1974 BMW CSE

JetDexter

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Another Blog post from bmwcse.com, repeating much of what has already been posted in this thread, but as a whole story:

Battery Box

Unless we plan to drive our car using a very long extension cord, we have to get our battery modules off of their cart and into the car. Our plan is to get the majority of the modules in the engine bay, with a couple more in the trunk. Here’s the story…

Volts, Watts & Cells = Snoozefest, or Skip this Section if you Like

I have written and deleted here several times a fairly detailed explanation of how battery cells work. How you chain them together to increase voltage. How you group some of these chains together to increase their endurance. It was all very fascinating, but it took several pages and I fell asleep just editing it. So feel free to google all about it if you like.

My point in writing about it was to answer the question I often hear: “Why do you need so many batteries in your car?” It’s a terrific question. In fact, one of my favorite classic car EV conversions uses a high voltage Tesla motor like ours, but with Chevy Volt battery modules. Each module is not only smaller than the Tesla modules, they also output twice the voltage. We could get by with 6 smaller modules to properly run our car. That’s 1/3 of the size, weight, and cost of the Tesla modules. That sounds like a perfect solution.

Why then would we choose to go with 12 larger, heavier, more costly Tesla modules? kWh is why. Kilowatts Per Hour is the measurement of how long your module will last when being used. The majority of non-Testa EV battery modules have a very low kWh rating. This is finally beginning to change now that more auto manufacturers are taking EVs seriously, but we are years away from seeing these better modules in the used (salvage) market the way Tesla modules are today.

Teslas are good for 240 miles of range in some of their least capable configurations. Our car will be much lighter than a Tesla, but far less aerodynamic. We are confident that our 72 kWh battery configuration will get us over 200 miles of mixed city and highway driving. And in case you are wondering: no, we won’t be able to plug into a Tesla Supercharger on road trips to extend the range. However, we will be able to plug into the generic charging stations that are popping up everywhere.

Starting with an Open Engine Bay

Wide-Open-Bay.jpg

We now can benefit from all the work we have done to open up that engine bay: The bulky steering box and linkage that we swapped out for our compact and low steering rack; The large brake setup which was swapped out and relocated into the transmission tunnel (thanks to Greg). We have earned ourselves a very wide open area for our new battery box.

A Sheet of Aluminum and a Table Saw

To properly mount and protect the battery modules inside the engine bay we need an enclosed box. To keep the weight down as much as possible, we built our battery box out of aluminum. By using all the space possible, our box will hold 12 Tesla modules. We will need to put 2 more modules into the trunk.
Aluminum cuts smooth and easy on a tablesaw as f it were a piece of thin plywood.

Aluminum cuts smooth and easy on a tablesaw as if it were a piece of thin plywood.
Tyler is a master with the tig welder. I learned a lot about welding aluminum on this project. Very tedious.

Tyler is a master with the tig welder. I learned a lot about welding aluminum on this project. Very tedious.
In between the car’s frame rails we are able to squeeze in a lower section holding two battery modules.

In between the car’s frame rails we are able to squeeze in a lower section holding two battery modules.
Here is our lower section complete with the modules slid into their tracks.

Here is our lower section complete with the modules slid into their tracks.
The full box is starting to take shape. We are able to get 9 modules across in the main body of the box.

The full box is starting to take shape. We are able to get 9 modules across in the main body of the box.
Here you can see the 3 tiers of the box: 2 on the bottom, 9 across the center and 1 more on top.

Here you can see the 3 tiers of the box: 2 on the bottom, 9 across the center and 1 more on top.

Load it up with Modules

Once the box was complete we then loaded it up with our 12 modules. We used a combination of 2/0 copper wire and copper bus bars. The wiring chain begins and ends in a junction box that was built into the bottom, and accessible under the car.

Here’s an example of a custom bus bar which connects the two bottom modules in the chain. It looks rough now but will be plated and dipped in orange to look like the ones in the next photo.

Here’s an example of a custom bus bar which connects the two bottom modules in the chain. It looks rough now but will be plated and dipped in orange to look like the ones in the next photo.
This photo shows the 9 modules across looking nice with custom bus bars. Also the cable running to the top module and down to the junction box.

