# Custom water cooling plates for LG Chem batteries out of a Chevy Bolt



## CyberBill (Jan 15, 2020)

Hi all - I'm looking for some ideas and/or links to try and cool my Chevy Bolt batteries. Each module is roughly 13"x18" and I'm using all of the other parts (water pump, radiator, etc) from the Chevy Bolt, but because I'm having to split up the battery into two boxes and arrange them differently, I need to re-design the cooling system.

I'm having a heck of a time finding properly sized water cooling plates / chill plates / cold plates that don't cost a fortune. Going through Send-Cut-Send and getting them CNC cut, we're talking over $150 just for one, which would then need to be sandwiched with another (non-CNC), we're easily talking $200/plate, and with 10 modules I'm sinking $2k into this solution, which doesn't seem reasonable.

Does anyone know of a solution out there that would be around the $100/each mark? I do have a pretty decent shop space available with drill press, table saw, welder, 3d printer, etc...but no mill or cnc plasma table or anything.


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## TeZla (Feb 18, 2021)

What does a cnc plasma table cost? or cnc water cutter? A cnc laser is an expensive piece of equipment but gives the best cut, literally no post clean up, whereas a water jet cutter needs some post cleanup work and a plasma cutter needs substantial post cleanup work.

If it cost $2k for the tooling, you'd obviously have to add your material cost on top, but then you have the tool for all the other parts you need to do along the way, all the little brackets, mounting points, assemblies etc. You could possibly even do some small jobs on the side for others that would recoup your costs?
Otherwise, It costs what it costs, because your engaging someone else to do the work for you using their equipment. Their time and experience has value.


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## cricketo (Oct 4, 2018)

TeZla said:


> What does a cnc plasma table cost? or cnc water cutter? A cnc laser is an expensive piece of equipment but gives the best cut, literally no post clean up, whereas a water jet cutter needs some post cleanup work and a plasma cutter needs substantial post cleanup work.


Is that a rhetorical question ?


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## cricketo (Oct 4, 2018)

CyberBill said:


> Does anyone know of a solution out there that would be around the $100/each mark? I do have a pretty decent shop space available with drill press, table saw, welder, 3d printer, etc...but no mill or cnc plasma table or anything.


Do you have a rendering of the part you envision ?


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## TeZla (Feb 18, 2021)

cricketo said:


> Is that a rhetorical question ?


No, its a serious question.

I needed a bunch of aluminium stuff tig welded, The price got high enough that it was easier to justify buying the welder myself for a little under $2k. Now I can tig aluminium at home and have been doing so for a few years now.
I did the same with a 3d printer, instead of paying someone else, I bought my own printer. I've since used it for a LOT of things and gotten my money's worth.
I've seen several home brew cnc setups that can be built for a pretty reasonable price and a water jet cutter can be made from a modified pressure washer which can be had for a little over $100.

This is a forum where we are all talking about diy'ing our own electric cars, why would it be a difficult proposition to diy a cnc cutting machine?
There are plenty of other people who have done it before, so its not like your going in uncharted territory. Plenty of other good solid examples to follow.

You want to be a customer? Or do you want to own the means of production?


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## MesquiteTim (Sep 30, 2021)

How many plates do you need? Put the total number into the SENDCUTSEND order page and see the price for all of them. The price for 1 at $150 includes all the setup charges. Or design your part so that 2 or 4 of the chill plates are joined together as a single plate. Maybe the total cost of setup will go down.

For your base plates, I bought aluminum "scrap" sheet on ebay from a company in Salt Lake City. They are called metal remnants inc.


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## piotrsko (Dec 9, 2007)

Plates? The correct sized ones are between the cells. You just need coolant flow via fittings you could drill and glue on or grab some assorted endplates. I use an old carbide tipped fine saw blade in a very old skillsaw to cut up to 1/2" aluminum, ditto for my chop and table saws.


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## CyberBill (Jan 15, 2020)

piotrsko said:


> Plates? The correct sized ones are between the cells. You just need coolant flow via fittings you could drill and glue on or grab some assorted endplates. I use an old carbide tipped fine saw blade in a very old skillsaw to cut up to 1/2" aluminum, ditto for my chop and table saws.


I believe you're confusing Bolt with Volt.  Volt has an integrated water cooling 'end cap' thing on each module, but the Bolt has a big water cooled plate at the bottom of the pack that all of the modules sit on.


