Mercedes S123 station wagon with Tesla SDU

[Bintang 5]

Hi everyone,

my name is Stefan and I am living in the southern part of Germany.

Currently I am in an early planning phase of converting a Mercedes S123 station wagon (E-class built between 1977 and 1985). Have been lurking around this forum and DIYelectriccar for quite a while now, still more questions than answers...

I want to replace the whole original drive train and fit in a Tesla drive unit controlled by Openinverter. Regarding power I want to stay within the max range of the original ICE which was 185 hp / 136 kW. I hope to get a minimum range of 150 km.
Regarding batteries I read that these PluginHybrid batteries seem to be a good source. What Voltage am I looking for when planning a pack?
No clear idea about my requirements for charging yet, the more charging power the better? Still trying to get my head around this topic generally...

My workshop is still blocked with my current project, a 1986 BMW 635CSI. This will stay on combustion engine, have already invested too much in it... Hope to finish this car soon, but in the meantime I'd like to play around with my new project and possibly already buy some components and get the electric drivetrain running on a bench.

So I think I am looking for a small Tesla drive unit. This could be a model S/X rear SDU or should I wait for the Openinverter solution for Model 3?
Any benefits from Model 3 drive units over S/X?

Concerning the rest of the components, I am also still quite confused what to look for.
Any proposals for charger, DC/DC, HV distribution and other components?

I hoped to stay within 15.000 € for the components only (no labour costs). Does this seem realistic to you guys with more experience?


thanks a lot

Stefan

[johu]

I won't answer all of your questions as others know better.
As for the drive unit the SDU is proven to work. As you're not looking for insane power I'd say it will suffice.

Charger choice really depends on your application.

Will you just go on trips in your region on one battery charge and then have enough time to charge back home? Then a small 2-3kW charger will do.

Do you want to take the car on long trips with charging stops in between? Then you should look into DC fast charging via ChaDeMo or CCS. DC fast charging does not require any charging power electronics in your vehicle.

Do you want to use public AC charging stations on a regular basis? Then you should look into 11 or even 22kW 3-phase chargers like from Tesla.

In my conversion I only have a DC fast charging port and then built a number of external chargers for home charging that connect to that port.

Battery-wise for 150km range with this car I'd suggest around 30kWh. Plugin hybrid batteries may not be the best choice for your project as they typically have low energy density. For medium performance of the SDU you should be in the 300V region. If you salvage a typical EV pack you will end up with 380V which is fine also. Better more voltage than too little.

[Kevin Sharpe]

I want to replace the whole original drive train and fit in a Tesla drive unit controlled by Openinverter.

Assuming the Merc is rear wheel drive then I'd recommend the Lexus GS450H as used in the BEXUS and numerous other conversions. This will be a much simpler installation than a Tesla and cost a lot less.

Regarding batteries I read that these PluginHybrid batteries seem to be a good source. What Voltage am I looking for when planning a pack?

Have a look and see whether you can fit the Tesla Model 3 battery modules under the car. Ideally you would want four but three would be ok. Try the short modules if you can't fit the long. These are the best value batteries if you want decent range.

No clear idea about my requirements for charging yet, the more charging power the better?

I'd install the Tesla Gen 2 AC and CHAdeMO DC rapid charging. Both are widely used in conversions and available at low cost. When installing your AC charge port put in the CCS connector so you can upgrade in the future.

So I think I am looking for a small Tesla drive unit. This could be a model S/X rear SDU or should I wait for the Openinverter solution for Model 3?
Any benefits from Model 3 drive units over S/X?

Model 3 is in development and a long way from a tested and supported product. If you are using Tesla then both the Model S and X parts have been widely used over several years. Do be very careful on the age and source of the drive unit (see my recent post on this topic here).

Concerning the rest of the components, I am also still quite confused what to look for.
Any proposals for charger, DC/DC, HV distribution and other components?

Try and select components that are running in conversions already and are well documented.

[Bintang 5]

ok, thanks for the answers so far!

Yes, the 123 Mercedes is rear wheel driven. Putting in a Lexus drivetrain is mechanically certainly easier, yet the mechanical aspect of this conversion is the "fun part" for me. I just like the idea of getting rid as much of the old drivetrain as possible.

That's why I want to go for the Tesla DU. I read the posts regarding problems of earlier Tesla motors, as far as I understood they suffered from worn rotor bearings. Yet I didn't really find a lot of detailled information on that. But focussing on 2018 motors only narrows the choice down drastically. Anyone changed the bearings himself already? Are sealings available from Tesla if you want to open the housings?

Regarding batteries I'm pretty sure Model 3 modules will not fit below the car without leaving way too little clearance.
The Mercedes 123 station wagon doesn't have a common spare wheel well (spare wheel is standing on the side inside the trunk), so the underbody is flat behind the rear axle. Making it easier to fit a motor there and probably giving some space for batteries as well, but certainly no Tesla Modules I'm afraid.

