2010/08/13
Fine grained house-wide power monitoring with Brultech ECM1240, ecmread.py (with net metering support), and graphing with cacti
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2010-08-13 00:00
in Computers, Linuxha, Solar
Introduction
Until recently, I had a Brand One Powermeter to measure PG&E Meter, PV system and my AC. It was bulky, unreliable, and impossible to reprogram. In other words, it was a poor and expensive solution. That said, I still got some data and reasonable graphs from it as per this earlier blog post. But let's be honest, I really didn't like that monitor and wanted to ditch it. After some research, the ECM1240 is the best feature/cost ratio power monitoring device I found (as of 2010). As of 2019, the ECM1240 is now obsolete and replaced by the Greeneye, see below: _Note, there seems to be a better monitor now, the Greeneye._ You may want to have a look at Brultech Greeneye. Why is it better than the alternatives?
I calibrated the TTs vs the split 60CTs and the small CT-40s by comparing measurements of the same load
the 2 white boxes are the ECMs1240s, but I also have my older and bigger brand one power meters in there
the small donut CT-40s are great, they take no room at all
Code
Gratuitous Graphs :)
Ok, first you can find all the graphs here: all regular owfs derived graphs.And here are the interesting composite graphs. So, US houses come with 2 120V phases. Now, if you wanted 100% exact wattage measurements, you'd have to measure the voltage on each and every circuit breaker you measure, but in reality measuring each phase is close enough.
In real life, measuring amps on one phase with voltage from another phase will only give you about a 1-2% error at worst, so it's not a lot to agonize about. In my setup I tried to measure phase 2 loads on my ECM that's plugged into phase 2 power, but wasn't fully able to do it, and it's not meaningful when you measure 240V loads anyway. This is what the phases look like, as the graph shows phase 1 typically gets more power than phase 2 for me, but depending on the load in my street and my house, they sometimes become close or equal:










