have single-purpose instruments that require their own desktop software to use.

Re: Testing UPS Output Waveforms

#30

Post by aspbee555 »

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…

I did something similar but made the batteries and solar priority, solar charges battery and wall power only used to top off as needed, otherwise always running on batteries

The Drok DC-DC did not work for my minipc that needed 19V/130W supply (would cut off with heavy draw), but the JacobsParts LTC3780 130W has been running my minipc's for almost a year now, gaming minipc, server minipc and networking

before that the solar panels barely charged the solix unit, but now my batteries fully charge and I still sometimes have left over solar I feed into the solix

Post reply on HN