Nut upsuser - Oct 2011 - Newbie question: real-time power usage monitoring?

Hi guys,

I'm very new to NUT, and power monitoring in general, so please
forgive me if this question is dumb.

I'd like to write a Linux app that will know, in approximate
real-time, how much power is being drawn by a computer plugged into an
outlet.

Is NUT well-suited to this usage?

And if so, can anyone recommend relatively cheap monitoring hardware
(ideally less than $200 US) that will meet my needs?

Thanks very much,
Christian

On Oct 18, 2011, at 10:18 PM, Christian Convey wrote:
> I'd like to write a Linux app that will know, in approximate
> real-time, how much power is being drawn by a computer plugged into an
> outlet.
Can you narrow down your definition of "approximate real-time"?

The default poll interval of NUT drivers is 2 seconds, but usbhid-ups  
has longer intervals for some values since retrieving values over low- 
speed USB takes a non-trivial amount of time.

If you are ultimately trying to integrate power over time to get  
energy consumption, you probably want a device that does this  
measurement for you (a watt-hour meter, basically). Then, the exact  
update rate doesn't matter as much - if you poll less frequently, the  
energy per interval will simply be proportionally larger. You can  
still divide out the time to get average power, but of course, that  
won't show surges as effectively.
> Is NUT well-suited to this usage?
>
> And if so, can anyone recommend relatively cheap monitoring hardware
> (ideally less than $200 US) that will meet my needs?
I haven't gone shopping for an UPS in a while, but I'd think you would  
need to spend at least USD $300-400 to get an UPS with decent current- 
monitoring hardware. (The voltage-monitoring side usually is good  
enough even in low-end UPSes.)

Do you need backup power as well as monitoring capability? What about  
power control?

If you just want monitoring, you might consider one of the Watts Up  
products:

    https://www.wattsupmeters.com/secure/products.php

(Disclaimer: I haven't personally tried any of them, and I can't vouch  
for any of their software, either.)

You could also look at power distribution units (PDUs) but I have a  
feeling that the monitoring capability is also not available in the  
under-$200 price range.

Hi Christian,
> I'm very new to NUT, and power monitoring in general, so please
> forgive me if this question is dumb.
it's about power, I don't see anything dumb here, no worries.
> I'd like to write a Linux app that will know, in approximate
> real-time, how much power is being drawn by a computer plugged into an
> outlet.
>
> Is NUT well-suited to this usage?
>
> And if so, can anyone recommend relatively cheap monitoring hardware
> (ideally less than $200 US) that will meet my needs?
>
> Thanks very much,
On the NUT side, there is currently not many devices that can provide
such information, with a sufficient granularity:
Eaton 5 PX and newer Eaton ePDU Managed.
Other NUT supported PDUs may also be fine, but I won't commit nor
elaborate on that (remember, I'm biased)
These kind of devices will clearly be out of your budget though!

Now, considering your use case, what you need is probably more a
"simple" meter.
Adding support for meters is planned in NUT, but I don't have much
visibility to give on this for now.

I know that Richard Hughes (UPower, Gnome Power Manager) once added
Watts Up Pro support:
https://www.wattsupmeters.com/secure/products.php?pn=0

I was (and I'm still) interested in doing the same for NUT.
But once more, since I've never used these devices, I can't commit on
the features.

Finally, I've asked some Eaton contacts for a such meter inside
Eaton's offering (through the acquisition of Moeller).
I'll forward you the answer when available.

cheers,
Arnaud
-- 
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/