Making a custom battery pack for MiEV

Frud · Feb 20, 2024

Hi all. I recently bought an i-miev with a faulty battery. I want to remake the battery myself with new elements. According to my calculations, the cost of the conversion will be about $3,000. The approximate battery capacity will be 25 kWh. Cells SK Innovations E777.
I have already designed a block with 44 cells. It is slightly smaller in size than the LEV50 5x8 units.

This is what it looks like in the picture.

I plan to integrate the original CMU boards into the free space of the 4S units, left and right, and connect them with wires to my 44S units.

Today I tried on the design elements of the unit in the battery case. All dimensions are completely identical and the top cover of the battery case closes tightly.

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MickeyS70 · Feb 20, 2024

I assume the reason you use this approach is down to cost as prismatic cells would be a lot easier to handle, i.e no change to the layout and thermal management would be required.

Do you have any specs on the E777 (77.7Ah) cells? Most interesting would be a diagram of the charge/discharge curve to see how much of the capacity the original BMU will recognise?

Link below shows the excellent work David (CZeroOwner) has done to outline the problem (post 92):
https://myimiev.com/threads/battery-capacity-testing.2386/page-5

Frud · Feb 20, 2024

You're right. The price per cell is 16 euros/piece. and European manufacturer. I don't really trust the quality of the Chinese.
In addition, I get a total reduction in battery weight of about 50 kg.
Here is a charge/discharge curve based on manufacturer data

Very similar to the curve from CZeroOwner

MickeyS70 · Feb 20, 2024

Frud said:
Very similar to the curve from CZeroOwner

Similar is not good enough I’m afraid as the BMU is ‘hardwired’ to the LEV50 characteristics. A rough estimate based on your graph gives an LEV50 equivalent of well below 45Ah which is quite disappointing considering the extensive modifications required to change the cells..

Frud · Feb 21, 2024

I have ideas on how to fix this. I won’t reveal all my cards for now, but if I succeed, I’ll definitely share it.

MickeyS70 · Feb 21, 2024

Pls do as regardless of the outcome, information like this will help to eventually ‘crack this nut’…

What has worked for others (at least temporarily) is to tell the BMU a new battery pack has been installed. This will set the capacity to 45Ah, you need a dealer diagnostic tool (MUT3 or Diagbox) to do that.

kiev · Feb 21, 2024

Frud said:
All dimensions are completely identical and the top cover of the battery case closes tightly.

That is a very clean looking modification.

How did you remove the ribs from the bottom cover? That was a good idea to open up more space.

Approximately how much clearance is there above the cells to the inside of the top cover?

Will you build up your own 4p Cells from the SK cells, or is there a product already available in that configuration?

The "Reset" function of the MUT described in the FSM writes the capacity back up to 45Ah. We are searching for a way to make it higher, e.g. 60, 75, 94.

With the 12 CMUs and wiring harnesses it might be worthwhile to design a single board to replace all that mess. The CAN messages are probably 90% known and understood.

i couldn't find a datasheet or any technical info about the SK cells, e.g. dimensions and other cell parameters. But found Lots of Press Releases about how great they are, joint venture with Ford, etc.

Frud · Feb 21, 2024

The ribs of the bottom cover were cut off with an angle grinder.

Clearance is approximately 15mm, it is difficult to measure more accurately, but the finger fits freely

Cells are sold separately. I will assemble 2 blocks of 44s in holders of my own design

SK cells are used by Hyunday/KIA, VW, Ford

Frud · Feb 21, 2024

MickeyS70 said:
Pls do as regardless of the outcome, information like this will help to eventually ‘crack this nut’…

What has worked for others (at least temporarily) is to tell the BMU a new battery pack has been installed. This will set the capacity to 45Ah, you need a dealer diagnostic tool (MUT3 or Diagbox) to do that.

