May 21-22, 2005

Homestead-Miami Speedway

Session 3

30 minute race -1:12 pm May 22

The pack is at 332 volts (adv per cell 3.77 volts) or about 40% discharged. SIADIS says 9.73 kWhr out of 22.8 kWhr pack or 43%.

We find we have used 1.235 kW-hrs per mile at full power on lap 1 without regen and .998 kW-hrs per mile at full power on lap 2 with regen. That is a gain of 24% from regen.

In a 30 minute race at 1:50 a lap, we might have to do 17 laps. At full power, we can only go 10 laps. At 1/3 power, we should be able to go the distance.

We charge for the pack for 49 minutes starting at 30 amps and tapering to 0 as cell #18 reads full. The next highest cell is reading 3.92 volts. The lowest cell (#1) reads 3.827 volts. We are unsure of how accurate cell #18 reading is and do not have time to pull the seat and cover to check directly. One of the burnt sensing wires was connected to cells #19 and #20 and this may influence the reading.

With the PFC50 charger connected we run a program that reads each cell's voltage and then connects the highest cell to resistors to discharge. We adjust the charge rate and the amount of time the highest cell will discharge until we are able to keep the high cell under 4.17. This works out to a charge rate of 12.5 amps and a 120 second discharge time.

By the end of charge, the lowest cell is still #1 but it reads 4.042. #18 is reading 4.124. Pack voltage is 366.3 volts. Since 366.3 divided by 88 cells equals 4.1625 volts adv per cell, we have to suspect our BMS of under reading the voltages.

We decide to treat this race as a testing opportunity. We will start at the back and run 1/3 power trying to get more information on our braking problems. After a few laps we will do a few full power laps and see what happens.

We start the race at the back. At 200 amps max draw, the cells are reading above 3.7 volts except #18 which shows 2.684 volts. Clearly it is not reading correctly.

The car handles fine. It does not have enough power to pass anyone but we can stay with the Mazda RX7 in front of us. Our brakes are better but still pretty ineffective. I can not lock the tires with the brakes. There does not seem to be any odd power spikes. After 3 laps, the crew chief calls over the radio and asks me to switch to full power.

I note that pack temperature has only climbed to 39.9 C from a starting temperature of 29.1 C. Then I flip the two switches that give me full power.

I feel some satisfaction as I power by two RX7s and a Pontiac. My lap time drops by 9 seconds despite not having a clear lap. It feels like the odd power on spike may have returned as I miss apexes.

Half way through my second full power lap, I smell a battery letting go. I put the switches back to 1/3 power and do another lap but the smell gets a lot worst. I pit. The pack temperature has climbed to 56.7 C. Pack voltage is 327.8 volts or 3.72 adv.



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My 21-22, 2005 Session #2
May 21-22, 2005 Sum Up


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