[time-nuts] Power monitoring

Hal Murray hmurray at megapathdsl.net
Thu Apr 17 14:10:11 EDT 2008

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?

If I was doing it myself, I'd start with a low power (quiet) PC and a UPS.  
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.   
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 

These are my opinions, not necessarily my employer's.  I hate spam.

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