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## CyberBill (Jan 15, 2020)

cricketo said:


> Do you have a rendering of the part you envision ?


Not yet - I'm waiting on my Bolt to get its battery replaced, then I'll be disassembling it soon after. 

General design is that I'm creating two battery boxes, each will hold 4 of the 'large' battery modules on edge with a small module on the back. That would require 3 large cooling plates (that each cool two modules) and one smaller one for each of the battery boxes - so 6 large plates and 2 small ones. The plates themselves - I'll design them in the typical fashion of some back and forth U-channels.


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## cricketo (Oct 4, 2018)

TeZla said:


> No, its a serious question.


Plasma units from reputable brands are not cheap. I have a Hypertherm Powermax 65, I think it goes for about $3000 new. Just the machine torch (the one for use with a CNC setup) alone for it is like $600. Chinese branded plasmas are significantly cheaper, but mileage varies there. CNC tables vary in price significantly depending on their size/features, for a 4x8 (feet) table $12,000 seems to be the average.

Fiber lasers (CO2 isn't good for metal cutting) are significantly more expensive, like $100,000 on average and again lots of variables that will affect the price. Safe to say other than 30W fiber engravers (still more expensive than plasma) these machines aren't for hobbyists.

Water jet... 20-30k, same deal with different features, sizes, etc.

With that said, CNC plasma is the most affordable metal cutting method for the garage use. If you have the patience and some skill, a CNC table can be built for fraction of the cost. I've built an 8x10 for about $2000 with everything. Plasma can also cut with a minimum kerf on thinner metal, Hypertherm makes "fine cut" consumables for their units.


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## CyberBill (Jan 15, 2020)

MesquiteTim said:


> How many plates do you need? Put the total number into the SENDCUTSEND order page and see the price for all of them. The price for 1 at $150 includes all the setup charges. Or design your part so that 2 or 4 of the chill plates are joined together as a single plate. Maybe the total cost of setup will go down.
> 
> For your base plates, I bought aluminum "scrap" sheet on ebay from a company in Salt Lake City. They are called metal remnants inc.


Wow, I didn't realize the prices at quantity 10 were so different. Thanks for the suggestion! I also realized that depending on what design I chose, it was using some different kind of cutting method or something - because two designs on the same material, one was coming back at like $75/each and another was $125 - I think it was because of the sharp corners rather than circles... But either way, my final design will be way more simple than the samples I chose (an American flag and one that was just a bunch of holes).

There is a 'Metal Supermarkets' near-ish to me that I can buy aluminum plate relatively cheaply. 13"x18" 1/8" plates are $25/each in quantity of 10. I'll keep an eye on eBay for scrap once I've settled on a design!


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## cricketo (Oct 4, 2018)

CyberBill said:


> Not yet - I'm waiting on my Bolt to get its battery replaced, then I'll be disassembling it soon after.


Alright then. Once you have it, post some visual aids


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## cricketo (Oct 4, 2018)

Forgot to add... CNC routers are probably the most affordable and versatile option for the small scale fabrication. Not as fast for the metal cutting (and ferrous stuff is typically too tough for them, so mostly talking aluminum), but the wide choice of materials and actual 3D capabilities make them very useful for these projects.


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## MesquiteTim (Sep 30, 2021)

If you can design your plates so they are all the same, it will be cheaper to machine. You might have a few more water connections but it may be cheaper to make a plate per pack.


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## brian_ (Feb 7, 2017)

I have no idea what they cost, but snowdog had custom cooling plates (of two different designs for different pack locations) made to work with LG Chem modules in his "_Electric Supercar_".

We discussed a commercially available chill plate many months ago, but it was expensive... and it's very difficult to find a past discussion without a good keyword for searching. If I run across it, I'll post a link.


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## CyberBill (Jan 15, 2020)

brian_ said:


> I have no idea what they cost, but snowdog had custom cooling plates (of two different designs for different pack locations) made to work with LG Chem modules in his "_Electric Supercar_".
> 
> We discussed a commercially available chill plate many months ago, but it was expensive... and it's very difficult to find a past discussion without a good keyword for searching. If I run across it, I'll post a link.


