[WIP] 1971 Beetle - Tesla SDU and CATL cells

[Daveturpin]

Hello all. Time to introduce myself. I am Dave, and while I have a long history with cars, this is the first EV conversion that I have attempted. I have gone through many phases in life, but right now I am a VW guy. So after lurking on the internet for some time, I have determined that I want to do a late-model Beetle, and have selected this decent-shape '71 standard hardtop as my project.

I chose the late-model for the IRS. I am not a pioneer here, many Tesla swaps have been done to these cars and kits are even available. However there are a few things that I want to do that are outside the norm.

1) Improved placement of the Tesla SDU. I decided to custom make the motor adapter mounts to get the axle shafts as low and even as possible in the Beetle frame. Here are the front and rear mounts that I fabricated:

Front mount connects the Beetle transaxle mount to the front Telsa motor mount. The rear mount connects the other two mounts and also provides mounting pads for the sway bar using off-the-shelf mounts. With those mounts here is the placement of the motor:

I sourced the axle stubs from Fellten in the UK. They are the Porsche 930 pattern, and I am rebuilding the Beetle rear suspension with disk brakes and 930 axle outers. Then the final connection will be via EMPI CVs and sway-a-way shafts. (15-1/4" both sides; I have not ordered these yet)

2) Improved placement of the batteries. All the Beetle conversions I have seen have used Tesla cylindrical cell packs and take up the entire frunk and cargo area. But the Beetle has quite a lot of ground clearance. So my goal is to put the majority of the battery pack in the floorpans under the seats. I searched for quite a while to find a module that would allow this. I needed modules that met the engineering constraints of:
a) At least 40 kWh
b) Less than 500 lbs
c) Compact enough to fit in a custom floor pan
d) Adequate voltage for the SDU

I looked at a lot of options, but it looked like CATL cells were going to be the way to go. I looked at Kia/Hyundai cells, Chevy Bolt cells, Tesla model 3 LFP cells... None would really fit. Finally, very recently, these Mercedes EQ modules popped up:

I bought 5. Now, these hit most of the wickets. 46.5 kWh. 315v. 460 pounds. And at 12-1/4" x 25" x 4", FOUR OF THEM will fit in recessed boxes in the floor pans between the seat rails and I will lose about 4" of ground clearance.

They do create two more challenges, though:
a) They are cooled by conduction. So I will have to custom make plates to sit under the modules to cool them.
b) While they all have a BMS, I don't know the first thing about incorporating a BMS into the OpenInverter architecture. Hopefully someone out there can help me out with details on how to use these BMS? It would be very nice to use them instead of having to go with a custom BMS.

Oh, and 3) Modernize the Beetle. Beetles are not known for their comfort. With no air-cooled engine anymore, I will have no heat, and battery cooling, motor cooling, etc, will be further challenges. However I got a great deal on a Tesla model 3 heat pump system (SuperManifold, compressor, etc).

Let me know what you think. If anyone has an idea on a controller for the SuperManifold and has any idea on if/how I can use these BMS, please let me know.

(edited to remove external links and in light of the Supermanifold probably going in the rear, see later posts)

[tonycoke]

Looks like a great start!!

[johu]

Hopefully someone out there can help me out with details on how to use these BMS?

I'm not sure whether these have been reverse engineered. I'm assuming they are "dumb" modules that report to some main module and executes its balancing commands. You can find code for calculating various high level values from just cell voltages and temperatures here: https://github.com/jsphuebner/stm32-car ... mebbms.cpp (targeted at the MEB BMS, so CAN comms would need to be customized)

[Daveturpin]

targeted at the MEB BMS, so CAN comms would need to be customized

Thank you. Fortunately I can code in C++ and I understand what is going on in this software. But what hardware is this running on? If you figured out the VW MEB family of batteries the Mercedes EQ family can't be too far off. (Except the former is LG and the latter is CATL)

[johu]

It runs on an STM32 but the code should be more or less hardware independent.
I didn't figure out the BMS that was Tomdb https://github.com/Tom-evnut/VW-bms/tree/master/VWBMSV2 and I shamelessly stole from him

[Daveturpin]

Update:

Started fabricating the battery boxes. This is the front box, which I have decided will go where the gas tank was. I will relocated the heat pump IF I can figure out the controls for it. Probably in the engine bay which has plenty of room and is already designed for airflow. The depth of the box is 5.125", which allows a full inch for the heat transfer system.

