Versions Compared

Version Old Version 3 New Version 4
Changes made by

Shem Kim

Shem Kim

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

Doing the same script with modified variables for P45B (36S9P, 0.09mOhm DCIR per cell, 300kg total car mass), the heat generated using area under the curve is 2.63Wh, which translates to 0.50 deg C. The temperature rise was cut by roughly half compared to the 50S.

...

...

For Scenario 2 I will consider a 15% grade uphill scenario at 34.2km/h (9.5m/s) with no solar because this seems like a plausible scenario and since it also requires almost ~5000W, which is the maximum power that the motor can take.

First for the 50S:

Here is the first scenario for 5 minutes at nominal cell voltage

Code Block
Enter time in minutes5
Total Mass: 296
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 129.6
Cell DCIR: 0.014
Parallel Count 8
Form Factor: 21700
Heat Energy Generated: 7.2539 Wh
Total Race Temperature Rise: 1.5606 deg C
Battery Power Consumed: 4904.4201 W
Total Battery Power Consumed: 408.7017 Wh
Current: 37.8427 A

Here is another scenario for 10 minutes at nominal cell voltage

Code Block
Enter time in minutes10
Total Mass: 296
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 129.6
Cell DCIR: 0.014
Parallel Count 8
Form Factor: 21700
Heat Energy Generated: 14.5077 Wh
Total Race Temperature Rise: 3.1213 deg C
Battery Power Consumed: 4904.4201 W
Total Battery Power Consumed: 817.4033 Wh
Current: 37.8427 A

Here is a scenario for 5 minutes at 3.0 cell voltage

Code Block
Enter time in minutes5
Total Mass: 296
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 108
Cell DCIR: 0.014
Parallel Count 8
Form Factor: 21700
Heat Energy Generated: 10.4456 Wh
Total Race Temperature Rise: 2.2473 deg C
Battery Power Consumed: 4942.7205 W
Total Battery Power Consumed: 411.8934 Wh
Current: 45.7659 A

Here is a scenario for 10 minutes at 3.0 cell voltage

...

The difference in power consumption in Scenario is shown below.

...

I did an actual comparison of the two arrays by just running the script two times, saving one of the arrays in a separate variable, and then subtracting the two arrays for the difference:

ans =

Columns 1 through 10

Code Block
4.8328    4.9403    5.0306    5.1052    5.1656    5.2133    5.2500    5.2775    5.2971    5.3105

Columns 11 through 20

Code Block
5.3192    5.3242    5.3269    5.3281    5.3284    5.3285    5.3285    5.3285    5.3281    5.3271

Columns 21 through 30

Code Block
5.3246    5.3197    5.3114    5.2985    5.2794    5.2527    5.2168    5.1701    5.1108    5.0375

Columns 31 through 37

Code Block
4.9486    4.8426    4.7182    4.5744    4.4103    4.2254    4.0192

So it seems like the 50S configuration would save 5.3W of power at most under Scenario 1 compared to P45B. 5.3W is like 1.5X a Noctua IPPC 3000 fan at max power….

50S vs P45B Scenario 2

For Scenario 2 I will consider a 15% grade uphill scenario at 34.2km/h (9.5m/s) with no solar because this seems like a plausible scenario and since it also requires almost ~5000W, which is the maximum power that the motor can take.

First for the 50S:

Here is the first scenario for 5 minutes at nominal cell voltage

Code Block
Enter time in minutes5
Total Mass: 296
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 108129.6
Cell DCIR: 0.014
Parallel Count 8
Form Factor: 21700
Heat Energy Generated: 207.89122539 Wh
Total Race Temperature Rise: 41.49475606 deg C
Battery Power Consumed: 49424904.72054201 W
Total Battery Power Consumed: 823408.78687017 Wh
Current: 4537.76598427 A

...

