Nissan Leaf Battery and BMS...

[Ed Lee]

According to Google, there are at least 34 views (114 - 70) on my posts on the other thread, but not a single response. So, i am trying more radical ideas for comments (good or bad are welcome). I am going to open up and relocate some of the rear stack modules for better cooling. I want to document it in a video course and post it later.

******

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

@
@

 

[Ed Lee]

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

Furthermore, we examine the possiblity of relocating some battery modules, allowing for additional passive cooling, especially for the rear stack of 24 modules. One of every four module will be relocated to allow for an air gap. This will be accompanished by opening the top of the cover near the rear stack and the back seat area with a cover of the cover plate. The back bench seat will be removed and auxilary balancing batteries will be installed.

 

[Don Y]

On 11/10/2020 8:45 AM, Ed Lee wrote:

Furthermore, we examine the possiblity of relocating some battery modules,
allowing for additional passive cooling, especially for the rear stack of 24
modules. One of every four module will be relocated to allow for an air
gap. This will be accompanished by opening the top of the cover near the
rear stack and the back seat area with a cover of the cover plate. The back
bench seat will be removed and auxilary balancing batteries will be
installed.

Assuming the battery pack is located under the seat, why not just try
pulling the seat (and possibly adding forced air) to get a feel for
whether further efforts MIGHT bear fruit?

 

[Ed Lee]

On Tuesday, November 10, 2020 at 10:17:29 AM UTC-8, Don Y wrote:

On 11/10/2020 8:45 AM, Ed Lee wrote:
Furthermore, we examine the possibility of relocating some battery modules,
allowing for additional passive cooling, especially for the rear stack of 24
modules. One of every four module will be relocated to allow for an air
gap. This will be accomplished by opening the top of the cover near the
rear stack and the back seat area with a cover of the cover plate. The back
bench seat will be removed and auxiliary balancing batteries will be
installed.

Assuming the battery pack is located under the seat, why not just try
pulling the seat (and possibly adding forced air) to get a feel for
whether further efforts MIGHT bear fruit?

The battery cover blocks access from the inside. The module terminals are side-way facing the front. However, the rear stack (12\"x9\"x48\") cannot be disassembled without removing it from the vehicle. Once removed from the vehicle, I can cut open access panel from the cover and wire taps into the cells. The exact cell conditions are available in real time CAN messages; however, it is difficult to find exact match in capacities. I need to replace 6 to 10 cells at around 70% cap, not too small and not too big. But once i open it up, might as well relocate them for better air flow and cooling.

 

[Lasse Langwadt Christensen]

tirsdag den 10. november 2020 kl. 16.42.22 UTC+1 skrev Ed Lee:

According to Google, there are at least 34 views (114 - 70) on my posts on the other thread, but not a single response. So, i am trying more radical ideas for comments (good or bad are welcome). I am going to open up and relocate some of the rear stack modules for better cooling. I want to document it in a video course and post it later.

******

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

@
@

maybe people are reluctant to comment on stuff involving a 400V battery

 

[Ed Lee]

On Tuesday, November 10, 2020 at 11:36:08 AM UTC-8, lang...@fonz.dk wrote:

tirsdag den 10. november 2020 kl. 16.42.22 UTC+1 skrev Ed Lee:
According to Google, there are at least 34 views (114 - 70) on my posts on the other thread, but not a single response. So, i am trying more radical ideas for comments (good or bad are welcome). I am going to open up and relocate some of the rear stack modules for better cooling. I want to document it in a video course and post it later.

******

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

@
@
maybe people are reluctant to comment on stuff involving a 400V battery

Once the high voltage service disable plug is disconnect. It\'s just two 200V batteries inside. I am tapping at 100V segments; so, each external modules are only 100V with 50V (actually 48V with 12V charging booster) center tap. I have two modules ready, and working on another two. 100V modules are fairly safe to handle. I have not been seriously shocked yet.