Yes, he has a great YouTube channel that I've watched. I saw the videos about the custom cooling plates and wrote down which company he had make them. I will reach out once I have a design - I'll also reach out to some local CNC places for quotes. On the back battery pack he uses one big plate that batteries press against, and on the front he took small water blocks (maybe 1"x2"x12"?) and attached it to a thin aluminum "cold finger" that is pressed against the modules.


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## iti_uk (Oct 24, 2011)

If the modules you are dealing with are the ones I think they are, could you use these? (no affiliation)









EV Battery Module Coolant Plate







zero-ev.co.uk












EV Battery Module Coolant Plate - Single







zero-ev.co.uk





Chris


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## brian_ (Feb 7, 2017)

iti_uk said:


> If the modules you are dealing with are the ones I think they are, could you use these? (no affiliation)
> 
> 
> 
> ...


I don't know what modules you think they are, Chris, but they Bolt modules...


CyberBill said:


> Hi all - I'm looking for some ideas and/or links to try and cool my Chevy Bolt batteries. Each module is roughly 13"x18"...


... and Bolt modules are much bigger that the modules that those plates are designed for; a single Bolt module is larger than the "double" plate.


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## iti_uk (Oct 24, 2011)

brian_ said:


> I don't know what modules you think they are, Chris, but they Bolt modules...


Clearly, the ones that these plates are designed for.

I work in PD for a major OEM and this format of pack is becoming somewhat standard across several OEMs. I had read someone earlier in the thread mention LG modules and that format immediately came to mind. Turns out I am unfamiliar with the Chevy Bolt. "These modules are a different format" would have been a more mature response I guess. 



brian_ said:


> ... and Bolt modules are much bigger that the modules that those plates are designed for; a single Bolt module is larger than the "double" plate.


Fair enough. Carry on.


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## BlueHorizon (Nov 27, 2018)

@CyberBill I’m in the same situation as you right now, albeit it different batteries (LG Chem 60.8v). I have my 12 batteries split into 2 packs, with 4 physically set next to each other and then 2 either above or in front in a T configuration. Besides trying to source these, I also wonder about the pattern of the heat extraction. I’m likely just going to go with a common “s” configuration that maps the individual metal plates underneath the batterie modules. 

Anyway, count me subscribed and I’ll share if I progress on this front.


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## asymptonic (Oct 14, 2021)

I'm planning to snake the coolant through my chill plates rather than pre-dividing the coolant. I wonder if anyone has hard numbers on the number of watts of heat generated in say fast DC charging? That'd help us scientifically work out how much cooling we need.


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## brian_ (Feb 7, 2017)

BlueHorizon said:


> @CyberBill I’m in the same situation as you right now, albeit it different batteries (LG Chem 60.8v)...


So now in this thread four different LG Chem modules - all of similar construction but different sizes - have been mentioned; listed in order from largest to smallest footprint:

from Chevrolet Bolt: 10S3P (8 modules), ~457 mm x ~330 mm
from Chevrolet Bolt: 8S3P (2 modules), ? x ~330 mm (shorter than 10S modules)
from Chrysler Pacifica: 16S (6 modules), 362 mm x 203 mm
VDA 355 format (available from aftermarket suppliers): 4P3S, 358 mm x 151 mm
All these modules are intended to be cooled or heated on their largest face, and to be bolted or bracketed to that surface, so they can be handled similarly (with appropriate dimensions).


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## asymptonic (Oct 14, 2021)

brian_ said:


> and to be bolted or bracketed to that surface, so they can be handled similarly (with appropriate dimensions).


Adding to that I believe they can only be mounted either with the largest face down or on it's side. I got pretty far into designing what I thought was a compact design with some modules upside down but apparently that's a no-no.


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## remy_martian (Feb 4, 2019)

I'd be careful about the gravity vector. On the Bolt, the cells are separated by a rubber membrane which could get compressed by the mass of the cell, messing up the contact with its metal enclosure. In other words, "on its side", with your chill plate in a vertical plane, is not an option. 

Upside down would reduce the pressure against the chill plate, again using mass, and would only rely on the mounting bolt...reduces heat transfer.


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## asymptonic (Oct 14, 2021)

Certainly not meant to be a universal comment. But Zero-EV seems to think sideways is okay for the 4p3s modules they used on their Miata conversion.


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## remy_martian (Feb 4, 2019)

I'm only talking about the paired cells in a Bolt EV. I have no idea how any other modules are assembled.