Here is a another scenario for 5 10 minutes at 3.6 nominal cell voltage
 Code Block
Enter time in minutes5minutes10
Total Mass: 300296
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 129.6
Cell DCIR: 0.009014
Parallel Count 98
Form Factor: 21700
Heat Energy Generated: 414.25545077 Wh
Total Race Temperature Rise: 03.813811213 deg C
Battery Power Consumed: 49324904.1344201 W
Total Battery Power Consumed: 411817.01124033 Wh
Current: 3837.05668427 A
Here is a scenario for 10 5 minutes at 3.6 0 cell voltage
 Code Block
Enter time in minutes10minutes5
Total Mass: 300296
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 108
129.6
Cell DCIR: 0.009014
Parallel Count 98
Form Factor: 21700
Heat Energy Generated: 810.51084456 Wh
Total Race Temperature Rise: 12.62762473 deg C
Battery Power Consumed: 49324942.1347205 W
Total Battery Power Consumed: 822411.02238934 Wh
Current: 3845.05667659 A
Here is a scenario for 5 10 minutes at 3.0 cell voltage
 Code Block
Enter time in minutes5minutes10
Total Mass: 300296
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 108
Cell DCIR: 0.009014
Parallel Count 98
Form Factor: 21700
Heat Energy Generated: 620.12788912 Wh
Total Race Temperature Rise: 14.17194947 deg C
Battery Power Consumed: 49544942.60257205 W
Total Battery Power Consumed: 412823.88357868 Wh
Current: 45.87597659 A
Next for the P45B:
Here is a scenario for 10 5 minutes at 3.0 6 cell voltage
 Code Block
Enter time in minutes10minutes5
Total Mass: 300
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 108129.6
Cell DCIR: 0.009
Parallel Count 9
Form Factor: 21700
Heat Energy Generated: 124.25562554 Wh
Total Race Temperature Rise: 20.343881381 deg C
Battery Power Consumed: 49544932.6025134 W
Total Battery Power Consumed: 825411.76710112 Wh
Current: 4538.87590566 A
Here is the battery power consumption difference between the two packs for each scenario:a scenario for 10 minutes at 3.6 cell voltage (nominal voltage)
Battery Power Consumption Difference: 4932.134W - 4904.4201W = 27.7139W
3.0 cell voltage 
Battery Power Consumption Difference: 4954.6025W - 4942.7205W = 11.882W
Summary 
Going with a P45B pack seems to have a very clear advantage over the 50S when it comes to high current thermal performance. But we aren’t likely going to be dealing with a lot of high current scenarios during race, and Scenario 1 results seem to show that a 50S pack will operate perfectly fine with only a ~1 deg C temperature rise. Even if we consider short transient scenarios where a high current draw is necessary, I think simply running a few fans at a higher RPM would be enough to cool the cells below 50C.
In order to contextualize this comparison though, I think it is fair to also take a look at the power consumption difference between the two packs.
...
I did an actual comparison of the two arrays by just running the script two times, saving one of the arrays in a separate variable, and then subtracting the two arrays for the difference:
ans =
 Columns 1 through 10
 Code Block
4.8328    4.9403    5.0306    5.1052    5.1656    5.2133    5.2500    5.2775    5.2971    5.3105
 Columns 11 through 20
 Code Block
5.3192    5.3242    5.3269    5.3281    5.3284    5.3285    5.3285    5.3285    5.3281    5.3271
 Columns 21 through 30
 Code Block
5.3246    5.3197    5.3114    5.2985    5.2794    5.2527    5.2168    5.1701    5.1108    5.0375
 Columns 31 through 37
 Code Block
4.9486    4.8426    4.7182    4.5744    4.4103    4.2254    4.0192
So it seems like the 50S configuration would save 5.3W of power at most under Scenario 1 compared to P45B. 5.3W is like 1.5X a Noctua IPPC 3000 fan at max power….
However, this is all armchair analysis without actual testing done. Ideally, we would have tested a P45B module and a 50S module in a wind tunnel, but I’m not too sure we have the luxury of time to do that now. 
To be honest, I think it’s fair to think about the P45B as costing 5.3W of extra power consumption, but providing a much higher thermal performance ceiling for the pack. Does the pack need that extra ceiling? Probably not. But it doesn’t seem like a huge cost to pay for greatly improved thermal benefits (half the temperature rise, 10C higher max charge temp), and 
 Code Block
Enter time in minutes10
Total Mass: 300
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 129.6
Cell DCIR: 0.009
Parallel Count 9
Form Factor: 21700
Heat Energy Generated: 8.5108 Wh
Total Race Temperature Rise: 1.6276 deg C
Battery Power Consumed: 4932.134 W
Total Battery Power Consumed: 822.0223 Wh
Current: 38.0566 A
Here is a scenario for 5 minutes at 3.0 cell voltage
 Code Block
Enter time in minutes5
Total Mass: 300
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 108
Cell DCIR: 0.009
Parallel Count 9
Form Factor: 21700
Heat Energy Generated: 6.1278 Wh
Total Race Temperature Rise: 1.1719 deg C
Battery Power Consumed: 4954.6025 W
Total Battery Power Consumed: 412.8835 Wh
Current: 45.8759 A
Here is a scenario for 10 minutes at 3.0 cell voltage
 Code Block
Enter time in minutes10
Total Mass: 300
Acceleration: 0
Velocity: 9.5
Grade: 0.15
Voltage: 108
Cell DCIR: 0.009
Parallel Count 9
Form Factor: 21700
Heat Energy Generated: 12.2556 Wh
Total Race Temperature Rise: 2.3438 deg C
Battery Power Consumed: 4954.6025 W
Total Battery Power Consumed: 825.7671 Wh
Current: 45.8759 A
Here is the battery power consumption difference between the two packs for each scenario:
3.6 cell voltage (nominal voltage)
Battery Power Consumption Difference: 4932.134W - 4904.4201W = 27.7139W
3.0 cell voltage 
Battery Power Consumption Difference: 4954.6025W - 4942.7205W = 11.882W
Summary 
Right off the bat, it seems fair to say that heat generation from cruising in normal conditions (with expected solar, 0% grade driving) is almost negligible. So I think it’s fair to say that the main concern with temperature rise should be regarding those high power draw scenarios. In those situations, a P45B pack would seem to perform significantly better thermally (1/2 the temp rise and a higher temperature ceiling).
However, this is all napkin math without actual testing done. Ideally, we would have tested a P45B module and a 50S module in a wind tunnel, but I’m not too sure we have the luxury of time to do that now. 
To be honest, I think it’s fair to think about the P45B as costing extra power consumption (5.3W cruising, 27.7W for high power), but providing a much higher thermal performance for the pack. Does the pack need that extra ceiling? Maybe not. But it doesn’t seem like a huge cost to pay for greatly improved thermal benefits. Having to potentially rely on fans a great deal isn’t ideal because: 
  1. It’s in our interest to impede the inlet to protect the pack from foreign objects or water from getting in, that would probably work against cooling/would require more fans or more powerful fans to overcome the added static pressure
  2. I don’t know how reliably we can scale up module results to a pack level 
  3. We can definitely develop a way to scale up module results to a pack level and model cooling using a wind tunnel and test jig, but that would be time consuming, and it wouldn’t be wise to push back final cell selection that far
Additionally, a P45B pack can likely still allow us to reduce overall battery system weight from MS15 and won’t massively increase our volume and testing + manufacturing + assembly time like an 18650 pack likely will (since that would massively increase cell count).
...