lorenfb
Posts: 1312
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: Battery temp management for new leaf

Sun Oct 08, 2017 2:43 pm

WetEV wrote:
SageBrush wrote:The other parameters in play are the temperature gradient, heat generation, and the case material.


So what about pack chemistry? Does that have anything at all to do with lifetime?


Besides having an effect on battery life, the battery chemistry also affects the internal impedance of each cell.
As has been noted on this forum, the original Tesla MS/X cell exhibits a significantly greater (3X) internal impedance
than the Leaf's. So at the same cell currents, the Tesla cells will develop more heat (3X), increasing the necessity
for TMS for the Tesla versus for the Leaf.

edatoakrun
Posts: 4643
Joined: Thu Nov 11, 2010 9:33 am
Delivery Date: 15 May 2011
Leaf Number: 2184
Location: Shasta County, North California

Re: Battery temp management for new leaf

Sun Oct 08, 2017 3:08 pm

lorenfb wrote:
...Besides having an effect on battery life, the battery chemistry also affects the internal impedance of each cell.
As has been noted on this forum, the original Tesla MS/X cell exhibits a significantly greater internal impedance
than the Leaf's. So at the same cell currents, the Tesla cells will develop more heat, increasing the necessity
for TMS for the Tesla versus for the Leaf.

BEV designers take varying (by both kW rate and temperature) rates of impedance into account in designing BEV battery packs and drive-trains.

2011-17 LEAF packs depend on this passive heat source for their battery heating needs, to keep the pack higher up in the temperature range, giving higher kWh capacity than that available from colder packs.

A major reason for the observable lower efficiency in m/kWh when driving colder temperatures is the greater amount of energy diverted to pack heating, both when charging and discharging, when the pack is colder.

The presumably larger thermal mass of the larger 2018-on LEAF pack(s) should allow them to retain heat longer, a net positive for operating efficiency.

The lower C rate of the larger packs, during both charge and discharge cycles, should also lower the amount of undesirable heat generated under the relatively unusual conditions (pack temperatures exceeding ~90 F to 100 F) when additional pack heating is undesirable.

So we should expect 2018-on LEAF packs to operate more efficiently and lose capacity at a lower rate than earlier lower kWh packs, even if AESC had made no improvements at all in cell chemistry.
no condition is permanent

lorenfb
Posts: 1312
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: Battery temp management for new leaf

Sun Oct 08, 2017 3:29 pm

lorenfb wrote:
WetEV wrote:
SageBrush wrote:The other parameters in play are the temperature gradient, heat generation, and the case material.


So what about pack chemistry? Does that have anything at all to do with lifetime?


Besides having an effect on battery life, the battery chemistry also affects the internal impedance of each cell.
As has been noted on this forum, the original Tesla MS/X cell exhibits a significantly greater (3X) internal impedance
than the Leaf's. So at the same cell currents, the Tesla cells will develop more heat (3X), increasing the necessity
for TMS for the Tesla versus for the Leaf.


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.

johnlocke
Posts: 142
Joined: Fri Jan 08, 2016 3:47 pm
Delivery Date: 14 Dec 2015
Leaf Number: 300582

Re: Battery temp management for new leaf

Mon Oct 09, 2017 10:02 am

lorenfb wrote:
lorenfb wrote:
WetEV wrote:
So what about pack chemistry? Does that have anything at all to do with lifetime?


Besides having an effect on battery life, the battery chemistry also affects the internal impedance of each cell.
As has been noted on this forum, the original Tesla MS/X cell exhibits a significantly greater (3X) internal impedance
than the Leaf's. So at the same cell currents, the Tesla cells will develop more heat (3X), increasing the necessity
for TMS for the Tesla versus for the Leaf.


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.
Jamul, CA
San Diego East County

johnlocke
Posts: 142
Joined: Fri Jan 08, 2016 3:47 pm
Delivery Date: 14 Dec 2015
Leaf Number: 300582

Re: Battery temp management for new leaf

Mon Oct 09, 2017 10:23 am

edatoakrun wrote:
lorenfb wrote:
...Besides having an effect on battery life, the battery chemistry also affects the internal impedance of each cell.
As has been noted on this forum, the original Tesla MS/X cell exhibits a significantly greater internal impedance
than the Leaf's. So at the same cell currents, the Tesla cells will develop more heat, increasing the necessity
for TMS for the Tesla versus for the Leaf.

BEV designers take varying (by both kW rate and temperature) rates of impedance into account in designing BEV battery packs and drive-trains.

2011-17 LEAF packs depend on this passive heat source for their battery heating needs, to keep the pack higher up in the temperature range, giving higher kWh capacity than that available from colder packs.

A major reason for the observable lower efficiency in m/kWh when driving colder temperatures is the greater amount of energy diverted to pack heating, both when charging and discharging, when the pack is colder.

The presumably larger thermal mass of the larger 2018-on LEAF pack(s) should allow them to retain heat longer, a net positive for operating efficiency.

The lower C rate of the larger packs, during both charge and discharge cycles, should also lower the amount of undesirable heat generated under the relatively unusual conditions (pack temperatures exceeding ~90 F to 100 F) when additional pack heating is undesirable.