 

[Don Y]

On 11/10/2020 11:39 AM, Ed Lee wrote:

On Tuesday, November 10, 2020 at 10:17:29 AM UTC-8, Don Y wrote:
On 11/10/2020 8:45 AM, Ed Lee wrote:
Furthermore, we examine the possibility of relocating some battery
modules, allowing for additional passive cooling, especially for the
rear stack of 24 modules. One of every four module will be relocated to
allow for an air gap. This will be accomplished by opening the top of
the cover near the rear stack and the back seat area with a cover of the
cover plate. The back bench seat will be removed and auxiliary balancing
batteries will be installed.

Assuming the battery pack is located under the seat, why not just try
pulling the seat (and possibly adding forced air) to get a feel for
whether further efforts MIGHT bear fruit?

The battery cover blocks access from the inside.

I found this:

<https://inspirationfeeeed.files.wordpress.com/2014/12/nissan-leaf-cabin-cross-section-exposing-its-battery-pack.jpg>

(but no idea if it is relevant to YOUR vehicle).

It looks like the battery pack underlays BOTH front and back seats (?).
And, that it sits below the floorboards? I\'d initially assumed it was
literally \"under the back seat\" (as in, remove seat, look upon battery).

So, the \"cover\" is the orange skin visible, there? Cut away here:

<https://468y981o84o43v2wo2600a0gcj-wpengine.netdna-ssl.com/wp-content/uploads/2014/06/LEAF-Battery-NissanEV-Flickr-copy.jpg>

(the rear pack being the taller stack on the left)

> The module terminals are side-way facing the front.

The strip of darker orange along the frontside of the back pack?

However, the rear stack
(12\"x9\"x48\") cannot be disassembled without removing it from the vehicle.
Once removed from the vehicle, I can cut open access panel from the cover
and wire taps into the cells. The exact cell conditions are available in
real time CAN messages; however, it is difficult to find exact match in
capacities. I need to replace 6 to 10 cells at around 70% cap, not too
small and not too big. But once i open it up, might as well relocate them
for better air flow and cooling.

But, you\'re also going to RELOCATE some cells? This begs the question:
why didn\'t the manufacturer do that in the initial design? Would it have
made the pack too \"sprawling\"?

Can you push air through from the sides -- possibly *pulling* it out on
the opposite side? (again, I\'m just suggesting as a means of testing
your theory before doing much surgery)

(gotta wonder what a nightmare it would be to have the pack catch fire
under your feet!)

Batteries look like frozen dinners stacked like that! :>

 

[legg]

On Tue, 10 Nov 2020 07:42:15 -0800 (PST), Ed Lee
<edward.ming.lee@gmail.com> wrote:

According to Google, there are at least 34 views (114 - 70) on my posts on the other thread, but not a single response. So, i am trying more radical ideas for comments (good or bad are welcome). I am going to open up and relocate some of the rear stack modules for better cooling. I want to document it in a video course and post it later.

******

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

The passive dissipative equalization only effectively occurs when
the charge current is low enough for the 400R resistor to HAVE
any effect - basically at the end of charge float, at ~ 200mA
charge cut-off point. The aim is to keep OEC terminal voltages
below a level where cell degradation occurs.

For large capacity imbalances, it won\'t be sufficient to do this,
so lower capacity cells become further degraded before the 200mA
charging condition is reached.

As the lower capacity cell terminal voltages determine the BMS
end-of-discharge, it\'s basically restricting all cells to the
capacity of the weakest cell in the string.

It\'s better than nothing.

A non-dissipative balancing method, with higher current capacity,
can actually distribute the storage capacities between series
-connected cells.

Depends on how much the customer is willing to pay fot the extra
range . . . . and it\'ll still be sourced off-shore.