If not Tesla and not any of these Plugin-Hybrid batteries (suprised that these are low-capacity, would have thought the opposite given the little space in a hybrid and trying to reach a decent range...), what to look for?

Nissan Leaf and Renaul Zoe are somewhat common in Germany. Some BMW I3 as well. Any preferences here, especially when it comes to BMS?

[Kevin Sharpe]

I read the posts regarding problems of earlier Tesla motors, as far as I understood they suffered from worn rotor bearings. Yet I didn't really find a lot of detailled information on that. But focussing on 2018 motors only narrows the choice down drastically. Anyone changed the bearings himself already? Are sealings available from Tesla if you want to open the housings?

The bearing problem was the result of large magnetic fields generating arcs which pitted the bearings. Tesla rolled out a temporary fix with the installation of ceramic bearings and then a redesign which prevented the formation of arcs in the bearings.

Obviously you are free to ignore the advice to buy a 2018 DU... it's your money

The Mercedes 123 station wagon doesn't have a common spare wheel well (spare wheel is standing on the side inside the trunk), so the underbody is flat behind the rear axle. Making it easier to fit a motor there and probably giving some space for batteries as well, but certainly no Tesla Modules I'm afraid.

That sounds like a lot of weight in the rear. Have you weighed the car and considered the weight distribution?

Nissan Leaf and Renaul Zoe are somewhat common in Germany. Some BMW I3 as well. Any preferences here, especially when it comes to BMS?

As I said previously use the OEM BMS and the SimpBMS controller. You want to avoid third party BMS and their desire to destroy batteries

[Zapatero]

ok, thanks for the answers so far!

Yes, the 123 Mercedes is rear wheel driven. Putting in a Lexus drivetrain is mechanically certainly easier, yet the mechanical aspect of this conversion is the "fun part" for me. I just like the idea of getting rid as much of the old drivetrain as possible.

I also have to suggest to NOT put in the Tesla DU for the following reasons:

- Totally expensive
- Result is not any better than the Lexus Gearbox
- But most important: You won't benefit of the power it can produce if you're not using Tesla batteries. All other batteries cant provide that much of Amperes without severe damage. You need a huge capacity of the battery to use the benefits of the Tesla DU.

[Bintang 5]

Obviously you are free to ignore the advice to buy a 2018 DU... it's your money

I'm not reluctant to advice, that's why I'm asking here
I thought the ceramic bearings were the fix, wasn't aware of a "real" design change... Any links to technical details?

That sounds like a lot of weight in the rear. Have you weighed the car and considered the weight distribution?

No, do not have the car available in my workshop yet. Weight distribution is of course a topic, I thought that the bulk of the batteries will go into the front / engine compartment. But will go into details once I have the car available.

As I said previously use the OEM BMS and the SimpBMS controller. You want to avoid third party BMS and their desire to destroy batteries

Have read about the SimpBMS, but it often says "no balancing possible", that's why I am uncertain what to look for.
I also read a lot about the Orion BMS when it comes to 3rd party solutions. Is it any good?

Plugin hybrid batteries may not be the best choice for your project as they typically have low energy density.

Really surprised, I thought the opposite was the case. Given the limited available space in a hybrid yet trying to reach somewhat of a "decent" range I thought these cells were rather high density?

I also have to suggest to NOT put in the Tesla DU for the following reasons:
- Totally expensive
- Result is not any better than the Lexus Gearbox
- But most important: You won't benefit of the power it can produce if you're not using Tesla batteries. All other batteries cant provide that much of Amperes without severe damage. You need a huge capacity of the battery to use the benefits of the Tesla DU.

yes, I hear you guys I do see the merit of this (mechanically) almost plug-and-play solution with the Lexus DU.
Just have to get used to the idea to implant a looks-like amputated drivetrain into my car.
I searched eBay and alike, the price span for Lexus 450 Hybrid gearboxes is huge. Starting around 400€ to more than 2000€. Some of the gearboxes come without the oilpump and flywheel/spline adapter, so need these parts, too. Inverter is also around 600 €.

If you really know what to look for and have some patience, I do think you can make a really good deal with a Lexus gearbox. Don't know exactly what to look for yet, so I have to dig into this topic first....


I have come a long way in my planning process of converting a car. I started with browsing German websites and shops where it seems the most common solution is mating a DC motors to the original gearbox. Prices for these motors and controllers etc. are quite upscale, no interesting solution for me.
Then I discovered the DIYelectriccar forum and finally this forum, which opend a completely new "universe" of possible solutions.

I've been reading a couple of weeks now in these forums, yet it's really difficult to get my head around many of the topics here... so sorry for asking questions, that might have already been answered elsewhere...

[Kevin Sharpe]

I thought the ceramic bearings were the fix, wasn't aware of a "real" design change... Any links to technical details?

