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Pics/Info: Inside the battery pack

scaesare

Well-Known Member
Mar 14, 2013
8,642
15,405
NoVA
Possibly a dumb question but what happened to the intumescent goo? Was it never in production packs or only in earlier/later versions?

Although I heard it discussed in some threads... and have heard of references to it in early pre-production packs and/or patent apps, I don't believe I've sever seen evidence of it making it in to a production pack...
 
Missed this almost...

The 18650 cells are bare, no label or anything. So the entire casing, including the negative end, is negative. So you're looking at the negative end of the cell. The bus plate sits on top of a piece of plastic with cut outs for each individual cell. The cutout in the plastic with it's raised walls around the hole (to protect the small fuse) are what you're seeing on top of the negative end of the cell. The cell level fuse then connects from the bus plate to the cell itself through this opening in the plastic.

The same for the positive side, except the positive end of the cell has a triangle-like positive terminal that is insulated from the negative casing.

Note that the plastic protective cover is in place on the modules in most of my pictures, also.

--------------

I know I'm seeing the top of the negative end of the cell but what I'm not certain about is if that end is an added endcap on the "raw" cell or has been added on over a "standard" panasonic cell. In the Tesla patent where they describe adding a the C-shaped or O-shaped vent. When I say raw cell vent I mean: "The venting region, defined by scoring on the battery terminal, ruptures when the internal battery pressure exceeds the predefined battery operating range"

This scoring is done is a C-shaped manner as seen on the 18650PD:
View attachment 58839


Or in an O-shaped manner such as the 18650BE
View attachment 58838

(note both these cells are the only on the market with the triangle shaped postive terminal as we see in the Model S and RavEV)

View attachment 58842View attachment 58843


Note in the Tesla patent they describe in Figure 19 adding an endcap that COVERS the O-shaped vent on the raw cell end such that when the raw cell vent breaks it blows off the end cap and break the wire bond/fuse.

View attachment 58840

"In an alternate embodiment, illustrated in FIGS. 18 and 19, the inner edge of mounting support substrate 1801 extends beyond, i.e., overlaps, scoring 1803. Note that scoring 1803 is shown in phantom in FIG. 19."

As I read it adding an endcap supposedly reduces the chances of a re-connect after the vent breaks the wire bond.


Can you get a closeup of this area...this picture shows maybe an endcap, not sure, also it appears to show something like black plastic sandwiched in between than maybe holds the cells spaced apart, or I could be seeing thing haha thanks:
View attachment 58844
 
On that board

U4 - Silabs isolator (http://uk.mouser.com/ProductDetail/Silicon-Labs/Si8642ED-B-IS/?qs=NVLsoTRMv1oBDPBFWNUX/g==) for the interface back to the BMS board
U100 - Silabs MCU (http://www.ko4bb.com/Manuals/12)_Components_Specs&Datasheets/Silabs/C8051F520A-F530A.pdf) very basic - probably only interfaces with TI chip
U1 - TI battery management IC, part number seems custom or possibly re-marked (it seems unlikely Tesla would be worth spinning an IC for - but maybe since this is a later revision it is?)

Interesting that they have a huge isolation barrier for the pack board. I wonder if the main BMS board is completely isolated from the pack, as I wouldn't have thought something like 8mm isolation would otherwise be necessary.

edit: nvm - the TI IC is definitely not custom or re-marked, it's this:
http://www.ti.com/product/bq76pl536a

designed specifically for EV/Hybrid, $8.00 a pop so Tesla must think it's simpler than a lot of diff-amps and a faster MCU with multiple channels. (it probably is in the end.)

Tesla use -Q1 variant "zero defect".
 
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wk057

Vendor & Senior Tinkerer
Feb 23, 2014
5,936
13,445
Hickory, NC, USA
There is a fuse on its own and the TI chip has a built in 5V LDO, so I suspect it's powered from that. There's also a device "U2" which might be a voltage regulator, but I can't read the part #.
I'm surprised they use an LDO for 25V -> 5V drop but I guess the quiescent current must be pretty low.

- - - Updated - - -

Dang!
I hate SiLabs parts. Tesla used them in the fob as well.
No rear surprise on the degree of isolation as the modules are at vastly different potentials.

Looks like Silabs got a big design win on the Model S then. 32 chips per car, plus fob, plus who knows what elsewhere. (Although TI get $128 per battery, not bad either.)

The modules are only about 25V apart from their neighbours but I guess that the BMS board doesn't chain them together, so the isolation makes some more sense, though it's still wider than I expect, they don't spend any more or less money on making it wider.
 

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
5,936
13,445
Hickory, NC, USA
Images I post in this thread and my related commentary are posted and published by me, the original photographer. All copyrights and all other rights reserved. These images may not be copied or otherwise distributed outside of this forum without my express permission.

OK! So, bunch of pics from my tear down phase...

2014-09-09%2019.32.03-1280.jpgURL]
Some tubing from a past PC water cooling project. I put some holes in the tube near the end so that when I put it into the quick disconnect there is a path for the fluid to flow...


