Nissan Leaf Battery and BMS

and Battery Management System (BMS). The Leaf was the first meaningful Batt ery Electric Vehicle (BEV) on the market. However, due to limited cooling a nd poor BMS, many early vehicles are down to 50% or lower usable range. Thi s course offer a teardown and reassembly of the battery module, and compens ation with auxiliary batteries to restore it to the original factory condit ion.

during charging, but not during discharging. This design relies on very we ll matched battery cells. There are problems with strong and weak cells. St rong cells prevent final peak voltage for charging, while weak cells disabl e the entire pack prematurely. We will attempt to install additional parall el battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are active ly managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) an d over-current (4A) for individual cells. By-pass charging shunts are provi ded 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 2

4 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 r ear 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 instal led.

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?

les,

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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 v ehicle, 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 repl ace 6 to 10 cells at around 70% cap, not too small and not too big. But o nce i open it up, might as well relocate them for better air flow and cooli ng.

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

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

n the other thread, but not a single response. So, i am trying more radica l 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 docu ment it in a video course and post it later.

and Battery Management System (BMS). The Leaf was the first meaningful Bat tery 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. T his course offer a teardown and reassembly of the battery module, and compe nsation with auxiliary batteries to restore it to the original factory cond ition.

during charging, but not during discharging. This design relies on very w ell matched battery cells. There are problems with strong and weak cells. Strong cells prevent final peak voltage for charging, while weak cells dis able the entire pack prematurely. We will attempt to install additional pa rallel battery cells to match storage capacities, as well as overall auxili ary modules to restore to factory condition. The auxiliary batteries are a ctively managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5 V) 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 a nd 32 TL431 in the auxiliary pack.

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

on the other thread, but not a single response. So, i am trying more radic al 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 docum ent it in a video course and post it later.

) and Battery Management System (BMS). The Leaf was the first meaningful Ba ttery 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. T his course offer a teardown and reassembly of the battery module, and compe nsation with auxiliary batteries to restore it to the original factory cond ition.

ge 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 disa ble the entire pack prematurely. We will attempt to install additional para llel battery cells to match storage capacities, as well as overall auxiliar y modules to restore to factory condition. The auxiliary batteries are acti vely 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 pro vided by the TL431 shunt regulators. There is an estimate of 28 8254A and 3

2 TL431 in the auxiliary pack.

Once the high voltage service disable plug is disconnect. It's just two 20

0V batteries inside. I am tapping at 100V segments; so, each external modu les 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 a re fairly safe to handle. I have not been seriously shocked yet.

I found this:

(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:

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

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

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! :>

Yes, correct.

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

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

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

Actually, my (or somebody's) butt.

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.

on the other thread, but not a single response. So, i am trying more radica l ideas for comments (good or bad are welcome). I am going to open up and r elocate some of the rear stack modules for better cooling. I want to docume nt it in a video course and post it later.

and Battery Management System (BMS). The Leaf was the first meaningful Bat tery 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. Th is course offer a teardown and reassembly of the battery module, and compen sation with auxiliary batteries to restore it to the original factory condi tion.

e during charging, but not during discharging. This design relies on very w ell matched battery cells. There are problems with strong and weak cells. S trong cells prevent final peak voltage for charging, while weak cells disab le the entire pack prematurely. We will attempt to install additional paral lel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are activ ely managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) a nd over-current (4A) for individual cells. By-pass charging shunts are prov ided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

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

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.

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

.

No, that's just plastic cover for the bus bar and terminal. I am talking a bout the heavy metal cover for the entire pack. I have to remove it from t he 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 dri ve into water, as long as the doors are closed. If i dive into the water h ead first with the window open, that's a different story.

Yes, correct.

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

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.

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.

on the other thread, but not a single response. So, i am trying more radica l ideas for comments (good or bad are welcome). I am going to open up and r elocate some of the rear stack modules for better cooling. I want to docume nt it in a video course and post it later.

and Battery Management System (BMS). The Leaf was the first meaningful Bat tery 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. Th is course offer a teardown and reassembly of the battery module, and compen sation with auxiliary batteries to restore it to the original factory condi tion.

e during charging, but not during discharging. This design relies on very w ell matched battery cells. There are problems with strong and weak cells. S trong cells prevent final peak voltage for charging, while weak cells disab le the entire pack prematurely. We will attempt to install additional paral lel battery cells to match storage capacities, as well as overall auxiliary modules to restore to factory condition. The auxiliary batteries are activ ely managed by the 8254A BMS chip for over-volt (4.2V), under-volt (2.5V) a nd over-current (4A) for individual cells. By-pass charging shunts are prov ided by the TL431 shunt regulators. There is an estimate of 28 8254A and 32 TL431 in the auxiliary pack.

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

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