[Nut-upsuser] variables between manufacturers

[Manuel Wolfshant]

On April 3, 2019 7:46:37 AM GMT+03:00, James <bjlockie at lockie.ca> wrote:
>On 2019-04-02 10:35 p.m., Charles Lepple wrote:
>> On Apr 2, 2019, at 9:42 PM, James wrote:
>>>
>>> I switched my desktop with my raspberry pi because I thought my
>desktop ups had a larger capacity.
>>> Now the ups.load of each is not what it was (it should be).
>> 
>> Note that ups.load is a percentage of "full load", which is up to
>each UPS vendor to define. (Some vendors use different margins, and I
>don't know that we have done a thorough check to see how well the load
>percentage tracks Watts or VA ratings when those are available.) If I
>am reading the model numbers correctly, you have an 850 VA CPS UPS, and
>a 550 VA APC, so at the very least, you would need to convert to a unit
>like VA to be able to compare the two directly. Or you can compare the
>numbers on one UPS with the two different loads.
>> 
>> The APC starts out with a load of 6 and a runtime of 98 minutes. It
>then changes to a load of 3 and a runtime of 147 minutes (not quite
>double). If nothing is plugged in, do you get a load of 0? If so,
>consider that the control electronics will require a certain amount of
>current from the battery just to keep the output running, and it may be
>in the same ballpark as a load of 3-6%.
>> 
>> Bear in mind the precision and accuracy of these measurements are not
>guaranteed by the vendor. Two points may determine a line, but this is
>an inverse relationship, so a small change in load means a larger
>change in runtime. You could add a dummy load and see if it tracks
>linearly up from there.
>> 
>> The CPS UPS seems to be in a similar situation. Starting with a load
>of 19%, it estimates a runtime of 45 minutes. A load of 9% yields 86
>minutes, or nearly double.
>> 
>> In both cases, you may want to check the owner's manual to see if the
>vendor has typical runtimes. The UPS electronics are probably sized for
>20-100% load, given the use case of several minutes on battery to let a
>generator kick in, or allow an orderly shutdown.
>
>Since I can't rely on the estimated runtime, is it reasonable to assume
>
>that my raspberry pi will run longer on the CPS compared to the APC?
>
>Is there a way to see the time elapsed between when the pi goes on UPS 
>and when it shuts down?

Power the pi from the UPS and log (say, every minute or two) the UPS status. 

Or just use a stopwatch :)
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