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
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!
Back in the 1990s, one could buy a "double conversion" UPS that converted AC to DC then back to AC, at all times. This was, supposedly, the best type of UPS (in my experience they were also the least reliable)
These are also the only variants which will protect you against things like a phase ending up on neutral in a 3 phase power system. I've seen this happen twice. Fried a lot of equipment.
They are "best" in the sense that your output is completely decoupled from your input so you got the most protection from any electrical noise. The trade-off is lower efficiency (AC-DC-AC roundtrip) and more battery wear (it's constantly 'in use').
Any >10kVA UPS is probably double-conversion/online.
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.
The only thing to be careful with is connecting different voltages to different connectors, but it's at least possible with the APP connectors to "Build your own" with different color housings and different ways of combining the housings.
So maybe 13.8v is red/black and something that's 5V is black/white, etc.
Yes, it's quite ugly. Open up one of these things and you'll find a big block of four transistors (if not more due to doubling up) on a big heatsink. That's the inverter drive bridge, and it's probably the single largest source of heat in the whole thing. It's not hard to find.
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
Evidence is the heat from that conversion
I even made an Arduino-based module that provides an SNMP UPS interface for my Synology NAS. It works surprisingly well and has almost 12 hours of autonomy compared to barely 2 hours for the much heavier lead-acid battery.
One trick that I'm kinda proud of: I powered my server directly from the 96V DC. And I periodically switch the current direction using a DPDT relay to avoid wearing out one side of the rectifier inside the PSU.
If you are seriously worried about this then the whole thing is trash. Either the design is marginal or it is not. You cannot possibly switch a relay fast enough to make a difference here (and have the relay survive).
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.
For about $300 you can buy a Tiepie differential usb scope: https://www.tiepie.com/en/usb-oscilloscope/handyprobe-hp3
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.
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!
> 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.
It really cannot -- the isolation transformer doesn't have control of its output, so it can't start or stop cleanly, and it can't ramp voltage cleanly. (An autotransformer kind of can, but it's still not really good enough.) The AC source can stop on a dime, with no inductance of its own, so it is the correct way to do this test.
Source: I have had to do this and refused to use the autotransformer anymore because it was just too much of a pain in the butt. (We rented the AC source.)
For such low frequency stuff, it feels way safer to just buy a cheap <$500 scope for this kind of work. Using a $50k scope when it's not needed just seems needlessly risky.
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!)
They should have spent $300 on a differential probe.
The higher end scopes can have some nice power analysis packages.
https://rvelectricity.substack.com/p/diy-generator-bonding-p...
I think the quality of your power is determined mainly by the size of the transformer serving your neighborhood as well as the presence of noisy heavy power equipment like AC with poor/no soft starters or big brush motors among the consumers. It's noticeably worse on our street compared to where we previously lived.
But, certainly, garbage devices are all over the place.
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.
Class D amplifiers and other topologies that depend upon SMPS for power delivery are usually unaffected. Class A/B is where you will typically hear it.
It typically shows up ‘randomly’ unless you know how to attribute it.
* 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.
The rationale I've heard to justify conventional UPSs not even trying to compete on runtime is that they're just for giving you a few minutes to cleanly shut down your crap software that isn't crash-safe and/or for your auto-start generator to start up. But what I actually want is to keep working for an hour+ after the power goes out without owning/installing/maintaining a generator.
Could be worse - could be lead acid and weigh 2x as much and you only get half the Ah.
20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. 10 milliseconds just over half a cycle.
They do not. You must be thinking of very old power supply technology with a simple bridge rectifier in front of some capacitors.
Switch mode power supplies with power factor correction spread the current draw across the cycle to keep the power factor high. They are drawing power from the line for most of the cycle. There is not a 8.3ms interruption.
> 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. 10 milliseconds just over half a cycle
The ATX 3.1 power supply standard only requires 12ms of hold up time.
I've read that the newest PSUs are only guaranteed to last 12ms. Of course they may last much longer, especially if running near idle, but I'd prefer something that works well with any compliant device.
Here's one source: "Measured in milliseconds, hold-up time indicates how long a PSU can sustain its output within specified voltage limits after a loss or drop in input power. ATX 3.1 features a shorter hold-up time of 12ms, compared to ATX 3.0's 17ms hold-up time. This results in a small improvement in the PSU's efficiency." https://www.corsair.com/us/en/explorer/diy-builder/power-sup...
I haven't dug through the spec itself.
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.
Would love to see how the waveform changes over load -- perhaps test at 0, 10, 20, 40, 80% load.
Also, how does waveform vary as the battery depletes?
Another metric is how capacity varies with load. If a UPS gives me 1 hour @ 100w, will it give me 10 hours @ 10w? How long will it power an idling rpi5 (<1w)? How long will it give my workstation PC?
It's worth noting that there's already ATX power supplies that are built to run directly off battery power. They don't look all that impressive but they exist. https://www.powerstream.com/DC_PC.htm https://synoceantech.com/index.php?page=lotinfo&lot=36
It’s cheap and easy (relatively) to transform AC voltages, and hence to manage AC power distribution. DC is trickier, and voltage switching is relatively more expensive and flakier. Hence why DC distribution tends to be within a device/controlled setup.
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.
No, they're not Class B. It's all digital PWM stuff inside. But the duty cycle gets tiny near zero cross, there's very little power in the waveform there, and there's overhead to have a switching device on at all (this is much more noticeable for IGBTs).
So it ends up being a massive simplification to just not care about that section. And it's a simplification that works pretty great, so people do it!
We had to get this truly right in the inverter I mentioned in sibling comment (as it wasn't a grid-feed or backup inverter, it was doing Something Else™ *) and just that piece was actually way harder than the entire rest of the waveform output design.
* hopefully NDA-OK spoiler: let's just say I know way, way more than I'd like to about what's inside that Chroma 61507 mentioned in the article.
We did a "big" inverter design a while back (500 VA was big for us; perhaps not for you). The guy who did the concept architecture suggested a PSFB design. He then quit to take a a great offer from a startup. Not really being a power electronics team, we hired a specialist consultant. The first consultant did... honestly, I don't know what he did. But it was weird. (This was a problem.) It wasn't a PSFB anymore. It also didn't work. The design then went through five more lead engineers and two more consultants, plus one more if you count me on the side watching and occasionally pitching in (I was the sister subsystem lead). It ended up being a full digitally programmable bridge and we had to figure out how to switch it. Guess how it ended up working?
Phase-shifted full bridge. Just like the first guy (and I!) said it should have been all along!