You'll need to do the research and I can't remember if Tesla ever said exactly what changes they made to the DU but it included 'grounding conductors' to route the induced voltage away from the bearings. I'd suggest you start with the TMC forum.

Note that my advice re buying a 2018 Tesla DU is designed to help users who have little understanding of the history and don't want to risk 1000's of euros. Obviously it would be possible to develop a wider list of 'good' DU's based on part numbers but I doubt anyone will publish that especially now the focus is on the Model 3/Y.

Have read about the SimpBMS, but it often says "no balancing possible", that's why I am uncertain what to look for.
I also read a lot about the Orion BMS when it comes to 3rd party solutions. Is it any good?

I'm aware of third party BMS that have mismanaged batteries to the point they catch fire. This happened recently to a Tesla pack and I hope at some point details will be shared. You are free to do whatever you like but understand that on our course Damien is clear that you should be using the OEM BMS for battery management with a third party controller like SimpBMS.

If you still don't get this then ask yourself one question... who knows most about Tesla batteries... Tesla or Orion?

Really surprised, I thought the opposite was the case. Given the limited available space in a hybrid yet trying to reach somewhat of a "decent" range I thought these cells were rather high density?

Hybrid batteries are power dense not energy dense.

I searched eBay and alike, the price span for Lexus 450 Hybrid gearboxes is huge. Starting around 400€ to more than 2000€. Some of the gearboxes come without the oilpump and flywheel/spline adapter, so need these parts, too. Inverter is also around 600 €.

eBay is one of the worst places to buy EV parts if you want decent prices. The cheapest way is to buy a complete donor car, strip it and sell the unwanted parts. For example last year we purchased a Lexus GS450H in the UK for 500 GBP and then drove it to Ireland... when we sell the engine and cats we will make more money than we paid for the car.

I've been reading a couple of weeks now in these forums, yet it's really difficult to get my head around many of the topics here... so sorry for asking questions, that might have already been answered elsewhere...

You are not alone, unfortunately a forum is not a great way of getting this information across. We need more people with hands on experience running courses that are focused on converting cars using today's solutions.

We also need to clone Damien and Johannes

[Kevin Sharpe]

Note that my advice re buying a 2018 Tesla DU is designed to help users who have little understanding of the history and don't want to risk 1000's of euros. Obviously it would be possible to develop a wider list of 'good' DU's based on part numbers but I doubt anyone will publish that especially now the focus is on the Model 3/Y.

This is worth a watch because it gives you a flavour of what the second hand Tesla parts market is like;

[Bintang 5]

I'd suggest you start with the TMC forum.

will do...

You are free to do whatever you like but understand that on our course Damien is clear that you should be using the OEM BMS for battery management with a third party controller like SimpBMS.

If you still don't get this then ask yourself one question... who knows most about Tesla batteries... Tesla or Orion?

I think you misunderstand the intention of my questions. Maybe I am also not putting them right, sorry English is not my native language.
I am not questioning your advice, I want to understand "why".
You recommend the OEM BMS with SimpBMS. Got it. Yet I read that the SimpBMS only supports balancing for Tesla Model X/S batteries. When I cannot/don't want to go with Tesla batteries, what is a BMS good for when it does not balance? I thought one main purpose of a BMS is to control Voltage of the cells to prevent under/overcharge. Isn't balancing an integral part of this?
There are a couple of sources (shops) for the SimpBms, are the all the same? Quite confusing at least for me.

For example last year we purchased a Lexus GS450H in the UK for 500 GBP and then drove it to Ireland... when we sell the engine and cats we will make more money than we paid for the car.

seems like a "steal". Haven't found any Lexus450h below 7000 €.

[Kevin Sharpe]

When I cannot/don't want to go with Tesla batteries, what is a BMS good for when it does not balance? I thought one main purpose of a BMS is to control Voltage of the cells to prevent under/overcharge. Isn't balancing an integral part of this?

Lithium batteries do not require 'balancing' because they have no self discharge capability and will not drift apart (many conversions have no BMS because of this). Indeed most of the battery fires are the result of third party BMS forcing 'balancing' and it's a topic we discuss a lot on our courses. Unfortunately, it's not possible to educate every new user about this topic which is why we keep the advice simple and suggest people simply use the OEM BMS with a controller such as SimpBMS.

There are a couple of sources (shops) for the SimpBms, are the all the same? Quite confusing at least for me.

I have no idea... why not send @tom91 a message?

For example last year we purchased a Lexus GS450H in the UK for 500 GBP and then drove it to Ireland... when we sell the engine and cats we will make more money than we paid for the car.

seems like a "steal". Haven't found any Lexus450h below 7000 €.

It's easy to buy cars within the EU and get them transported if you don't want to pick it up yourself. Here's an example of a Leaf that was purchased recently for 1200 euro including transportation;

viewtopic.php?f=12&t=959&hilit=leaf#p15484