[Nut-upsdev] RFC: adding new data "ups.efficiency"

Arnaud Quette aquette.dev at gmail.com
Mon Apr 18 08:04:13 UTC 2011

Hey Arjen,

hope you're doing fine.

2011/4/16 Arjen de Korte <nut+devel at de-korte.org>

> Citeren Arnaud Quette <aquette.dev at gmail.com>:
>  we (Eaton) have created a new data to expose efficiency of the UPS
>> (basically it is the ratio of the output current on the input current).
>> I know that at least APC should also provide it on some units, since I've
>> seen evidence in an EPA presentation [1].
>> So I'd like to create the following new data:
>> - Name: ups.efficiency
>> - Description: Efficiency of the UPS (ratio of the output current on the
>> input current) (percent)
>> - Example value: 99
>> As usual, comments and feedback are very welcome...
> Two comments:
> 1) What would be reported if the UPS is running on battery? There clearly
> would be no input power at that time. What is reported in that case?

in Eaton implementation, switching to battery gives an "ups.efficiency = 0"

> 2) Calculating the efficiency based on the ratio of input and output
> *current* leaves a giant loophole to artificially increase the reported
> efficiency. On an online UPS one could increase the 'efficiency' by setting
> the output voltage a few percent above the input voltage. Similarly, if a
> system would have a near unity power factor on the input, but a crappy one
> on the output, you'd also inflate the reported efficiency by using the RMS
> figures.

indeed. and that's what we'll get if marketing takes over engineering.
note that the standard disclaimer on device's data applies: this is not a
lab measurements tool. Data are only approximations...

as for Eaton implementation, I don't have the exact formula used in Eaton
devices, but this is an approximation that also takes in account some
percentage loss.
As an example, here is a data excerpt of what I have with a unit here:
ups.efficiency: 72
ups.load: 13
ups.power: 209
ups.power.nominal: 1500
ups.realpower: 108
ups.realpower.nominal: 1350
ups.type: offline / line interactive

note that this unit is a line interactive.

I'd only see some merit in reporting this, if it would be the ratio of input
> and output real power values. I would be surprised if in a real world
> scenario however if one would get very close to 99% (if not in running in
> bypass mode). A more typical value of a double conversion UPS would be
> something between 90-95% and even then only when the UPS is properly scaled
> for the designed load. The good thing would be that people might be made
> aware how much power they are wasting, given that fact that in many cases a
> UPS will not be operated near the optimum efficieny load.

indeed. I at least consider this as a first step in the right direction.
And it's also true that the example value may seem like a troll (putting
something like 92 % would probably be more suitable).
As for a 99 % efficiency, apart from running on bypass, I only know units
like Eaton 9395, that have internal modules powered up or down depending on
the ups load.
which helps a lot in improving efficiency.

Linux / Unix Expert R&D - Eaton - http://powerquality.eaton.com
Network UPS Tools (NUT) Project Leader - http://www.networkupstools.org/
Debian Developer - http://www.debian.org
Free Software Developer - http://arnaud.quette.free.fr/
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