johnlocke
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Re: Battery temp management for new leaf

Mon Oct 09, 2017 8:21 pm

lorenfb wrote:
johnlocke wrote:
lorenfb wrote:
A further comparison of MS battery heat versus the Leaf's (24kWhr) becomes interesting. Since the Tesla's
and Leaf's overall internal battery impedance is about the same, and the MS weighs about 1.4X the Leaf's weight,
the MS' battery will generate 2X the heat as will the Leaf's battery:

Battery Heat = Rs (internal impedance) X I (battery current)^2
Vehicle Power Losses (moderate freeway speeds - same rolling resistance + moderate drag) =
V (battery) X I (battery current)

Since the battery voltage is the same for both the MS & Leaf, the MS will require about 1.4X (MS weight)
the current than the Leaf at the same speed. Since both the MS & the Leaf have about the same internal
impedance, the MS battery will develop about 2X the battery heat as the Leaf at about the same speeds.

Not true. The model S has only slightly lower efficiency than the Leaf (330wh/mi vs 300wh/mi). So figure 10% more heat not twice the heat. Also there are 7000 cells in a Tesla battery pack as compared to 96 in a Leaf pack. There are a lot of cells in parallel in each module in a Tesla pack so the the current draw from each is much lower. The current draw on a Leaf is though 96 cells in series. Bottom line is that despite being heavier, the Tesla is nearly as efficient as a Leaf and seats up to 7 with the jump seats installed. Weight is less of a factor than aerodynamics particularly at highway speeds.


Here's my data source: https://rennlist.com/forums/mission-e/984855-probable-base-price-2.html

Where're your data to refute mine, i.e simple math based on simple electronics & NOT EPA data.
You do understand internal battery impedance (a common term used in electronics to measure battery
characteristics), right? You have been using TeslaSpy to actually measure the MS' battery output impedance too?
Or maybe you actually used a 18650 cell as was done in the link, right?

My results are NOT based on how each vehicle was driven and under what conditions, i.e. open to question,
but an actual analysis of each vehicle's battery!

Your first error is to equate vehicle weight to power consumption.

Your second error is your source for impedances. They were calculated incorrectly. They forgot to account for the fact that the cells in a Tesla are connected in parallel for the modules and the modules are in series. In a Leaf all the cells are in series even though the cells are packed as pairs. The correct values are 115.2 mohms for the Leaf and 76.5 mohms for the 95 KWH Tesla. That's using your source's figures for the battery's internal impedance. if you are driving at 60 mph on level ground power consumption is about 16KWH per hour or 42 amps current at 375VDC. In a Leaf, that 42 amps flows through each cell in the pack. Those cells had better have a very low impedance. In a Tesla pack those 42 amps are divided among 74 batteries or about 560ma each. The Leaf has a .55 c discharge rate while the discharge rate on the Tesla is .16 c. Which battery do you think is working harder?

Your third error is to dismiss the EPA numbers as irrelevant. They are run under controlled conditions in a lab setting. They do correlate to real world numbers provided by both Leaf and Tesla drivers.

Your fourth error is to state that the battery impedances for both the Tesla and the Leaf are the same. Tesla batteries have about 2/3 of the impedance of a Leaf. Teslas can be equipped with dual 275hp motors. That translates to 1100 Amps current draw and they can actually draw even more on fully charged batteries. See ludicrous mode on Youtube for a demo. Try drawing anywhere near that out of a Leaf battery. I had to do the math 3 times before I believed that current draw. It equates to 15,27 amp draw from each cell in the module.

The purpose of this thread is to discuss whether the 2018 Leaf needs a TMS in hot climates. It's already been proven that Leafs do well in cool climates like England,Canada and the northern U.S. The French Zoe with a 40KWH battery does well in Europe as well.
Last edited by johnlocke on Mon Oct 09, 2017 9:49 pm, edited 1 time in total.
Jamul, CA
San Diego East County

lorenfb
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Re: Battery temp management for new leaf

Mon Oct 09, 2017 9:38 pm

johnlocke wrote:


johnlocke wrote:Your first error is to equate vehicle weight to power consumption.


