[time-nuts] Power monitoring
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
> 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
Lots of these available, in the few hundred dollar range..
you can also do something like watch the wheel goaround on the meter
with a photocell
put a suitable current transformer ($5 surplus, $50 new) on the mains
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