RL

 

[Ed Lee]

On Tuesday, November 10, 2020 at 11:51:15 AM UTC-8, Don Y wrote:

On 11/10/2020 11:39 AM, Ed Lee wrote:
On Tuesday, November 10, 2020 at 10:17:29 AM UTC-8, Don Y wrote:
On 11/10/2020 8:45 AM, Ed Lee wrote:
Furthermore, we examine the possibility of relocating some battery
modules, allowing for additional passive cooling, especially for the
rear stack of 24 modules. One of every four module will be relocated to
allow for an air gap. This will be accomplished by opening the top of
the cover near the rear stack and the back seat area with a cover of the
cover plate. The back bench seat will be removed and auxiliary balancing
batteries will be installed.

Assuming the battery pack is located under the seat, why not just try
pulling the seat (and possibly adding forced air) to get a feel for
whether further efforts MIGHT bear fruit?

The battery cover blocks access from the inside.
I found this:

https://inspirationfeeeed.files.wordpress.com/2014/12/nissan-leaf-cabin-cross-section-exposing-its-battery-pack.jpg

(but no idea if it is relevant to YOUR vehicle).

It looks like the battery pack underlays BOTH front and back seats (?).
And, that it sits below the floorboards? I\'d initially assumed it was
literally \"under the back seat\" (as in, remove seat, look upon battery).

So, the \"cover\" is the orange skin visible, there? Cut away here:

https://468y981o84o43v2wo2600a0gcj-wpengine.netdna-ssl.com/wp-content/uploads/2014/06/LEAF-Battery-NissanEV-Flickr-copy.jpg

Yes, correct.

(the rear pack being the taller stack on the left)
The module terminals are side-way facing the front.
The strip of darker orange along the frontside of the back pack?

Yes, battery terminals are behind the orange cover plate next to the orange cables.

However, the rear stack
(12\"x9\"x48\") cannot be disassembled without removing it from the vehicle.
Once removed from the vehicle, I can cut open access panel from the cover
and wire taps into the cells. The exact cell conditions are available in
real time CAN messages; however, it is difficult to find exact match in
capacities. I need to replace 6 to 10 cells at around 70% cap, not too
small and not too big. But once i open it up, might as well relocate them
for better air flow and cooling.rear
But, you\'re also going to RELOCATE some cells? This begs the question:
why didn\'t the manufacturer do that in the initial design? Would it have
made the pack too \"sprawling\"?

They did not realize that the cells would degrade so far under heat. The rear cells are packed too closely together.

Can you push air through from the sides -- possibly *pulling* it out on
the opposite side? (again, I\'m just suggesting as a means of testing
your theory before doing much surgery)

The existing pack is air tight. No easy way to cut holes without removing the cover.

> (gotta wonder what a nightmare it would be to have the pack catch fire under your feet!)

Actually, my (or somebody\'s) butt.

> Batteries look like frozen dinners stacked like that! :>

Yes, but internally cooking dinners.

The battery is actually rather safe, with many level of metals (module, cover and seat base). With my modification, nobody would be sitting on top of the rear stack.

 

[Ed Lee]

On Tuesday, November 10, 2020 at 12:05:05 PM UTC-8, legg wrote:

On Tue, 10 Nov 2020 07:42:15 -0800 (PST), Ed Lee
edward....@gmail.com> wrote:

According to Google, there are at least 34 views (114 - 70) on my posts on the other thread, but not a single response. So, i am trying more radical ideas for comments (good or bad are welcome). I am going to open up and relocate some of the rear stack modules for better cooling. I want to document it in a video course and post it later.

******

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

The passive dissipative equalization only effectively occurs when
the charge current is low enough for the 400R resistor to HAVE
any effect - basically at the end of charge float, at ~ 200mA
charge cut-off point. The aim is to keep OEC terminal voltages
below a level where cell degradation occurs.

For large capacity imbalances, it won\'t be sufficient to do this,
so lower capacity cells become further degraded before the 200mA
charging condition is reached.

As the lower capacity cell terminal voltages determine the BMS
end-of-discharge, it\'s basically restricting all cells to the
capacity of the weakest cell in the string.

