Serial Fun

Peter Ohler has written some excellent software for the Palm OS which lets it interface with the Emeter in my truck.  It can display data from an Emeter in real time, make calculations regarding battery state of charge, and display historical data.  It will also save the Emeter data as a text file which I can then play with on my PowerBook G4.  Here are two graphs that I made:  the first of a short drive around the block, and the second a longer drive into Brunswick.




If you look carefully, you can see that the system voltage graph is more or less the inverse (on a different scale) of the current graph, with an overall slightly negative slope.




As you can see from the high voltage at the beginning, the truck had just come off of the charger - the voltage starts to drop slowly before there's even any load, approaching the nominal voltage.  By the end of the drive, the resting voltage has dropped to about 124 volts.  The first major current spike is me pulling out of the driveway, followed by a very brief drop to zero while I shift to second gear, then a nice downward curve while I accelerate to around 40mph, then another quick zero-current into third gear, and then it's smooth sailing until I have a left hand turn about 2/3 of the way through.  There's a stop sign about 3/4 of the way, a slight wait for traffic near then end, then uphill into another driveway.  Cool!


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