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.
> 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.
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.
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
I've been looking at Victron gear for an off-grid power system up north (initially for a caravan, will get migrated across to a house once the upgrading and repairing is done).
A huge decision on that was that they publish a fat PDF with the full spec of the serial data they emit and can be programmed with, and a service sheet to allow a suitably skilled engineer to fully bench test them if there are any perceived problems.
They're not cheap, but my late father always used to say he didn't have enough money to buy cheap tools.
Edit: handy hint too - many cheap crappy power bricks will work down to 90V and will work just as well off DC as well as AC because the very first thing they do is rectify and smooth the incoming supply.
I do not recommend having 90V DC kicking around unless everyone involved knows what they're getting into.
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.
> 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.
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.
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[ 3.0 ms ] story [ 31.0 ms ] thread> 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.
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.
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
A huge decision on that was that they publish a fat PDF with the full spec of the serial data they emit and can be programmed with, and a service sheet to allow a suitably skilled engineer to fully bench test them if there are any perceived problems.
They're not cheap, but my late father always used to say he didn't have enough money to buy cheap tools.
Edit: handy hint too - many cheap crappy power bricks will work down to 90V and will work just as well off DC as well as AC because the very first thing they do is rectify and smooth the incoming supply.
I do not recommend having 90V DC kicking around unless everyone involved knows what they're getting into.
* 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.
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.
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.