Correct. That\'s why i need to parallel some additional 18650 cells to compensate the capacities to 70%, then auxiliary packs to restore the rest.

It\'s better than nothing.

A non-dissipative balancing method, with higher current capacity,
can actually distribute the storage capacities between series
-connected cells.

That\'s the problem when real chargers are too far apart. If i can fake the BMS into charging cycle, it can unlock some additional capacities.

Depends on how much the customer is willing to pay fot the extra
range . . . . and it\'ll still be sourced off-shore.

Someone in Finland already developed the CAN bridge (AVR CAN based) to take control of the BMS.

 

[Ed Lee]

It looks like the battery pack underlays BOTH front and back seats (?).
And, that it sits below the floorboards? I\'d initially assumed it was
literally \"under the back seat\" (as in, remove seat, look upon battery)..

So, the \"cover\" is the orange skin visible, there? Cut away here:

https://468y981o84o43v2wo2600a0gcj-wpengine.netdna-ssl.com/wp-content/uploads/2014/06/LEAF-Battery-NissanEV-Flickr-copy.jpg
Yes, correct.

No, that\'s just plastic cover for the bus bar and terminal. I am talking about the heavy metal cover for the entire pack. I have to remove it from the pack and cut open an access panel near the top, above water level. The water level is half way at the rear stack. It should be safe enough to drive into water, as long as the doors are closed. If i dive into the water head first with the window open, that\'s a different story.

 

[Don Y]

On 11/10/2020 1:34 PM, Ed Lee wrote:

It looks like the battery pack underlays BOTH front and back seats (?).
And, that it sits below the floorboards? I\'d initially assumed it was
literally \"under the back seat\" (as in, remove seat, look upon
battery).

So, the \"cover\" is the orange skin visible, there? Cut away here:

https://468y981o84o43v2wo2600a0gcj-wpengine.netdna-ssl.com/wp-content/uploads/2014/06/LEAF-Battery-NissanEV-Flickr-copy.jpg


Yes, correct.

No, that\'s just plastic cover for the bus bar and terminal. I am talking
about the heavy metal cover for the entire pack. I have to remove it from

Yes, I understood. Two different \"oranges\" (the LARGE yellow-orange being the
pack-cover and the deeper orange BAR being the interconnect cover)

the pack and cut open an access panel near the top, above water level. The
water level is half way at the rear stack. It should be safe enough to
drive into water, as long as the doors are closed. If i dive into the water
head first with the window open, that\'s a different story.

So, you\'re going to leave this \"open\" (and uncovered by the rear seat)?
Instead of trying to duct air in/out of the \"case enclosure\"?

 

[Don Y]

On 11/10/2020 1:08 PM, Ed Lee wrote:

On Tuesday, November 10, 2020 at 11:51:15 AM UTC-8, Don Y wrote:

Can you push air through from the sides -- possibly *pulling* it out on
the opposite side? (again, I\'m just suggesting as a means of testing your
theory before doing much surgery)

The existing pack is air tight. No easy way to cut holes without removing
the cover.

Yes, but can\'t you remove cover TO cut the holes (without risking damage
to the cells) and affix/install active cooling measures while replacing
the cover?

The battery is actually rather safe, with many level of metals (module,
cover and seat base). With my modification, nobody would be sitting on top
of the rear stack.

So, you intend to turn the car into a \"sports car\" (no rear seat)?
Or, geek-mobile?

 

[Ed Lee]

On Tuesday, November 10, 2020 at 1:44:25 PM UTC-8, Don Y wrote:

On 11/10/2020 1:34 PM, Ed Lee wrote:

It looks like the battery pack underlays BOTH front and back seats (?).
And, that it sits below the floorboards? I\'d initially assumed it was
literally \"under the back seat\" (as in, remove seat, look upon
battery).

So, the \"cover\" is the orange skin visible, there? Cut away here:

https://468y981o84o43v2wo2600a0gcj-wpengine.netdna-ssl.com/wp-content/uploads/2014/06/LEAF-Battery-NissanEV-Flickr-copy.jpg


Yes, correct.