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## brian_ (Feb 7, 2017)

asymptonic said:


> Certainly not meant to be a universal comment. But Zero-EV seems to think sideways is okay for the 4p3s modules they used on their Miata conversion.


All of these LG Chem modules are stacks of cells, normally used with the cell plane vertical so the axis of the stack is horizontal. Rotating them so the stacking axis is vertical (so, "on end") certainly could be problematic, but it's hard to see how rotation would matter mechanically as long as the cells remain in a vertical plane.


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## remy_martian (Feb 4, 2019)

The weight of the cells presses the thermal housing of the paired cells against the cooling plate and the rubber membrane acts as a horizontally acting spring to press one face of each cell against their thermal housing. Cells in a vertical plane addresses the latter, but not the face pressure against the cooling plate.

I only have the cased cells, not the modules and took one apart to see what was inside....it looks like there may be a clamp of some kind at the center of the face that contacts the cooling plate, but no idea how it works.


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## brian_ (Feb 7, 2017)

This type of module has heat-conduction plates between cells (usually every second cell interface, regardless of electrical configuration) which protrude from between the frame segments, and are simply folded on one long cell edge to lay flat against the largest face of the module... and that's the face that is clamped against the heat transfer plate.

In the forward half of the modules in the classic Leaf pack (24 to 40 kWh) the (optional) heating plates are mounted to ones of the module faces with the long cell edge like this, which are vertical faces (because those modules are in vertical stacks) but folded heat tansfer plates are not used... and thermal management is not a high priority in this battery design.


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## remy_martian (Feb 4, 2019)

"This type of module..."

What does "this type" mean?

The LG Chem cells, used in the Bolt, and looking at the pics and video for the the Zoe, are in a rectangular can of two cells that use a sheet of RUBBER between the two cells as a spring to press outwards on the can walls. Those outer can surfaces conduct heat and turn the corner to a faceplate that contacts a cooling plate. That faceplate is double walled, one from each side of the can.

There's no "heat conduction plate" between cell pairs or adjacent cell pairs. I have no idea what you're talking about with plates between cells. There aren't any.


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## brian_ (Feb 7, 2017)

remy_martian said:


> "This type of module..."
> 
> What does "this type" mean?
> 
> ...


"This type" is modules like the Bolt. What you're calling a "can" is a pair of those plates; Bolt modules are not constructed like early Leaf modules, but they're effectively the same as other LG Chem modules with the same heat transfer approach (but not the Voltage modules). Check out the threads about disassembly and rebuilding of Bolt modules for illustration.


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## remy_martian (Feb 4, 2019)

Brian - I have the f*cking modules and have taken them apart. There is no thermal plate between the cells. It's a sheet of rubber. I just took this pic, just for you:










The cells are in a snap-together two-halved can.


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## asymptonic (Oct 14, 2021)

I don't want to get in the middle of this, but it seems the Bolt modules are different than the Poland LG Chem cells in the i-Pace or the e-tron. Forgot about this nice teardown of the latter from this thread. One takeaway is that it's really not enough to say LG modules. Looks like the prismatic cells are pretty similar but packaging is a bit different.

In the i-Pace modules I don't see how any heat transfer reaches the shell except through the contact on the thin edges with the bottom face. I guess it's enough though.


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## remy_martian (Feb 4, 2019)

Discussion is always welcome - it's how we learn from each other.

That teardown does not take the module down to the cell level. The cells are in rectangular pouches and have one metal electrode foil coming out of each of the long-side ends. 

In your teardown, those foils are still connected to each other. So, no, what he calls cells are not cells.


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## CyberBill (Jan 15, 2020)

My current plan is to have my front 4 modules "sitting flat" like they are in the Bolt pack - but stacked 2 high. There will be 4 individual cooling plates - one for each battery, just like in the Bolt - foam spacer, cooling plate, battery on top. I'll make a frame out of steel angle that will hold onto the 4 through-bolts on the module so that the upper modules aren't putting their weight on the lower ones. The 5th module, the small one, is going just behind it in the gas tank area.

In the rear, I'll have 5 modules (4 'big', 1 'small') sitting "upright" with the main terminals on top and the BMS connectors on the side. This will have a similar layered approach as the front pack - foam, cooling plate, battery, foam, cooling plate, battery, repeat.

