4 ms·

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 th

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.

LeifCarrotson 5mo ago
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.
- scottlamb 5mo ago
  > 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-supply-units/atx-30-vs-atx-31-whats-the-difference/ https://www.corsair.com/us/en/explorer/diy-builder/power-sup... I haven't dug through the spec itself.
  - Dylan16807 5mo ago
    How is that supposed to improve efficiency? Also that change sucks, it's cutting the margins way too tight. At least I can be comforted that for my current power supply, the most recent version of it made for ATX 3.1 actually increased the hold-up time. So not all manufacturers are cutting that corner.
- Aurornis 5mo ago
  > 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.
- Dylan16807 5mo ago
  > The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle. It's not an 8ms interruption, it's 8ms between peaks. The part you could call an interruption is more like 2.5ms and even then it's not zero power draw. You need an order of magnitude more buffering to handle a 20ms dropout. > 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. Right, so think about that harder. A 60Hz sine wave has two wide periods of power and two narrow gaps. And 20 milliseconds is longer than that entire process combined.
dylan604 5mo ago
Can these LifePO4 batteries be safely drained to 0% and then charged numerous times?
- scottlamb 5mo ago
  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.
- mbesto 5mo ago
  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.
  - dylan604 5mo ago
    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.
    - mbesto 5mo ago
      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.
    - scottlamb 5mo ago
      I've found the difference in runtime between similarly-priced low-end units with similar power rating is hour+ (LifePO4 power station) vs not advertised but actually just minutes (lead acid UPS). And you can spend a bit more on the LifePO4 power station and get a proportional increase in runtime and power, vs. the lead acid UPS where the cost would quickly become prohibitive. And the LifePO4 power station 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. You can choose a spot on a Pareto frontier that lead acid can't even approach. 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.

LeifCarrotson 5mo ago

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.

scottlamb 5mo ago
> 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-supply-units/atx-30-vs-atx-31-whats-the-difference/ https://www.corsair.com/us/en/explorer/diy-builder/power-sup... I haven't dug through the spec itself.
- Dylan16807 5mo ago
  How is that supposed to improve efficiency? Also that change sucks, it's cutting the margins way too tight. At least I can be comforted that for my current power supply, the most recent version of it made for ATX 3.1 actually increased the hold-up time. So not all manufacturers are cutting that corner.
Aurornis 5mo ago
> 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.
Dylan16807 5mo ago
> The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle. It's not an 8ms interruption, it's 8ms between peaks. The part you could call an interruption is more like 2.5ms and even then it's not zero power draw. You need an order of magnitude more buffering to handle a 20ms dropout. > 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. Right, so think about that harder. A 60Hz sine wave has two wide periods of power and two narrow gaps. And 20 milliseconds is longer than that entire process combined.

dylan604 5mo ago

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

scottlamb 5mo ago
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.
mbesto 5mo ago
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.
- dylan604 5mo ago
  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.
  - mbesto 5mo ago
    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.
  - scottlamb 5mo ago
    I've found the difference in runtime between similarly-priced low-end units with similar power rating is hour+ (LifePO4 power station) vs not advertised but actually just minutes (lead acid UPS). And you can spend a bit more on the LifePO4 power station and get a proportional increase in runtime and power, vs. the lead acid UPS where the cost would quickly become prohibitive. And the LifePO4 power station 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. You can choose a spot on a Pareto frontier that lead acid can't even approach. 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.