I have extensive experience repacking Nissan Leaf and KIA Soul batteries using these cells. I solve the issue with battery capacity using a CAN bridge and my own software. This allows these vehicles to use the full capacity of the new battery.
At first glance, the i-miev algorithms are much simpler than those with which I have already dealt.

piev · Feb 22, 2024

Hey Mickey, I am doing a similar project.
https://myimiev.com/newsletter/47728-1708605811-81c8b44c798e150a4b83a0364aeb611f/click

If you want a collaborator on developing the CAN bridge I am available.

MickeyS70 · Feb 22, 2024

piev said:
If you want a collaborator on developing the CAN bridge I am available.

You are correct, so far the only proven concept seems to be the ‘CAN man in the middle’ solution. I gather you have successfully corrected a faulty temp sensor this way, my intention is to use this method to correct a dodgy CMU voltage reading.

However fooling the BMU into accepting NMC batteries is a different task, for starters the CAN bridge will be between the BMU & EV-ECU but luckily Frud has done this before seems to be confident he can do it again.

Mickey

Negue · Feb 26, 2024

Nice

I hope to end this good project soon

Negue · Feb 26, 2024

Frud said:
I have extensive experience repacking Nissan Leaf and KIA Soul batteries using these cells. I solve the issue with battery capacity using a CAN bridge and my own software. This allows these vehicles to use the full capacity of the new battery.
At first glance, the i-miev algorithms are much simpler than those with which I have already dealt.

Can you give me a link to your Leaf projects ? I'm interested that to.

jray3 · Mar 3, 2024

Frud, I'm glad to see you here. I was the first in the USA to commercially repack LEAFs (using the discontinued ingenext/SimonAndre CANbridge) I also drive a 2016 SOUL EV, but it has only 20k miles on the warranty-replaced 30 kWH pack. Repacking the i-MiEVs is a higher priority, so I'll be following your work closely!

piev · Mar 8, 2024

MickeyS70 said:
You are correct, so far the only proven concept seems to be the ‘CAN man in the middle’ solution. I gather you have successfully corrected a faulty temp sensor this way, my intention is to use this method to correct a dodgy CMU voltage reading.

However fooling the BMU into accepting NMC batteries is a different task, for starters the CAN bridge will be between the BMU & EV-ECU but luckily Frud has done this before seems to be confident he can do it again.

Mickey

Agreed, it’s really just a matter of time. I see no technical roadblocks. Figuring out which PIDs the ECU needs is where I’m at currently. Some of these OBD programs use a lot of PIDs that the BMU doesn’t send without a request. Just taking data while driving down the road all I see is 373, 374, 375, 5A1 and 6E1-6E4. I believe this is the only information the ECU needs.

I successfully modified 374 [0] and [1] and saw the range and the fuel bar gauge change. I don’t believe the ECU is using much of the other information for control but I’ll need to do some driving to see.

MickeyS70 · Mar 8, 2024

Looks like you’re right on the button; 374 is also what Francisco.si has identified as the relevant SOC…

https://www.forums.aeva.asn.au/viewtopic.php?t=5515&start=575

Frud · Mar 13, 2024

Hi all. I finally assembled the first block of 44s. Missile attacks by russian terrorists did not allow me to do this quickly enough.

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MickeyS70 · Mar 13, 2024

Looking good, any idea how you’re going to connect the temperature sensors on the CMU boards to the actual cells?

Sandrosan · Mar 15, 2024

Hi Frud,
Congratulation! Your cells assembly design looks so clean and good looking. I am following your project with great interest.
My regards and take care there.
Sandrosan from Italy

Frud · Apr 17, 2024

The second battery pack is ready.

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While the old battery is on the car, I assembled and tested the CAN bridge.

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I used Arduino Nano and 2 MCP2515 boards. So far everything is working well. I managed to change the SoC, cell voltage, battery voltage.

The bridge is powered by an Ignition BMU.

I also started manufacturing CAN bridge v2, based on Arduino Mega 2560.

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I express my deep gratitude

Making a custom battery pack for MiEV

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