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.
