[time-nuts] Power monitoring
Jim Lux
james.p.lux at jpl.nasa.gov
Thu Apr 17 14:34:54 EDT 2008
Quoting Hal Murray <hmurray at megapathdsl.net>, on Thu 17 Apr 2008
11:10:11 AM PDT:
> My power went out the other day. That reminded me that I've always been
> slightly curious about that area.
>
> Are there any not-expensive boxes made for this? Or something that shows up
> on eBay occasionally?
Lots of dataloggers out there in the <$200 range.
Check out things like the HOBO from Onset.
you can also get embedded style computer from someone like Tern or
Z-world or Vesta that has all the hardware needed, and comes with some
basic software that you could use.
>
>
> If I was doing it myself, I'd start with a low power (quiet) PC and a UPS.
Battery and single board computer or data logger is much better...
such an application doesn't need a video monitor, keyboard, etc.
> Then I'd have a platform that could monitor other things too, like
> temperature.
>
> Step 0 is just to measure when power is/isn't there.
> I assume the UPS has a signal for that.
>
> Step 1 is to measure the voltage.
> This takes an A/D. The standard PC audio input might be appropriate.
no DC coupling on the audio card. Much better to either get something
with the appropriate A/D OR a "one-wire" style interface.
You could transformer down the 60 Hz, digitize as an audio signal, and
process it appropriately.
> I'd probably use an AC wall-wart transformer for isolation and a couple of
> resistors to get down to a reasonable voltage.
>
> Step 2 is to catch dips and spikes.
> That's just software behind the A/D. (assuming the A/D is fast enough)
>
>
> As long as I'm dreaming... Suppose I wanted to measure the power my whole
> house is drawing. What's available along the lines of a current transformer
> on the main lines? My first thought is that nobody does that (for homes) so
> it's probably horribly expensive. On the other hand there is a lot of
> interest in energy conservation these days so it might only be somewhat
> expensive.
Lots of these available, in the few hundred dollar range..
http://www.powercostmonitor.com/p3982/power_cost_monitor.php
http://www.theenergydetective.com/index.html
you can also do something like watch the wheel goaround on the meter
with a photocell
or
put a suitable current transformer ($5 surplus, $50 new) on the mains
coming in.
More information about the time-nuts
mailing list