Winning with the Total Discharge Controller
We were at Pacific Raceway Park (the old timers know it as Seattle International Raceway or SIR) for the Memorial Day weekend. This was a double header weekend with SCCA National races being held on Sunday and the holiday Monday. Sunday went very well, with a win in the GT Lite class, finishing 3rdoverall in our race (the SCCA runs multiple classes of cars in one race, each race competing for its own result, but if you are one of the faster cars, you always want to win overall). Everything was prepared for the race on Monday. We were watching the battery voltage using our Radio Shack digital voltmeter, andit looked like the battery wasn’t charging properly (more about voltmeters in a later article). An hourbefore the race, we made the decision to change to our backup battery. As it turned out, the BCM20didn’t have enough time to fully charge the backup battery before we rolled to pregrid. I didn’t think ofit later, but I should have brought the team truck over beside the car and used the Alligator Clip cable to jump the battery as the Optima battery we use can tolerate a very high charging current.
I knew we were in trouble as I have my AIM dashboard set to alarm on battery voltage. There are three led lights on the right side, and as the battery get’s lower, first one, then two and finally all three ledscome on. The first led came on after only one lap! It was a wet race, and our Goodyear rain tires were performing exceptionally well and I ran away from the entire field. I even lapped the car in 2nd place in GT Lite, all the while wondering when the car would stop. But even with all three led indicators on, it kept on going and going. Finally with one lap to go, the engine stopped while on the front straight, and I safely parked the car at the exit of pit lane. Because I had lapped the 2nd place car, I was still credited with the race win!
You can see from the above graph where I have overlaid laps two, nine and fourteen that the battery voltage fell from 10.9 to 10.3 and finally 7.7 volts. The output from the TDC30 remained relatively constant at over 13 volts for almost the entire race, only dropping off in the last couple of laps. The car stopped when the TD voltage reached 11.2 volts – still higher than the actual battery voltage on lap 2! So without the TDC, the car would not have finished even a couple of laps, but with it, we won!