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
> 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!
> The UPS consumes almost nothing when AC is on, so that can't be that.
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)
> 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)
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.
If built correctly this design also suffers no transition transients. You can switch the external power off/on all day and downstream equipment will never see a glitch.
As far as I know the more expensive UPS models are all still "online" (ie. double conversion) UPS'es.
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.
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.
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
I toyed with this too, but I guess I have a slightly more diverse set of devices than you do. A few more weird voltages, and some things that expect mains. I looked into finding a DC version of their power supplies (e.g. the pico-box X9-ATX-500 to replace a conventional ATX PSU, tracking down DC versions of network switch hot-swappable PSUs from eBay) but decided it wasn't worth it. I just bought a stock LifePO4 power station. I found that I got most of the benefit [edit: measured in terms of runtime after power outage, not power draw while input power was available] just from switching to LifePO4 rather than from avoiding DC->AC->DC, and it was cheap and easy.
I have thrown out my Tripplite UPS because its battery has degraded to the unusable levels. I replaced it with a 5kWh LiFePo4 rack-mounted battery and an AIMS rack-mounted inverter. I'm really surprised that there are no off-the-shelf solutions for this. The traditional UPS makers are just neglecting the recent 10 years of battery advances.
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.
> 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.
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.
> 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.
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!)
> 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.
They should have spent $300 on a differential probe.
The higher end scopes can have some nice power analysis packages.
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.
My furnace is protected by an old school fast-acting fuse. One day it blew and at first I thought it was an anachronism from the house's original wiring but then realized it's intentional / the standard breaker upstream of it is not fast enough. Not clear if it mainly protects the blower fan motor or the circuit board - I suspect it's the motor. At least one other fan motor in the house got fried previously.
The quality of your power is determined mainly by the age and quality of the transformer serving your neighborhood as well as the presence of noisy heavy power equipment like AC with poor startup dampers anywhere else among the consumers. It's noticeably worse on our street compared to where we previously lived.
I discovered the same thing a few months ago with my home's furnace (which was a bit of a shock, because one reason for picking natural gas is so you can still have heat when the power is out). It runs just fine on a pure sine wave inverter though.
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.
Audio amplifiers can be strongly affected by noisy waveforms.
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.
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.
‘It lets the smoke out’ is a classic, and happens periodically. Bad waveforms cause weird heating issues, (literal) audio noise, and sometimes sporadic stability issues with computers.
It typically shows up ‘randomly’ unless you know how to attribute it.
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.
Yes and no. 0% you should be fine, but generally speaking you'll get longer life out of LifePO4 if you stay between 10% and 80%. Most battery based PV systems are installed to shut off (or switch to grid) at the 10% SOC mark for this reason.
This is my issue with LiPo whatever flavor where they tell you it has a "runtime" of X minutes, yet you are strongly advised to only use 70%-80% of that value. It's worse than hard drives using 1000 vs 1024.
I've found the difference in capacity between similarly-priced units with similar power rating is hour+ (LifePO4 power station) vs not advertised but actually just minutes (lead acid UPS). And the LifePO4 gives you the choice to cut off above 0% or not, where the lead acid unit doesn't give you any control. So you can trade off 30% of your capacity for increased longevity if you choose and still come out way way ahead on runtime. Or you can not and still have much better battery longevity than lead acid.
The rationale I've heard to justify lead acid battery 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.
I have most certainly used 100% of the runtime. So you're more than welcome to do so as well, you might just have to replace it in 8 years instead of 10. YMMV.
Could be worse - could be lead acid and weigh 2x as much and you only get half the Ah.
Yes, thousands of times, an order of magnitude improvement over lead acid. And the increased capacity means that they're much less likely to hit 0% (or whatever defined cut-off you set) during a typical outage anyway.
> The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. 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.
> 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period.
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...
Please just buy a pair of mains voltage diff probes. They're not expensive (around $500 each new, much less used) and they will eliminate the crazy connection scheme and give you true input -> output fidelity.
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.
Great to see LTT in this space, you're well positioned for it (access to a variety of hardware.) Would love to see a more developed experiment design.
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?
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.
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.
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.
There's not much to standardize, basically just pick a plug shape for your desired voltage and current, it's really about building enough desire for manufacturers to take interest.
Issue is mostly lack of standard dc power distribution standards - outside of old telco ones anyway.
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.
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)
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.
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.
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 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.
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.
> 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.
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...
The quality of your power is determined mainly by the age and quality of the transformer serving your neighborhood as well as the presence of noisy heavy power equipment like AC with poor startup dampers anywhere else among the consumers. It's noticeably worse on our street compared to where we previously lived.
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.
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.
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 lead acid battery 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?
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.
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.