[Nut-upsuser] variables between manufacturers

James bjlockie at lockie.ca
Wed Apr 3 05:46:37 BST 2019

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?

More information about the Nut-upsuser mailing list