openinverter forum

Hi,

I have been absent for quite a while, but once the EV bug bites you, it is hard to keep your hands off the next project.

This time I did not want to start completely from scratch, although I had some crazy ideas. I bought a bricked Tesla Roadster. I have always admired these cars because they are a real part of EV history and, in my opinion, always will be. Tesla delivered about 2,450 first-generation Roadsters worldwide.

I recently bought Roadster #802, a May 2012 Roadster 2.5. The high-voltage battery is dead on this one, the car does not drive, and the mileage is roughly 78,500-80,000 km. According to the history I got with the car, it ended up with a dead pack after body-shop work in 2023 and then apparently sat too long without proper charging. On a Roadster, that is a serious problem: if charging is interrupted for long enough, the pack can deep-discharge into a bricked state, and even 2-3 months unplugged can already be enough to cause major trouble. After roughly three years, I think it is fair to assume the original pack is beyond recovery.

So I purchased a VW ID.3 battery from a 2024 model year with about 15,000 km. With the help of Johannes and his BMS, I am going to build a new battery pack for the Tesla Roadster. I will use 8 of the 9 VW ID.3 modules. Since the 62 kWh MEB modules are 12s2p, that gives me a 96s pack. The original Roadster pack has 99 monitored brick voltages, so the conversion will handle the 96s-to-99-brick by "faking" the 3 Cells on the CAN Bus.

The goal is to make the conversion open source so it can help other Roadster owners keep these cars on the road without having to rely on an OEM-style replacement path that is very expensive. Tesla’s Roadster 3.0 battery upgrade is around $40.000 USD as far as i know!

The pack will be liquid-cooled as the original Roadster pack and also have CCS charging capability, based on all the developements that this community has made so far.

Follow this thread for more updates over the next few weeks.

Philip

Good luck, I have very very little confidence this will package.

Original roadster packs are packed super super tight and a weird shape.

There is already a running conversion out there with taycan packs and according to my measurements the ID3 modules will fit nicely We'll see

You have access to a 3D scanner to scan the old pack or space?

According to my measurements 8 ID.3 modules in a 2 × 4 stack would be about 59 × 46 × 48 cm and should fit into the box that has available room without the weird shaped lower part of 95 × 48 × 48 cm

This is the Conversion with Taycan Modules: There is the other conversion which gave me confidence to build this:

https://teslamotorsclub.com/tmc/threads ... er.316367/

Are the CAN interfaces understood as this is very cool

edit: Just read Tesla have released this info, so should be easily doable if you can code.

tom91 wrote: ↑Wed Mar 25, 2026 9:38 pm Are the CAN interfaces understood as this is very cool

edit: Just read Tesla have released this info, so should be easily doable if you can code.

Yes, as you've seen this is all open source meanwhile.
That is exactly where Johannes will be involved: Coding! He will do a much better job than me!

Built off of the SimpBMS work for VW modules

If it all works out should be a cool kit and "simple" to do as VW modules are plentiful.

I asked Gruber Motors (They are incredibly helpful! Tesla Roadster specialist in Arizona: https://grubermotors.com/) if they could provide me with the internal measurements of the battery box.

They came back with the following:

A = 53 cm
B = 53 cm
C = 45 cm

Based on that, I did some calculations for an ID.3 MEB module setup:

Configuration:

2 modules in parallel (side by side)
4 layers stacked
= 8 modules total

This results in the following dimensions (without cooling plates):

Height: ~44.0 cm (assuming ~110 mm per module × 4)
Length: ~53.66 cm
Width: ~53.66 cm

There are readily available MEB cooling plates, but buying 8 of those would have been close to €1500.
https://esdi-shop.de/products/batterie- ... 5432523017

Instead I ordered 4 custom cooling plates from Alibaba.
I paid €680 for 4 custom plates, each designed to hold 2 modules per layer.
Each cooling plate is 12 mm thick.