No, that\'s just plastic cover for the bus bar and terminal. I am talking
about the heavy metal cover for the entire pack. I have to remove it from
Yes, I understood. Two different \"oranges\" (the LARGE yellow-orange being the
pack-cover and the deeper orange BAR being the interconnect cover)
the pack and cut open an access panel near the top, above water level. The
water level is half way at the rear stack. It should be safe enough to
drive into water, as long as the doors are closed. If i dive into the water
head first with the window open, that\'s a different story.

So, you\'re going to leave this \"open\" (and uncovered by the rear seat)?
Instead of trying to duct air in/out of the \"case enclosure\"?

Not sure yet. Once i have the access panel inside the car, i can try out different things. The battery should still be sealed, but could pipe air or liquid inside to cool it.

 

[Ed Lee]

On Tuesday, November 10, 2020 at 1:46:37 PM UTC-8, Don Y wrote:

On 11/10/2020 1:08 PM, Ed Lee wrote:
On Tuesday, November 10, 2020 at 11:51:15 AM UTC-8, Don Y wrote:

Can you push air through from the sides -- possibly *pulling* it out on
the opposite side? (again, I\'m just suggesting as a means of testing your
theory before doing much surgery)

The existing pack is air tight. No easy way to cut holes without removing
the cover.
Yes, but can\'t you remove cover TO cut the holes (without risking damage
to the cells) and affix/install active cooling measures while replacing
the cover?

Yes, but still need to umount and remount the battery in a shop with vehicle lift.
So, i need to plan everything before renting a bay for few days.

The battery is actually rather safe, with many level of metals (module,
cover and seat base). With my modification, nobody would be sitting on top
of the rear stack.
So, you intend to turn the car into a \"sports car\" (no rear seat)?
Or, geek-mobile?

It\'s already a two seater. My back is packed with 12V batteries and inverting charger for emergency. Going directly into 400V would be more efficient.

 

[Don Y]

On 11/10/2020 3:11 PM, Ed Lee wrote:

On Tuesday, November 10, 2020 at 1:46:37 PM UTC-8, Don Y wrote:
On 11/10/2020 1:08 PM, Ed Lee wrote:
On Tuesday, November 10, 2020 at 11:51:15 AM UTC-8, Don Y wrote:

Can you push air through from the sides -- possibly *pulling* it out
on the opposite side? (again, I\'m just suggesting as a means of
testing your theory before doing much surgery)

The existing pack is air tight. No easy way to cut holes without
removing the cover.
Yes, but can\'t you remove cover TO cut the holes (without risking damage
to the cells) and affix/install active cooling measures while replacing
the cover?

Yes, but still need to umount and remount the battery in a shop with vehicle
lift. So, i need to plan everything before renting a bay for few days.

Ahhh! The battery pack mounts to the UNDERSIDE of the vehicle! The
floorboards aren\'t removed to access it from above!

(the mounting flanges visible in the photo aren\'t to hold the pack
DOWN to a surface but, rather, *up*!)

 

[Ed Lee]

On Tuesday, November 10, 2020 at 2:26:42 PM UTC-8, Don Y wrote:

On 11/10/2020 3:11 PM, Ed Lee wrote:
On Tuesday, November 10, 2020 at 1:46:37 PM UTC-8, Don Y wrote:
On 11/10/2020 1:08 PM, Ed Lee wrote:
On Tuesday, November 10, 2020 at 11:51:15 AM UTC-8, Don Y wrote:

Can you push air through from the sides -- possibly *pulling* it out
on the opposite side? (again, I\'m just suggesting as a means of
testing your theory before doing much surgery)

The existing pack is air tight. No easy way to cut holes without
removing the cover.
Yes, but can\'t you remove cover TO cut the holes (without risking damage
to the cells) and affix/install active cooling measures while replacing
the cover?