I don't see any reason why the Bolt pack wouldn't like to be in the upright position. Especially not for cooling. As shown here, every battery cell in the Bolt pack is pressed up against a thin aluminum plate. The water cooled plates that I'm making (just like the ones that come with the Bolt) are pressed up against these plates with a thermal bridge material. In the Bolt, the cells are upright (imagine the picture rotated 90 degrees to the right - with the cooling only happening on the folded over aluminum on the bottom) - and in my configuration they will be just as they are in this picture. The plastic frame of the modules ensures that there is structural integrity, so the weight of the upper cells is not pushing on lower cells.









I don't really understand your comment #30, remy. You explain clearly that there is a "can" (it's not a continuous piece, it's U shaped, but same thing) and then say it doesn't exist, so I don't really follow. It seems like you and _brian are saying the same thing. All of the cooling and heating for the cells goes through that thin aluminum plate between pairs of cells.


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## remy_martian (Feb 4, 2019)

That photo is misleading. It is not U shaped. There are two cell casings or shells, that form what I call the can:










The one I've outlined on the bottom is a C shape (what you call a U shape) with a dent in it to hold half a cell in place. It's UPSIDE DOWN for artistic license by the photographer, but that is not how it sits in the assembly.

That bottom half shell needs to be flipped over. The bottom half of the lower cell, the one touching the foam with its top, fits into it.

The third cell sitting on top of the upper can I've outlined in that pic is not used. No idea why it's there.

The "legs" on the outer left and right of that lower shell that needs to be flipped over in the pic snap together with the shell above it that houses half the upper cell, the cell whose bottom is touching the foam in the pic. The foam pad separates the two cells inside this snap together can.

The cooling face is two plies of those can legs on the right or left and in a module in the Bolt

All of this is turned 90 degrees in terms of orientation in the car. While the cells are in PAIRS in these cans, the electrical connections are 3P.

As long as you are not compressing that foam with cell weight, an orientation is good. An orientation where the cells are flat is a bad idea as it compresses the cells at the bottom due to module stack weight and almost not at all for the top cell.

That picture totally sucks for showing how the cells are assembled in pairs in that tin casing. It just shows the pieces in the assembly in an almost random orientation and adds a third cell that is not there.

They seem to have known that the electrical connection was 3P and somehow got ahead of themselves on how it all goes together. Completely misleading.

Cells are in pairs, inside a two shelled snap together can, the tabs are electrically connected as 3P in the module the pairs go into.


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## remy_martian (Feb 4, 2019)

C is the cooling face, comprised of two metal layers, one from the face of the cell pair you see and one from the back face you do not.

S is the snap points where the two case halves get held together

2X are the negative tabs from the two cells inside the cased pair of cells. Two positive tabs emerge from the opposite side.

There have been a lot of bullshit theories put forth on how a Bolt EV works thermally at the cell level based on this photograph:










That photo is a jumble of pieces that form a cell pair inside a casing with a third cell thrown in for no apparent reason other than not having a clue how it all goes together.

3P electrical happens in the connections made after the encased cell PAIR gets inserted into the module housing. Each face cools two cells, not three and only one face of each cell has a thermal path to that face. The other cell face is attached to the foam separator between the cell pairs.


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## remy_martian (Feb 4, 2019)

This is a pic I just took of the two can shells snapped together.

These do not have the two cells, and the cell separating foam, that go inside it.

You can see the snap feature that joins the two can shells, holds the cells, mildly compressing that foam between them. The thermal face is two plies of metal each ply being a thermal path to one of the cells' faces. You can see the dent in the shell that cradles almost half of one cell.









This pic also omits the plastic piece through which the compression bolts for the module run. You can see the black plastic piece in the cell pair assembly shown my immedately prior post.


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## CyberBill (Jan 15, 2020)

remy_martian said:


> This is a pic I just took of the two can shells snapped together.
> 
> These do not have the two cells, and the cell separating foam, that go inside it.
> This pic also omits the plastic piece through which the compression bolts for the module run. You can see the black plastic piece in the cell pair assembly shown my immedately prior post.


Thank you for this explanation, remy! I understand what you're saying now - and I'll go out in the shop later today and get some video of the pack I just disassembled.


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## CyberBill (Jan 15, 2020)

Hopefully this makes it a bit more clear.  

You're right that the first pair of cells is wrapped in a can - but the other cells aren't. They are more of a lasagna. You're also right that the picture they took is a bit misleading - it's showing the IDEA of all of the middle cells, but it's using the pieces from the first pair, which isn't right.


