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Report from Bear Kaufmann:

A couple weeks ago, Trystan Lea, who runs OpenEnergyMonitor ( came by and we worked on testing his system on our in house 10kw Power Pallet.

The OpenEnergyMonitor is “a project to develop and build open source energy monitoring and analysis tools for energy efficiency and distributed renewable microgeneration.” The project is developed around the Arduino, thus will integrate nicely with our Arduino based Gasifier Control Unit. Trystan has some cool code and great explanations of the circuits on the site.

We tested his system on the skid, monitoring 2 legs of current and voltage from the genhead (split phase). The system doesn’t just measure the RMS amperage, voltage, and frequency, but also uses the waveform to compute real power, apparent power, power factor (wikipedia links), as well as cumulative sums and ranges over time.

We adapted the usual Power Monitor code to run on the GEK GCU. When the Power Monitor is running on a dedicated arduino, its takes a ~2 second solid block of time to sample the AC signal and compute the power measurements. With an Arduino dedicated to that task, thats fine, but when we need to also monitor and control other processes on the Power Pallet, we can’t take a full block of time like that. So, we implemented code to do sampling calculations on a single cycle and then average them.

The results were quite good (low noise). We could even see the inrush current when turning on large motors. If we’re datalogging over 1 second intervals and get averages of 10 samples over that second, we only need to use ~1/60 * 10 = 1/6th of the processor time on power monitoring, leaving the rest of the time open for other tasks. Here’s a test of that method that was run on the GCU on Monday (4/19/10) as various dump loads (heaters) and lights were turned on and off:

With this system in place, we can now gather much more accurate data on power output when datalogging Power Pallet runs, including better information on fuel consumption per kWh and system efficiency.

There are more pictures of Trystan’s visit here in the GEKforum:


Remember also our upcoming Gasification and Biochar Workshop Weekend on June 4-6. See here for more info:

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