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Testing UPS Output Waveforms

lttlabs.com

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Re: Testing UPS Output Waveforms

#11

Post by hex4def6 »

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!)

Re: Testing UPS Output Waveforms

#12

Post by LeifCarrotson »

scottlamb wrote: post #10

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…

The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle.

20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. 10 milliseconds just over half a cycle.

Re: Testing UPS Output Waveforms

#13

Post by scottlamb »

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 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.

Re: Testing UPS Output Waveforms

#14

Post by Dylan16807 »

zokier wrote: post #3

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.

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

Re: Testing UPS Output Waveforms

#15

Post by nomel »

scottlamb wrote: post #13
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 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 powe…

If you get your battery pack up to 48VDC, it opens up a whole world of low voltage power converters, since this is standard in telecom/PoE.

Re: Testing UPS Output Waveforms

#16

Post by scottlamb »

LeifCarrotson wrote: post #12
scottlamb wrote: post #10

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…

The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle. 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. 10 milliseconds just over half a cycle.

> 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...

I haven't dug through the spec itself.

Re: Testing UPS Output Waveforms

#17

Post by markus92 »

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.

Capacitive touch screens when plugged in with cheap chargers to crappy waveforms, behave weird.

Re: Testing UPS Output Waveforms

#18

Post by dylan604 »

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

Evidence is the heat from that conversion

Re: Testing UPS Output Waveforms

#19

Post by dylan604 »

scottlamb wrote: post #10

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…

Can these LifePO4 batteries be safely drained to 0% and then charged numerous times?

Re: Testing UPS Output Waveforms

#20

Post by Aurornis »

LeifCarrotson wrote: post #12
scottlamb wrote: post #10

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…

The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle. 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. 10 milliseconds just over half a cycle.

> 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.

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