[Nut-upsuser] ups.test.result meaning

[Charles Lepple]

On Oct 31, 2020, at 10:53 PM, Charles Lepple <clepple at gmail.com> wrote:
> 
> On Oct 31, 2020, at 8:30 PM, Gene Heskett <gheskett at shentel.net> wrote:
>> 
>>> battery.voltage: 16.0
>> At that voltage, 5 of the 12 cells are shorted
>>> battery.voltage.nominal: 24
> 
> The 16.0 is a scaled version of the fixed (bogus) 24.0 V reading, similar to this unit:
> 
> https://networkupstools.org/ddl/Cyber_Power_Systems/CP1500PFCLCD.html

Gene,

you might have missed this email, and I admit I wasn't very precise with my wording.

This particular UPS model is returning a fixed (in the sense of "constant") integer "24" (not 24.0) for both battery voltage and nominal battery voltage, likely because according to the vendor, some models do not have a battery voltage sensor (or, I suspect, it isn't accessible to the microprocessor that sends stats back over USB). Given the broken HID report descriptor that the UPS provides, NUT 2.7.2 scales "24" to "16.0". NUT 2.7.4 uses a heuristic to "fix" that value back to 24.0, but "garbage in, garbage out".

Another way to look at it: if you had two 12V lead-acid batteries in series, and someone gave you many readings of 27.0V, 26.0V, 25.0V, and 24.0V over time, would you be suspicious that you weren't seeing, say, 26.5V at some point?

Rick's batteries may be low, but I would be surprised if he actually saw 16.0V on a multimeter.

I wish we had a better way to flag these bogus values in NUT, but we're still collecting the data in order to programmatically figure out which models really do have a voltage sensor hooked up to USB, and which ones don't. For now, the next best thing is annotating the DDL entries from user-submitted data, like the link above.

See also the output.voltage discussion below. The scaling issue isn't as bad, but it's rooted in the same USB HID descriptor (the decoder ring for the values the UPS sends back).

> 
> I think we even "fixed" that after NUT 2.7.2, before I realized that many units are providing a bogus value:
> 
> https://github.com/networkupstools/nut/commit/c8950dee9c91ce45d05d8f220ea26891fb92329e
> 
>>> output.voltage: 138.0
>> too high by about 15 volts
>> 
> 
> From the other CPS UPS thread on Monday:
> 
>> This is another known CyberPower issue, and fixing it properly requires making some changes deep in the core USB HID code (that would require a lot of testing on other vendors' equipment) for what is basically a cosmetic issue:
>> 
>> https://github.com/networkupstools/nut/issues/439
> 
> https://alioth-lists.debian.net/pipermail/nut-upsuser/2020-October/012126.html
>