This photo shows the 9 modules across looking nice with custom bus bars. Also the cable running to the top module and down to the junction box.
Each corner of the box has brackets to secure it to the car. The corners of the box are steel reinforced on the inside for this purpose and also for living the box.

Each corner of the box has brackets to secure it to the car. The corners of the box are steel reinforced on the inside for this purpose and also for living the box.

Continued...
 
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JetDexter

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...Continued (due to 10,000 character limit)

A little bit of logo work and the box looks very nice in the car. She comes in around 750 lbs. That’s about what the stock engine was so the car is comfortable with the weight.

A little bit of logo work and the box looks very nice in the car. She comes in around 750 lbs. That’s about what the stock drive train and accessories, so the car is comfortable with the weight.
Very tidy underneath. You can see that we used every inch of space. If you look close you can see inside the junction box. A fuse is inserted as well. Any electrical short behind the box will blow the fuse - not the modules.

Very tidy underneath. You can see that we used every inch of space. If you look close you can see inside the junction box. A fuse is inserted as well. Any electrical short behind the box will blow the fuse - not the modules.

Finally, we installed the 2 last modules in the upper trunk area. This leaves plenty of trunk space. There’s even room for one more module if we ever get the desire for “more”.

Finally, we installed the 2 last modules in the upper trunk area. This leaves plenty of trunk space. There’s even room for one more module if we ever get the desire for “more”.

Close it up and Lift it in

Here’s a short video showing how the doors attach and how the box lifts to easily drop into the car- all 750 lbs of it.


This battery box was far more work than we ever anticipated. But it turned out terrific and well worth all the efforts. This brings us extremely close to driving the car around the building. Stay tuned!

Cheers,

Paul
 
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JetDexter

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Here's another bmwcse.com blog post:

UNTETHERED

It’s been several months since we spun the rear wheels with the Tesla motor. When we did, the batteries were stacked in our wooden crate with a very large extension cord going to the car. Since then we have installed all of the batteries and accessories into the car, so we are able to run the car self-contained.
This time around I’ll show you the end result before telling you the whole story. Here’s the video:


Finish the Trunk

Last time you saw the trunk it looked something like this photo - a gaping hole in the back of the car. Before we can move forward we need to finish out the trunk so we can keep the water out and the golf clubs in.
Notice I am using a golf reference as a story telling device. While I don’t play the “sport” I have often heard people evaluate their trunks based on its ability to haul golfing equipment.

Exposed Trunk.jpg


Here's the process:

First we install the upper trunk floor. We had grand ideas of this section being plexiglass so we could show off the Tesla motor from up above. But batteries need to be installed into this area, so we put in a steel floor.

First we install the upper trunk floor. We had grand ideas of this section being plexiglass so we could show off the Tesla motor from up above. But batteries need to be installed into this area, so we put in a steel floor.
For the lower trunk floor Tyler started with creating a cardboard template of the trunk shape.

For the lower trunk floor Tyler started with creating a cardboard template of the trunk shape.
He then traced it to a sheet of steel, then cut the shape. Just like in 2nd grade art class, but don’t tell that to Tyler.

He then traced it to a sheet of steel, then cut the shape. Just like in 2nd grade art class, but don’t tell that to Tyler.
Tyler created ribs using a hammer and chisel. Ribs add rigidity and strength to an otherwise flimsy piece of sheet metal.

Tyler created ribs using a hammer and chisel. Ribs add rigidity and strength to an otherwise flimsy piece of sheet metal.
Now it’s starting to look like a professional car part.

Now it’s starting to look like a professional car part.
She drops beautifully into the car to create a clean floor. The sections without ribs are where our devices will be mounted.

She drops beautifully into the car to create a clean floor. The sections without ribs are where our devices will be mounted.
Next up is the vertical piece that connects the upper and lower trunk floors.

Next up is the vertical piece that connects the upper and lower trunk floors.
The panel fits nicely and is ready to be welded in place.

The panel fits nicely and is ready to be welded in place.
But first we add square tube supports which will support the weight of the equipment, while also reinforcing the rear of the car.

