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Testing UPS Output Waveforms

65 points by LabsLucas

by chimpontherun

9 subcomments

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 converters work great.
Result: threw away 3 UPSes (different APC models). Overall power consumption with AC present dropped by about 40%. Time on batteries (same Wh battery capacity) increased by a factor of about 20 (yes, 20 times: that's not a typo). Evidently, AC waveform generation is extremely power-hungry

by Aurornis

1 subcomments

> 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.

by teraflop

2 subcomments

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 a floating source.
This too seems to be a pretty expensive piece of gear (the price I found with a quick Google was >$28,000) so I think it's worth mentioning that the same job could be done with an isolation transformer, which costs maybe a couple hundred bucks.

by xenadu02

1 subcomments

For some time I've been curious why none of the major UPS manufacturers offer LiFePO4 UPS units. They'd be smaller, lighter, and have a longer run time all else equal (dramatically lower shipping charges). Batteries wouldn't need replacing nearly as often.
Yet as far as I can tell none of them offer anything in this area except at the extremely high end. Even Ubiquiti's UPS offerings are garbage simulated sine wave with lead acid batteries.
Are UPSes such a niche product there's no money in it? Are they really content to just give up the whole "power station" market to upstart competitors?
Even aviation jump packs (that connect to aircraft ground power ports) offer lithium versions and that's an industry that moves like sloths toward new technology!

by mbesto

8 subcomments

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.

by scottlamb

2 subcomments

I would be curious to see how LifePO4 power stations compare.
* These power stations are better than conventional (lead-acid battery) UPSs in the sense that they're cheaper, more flexible, have dramatically longer battery life, and require battery replacement less often.
* ...but I haven't seen any that claim to be "line-interactive" or even say specifically when they fail over (other than a total power cut). They do talk about how long it takes to fail over: older models are >20ms (long enough that your machine will probably reboot); many newer ones are <10ms. I'm not sure how high-quality their sine wave is when on battery.

by LabsLucas

4 subcomments

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

by zokier

3 subcomments

its a shame that we don't have mainstream dc ups standards (telcos are their own niche). its kinda silly to generate fancy sinewave, manage transitions, and maintain phase of ac just to get immediately converted to dc.

by dreamcompiler

2 subcomments

The crossover distortion seen here suggests an analog Class-B output stage and that surprises me, because a digital output stage would be much more efficient. Class-D in other words. I've built digital inverters using IGBTs that produced an output sinusoidal power wave with lower distortion than the mains power. Granted these were one-offs and probably not cheap enough for production, but modern IGBTs and MOSFETS should be cheap enough nowadays that medium-priced UPSes could just use Class-D as the default solution.
Assuming you really need a sinewave at the output at all. DC output UPSes are the most efficient way to go if you can bypass the switched-mode power supply at the input of your equipment. Which most equipment has these days unless AC motors are involved.