The bottom battery shares the same basic configuration. I have not yet cut into the floor pans, but they will be recessed under the seat, for, again, a loss of about 4" of ground clearance.


And more data on the Mercedes modules. I asked questions in the BMS section, took the BMS apart and investigated: They don't use CANBus. They use iso-SPI protocol. The recommendation was to look into the Thunderstruck MCU which (might) be able to control them. Otherwise it will be a 90-channel BMS.

[Daveturpin]

Some updates!

I finally actually installed the openinverter SDU v.8 card, which was assembled and given initial setup by Westside EV www.westside-ev.com. Now I finally understand the “try to desolder the Tesla current sensors and if you f it up use new ones”. Yeah, I found it a lot easier to de-pot the Tesla ones and solder in new sensors. Otherwise I think the install went fine.

Now that the SDU is back out of the car I am painting up the engine bay better, and replacing the ATF in the SDU.

Also, with great help from the community I figured out the BMS. They use Linear Technologies’ isoSPI protocol and I can communicate with them using an Arduino-based demo card from LT. So that means my FINAL BMS can be the same protocol. Therefore I am getting the Thunderstruck MCU. That also solves the charger and display issues: I can use Dilithium peripherals. So I also picked up a 3kW charger and a charger connector from a Leaf. (J1772 which the MCU can also control via CAN)

Next I am going to finalize the battery module install and start building a wiring harness. I also still need to get cooling working.

Also got the battery box fabrication done. Just a little massaging and spot welding before these are ready to receive the cooling plates and battery modules.

[Daveturpin]

Update 11/4/24:

I am very close to getting the basic stuff done. Battery boxes complete, brakes rebuilt, accelerator pedal done. I at least have ON HAND most of the rest of the pieces: Contactors, 12v battery, DCDC converter, Thunderstruck MCU (BMS and Charging) and a 3kW charger. Have the 00-gauge HV wires, 12-gauge wires for the charging and 12v, 18-gauge wires for comms (CAN and isoSPI). I am really feeling it coming together. From this point on, it is much less mechanical stuff, and much more electrical and programming. Here are some pictures:

Finally did the last couple of steel patches. No more holes. Ended up replacing both quarterpanels, both heater channels, the rear apron, and some holes in the pans (besides the quite large holes I made myself)

The acellerator pedal is a late-model Prius. A couple of iterations and I am happy with the position and operation. I might swap out the brake pedal with the larger autostick pedal.

Front battery box and one module.

Pan battery boxes with two modules test fit.

And rebuilt the rear suspension. EMPI rear disk kit. Although the EMPI kit used a sort of dumb flex hose. I did hard line and braided stainless to the stock locations. Master cylinder also replaced with large-bore unit.

Mechanical tasks I still need to finish:
1) Seam seal and paint underbody and interior
2) Aerodynamic work on the underbody to smooth-in the battery boxes
3) Build cooling plates and radiator
4) Plumb in cooling for motor, inverter, batteries
5) Build enclosure for 12v, contactors, fuses (under rear seat)
6) Last piece of the CV axles: Custom length axles from 930 stump to 930 stubs

Electrical and computer tasks to do:
1) HV battery wires and current sensor
2) J1772 and charger wiring
3) New Beetle 12v harness install
4) OpenInverter harness install
5) BMS satellite wiring to MCU (and get the polarity of the isoSPI correct using my Linduino)

What else am I not thinking of?

1) Gauges?
2) M3 heat pump / supermanifold?
3) Stereo?

[ianlighting]

Just because I am naive on these things, your battery boxes - steel? Aluminium? What thickness? I have a lot to learn on this topic! Thanks.

[Daveturpin]

Steel, cold rolled, 20 gauge. The front box is reinforced with steel bar and the pan batteries are reinforced by the structure of the floor pans. Bolts go into nut rivets for strength. There will be covers made out of a non-conducting material, like fiberglass.

Edit: I originally put 16ga, it is actually 20ga. I am using 16ga for the underbody fairing so that it also gives some rock strike protection.

[Daveturpin]

Christmas update!

