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Testing UPS Output Waveforms

lttlabs.com

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Re: Testing UPS Output Waveforms

#41

Post by mbesto »

dylan604 wrote: post #19
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?

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.

Re: Testing UPS Output Waveforms

#42

Post by cyberax »

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.

You actually can run most ATX power adapters directly from 96V DC! You can get that by connecting two 48V batteries in series.

They do rectification as the first step anyway, and then they use high-frequency switching that works just fine with the DC current.

Re: Testing UPS Output Waveforms

#43

Post by cyberax »

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 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.

Re: Testing UPS Output Waveforms

#44

Post by throw0101c »

michaelt wrote: post #34
tredre3 wrote: post #28

Earlier quoted context omitted.

> 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 ac…

> 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.

Re: Testing UPS Output Waveforms

#45

Post by dreamcompiler »

throw0101c wrote: post #44
michaelt wrote: post #34

Earlier quoted context omitted.

> 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…

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.

Re: Testing UPS Output Waveforms

#46

Post by dreamcompiler »

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…

This is the way to go IMHO: Keep the outputs DC. Put a bunch of USB-C PD ports on the thing and you're good with a lot of modern equipment.

Re: Testing UPS Output Waveforms

#47

Post by ak217 »

mikeyouse wrote: post #35
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.

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. https://rvelectricity.substack.com/p/diy-generator-bonding-p...

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.

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.

Re: Testing UPS Output Waveforms

#48

Post by dreamcompiler »

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.

Re: Testing UPS Output Waveforms

#49

Post by dylan604 »

mbesto wrote: post #41
dylan604 wrote: post #19

Earlier quoted context omitted.

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

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.

Re: Testing UPS Output Waveforms

#50

Post by scottlamb »

Aurornis wrote: post #38
michaelt wrote: post #34

Earlier quoted context omitted.

> 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)

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.

Where is it a good option? I'd expect datacenters to be more focused on efficiency, not less.
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