With cooling plates included, the total stack height becomes:

Height: ~48.8 cm
(4 × (110 mm module + 12 mm plate))


Conclusion:

This confirms that the ID.3 modules are a really nice fit for the Roadster battery box — but i will have to modify the box slightly where the original 11 cooling pipes exited the box. See red marked area, of course over the whole width of the box.

I would scan or CAD up the OEM box and design a new box that has built in mounts for the ID3 batteries and other bits.

Could be easier then modifying the OEM box and components.

Here on the logic side I will revive the old CAN Isolator that was meant for the BMS. It has 2 CAN buses, a relay and two OC outputs. It'll run a remix of stm32-car which includes SimpBMS derived MEB BMS code.

Of course no Olimex module but ESP32 CAN for this and Foccci

I have some news on the cooling plates. Looks good i think

How will they be made?

Who came up with the hole spacing as it looks strange at 203.4mm for the pitch.

why a series loop on the coolant plate? why not in parallel. yeah some strange numbers a tom said, is that based on mounting holes in the original battery enclosure? strange they are not whole numbers

To be honest, i can't verify the numbers. I sent them a CAD drawing (*.step) of the module that they sent me the recent drawings of the cooling plate.
I know Johannes has a spare module from his build. So i asked him to use a measuring tape and double check the measurements for me. Let's see what he says, if he is able to measure his module for me.

johu wrote: ↑Sat Mar 28, 2026 5:40 am no Olimex module but ESP32 CAN

Wemos? https://www.wemos.cc/en/latest/s3/s3_mini.html

Zapatero wrote: ↑Tue Mar 31, 2026 6:31 pm To be honest, i can't verify the numbers. I sent them a CAD drawing (*.step) of the module that they sent me the recent drawings of the cooling plate.
I know Johannes has a spare module from his build. So i asked him to use a measuring tape and double check the measurements for me. Let's see what he says, if he is able to measure his module for me.

Those measurements match the CAD file I have for the ID3 modules and I know that model is right, so the numbers look good.

Would you mind sharing the Alibaba seller of those cooling plates? I'm leaning heavily towards ID3 or ID4 modules for my Land Rover conversion and those cooling plates would be ideal.

As previously mentioned, Tesla released the Can Bus Data, which makes this much easier

https://github.com/teslamotors/roadster ... tEvBHOLFuw

LRBen wrote: ↑Wed Apr 01, 2026 5:17 pm Those measurements match the CAD file I have for the ID3 modules and I know that model is right, so the numbers look good.

Would you mind sharing the Alibaba seller of those cooling plates? I'm leaning heavily towards ID3 or ID4 modules for my Land Rover conversion and those cooling plates would be ideal.

Hebei Bide Trade Co., Ltd.
CN,Hebei,Shijiazhuang,Room 1105,
Building A, Shangfenghui, No. 218 Youyi
South Street

Zapatero wrote: ↑Wed Mar 25, 2026 10:41 pm Yes, as you've seen this is all open source meanwhile.
That is exactly where Johannes will be involved: Coding! He will do a much better job than me!

Unfortunately the DBC which has been released by Tesla is missing the most important messages for the battery. There are no messages released for the communication of the BMS, just the BMB.

I assume the BMS is a separate control module that receives info from the BMB modules. Then we could just leave the BMS where it is and spoof the BMB messages.

johu wrote: ↑Fri Apr 10, 2026 7:15 am I assume the BMS is a separate control module that receives info from the BMB modules. Then we could just leave the BMS where it is and spoof the BMB messages.

We will find it out, i am very certain. Johannes did solve much more complicated things than that
Also i still have the old battery, we should listen to the messages at least once before we take it apart.

I now have the finalized STP file for the cooling plates - and of course open source as always:

Looking forward to seeing this progress as I don't live too terribly far away... (Heidelberg) ... I am Stuttgart often so maybe when I get time I will take a look once it gets closer to being finished!