May 21-22, 2005

Homestead-Miami Speedway

Sum up

Another development weekend. This track presents different challenges than West Palm Beach. There is much more braking and the turns are more abrupt. Both of these attributes have brought out hidden problems. The sharp turns cause the battery pack to shift minutely which chafes through the insulation on the sensor wires. The hard braking demands of this circuit are showing that our friction brakes are undersized. The more time braking has also spotlighted that we might be having some sort of problem with 'unintended acceleration'.

Cell #18 died in the final session. One possibility is that it was at the same state of charge as the other cells before charging (about 3.82 volts) and was just reading incorrectly due to the damaged sensor wires in the cell next to it. In this case, we held it's voltage steady while charging the other cells. 3.82 is about 65% charged. Since we used about 68% of pack capacity during the race, it would fit that the cell reached empty and then reversed.

The other possibility is the cell was already damaged. The resistance in a damaged cell tends to make the cell read higher during charge and lower during discharge. There is some evidence of this for #18. The day before the race we did a thirty mile road test. Cell #18 was the lowest cell at the end of the drive (3.749 vs. 3.816 highest) and the first to reach full voltage during charge.

What do we take home from this weekend? More information and another couple of steps towards a winning car.

Imp at Speed Homestead Speedway 0505



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May 22, 2005 Session #3
June 12, 2005 autocross


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