So we should expect 2018-on LEAF packs to operate more efficiently and lose capacity at a lower rate than earlier lower kWh packs, even if AESC had made no improvements at all in cell chemistry.

The discharge rate for a 2018 Leaf will be the same as an older leaf. There have been no major changes to the design so the amount of energy required to drive the car remains the same. Current flow is the same so the amount of heat generated by the battery is similar. The battery weight is slightly increased but fits in the same case. There is no reason to expect the heating effect to change much and in fact it might be lower if the internal resistance of the battery has dropped due to improvements. Although there might be an improvement in cold weather performance, this battery is still likely to have problems in the south and southwest due to heat management issues.
Jamul, CA
San Diego East County

lorenfb
Posts: 1312
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: Battery temp management for new leaf

Mon Oct 09, 2017 5:43 pm

johnlocke wrote:
lorenfb wrote:
lorenfb wrote:
Besides having an effect on battery life, the battery chemistry also affects the internal impedance of each cell.
As has been noted on this forum, the original Tesla MS/X cell exhibits a significantly greater (3X) internal impedance
than the Leaf's. So at the same cell currents, the Tesla cells will develop more heat (3X), increasing the necessity
for TMS for the Tesla versus for the Leaf.


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!

lorenfb
Posts: 1312
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: Battery temp management for new leaf

Mon Oct 09, 2017 6:00 pm

johnlocke wrote:
There is no reason to expect the heating effect to change much and in fact it might be lower if the internal resistance of the battery has dropped due to improvements. Although there might be an improvement in cold weather performance, this battery is still likely to have problems in the south and southwest due to heat management issues.


Ah, so we're now talking in terms realistic battery terms, i.e. "internal resistance". Now apply that battery theory
and logic to your other post related to power loss of an MS battery using 18650 cells versus the Leaf's battery.

OK, maybe my referenced source mis-calculated the typical output impedance of the MS 18650 cell. Then I'm sure
you''ll have another source that measured the 18650 cell which refutes my source's calculations, right?
Based on simple HS electronics used to calculate series & parallel resistor connections, you should be
able to arrive at an equivalent overall impedance for each battery, i.e. MS vs Leaf. I'm been monitoring my
Leaf's battery for over 2 years at various battery temps, so my Leaf number is fairly reliable.

Remember:
Rs (battery output impedance) = Delta V (change in battery voltage) / Delta I (change in load current)
Last edited by lorenfb on Mon Oct 09, 2017 6:50 pm, edited 1 time in total.

Levenkay
Posts: 426
Joined: Mon Sep 26, 2011 10:01 pm
Delivery Date: 16 May 2013
Leaf Number: 19196
Location: Portland, OR

Re: Battery temp management for new leaf

Mon Oct 09, 2017 6:49 pm

Argh; just when the wailing over confusing kW and kWh dies down, now we have impedance and resistance being used as if they were interchangeable terms. They're not, as hinted by the spelling. You almost certainly mean resistance; why not just stick with that term?

lorenfb
Posts: 1312
Joined: Tue Dec 17, 2013 10:53 pm
Delivery Date: 22 Nov 2013
Leaf Number: 416635
Location: SoCal

Re: Battery temp management for new leaf

Mon Oct 09, 2017 6:55 pm

Levenkay wrote:Argh; just when the wailing over confusing kW and kWh dies down, now we have impedance and resistance being used as if they were interchangeable terms. They're not, as hinted by the spelling. You almost certainly mean resistance; why not just stick with that term?


So what! Impedance is a more general term, as there may be some inductance within each cell.
For you, I'll still use impedance and state that the Ls is zero. OK?

Oils4AsphaultOnly
Gold Member
Posts: 197
Joined: Sat Oct 10, 2015 4:09 pm
Delivery Date: 20 Nov 2016
Leaf Number: 313890
Location: Arcadia, CA

Re: Battery temp management for new leaf

Mon Oct 09, 2017 8:02 pm

johnlocke wrote:
SageBrush wrote:
Dooglas wrote:Number 1 - Heat loss rate is NOT simply a result of pack dimensions. The pack is not solid.

This has nothing to do with being solid or not, it has to do with surface area for passive heat dissipation. The other parameters in play are the temperature gradient, heat generation, and the case material. Since no mention was made of changes to the pack casing, the power to move the car stays about the same, and we do not control ambient temperatures, the surface area becomes the difference. Same pack, same surface area.

Same dimensions but higher energy density. 40KWH vs 30KWH or 24KWH. Not a huge effect while driving (lots of airflow around the battery) but a substantial difference while charging (longer charge time and no airflow to dissipate heat buildup). Unless you intentionally limit the battery capacity (I.E. 12% to 88%) there will be more heat buildup due to a longer charge time. Plus the fact that you are likely to charge it to 100% from a low state(30% or less). This likely to really problematic if you are DCFC'ing on a trip. With the 30KWH battery, adding 2 temp bars during fast charging is common. I expect it to be worse with 40KWH battery. Add in the heating effect from high discharge rates from freeway driving and long trips encouraged by the longer range battery and you could have a recipe for a disaster.


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.
[2013 leaf traded for 2016 leaf S30:
build date: Sep '16 :: purchased: Nov '16
1 May 2017 - 7300 miles & 363 GIDs
6 Sep 2017 - 13k miles & 359 GIDs]

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