Really? You're unaware that vehicle weight is the key factor in rolling resistance energy loss?

johnlocke wrote:Your second error is to use the internal impedance of a single cell when the module is composed of 72 cells wired in parallel. If the internal resistance of the 18650 cell is 3 times higher than that of a Leaf cell as you claim then the internal resistance of a Tesla module is 3/72 or about 4% of a leaf cell. The current flow in a module is divided among the 72 cells. if you are driving at 60 mph on level ground power consumption is about 16KWH per hour or 42 amps current at 375VDC. In a Leaf, that 42 amps flows through each cell in the pack. Those cells had better have a very low impedance. In a Tesla pack those 42 amps are divided among 72 batteries or about 600ma each. The Leaf has a .55 c discharge rate while the discharge rate on the Tesla is .16 c. Which battery do you think is working harder?


Read the analysis in the above link, that may help you understand how the equivalent series resistance/impedance
of the overall battery is determined. It's is a very simple analysis, i.e. a series/parallel resistance equivalency.

johnlocke wrote:Your third error is to dismiss the EPA numbers as irrelevant. They are run under controlled conditions in a lab setting. They do correlate to real world numbers provided by both Leaf and Tesla drivers.


1. Fact - The MS weighs 1.4X heavier than the Leaf.
2. Fact - Power loss (consumed) while moving is the result of rolling resistance & drag. (neglecting motor efficiency) plus battery power loss (heating - battery series resistance)
3. Fact - Power loss = Battery Voltage X Battery Current
4. Fact - Battery Power loss = Battery resistance X battery current squared

The above facts then determine each vehicle's theoretical efficiency the result of losses.

johnlocke wrote:Your fourth error is to state that the battery impedances for both the Tesla and the Leaf are the same. Teslas can be equipped with dual 275hp motors. That translates to 1100 Amps current draw and they can actually draw even more on fully charged batteries. See ludicrous mode on Youtube for a demo. Try drawing anywhere near that out of a Leaf battery. I had to do the math 3 times before I believed that current draw. It equates to 15,27 amp draw from each cell in the module.


Again, please read the link and then comment. I said the overall battery effective resistance is basically
the same for the MS & Leaf, i.e. NOT that each MS cell & each Leaf cell has the same resistance.

johnlocke wrote:The purpose of this thread is to discuss whether the 2018 Leaf needs a TMS in hot climates. It's already been proven that Leafs do well in cool climates like England,Canada and the northern U.S. The French Zoe with a 40KWH battery does well in Europe as well.


You challenged my analysis, so please read the link and show mathematically how to determine the effective
internal series resistance of a multiple cell battery, e.g. knowing the single cell value of the MS or Leaf,
as presented in the link.

If you really want to refute the MS' effective battery resistance, then invalidate the methodology used in the
link to calculate the 18650 cell's internal resistance. I've assumed the writer a knowledgeable Tesla insider/consultant.
His overall mathematics are correct, notwithstanding his determination of the single 18650 cell resistance.

johnlocke
Posts: 144
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Re: Battery temp management for new leaf

Mon Oct 09, 2017 10:10 pm

lorenfb wrote:
johnlocke wrote:


johnlocke wrote:Your first error is to equate vehicle weight to power consumption.


Really? You're unaware that vehicle weight is the key factor in rolling resistance energy loss?

johnlocke wrote:Your second error is to use the internal impedance of a single cell when the module is composed of 72 cells wired in parallel. If the internal resistance of the 18650 cell is 3 times higher than that of a Leaf cell as you claim then the internal resistance of a Tesla module is 3/72 or about 4% of a leaf cell. The current flow in a module is divided among the 72 cells. if you are driving at 60 mph on level ground power consumption is about 16KWH per hour or 42 amps current at 375VDC. In a Leaf, that 42 amps flows through each cell in the pack. Those cells had better have a very low impedance. In a Tesla pack those 42 amps are divided among 72 batteries or about 600ma each. The Leaf has a .55 c discharge rate while the discharge rate on the Tesla is .16 c. Which battery do you think is working harder?


Read the analysis in the above link, that may help you understand how the equivalent series resistance/impedance
of the overall battery is determined. It's is a very simple analysis, i.e. a series/parallel resistance equivalency.

johnlocke wrote:Your third error is to dismiss the EPA numbers as irrelevant. They are run under controlled conditions in a lab setting. They do correlate to real world numbers provided by both Leaf and Tesla drivers.