I have been finishing up a lot of the fab work, doing final fitting on the batteries, etc. Here is the SDU reinstalled for the first time since the suspension was redone:

Here are the locations of the non-motor electricals mocked up. Thunderstruck charger and Elcon DCDC convertor on the firewall. Supermanifold assembly (just) fits in the rest of the space, after trimming down the mounting bar and sawzall-ing off the 12v battery box.

And the Model 3 radiator fit overhead. Unfortunately this block off the fill hole for coolant. Might try fixing it to the deck lid instead which will require flexible hoses. I also have all the fittings to connect the Supermanifold to the radiator, motor/inverter, and battery cooling. (And what a PITA that was. Tesla uses proprietarily-sized fittings just to Musk us good) I can provide the part numbers but trust me when I say eBay is the best place to get these...

Oh, and good news... The Porsche 930 axles for the bug actually give MORE clearance. I measured again and I can use inexpensive 16-3/4" EMPI axles to finish the connections! No machining required. (to be confirmed when I install them)

Also still need to figure out battery cooling, but the more I am reading, the less I think it is strictly necessary? Unless I want to race or use DC fast charging? Also not sure I can ever get the heat pump compressor working, but I will give it a shot and have been picking wimboone's brain on the subject. I am confident I can get the radiative cooling loops working with an Arduino, which will be good enough for a first drive. Suffice to say, however, there is a LOT of wiring to do now.

[johu]

Unless I want to race or use DC fast charging?

My observation as well. Never managed to significantly heat up the battery just by driving (this excludes my 200 kph experiment). When rapid charging temperatures quickly go out of check.

[Daveturpin]

And the Model 3 radiator fit overhead. Unfortunately this block off the fill hole for coolant.

Just thinking about this a teeny bit more, in order to get the coolant system filled, I either need to locate the radiator further down, or extend the fill hole further up...

[Bratitude]

Are you going to fully loop the rear DU mount?

Counter leaverd off the one side of the frame horns with a flat metal interface won’t be strong enough.

Very cool packing all around. Heat pump in the back looks awesome

[ianlighting]

My observation as well. Never managed to significantly heat up the battery just by driving (this excludes my 200 kph experiment). When rapid charging temperatures quickly go out of check.

Is there a separate thread exploring the need or not for a radiator?

I wondered about a PC radiator instead of a car rad for space saving.

I’m not fixed on the idea, just pondering. This is just a random example.

https://www.corsair.com/uk/en/p/custom- ... 9030007-ww

[tom91]

Is there a separate thread exploring the need or not for a radiator?

For batteries? As the OP (original Poster mentions and so does Johu) Battery cooling is only needed if you are doing long duration high power pulling (heavy large vehicles) or DC Fastcharging.

[CapriV]

Here's my 2c, would other factors be more influential on the battery temp.? Like a vehicle with multiple battery boxes, some within the engine bay and some within the cabin area, cabin area including the trunk, a sealed area unlike the engine bay.
Leave that car in the summer sun for 12 hours and it will get hot. Could easily fry an egg on the dashboard of my car here in the summer months.
Once driving, the battery in the engine bay will get flowing air, the battery within the vehicle will not. Now you have a hot battery and a cooler battery.
There could be a large differential between different modules. The data sheet for my a123 batteries suggested no more than a 20c differential.
This is why I'm gonng to implement cooling at the design stage. Easier done now than later.

[tom91]

There could be a large differential between different modules.

Correct, so you are heat balancing and not cooling. Every build has its own quirks so one can really only comment on high level aspects.

-For cooling, most builds do not need it if not fast charging or requesting high duration of power levels

-As for battery degradation, the ideal scenario has the batteries all at the same temperatures, so depending on if you have multiple boxes the temperatures can vary and thus you can/want to compensate with a coolant system there the have the modules reach an equilibrium (note coolant and not cooling)

[CapriV]

(I hope we are not littering this build thread?)
deleted

[tom91]

(I hope we are not littering this build thread?)

Info in your thread about this? As this is getting strongly off topic now. (including me)

[ianlighting]

Info in your thread about this? As this is getting strongly off topic now. (including me)

This is my fault for steering people off topic. But it’s why I asked if there was a separate thread covering this.

Apologies to @daveturpin for polluting his build pages!