2014-09-09%2019.37.37-1280.jpgURL]
Yup. Shoved the tubes in and taped it up...


2014-09-09%2019.49.52-1280.jpgURL]
Pumped air into the one tube and pushed the coolant out.


2014-09-09%2019.57.05-1280.jpgURL]
One final check of the full pack voltage before I start electrical tear down. 368.2V (3.835V per cell after topping off with HV charger).


2014-09-09%2020.02.41-1280.jpgURL]
Removal of the pack main fuse and plastic housing.


2014-09-09%2020.05.42-1280.jpgURL]
Removal of the first bus bar!


2014-09-09%2020.08.05-1280.jpgURL]
Side view of the BMS boards on the front oddball modules. Clearly shows the top module is upside down.


2014-09-09%2020.08.13-1280.jpgURL]
Small bus bar connecting the two oddball modules. It is layers of copper pressed together and tin coated.


2014-09-09%2020.09.59-1280.jpgURL]
Starting to remove the next bus bar.


2014-09-09%2020.11.53-1280.jpgURL]
Disconnecting the coolant loop from the top oddball module. Turns out I drained 99% of the coolant out.
Does anyone know what the heck kind of fitting this is?


2014-09-09%2020.13.54-1280.jpgURL]
Top module removed!


2014-09-09%2020.14.01-1280.jpgURL]
Oddball module is now loose! First one! (Bottom view)

2014-09-09%2020.14.28-1280.jpgURL]
Side view of the module... and my shoe.


2014-09-09%2020.14.38-1280.jpgURL]
"Front" of module, still has small extensions connected to the terminals for the odd placement.


2014-09-09%2020.14.58-1280.jpgURL]
Oddball module top view with extension pieces still in place...


2014-09-09%2020.15.24-1280.jpgURL]
Removal of small extension pieces, revealing that the oddball module isn't actually all that odd...


2014-09-09%2020.23.28-1280.jpgURL]
Tesla part label for the module. 1009312-00-E.


2014-09-09%2020.23.51-1280.jpgURL]
Bottom front module removed.


2014-09-09%2020.36.18-1280.jpgURL]
Removal of remainder of bolts for electrical connections to the modules.


2014-09-09%2020.49.06-1280.jpgURL]
Removal of the first bus bar which is revealed to be inside some kind of injection filled solid rubber inside the spine of the pack... the inner modules can't be removed easily without removing the bus bars first because there is not enough room to disconnect the coolant loop without first lifting the module up and out a bit...


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 20.52.20.jpg"]2014-09-09%2020.52.20-1280.jpgURL]

Surprise! Not a bus bar afterall... ~2/0 gauge wire runs the length of the spine, surrounded in thick fireproofing material. This image is really showing the shunt and its PCB.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 20.52.29.jpg"]2014-09-09%2020.52.29-1280.jpgURL]

Close up of the weld on the 2/0 wire.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 20.58.40.jpg"]2014-09-09%2020.58.40-1280.jpgURL]

Ripping more of the spine out. Yep... spineless pack soon.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 20.58.45.jpg"]2014-09-09%2020.58.45-1280.jpgURL]

Close up of one of the small bus bars from the side.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.05.17.jpg"]2014-09-09%2021.05.17-1280.jpgURL]

Attacking from the other end.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.19.06.jpg"]2014-09-09%2021.19.06-1280.jpgURL]

Man that stuff is really in there...


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.21.10.jpg"]2014-09-09%2021.21.10-1280.jpgURL]

First module from the rear of the pack.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.21.23.jpg"]2014-09-09%2021.21.23-1280.jpgURL]

And its former home.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.21.31.jpg"]2014-09-09%2021.21.31-1280.jpgURL]

Close up of some kind of safety relief vales on the outside edge of the pack where the module used to be and the coolant loop connectors.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.42.54.jpg"]2014-09-09%2021.42.54-1280.jpgURL]

Label on the cable removed from the spine.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.43.30.jpg"]2014-09-09%2021.43.30-1280.jpgURL]

Spine removed, More modules liberated!


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.56.36.jpg"]2014-09-09%2021.56.36-1280.jpgURL]

Modules off to the side. (sticker is from me not Tesla)


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 21.56.46.jpg"]2014-09-09%2021.56.46-1280.jpgURL]

More modules, shot of the empty spine.

[URL="http://files.wizkid057.com/teslapack/update3/2014-09-09 22.14.50.jpg"]2014-09-09%2022.14.50-1280.jpgURL]

The bus bar collection that was removed.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-10 22.09.53.jpg"]2014-09-10%2022.09.53-1280.jpgURL]

Pack casing ready to be scrapped, coolant loop removed, main BMS board removed...


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-10 22.10.09.jpg"]2014-09-10%2022.10.09-1280.jpgURL]

Stacked the modules out of the way with their original covers in place for weight distribution.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-10 22.10.19.jpg"]2014-09-10%2022.10.19-1280.jpgURL]

Whats left of the coolant loop, main BMS board, some bus bars in a bin.


