Saturday, March 7, 2009

1000 Miles and Still Going...

There's not too much to report on the Civic. I just passed 1000 miles yesterday and it still seems to work fine. I've definitely noticed over the past several weeks of commuting that my range is highly dependent on my speed. Even driving at 55mph instead of 60mph on the freeway gives me a few extra percent of battery life on the Link-10 E-meter.

I've ended up driving with the LVP protection disconnected from the Belktronix controller because it tends to make my speed go way down even though I have plenty of battery left. The LVP circuit is still attached to the battery light on the dash, so I know when to start being very careful of my driving habits.

The charging system seems to be working fine now that I have the BatMon boards inside boxes, protected from the elements. I've driven in a hard-driving rain several times without any problems. The final voltage on the batteries differs slightly from battery to battery due to the analog nature of the Batmon circuits. The BatMon boards rely on the calibration and tolerances of analog components to activate the shunt resistors at 14.5 volts or so.

I'm starting an experiment with several prototype digital battery monitoring boards from Synkromotive. I'm going to see if I can determine which battery is causing the LVP fault earliest with this monitoring system. For you circuit geeks out there, the Synkromotive system (prototype only at this phase) has a 12-bit A2D converter which makes it more accurate than the PakTrakr system used in many EVs today. Those extra bits can make a big difference when your batteries are close to the end of charge and the balancing system needs to compensate for small differences like 50mV. The digital nature of the system (each battery gets an 8051 microprocessor) allows for easy adjustment of calibration values in case things drift over time.

I'll report back when I get some more results.


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