Saturday, Dec 29, 2007

SARCC Race

03:00 PM

 

We must decide on a current limit for this race.

The data from the qualifing session is inconclusive. We averaged 0.883 kWhrs per mile, but the session included slow black flag laps which use less power. A computer problem allows us to see only the total power usage and not the lap by lap.

Based on running 375 amps during test day, we found we were averaging 0.981 kWhrs per mile. 13 laps on a 2.25 mile course plus 1.5 kWhrs for pace lap and cool down lap (combined) means 30.194 kWhrs capacity is needed.

13 x 2.25 = 29.25 total racing miles
29.25 x 0.981 = 28.69 total KWhrs for 13 laps
28.694 +1.5 = 30.194 KWhrs required for the entire race event.

We know from our race at Savanah that we can get 31.595 kW-hrs out of the pack at 400 amps.

 

When they start lining up the cars for the race, the only other SPU, which had qualified far behind us, is having problems. They push that car off the grid and out of the race.

 

We decided to run 400 amps (2/3 power).
We are confident that we could complete the 14 lap race at 375 amps, but 400 amps will be very close.
Without any competition, we can experiment.

 
2/3rds power is more than we qualified with. I have no problem holding my position on the start. The Spec Racers surrounding me have a little better acceleration but my timing is good.

The only cars around me are Spec Racers, 1670 pounds, 105 horsepower purpose built race cars. I play with them but not too aggressively. Lap 2, turn 2., the one ahead brakes too late and I slip by. He catches me back in T9 and his buddy catches me in T2.

 

Next lap, another Spec Racer gets by at T2 again but I get him back at the chicane.

 

I put in a clean lap.
I repass #19 between T2 and T3.
I put myself up one position as I recatch #6 into the chicane.
They return the favor in T2 and into T9.

 

I have to work around a lapped car through T10 and that breaks up the action. I try to close again but the car is not accelerating as well. My time drops from a 1:51 to a 1:54, then a 2:10.

I suspect the motors are too hot.
No need to risk damage. The other SPU did not start.
My first place is safe...

 

...Except it turns out that the other SPU driver had a back-up car.

My crew did not notice him start from pit lane and we did not know we had competition.

The classic turtle and hare story. My fastest lap was a 1:48.974 against his 1:53.369 but he finished 12 laps and I only did 10. Getting that first victory is not going to be that easy.

 

Our data shows that the motors reached 175 Celsius and that the inverters were cutting back power to keep the motors from getting any hotter.

The coolant temperature after leaving the hot motors and before entering the radiator reached only 46 Celsius.

The radiator was able to cool the liquid down to 40 Celsius which is fairly respectable since the air temperature was around 35 Celsius.

 

It is clear that not enough heat is being picked up by the coolant while it is passing through the motor.

The motor's limit is 60 minutes at 125 amps or 5 minutes at 305 amps.

During our 400 amp maximum current lap, we average 135 amps per motor. After around 15 minutes of racing, the motors reach their limit. The motor's internal cooling system is not designed to cope with this much high power running.

 
Motor rating
 
 


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