SageBrush
Forum Supporter
Posts: 6266
Joined: Sun Mar 06, 2011 2:28 am
Delivery Date: 13 Feb 2017
Location: NM

Re: How to sell a 2018 LEAF?

Thu May 20, 2021 5:35 am

We have discussed heat generation more than a few times, and I think there is agreement that larger capacity packs generate less heat since the pack current is divided up proportional to the pack parallelism. It works out that a 62 kWh pack that is ~ 1.5x larger capacity than a 40 kWh pack will generate ~ 1/2 the heat for the same power **.

The trade-off is in heat dissipation, presumed worse in tightly packed cases but no where as easy to calculate or model. Some empiric testing using e.g the EPA cycle, 40 mile a day, and at a couple ambient temperatures would be informative.


**
(2/3)^2
Last edited by SageBrush on Thu May 20, 2021 6:44 am, edited 2 times in total.
2013 LEAF 'S' Model with QC & rear-view camera
Bought Jan 2017 from N. California
Two years in Colorado, now in NM
03/18: 58 Ahr, 28k miles
11/18: 56.16 Ahr, 30k miles
09/20: 54.3 Ahr; 38k miles
-----
2018 Tesla Model 3 LR, Delivered 6/2018

SageBrush
Forum Supporter
Posts: 6266
Joined: Sun Mar 06, 2011 2:28 am
Delivery Date: 13 Feb 2017
Location: NM

Re: How to sell a 2018 LEAF?

Thu May 20, 2021 5:35 am

duplicate post
2013 LEAF 'S' Model with QC & rear-view camera
Bought Jan 2017 from N. California
Two years in Colorado, now in NM
03/18: 58 Ahr, 28k miles
11/18: 56.16 Ahr, 30k miles
09/20: 54.3 Ahr; 38k miles
-----
2018 Tesla Model 3 LR, Delivered 6/2018

lorenfb
Posts: 2510
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: How to sell a 2018 LEAF?

Thu May 20, 2021 6:50 am

SageBrush wrote:
Thu May 20, 2021 5:35 am
We have discussed heat generation more than a few times, and I think there is agreement that larger capacity packs generate less heat since the pack current is divided up proportional to the pack parallelism.
And that implies that the series resistance of the larger battery is less.
SageBrush wrote:
Thu May 20, 2021 5:35 am
Effectively, a 62 kWh pack that is ~ 1.5x larger capacity than a 40 kWh pack will generate ~ 1/2 the heat for the same power **.

The trade-off is in heat dissipation, presumed worse in tightly packed cases but no where as easy to calculate or model. Some empiric testing using e.g the EPA cycle, 40 mile a day, and at a couple ambient temperatures would be informative.


**
(2/3)^2
Remember, the heat loss power (P) in the battery the result of its series resistance (R) is equal to; P = I^2 * R
So the P (series resistance loss) is actually just 2/3 of the smaller battery, i.e. both batteries provide the same load current.
Other significant power losses occur the result of the entropy losses which can equal the series resistance losses.
#1 Leaf SL MY 9/13: 76K miles, 47 Ahrs, 5.0 miles/kWh (average), Hx=70, SOH=73, L2 - 100% > 1000, temp < 95F, (DOD) > 20 Ahrs
#2 Leaf SL MY 12/18: 10.3K miles, SOH 109Ahrs/115Ahrs, 5.2 miles/kWh (average), DOD > 20%, temp < 105F

SageBrush
Forum Supporter
Posts: 6266
Joined: Sun Mar 06, 2011 2:28 am
Delivery Date: 13 Feb 2017
Location: NM

Re: How to sell a 2018 LEAF?

Thu May 20, 2021 7:01 am

lorenfb wrote:
Thu May 20, 2021 6:50 am
SageBrush wrote:
Thu May 20, 2021 5:35 am
Effectively, a 62 kWh pack that is ~ 1.5x larger capacity than a 40 kWh pack will generate ~ 1/2 the heat for the same power **.