[URL="http://files.wizkid057.com/teslapack/update3/2014-09-11 20.58.43.jpg"]2014-09-11%2020.58.43-1280.jpg

Shot of the bare cells from the side. This one has a barcode printed on it...

Images I post in this thread and my related commentary are posted and published by me, the original photographer. All copyrights and all other rights reserved. These images may not be copied or otherwise distributed outside of this forum without my express permission.
[/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL]
 
Last edited by a moderator:
WOW! As I install LiFe in my little car I am in awe of the beauty of this pack!! I love the international nature of all the components.. hopefully this means more ships than one are rising on this tide!
teslaspotter

I figured someone would find these pics and comments interesting and/or informative. I will try to take some more as I get to actually doing something with the pack.

-wk

Update 2014-09-10 --- Added scans of BMS board from a module.
Update 2014-09-11 --- Added link to new post with more pics (so not to make this page impossible to load...)[/QUOTE]
 

stopcrazypp

Well-Known Member
Dec 8, 2007
12,043
7,842
Ok, so the excess electricity is wasted as heat, right? Sounds to me that balancing can occur at any SOC regardless of whether or not the car is charging. So does this bust the long standing TMC theory that pack balancing only occurs on a max range charge?
You can balance at any SOC, but if you want the absolute max capacity out of your pack, balancing at 100% SOC (or close) is going to give you the highest number.
This link kinds of explains how top balancing stores more energy (vs bottom balance).
http://books.google.com/books?id=o-...allows batteries to store more energy&f=false

Also, because of how the voltage curve is shaped vs. SOC, balancing at 100% is a lot more accurate than anywhere near the middle (because the slope of the curve is much higher). It's also possible the software is set so it doesn't balance unless it is near 100% SOC.
 

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
5,936
13,445
Hickory, NC, USA
So, any thoughts about what that small shunt board attached to the bus bars is?

It is a current monitoring board for the BMS to know how much energy is flowing in or out of the pack as a whole. The shunt is a piece of metal with an accurate and known resistance, and the voltage drop across it at various current draws is directly proportional to the amount of current flowing through it. The small board reads this and calculates the power flow and reports it to the main BMS board.

The one thing I haven't been able to figure out is how the coolant actually flows through the modules to cool the individual cells. Is that grey rubber-like material shown on the last picture related to the cooling?

The grey rubber like material is actually thermally conductive material (like thermal pad material), and it presses against the coolant loop and every cell. The coolant loop goes into the module, flattens out, then weaves around all of the cells conducting heat through the thermal material.

- - - Updated - - -

I'll also note for completeness that the presence of the isolation IC on the BMS module board rules out any inter-module active balancing.
 
Expanding on that, the BMS could at most draw about 42W from the pack if all 96 bleeders were active at once... which would take 84 days to bring the pack (85kWh) from 100% to 0%, lol.

I think most imbalances would be a few 10s of mV, which should be only a couple hours of bleeding probably.

That sounds about right. When the pack is not connected to the vehicle the max intentional self discharge rate is 50w (10W preferred) using the bleed resistors

When connected to the vehicle it can use the load from the heater and fans and what not to intentional self discharge up to 20kw (10kw preferred)

This feature is so you dont have to have an external load to dischrage the pack down to a safer voltage for shipping or after an accident or for service
 
It is a current monitoring board for the BMS to know how much energy is flowing in or out of the pack as a whole. The shunt is a piece of metal with an accurate and known resistance, and the voltage drop across it at various current draws is directly proportional to the amount of current flowing through it. The small board reads this and calculates the power flow and reports it to the main BMS board.



The grey rubber like material is actually thermally conductive material (like thermal pad material), and it presses against the coolant loop and every cell. The coolant loop goes into the module, flattens out, then weaves around all of the cells conducting heat through the thermal material.

- - - Updated - - -

I'll also note for completeness that the presence of the isolation IC on the BMS module board rules out any inter-module active balancing.

Inter-module active balancing is done by shuttling during charging but this shuttling is not done in the traditional dangerous way. Balancing is done by increasing the voltage not only bleeding. Bleeding is not an efficient way of balancing as it just creates heat. Virtual shuttling is done by continuously changing the target balance voltage which will in effect shift charge through the whole pack
 

rabar10

Model 3 >> Focus Electric
Moderator
Dec 3, 2010
1,455
190
Indianapolis, IN
Inter-module active balancing is done by shuttling during charging but this shuttling is not done in the traditional dangerous way. Balancing is done by increasing the voltage not only bleeding. Bleeding is not an efficient way of balancing as it just creates heat. Virtual shuttling is done by continuously changing the target balance voltage which will in effect shift charge through the whole pack
Changing the target balance voltage for one module to be different than others (based on small V/Ah differences between modules) would still result in passive balancing -- as the pack charges, some modules' bleed resistors would be used before others. As others have posted, I don't see any way to do inter-module active balancing with the circuitry shown.
 

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