Yes, but still need to umount and remount the battery in a shop with vehicle
lift. So, i need to plan everything before renting a bay for few days.
Ahhh! The battery pack mounts to the UNDERSIDE of the vehicle! The
floorboards aren\'t removed to access it from above!

(the mounting flanges visible in the photo aren\'t to hold the pack
DOWN to a surface but, rather, *up*!)

Yes, exactly. It\'s like servicing the transmission, but i can\'t just go to the local transmission shop. Not enough qualified technician to even touch the 600 pounds 400V battery pack. For EVs to improve market share, we need to have more technicians in this area. I am hoping to make the video for people to get familiar with servicing EVs.

 

[Don Y]

On 11/10/2020 4:11 PM, Ed Lee wrote:

On Tuesday, November 10, 2020 at 2:26:42 PM UTC-8, Don Y wrote:

(the mounting flanges visible in the photo aren\'t to hold the pack DOWN to
a surface but, rather, *up*!)

Yes, exactly.

That also explains your \"high water mark\" comment (if the battery was
enclosed within the passenger compartment, I figured \"high water\" would
be the least of your concerns as the vehicle\'s interior would already
be compromised!)

It\'s like servicing the transmission, but i can\'t just go to
the local transmission shop. Not enough qualified technician to even touch
the 600 pounds 400V battery pack. For EVs to improve market share, we need
to have more technicians in this area. I am hoping to make the video for
people to get familiar with servicing EVs.

It is possible to rent a lift (bay) where you live? (dunno, I\'ve never tried
to; a friend has a lift in his garage to service his earthmoving equipment so
getting access to one hasn\'t been a problem, for me)

 

[John Larkin]

On Tue, 10 Nov 2020 07:42:15 -0800 (PST), Ed Lee
<edward.ming.lee@gmail.com> wrote:

According to Google, there are at least 34 views (114 - 70) on my posts on the other thread, but not a single response. So, i am trying more radical ideas for comments (good or bad are welcome). I am going to open up and relocate some of the rear stack modules for better cooling. I want to document it in a video course and post it later.

******

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

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Are you proposing to put a TL431 across each cell to equalize voltages
during charging? Sounds like they would fry to me.

I don\'t see that 400 ohm resistors are much help either.

I just get a tank of gas every couple of weeks.

 

[Ed Lee]

On Tuesday, November 10, 2020 at 3:51:19 PM UTC-8, John Larkin wrote:

On Tue, 10 Nov 2020 07:42:15 -0800 (PST), Ed Lee
edward....@gmail.com> wrote:
According to Google, there are at least 34 views (114 - 70) on my posts on the other thread, but not a single response. So, i am trying more radical ideas for comments (good or bad are welcome). I am going to open up and relocate some of the rear stack modules for better cooling. I want to document it in a video course and post it later.

******

This course offers a case study of the Nissan Leaf Electric Vehicle (EV) and Battery Management System (BMS). The Leaf was the first meaningful Battery Electric Vehicle (BEV) on the market. However, due to limited cooling and poor BMS, many early vehicles are down to 50% or lower usable range. This course offer a teardown and reassembly of the battery module, and compensation with auxiliary batteries to restore it to the original factory condition.

The Leaf BMS uses small 400 ohms resistors to shunt off excessive voltage during charging, but not during discharging. This design relies on very well matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells disable the entire pack prematurely. We will attempt to install additional parallel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are actively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) and over-current (4A) for individual cells. By-pass charging shunts are provided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

@
@
Are you proposing to put a TL431 across each cell to equalize voltages
during charging? Sounds like they would fry to me.

Across the 12V 8254A with high current drivers, as we discussed before. Should be 32 8254A and TL431. The 28 was for something else between the 8254A, but it might not be necessary. Charging current should be limited by the power resistors into each taps.

I don\'t see that 400 ohm resistors are much help either.

I just get a tank of gas every couple of weeks.

Yeah, but what\'s the fun of designing gas tanks.