**
(2/3)^2
Remember, the heat loss power (P) in the battery the result of its series resistance (R) is equal to; P = I^2 * R
So the P (series resistance loss) is actually just 2/3 of the smaller battery, i.e. both batteries provide the same load current.
We seem to disagree, so here is more detail

Starting from constant (P)ower
Same (R)esistance across each cell
Two packs have the same 96S, but pac(K) #2 has 1.5x the parallelism of pack(K) #1 (that is, 50% larger capacity)

If the current through a K1 cell is C,
then the current through a K2 cell is 2C/3

Since resistance related heat generation is proportional to the square of the current,
the K2 cell generates (2/3)^2 the heat of the K1 cell

---
Any errors ?
2013 LEAF 'S' Model with QC & rear-view camera
Bought Jan 2017 from N. California
Two years in Colorado, now in NM
03/18: 58 Ahr, 28k miles
11/18: 56.16 Ahr, 30k miles
09/20: 54.3 Ahr; 38k miles
-----
2018 Tesla Model 3 LR, Delivered 6/2018

SageBrush
Forum Supporter
Posts: 6266
Joined: Sun Mar 06, 2011 2:28 am
Delivery Date: 13 Feb 2017
Location: NM

Re: How to sell a 2018 LEAF?

Thu May 20, 2021 7:12 am

SageBrush wrote:
Thu May 20, 2021 7:01 am
---
Any errors ?
... I think I see one. Each cell in the 1.5x larger pack generates 4/9 the heat of the smaller pack but there are 1.5x the cells so the heat generation in the pack is
(4/9) * (3/2) = 2/3
2013 LEAF 'S' Model with QC & rear-view camera
Bought Jan 2017 from N. California
Two years in Colorado, now in NM
03/18: 58 Ahr, 28k miles
11/18: 56.16 Ahr, 30k miles
09/20: 54.3 Ahr; 38k miles
-----
2018 Tesla Model 3 LR, Delivered 6/2018

lorenfb
Posts: 2510
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: How to sell a 2018 LEAF?

Thu May 20, 2021 7:13 am

SageBrush wrote:
Thu May 20, 2021 7:01 am
lorenfb wrote:
Thu May 20, 2021 6:50 am
SageBrush wrote:
Thu May 20, 2021 5:35 am
Effectively, a 62 kWh pack that is ~ 1.5x larger capacity than a 40 kWh pack will generate ~ 1/2 the heat for the same power **.

**
(2/3)^2
Remember, the heat loss power (P) in the battery the result of its series resistance (R) is equal to; P = I^2 * R
So the P (series resistance loss) is actually just 2/3 of the smaller battery, i.e. both batteries provide the same load current.
We seem to disagree, so here is more detail

Starting from constant (P)ower
Same (R)esistance across each cell
Two packs have the same 96S, but pac(K) #2 has 1.5x the parallelism of pack(K) #1 (that is, 50% larger capacity)

If the current through a K1 cell is C,
then the current through a K2 cell is 2C/3


Since resistance related heat generation is proportional to the square of the current,
the K2 cell generates (2/3)^2 the heat of the K1 cell

---
Any errors ?
Given the same load currents, e.g. same speeds, for the 40 & 60 kWh Leafs, the 60 kWh has just 2/3 the losses.
Again, the it's just P = I^2 * R, and not the square of the resistance ratios.
#1 Leaf SL MY 9/13: 76K miles, 47 Ahrs, 5.0 miles/kWh (average), Hx=70, SOH=73, L2 - 100% > 1000, temp < 95F, (DOD) > 20 Ahrs
#2 Leaf SL MY 12/18: 10.3K miles, SOH 109Ahrs/115Ahrs, 5.2 miles/kWh (average), DOD > 20%, temp < 105F

lorenfb
Posts: 2510
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: How to sell a 2018 LEAF?

Thu May 20, 2021 7:13 am

SageBrush wrote:
Thu May 20, 2021 7:12 am
SageBrush wrote:
Thu May 20, 2021 7:01 am
---
Any errors ?
... I think I see one. Each cell in the 1.5x larger pack generates 4/9 the heat of the smaller pack but there are 1.5x the cells so the heat generation in the pack is
(4/9) * (3/2) = 2/3
Good!!!
#1 Leaf SL MY 9/13: 76K miles, 47 Ahrs, 5.0 miles/kWh (average), Hx=70, SOH=73, L2 - 100% > 1000, temp < 95F, (DOD) > 20 Ahrs
#2 Leaf SL MY 12/18: 10.3K miles, SOH 109Ahrs/115Ahrs, 5.2 miles/kWh (average), DOD > 20%, temp < 105F

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