1. Fact - The MS weighs 1.4X heavier than the Leaf.
2. Fact - Power loss (consumed) while moving is the result of rolling resistance & drag. (neglecting motor efficiency) plus battery power loss (heating - battery series resistance)
3. Fact - Power loss = Battery Voltage X Battery Current
4. Fact - Battery Power loss = Battery resistance X battery current squared

The above facts then determine each vehicle's theoretical efficiency the result of losses.

johnlocke wrote:Your fourth error is to state that the battery impedances for both the Tesla and the Leaf are the same. Teslas can be equipped with dual 275hp motors. That translates to 1100 Amps current draw and they can actually draw even more on fully charged batteries. See ludicrous mode on Youtube for a demo. Try drawing anywhere near that out of a Leaf battery. I had to do the math 3 times before I believed that current draw. It equates to 15,27 amp draw from each cell in the module.


Again, please read the link and then comment. I said the overall battery effective resistance is basically
the same for the MS & Leaf, i.e. NOT that each cell within each the battery pack has the same resistance.

johnlocke wrote:The purpose of this thread is to discuss whether the 2018 Leaf needs a TMS in hot climates. It's already been proven that Leafs do well in cool climates like England,Canada and the northern U.S. The French Zoe with a 40KWH battery does well in Europe as well.


You challenged my analysis, so please read the link and show mathematically how to determine the effective
internal series resistance of a multiple cell battery, e.g. knowing the single cell value of the MS or Leaf,
as presented in the link.

If you really want to refute the MS' effective battery resistance, then invalidate the methodology used in the
link to calculate the 18650 cell's internal resistance. I've assumed the writer a knowledgeable Tesla insider/consultant.

Please see the revised post . I did check your source who is a contributor on a Porsche website. I have no idea about his expertise but his math has errors. He also didn't seem to realize that the Leaf cells are all in series despite being in paired modules.

As to weight vs power consumption, yes weight increases rolling resistance but at speeds over 30-40 mph aerodynamics trumps all other effects. Since both the EPA results and real word data from both Tesla and Leaf drivers seem to agree as to power consumption, I'l take their word over yours.
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SageBrush
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Re: Battery temp management for new leaf

Mon Oct 09, 2017 11:37 pm

@johnlocke ,
This article
https://cleantechnica.com/2016/01/06/a- ... ery-packs/
says that the 24 kWh LEAF has 192 cells. Since we know it has a 96S arrangement, it must have a 2P arrangement

I had earlier posted that I expected the 40 kwh pack to have as poor a longevity as the 24 kWh, but given the tighter packing in the same volume and therefore higher impedance, I'm now wondering if the dense packs will do even worse.
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Bought off-lease Jan 2017 from N. California with 63.9 Ahr after 22k miles
Car is now enjoying an easy life in Colorado

lorenfb
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Re: Battery temp management for new leaf

Tue Oct 10, 2017 1:37 am

SageBrush wrote:@johnlocke ,
This article
https://cleantechnica.com/2016/01/06/a- ... ery-packs/
says that the 24 kWh LEAF has 192 cells. Since we know it has a 96S arrangement, it must have a 2P arrangement

I had earlier posted that I expected the 40 kwh pack to have as poor a longevity as the 24 kWh, but given the tighter packing in the same volume and therefore higher impedance, I'm now wondering if the dense packs will do even worse.


To make it simple to understand comparatively:

1. The Leaf has 96 cells stacked in series at about 12.5 Whrs per cell, about 4.1V per cell.
There are essentially 20 parallel stacks (or 2 groups with 10 parallels) resulting in 1920 cells for a total capacity of 24kWhrs.
2. The MS has 96 18650 cells essentially stacked is series and assuming about 12.5 Whrs per cell .
There are essentially 70 parallel stacks resulting in 6720 cells for a total capacity of 84kWhrs.

The key point from the noted reference is that the internal battery resistances are essentially equal:

The P95D pack is 96S74P, so (96/74)*(59 mOhm) = 63.5 mOhm. Altogether the bolted joints and busbars and such come to another 0.5 mOhms, for a net 64 mOhms per pack.


The Nissan Leaf uses pouch cells that are laserwelded together; these particular pouches are optimized for impedence at the expense of energy density at around 1.2mOhm and 30Ah per cell. This makes cooling significantly easier (and therefore the pack much cheaper), and there are 48x 2S2P modules. The net resistance is (48*2/2)*(1.2mOhm) = 57.6mOhm.


