On Thu, Mar 2, 2023 at 9:42 PM Tim via users users@lists.fedoraproject.org wrote:
I have a UPS sitting next to me, right now, in pieces, which (half) died in a most peculiar manner:
A burning smell was eventually traced to it. There's no visible signs of burning, and no schematic available for the model, that I can find. A rather acrid smell, not one I'm used to with component failure, I'm beginning to suspect a large AC transformer.
While running off the mains its output is a (too) low voltage, but still high enough for most switch-mode power supplies to run normally (i.e. the computer and monitor). It has some kind of AC voltage regulation built into it to deal with under and over-voltage. The AC supply was normal, at the time.
But running off its battery it produces the full 240 volts it's supposed to.
If you read about normal UPSes they are not normally designed to run 100% duty cycle (ie on battery for days, or fixing up a low voltage for days). So if you run yours at say 40% load it will probably survive under the higher duty cycle, but if you run it close to 100% load and it gets into cleaning up low voltages the UPS electronics may not survive long (ie if fixing the voltages for hours/days).
So if they end up running in that state for long periods of time (either because of adding bigger batteries--my UPS came with 12AH batterys but now has external 35AH ones) and/or extended low voltages various components may burn out.
There is also a setting on at least some UPSes that you can change so that it does not regulate the lower voltages (wider acceptable voltage range) and accepts those voltages as ok. I have done that with both of my UPSes because the default setting prevents the UPSes from charging when on a small generator, and would if the voltages was low but still good enough cause the UPS to keep fixing the slightly low voltages and possibly burn out.