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## remy_martian (Feb 4, 2019)

Wow..."none of the others are"

I have a bunch of "first cells", then. Weird.


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## CyberBill (Jan 15, 2020)

remy_martian said:


> Wow..."none of the others are"
> 
> I have a bunch of "first cells", then. Weird.


Wow!! Yeah, for clarification - this is a BRAND NEW battery, replaced from the recall. As far as I know, I'm the first to disassemble it. What model year did yours come from?

I looked at the Weber Auto YouTube video where he disassembles/reassembles the 2017 pack, and you can see that the 'cold finger' plates are slightly different. His has notches cut out of the corners, whereas mine does not.

Also, as far as I know, this is the first confirmation that the assembly of the pack (not just the chemistry) has changed since the 2017 model.


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## remy_martian (Feb 4, 2019)

No idea on model year...mine are module assembly yield reject cell pairs from LG. All, and I have a pallet of them for my personal projects, are "first cells" in that can.

Running design changes are not unusual. Thanks for taking the time & sharing the vid and setting me straight on what's in a module.


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## asymptonic (Oct 14, 2021)

That actually makes a ton of sense. By cooling the "trailing" cell of the next group on the leading plate of the previous one, you halve the amount of metal you need and thus weight and BoM vs a wraparound element per cell pair.

Sort of like [||[||[|| where | are cells and [ are the metal C/U surrounds.


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## brian_ (Feb 7, 2017)

asymptonic said:


> ... Sort of like [||[||[|| where | are cells and [ are the metal C/U surrounds.


I find character graphics amusing, so I'll take that and add the springy foam layers that remy_martian mentioned:
 [*|*:*|*[*|*:*|*[*|*:*|* where 
| are cells,​: are foam sheets, and​[ are the metal C/U surrounds​


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## remy_martian (Feb 4, 2019)

( . )( . ),

You forgot to start with: <- not foam

[|:|]

: - ]


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## brian_ (Feb 7, 2017)

remy_martian said:


> ( . )( . ),
> 
> You forgot to start with: <- not foam
> 
> ...


The combination of [ and ] is only at the end. It's looking like this (for the shorter 8S3P module, for less repetition):
[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*] where
*| *are cells,
: are elastomeric sheets, and
[ are the regular metal C/U elements
] is the special metal C/U element on the end

The elastomeric material is foam or rubber, depending on who is reporting it. I don't know what it really is, but a closed-cell poly, neoprene, or natural rubber foam would be suitable. Solid rubber wouldn't make sense.


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## asymptonic (Oct 14, 2021)

So I'm somewhat curious what the closed cell foam is for? Maintaining a certain amount of compression but avoiding vibration? It's not electrical isolation obviously, since the metal shells are in contact with the cells.


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## CyberBill (Jan 15, 2020)

asymptonic said:


> So I'm somewhat curious what the closed cell foam is for? Maintaining a certain amount of compression but avoiding vibration? It's not electrical isolation obviously, since the metal shells are in contact with the cells.


Lithium ion batteries 'bulge' a bit when fully charged. The foam allows them to have a reasonably consistent pressure pushing up against the cold plate, and to allow for that expansion to not bulge the pack. I would also guess that the foam they use is fire retardant, to (try to) resist battery fires.

Also, the aluminum fins/'shells' are not in electrical contact with the cells. The cells are in insulated pouches.


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## remy_martian (Feb 4, 2019)

CyberBill said:


> Lithium ion batteries 'bulge' a bit when fully charged. The foam allows them to have a reasonably consistent pressure pushing up against the cold plate, and to allow for that expansion to not bulge the pack. I would also guess that the foam they use is fire retardant, to (try to) resist battery fires.
> 
> Also, the aluminum fins/'shells' are not in electrical contact with the cells. The cells are in insulated pouches.


Fire retardant is pointless in a lithium fire

Everything else sounds right.


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## remy_martian (Feb 4, 2019)

brian_ said:


> The combination of [ and ] is only at the end. It's looking like this (for the shorter 8S3P module, for less repetition):
> [*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*[*|*:*|*] where
> *| *are cells,
> : are elastomeric sheets, and
> ...


Not poly
Not natural rubber
Not solid rubber - it does have a spring constant to it

Neoprene with adhesive on each of the two faces.


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