LG E78 battery build

[larsb]

I bought some LG E78 cells from Tumich here at ES so i'm planning a pouch cell battery build. Original goal was to do four 6s packs that i could use in different builds, on my emoto/Efoil/Tow boogie etc. but they might become too high for the efoil with the casing around them.

Basic dimensions so far:

the cell tabs aren't symmetric - which is an issue with these reclaimed cells, tabs are only 9mm wide so they can't be clamped towards each other directly, the tabs are simply too short. This means they will be be assembled staggered and that full current will go through the clamping part. That kinda sucks.


I can't really see a smart way of getting around this..

 

[dominik h]

Make a 10mmx10mm copper part that goes from the beginning of one tap to the end of the other and clamp the taps with two clamps onto the copper part in their complete lenght. So the current should be distrubuted on the complete rest of the tap width.

 

[larsb]

Yeah, I thought about something like this:

It's simple and will work with some clamping points but it's not the way i hoped to do it
A 10x10 copper bar will cost a lot with the prices for copper now so i think i'll try to avoid it even if it's the obvious solution.

 

[eee291]

I'm pretty sure you just need to flip every other cell

 

[larsb]

Flipping doesn't work, at least not as i see it with the cells as they were delivered from Tumich. cells are 10mm high, tabs are 5-15mm long and offset to the bottom side - so they will be alternating from being next to each other and being 20mm apart if you start flipping the cells.

I don’t want to bend or apply pressure on the cell casing foils, as would be needed to make the tabs centered on the height. It could be done with longer cell tabs so it really blows that they are cut too short on the cells.


Anyway, it turned out pretty OK, question now is if it's worth checking on Alibaba to get these made? Pretty simple design, one bend and six holes so shouldn't cost too much if you can get a fair price.


? Does anyone have a bus bar source that they're happy with?

 

[amberwolf]

How are you actually going to do the clamping?

I don't see how you could install screws, rivets, or anything else into the holes without shorting to the other tabs nearby, or placing mechanical stress on them?

 

[larsb]

It will be pretty tight vs the next cell clamp, i agree. I am hoping to make a separation/fixation lip for each row, integrated in the sideplate, i’ll upload a pic later.

 

[amberwolf]

So something that inserts between the clamps that is slightly larger than the space between the clamps, forcing them together? If so, make sure it is not somethign that has a much higher deformation / flow temperature than any temperature the pack will ever reach, or it will loosen the clamping force, increasing the resistance, increasing the heat, and you may eventually have melting and a short circuit as a bar moves across a cell.

 

[larsb]

No, i still plan to clamp it with screws. There's no room for screw insertion and i want to have only metal to metal contact in the clamp
I will have to figure that out

 

[dominik h]

Can you write something about the price you paid for shipping and how many you bought?
Did you know before that the taps are cut?

I´m also thinking about th LG E78 for my next build , but I´m not shure if I should stay with 2x12S VW MEB modules (24s - 13,5kw/h aproximatly 1600€ for used modules) or with a 28S2P ( 16kwh 1900€ for "new" cells) setup with loose pouch cells, and have all the problems with connections and housing, or even build two seperate 28S1P batteries with reduced weight and output power when only one is battery is used.
Have you ever found an information about output power burst in the range 5-10 seconds, can they handle 5c for short bursts?

 

[AGS]

Other people have had the same dilemma. There are several YouTube videos of how they have tried to resolve the problem of clamping/bolting them together.

This is the best solution that I have seen. Other solutions look a bit dodgy to me,

 

[larsb]

These are different modules with centered tabs, would be easier to solve. I guess i could do each series connection one by one to build the stack of cells, that would give me access to tighten screws.

 

[larsb]

Can you write something about the price you paid for shipping and how many you bought?
Did you know before that the taps are cut?
Have you ever found an information about output power burst in the range 5-10 seconds, can they handle 5c for short bursts?

I paid 29Eur per cell, 24 cells and 34Eur shipping to sweden. Unfortunately DPD had ripped the package and it couldn’t have been packaged well enough from Tumich. I didn’t know that the cells were cut, on the pics here on ES the cells are new and uncut as far as i can see.

If you can fit the modules i’d go with that, they are better designed than something we will ever make as diy, especially for these cells which seem to be designed for parallell spotweld connections and then separate bus bars for series connections.

They are 5c pulse discharge according to this:

Аккумуляторный елемент LG-Chem LGX-e78 химия NMC 3.6v (пакет) емкость 78А/Ч разряд 3-5c 2000 циклов 1180грам - LG-CHEM химия

lg e78 1 140грн.

lgx.com.ua

390A for a single cell is quite a lot to transfer in the series connections..

 

[larsb]

I tried a front clamp setup, would be a lot of screws but in the right direction. Tabs would have to be folded but might work, at least for the 100A burst i normally use.

 

[dominik h]

I would go for the front clamp.
Looks a lot smaller than your first solution and should be ok for 100A.

 

[larsb]

Yes, should be ok to build too. i'll suss out the details in a few days, then start ordering parts

 

[larsb]

Moving closer to a more finished state. I'll do a test with this design on the 3D printer to see how they feel, then i'll move on to the casing and balance wires etc. Eventually i'll get them professonally 3d-printed in some heat resistant material like PC

 

[larsb]

Got the 3d prints ready, they fit nicely and are stiff enough to just optimise a bit. I’ve ordered the thread inserts and copper so i can do a test assembly before ordering the real sideplates.

As they print OK on my 200$ printer they’ll be good when ordered

 

[larsb]

I started on the outer casing and refined the sideplates. I'll have to decide on a sealing method for the endplate so there will be some changes to the outer flange.


I'll need a balance connector with 7 pins that is either IP67 or IP68 and comes with a sealing cap. Tips are welcome

 

[larsb]

Some bad news, I checked the all cells today and they have a wide spread on the cell tab length and one is punctured. I plan to use the packs at full current in my emoto - i can’t have 6mm tabs at 390A.
I'll get replacements from Tumich as it seems but it sucks to lose quite a lot of time and efforts.

 

[larsb]

After some thinking back and forth on my options I sent 12 cells back for a refund - i’ll do two 6s packs and not four to lower the costs since i’ve come to doubt the cells.

Purpose of the build will then be more modest, to learn a bit on pouch cell pack building and then hopefully get at least 300 cycles out of them on my efoil.

 

[larsb]

Got the refund for the cells so all was handled OK, even if i lost some time.

In the meantime i got the threaded inserts and copper wire for bus bars so i will update my models and do i final test print.