So given that both battery packs have essentially the same internal resistance but the Tesla weighs 1.4X the Leaf,
it will theoretically use 2X power (1.4X the current) of the Leaf for its rolling resistance at moderate speeds
(~ 40 - 50 MPH).

Use this for power losses: http://ecomodder.com/forum/tool-aero-rolling-resistance.php

lorenfb
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Re: Battery temp management for new leaf

Tue Oct 10, 2017 1:53 am

johnlocke wrote:I have no idea about his expertise but his math has errors. He also didn't seem to realize that the Leaf cells are all in series despite being in paired modules.


Re-read it.

johnlocke wrote:As to weight vs power consumption, yes weight increases rolling resistance but at speeds over 30-40 mph aerodynamics trumps all other effects. Since both the EPA results and real word data from both Tesla and Leaf drivers seem to agree as to power consumption, I'l take their word over yours.


So weight is a factor in power consumption. Read here to calculate the crossover between rolling resistance
and drag: http://ecomodder.com/forum/tool-aero-rolling-resistance.php

A point that should now become more apparent relative to battery TMS is the battery's internal resistance,
i.e. heat generated internally besides externally from ambient. Factors such as vehicle weight, speed, length
of QCing, & etc., all play a role in whether to have TMS or not. As the reference noted, capacity density at the
expense of higher internal resistance was likely a factor contributing to use of TMS in the Tesla.
Last edited by lorenfb on Tue Oct 10, 2017 2:23 am, edited 1 time in total.

SageBrush
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Re: Battery temp management for new leaf

Tue Oct 10, 2017 2:15 am

I don't know why you are harping about weight and ignoring everything else.
Just look at the EPA MPGe figures. The packs will generate similar amounts of heat and require similar amounts of power.

The LEAF pack will heat up in warm weather and the Tesla will be cooled down by its TMS.
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Bought off-lease Jan 2017 from N. California with 63.9 Ahr after 22k miles
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lorenfb
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Re: Battery temp management for new leaf

Tue Oct 10, 2017 2:37 am

SageBrush wrote:I don't know why you are harping about weight and ignoring everything else.


Where did I ignore "everything else"?

SageBrush wrote:The packs will generate similar amounts of heat and require similar amounts of power.


I just provided an example where that's not the case. You and others might find it trivial, but the analysis
makes a point about what contributes to battery thermal increases besides ambient on both the MS & Leaf.

SageBrush wrote:The LEAF pack will heat up in warm weather and the Tesla will be cooled down by its TMS.


That's true. Just like you, I don't have all the Nissan engineering data related to using TMS and what the cost
trade-offs are. So at this point, we are all just guessing.

DaveinOlyWA
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Re: Battery temp management for new leaf

Tue Oct 10, 2017 6:24 am

Oils4AsphaultOnly wrote:This.

After my discussions with lorenfb, where (s)he only saw a few degrees temp increase from QC'ing less than 15 mins, I saw an almost 30 degree increase from a 27 min QC. QC'ing that 40kwh pack will make for even higher temp increase from the higher sustained fast charging.


the temp rise especially from LEAF Spy readings takes time to equalize and as always the rise has to do with starting temp as it relates to ambient so your statement needs a lot more info to mean anything.
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Oils4AsphaultOnly
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Re: Battery temp management for new leaf

Tue Oct 10, 2017 7:01 am

DaveinOlyWA wrote:
Oils4AsphaultOnly wrote:This.

After my discussions with lorenfb, where (s)he only saw a few degrees temp increase from QC'ing less than 15 mins, I saw an almost 30 degree increase from a 27 min QC. QC'ing that 40kwh pack will make for even higher temp increase from the higher sustained fast charging.


the temp rise especially from LEAF Spy readings takes time to equalize and as always the rise has to do with starting temp as it relates to ambient so your statement needs a lot more info to mean anything.


It was in my discussion with lorenfb. Here's the relevant posting: viewtopic.php?f=55&t=24379&p=504979#p504979

Following that chain will provide the context. It was a very warm day that day.

I think one other poster said it best. Those of us in hot areas should just protect ourselves and NOT consider the leaf.
[2013 leaf traded for 2016 leaf S30:
build date: Sep '16 :: purchased: Nov '16
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6 Sep 2017 - 13k miles & 359 GIDs]

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