But first we add square tube supports which will support the weight of the equipment, while also reinforcing the rear of the car.

We now have a complete enclosed trunk.

We now have a complete enclosed trunk.
Here is the trunk from under the car. The motor now feels like it has a home, rather than hanging there exposed.

Here is the trunk from under the car. The motor now feels like it has a home, rather than hanging there exposed.

Install More Equipment

Now that we have a trunk, there are a handful of items that need to be installed as part of our EV conversion. These devices will sit in the lower trunk section. There will be a carpeted false floor installed on top of this equipment, similar to the panel that hides a spare tire in many cars.

Trunk-Equipment.jpg


Here’s what we’ve got back there:

1 - 12v “car” battery.
When the ignition is turned off, our Tesla batteries are disconnected from use. We need a small 12 volt car battery to power things like dome lights and other accessories. When the Ignition is turned on, the Tesla batteries effectively charge this car battery the way a traditional alternator would.

2 - 057 Tesla Drive Unit Controller. This 3rd party unit talks to the Tesla drive unit controlling speed, power limits, cruise control, and much more. There is more information about the 057 in a previous post.

3 - DC/DC Transformer. This box receives high voltage from our Tesla batteries and converts it to 12 volts DC. It charges our car battery while powering traditional essentials such as headlights, power steering pump and more.

4 - HV Junction Box. Just like it says- it is a junction receiving the high voltage from the Tesla batteries, the AC voltage when the car is plugged in to charge, and sends that power to and from the charger, the DC/DC converter and the Tesla Motor.

5 - Tesla Charger. This unit receives power when we plug the car in to charge. The unit converts and controls the input voltage as needed to properly charge the batteries. (Another computer will be added to control this unit).

6 - 057 Precharge Unit. This unit automates the precharge of the Tesla drive unit’s DC/AC power inverter. This is a temporary unit, whose function will be rolled into our eventual Battery Management Computer (BMS).

7 - HV Contactors. These devices switch on and off the high voltage power to the Tesla drive unit as we turn the ignition on or off. These units will be covered for safety once our charge port is installed into the old fuel fill door above.
The orange high voltage lines are complete, but the low voltage wiring is temporary. Much will be done with fuse block, relays, multi-connectors and such for a clean final result.


We leave you with this. A shot of our graceful cockpit with our custom control panel. It’s a long way off from performing any date night duties, but it’s beautiful to me.
Now for the last bit of work on the brakes then we can drive this thing around the building!
Cheers!
Paul
Cockpit.jpg
 

JetDexter

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On Friday the whole crew was on-hand for an inaugural drive of the coupe! Jeff was there working on his car so he joined in the fun. Brett and Tyler were there. We all took turns driving and riding in the rear passenger seat!

I was extremely happy with the overall feel of things. We kept it very slow (under 30MPH) but even at that the suspension felt comfortable (for a low car). The steering felt very nice to me- which was a huge relief. Of course the alignment is eyeballed at this point, but she tracks wonderfully all the same!

We have a lot more work to do yet- plumbing the cooling of the batteries and drive unit, power steering pump and more. We will do some of that right away, but some will happen after paint. I hope to get her stripped down and to paint by the end of the month. If all goes well I'll be driving her daily by summer!

Mostly, it just feels great to have made it THIS FAR.

 

JetDexter

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Were the slowing tests you were doing around 1:48 strictly regen or was that actual braking?

Bo, that was all region braking at that spot- or any time where you hear the motor wind down like that. The brakes don't really come into play until the the very end of a stop, or if you are needing to stop much quicker.
 

JetDexter

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Wow wow wow! Congrats!

Now where's the burnout? :D

Hahaha it was tempting to be sure. The torque limit was set very low preventing any real fun:) This week I want to check suspension, brakes, drive unit bolts and such then we can begin to test at speed and perhaps give you your burnout! Very interested to test the weight of the batteries up front in turns at speed too.
 

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Hey guys, just a note to thank you for the kind comments. When I started this thread 15 months ago you guys were generally kind to me, but I knew that the jury was clearly out. Not only was converting an E9 to an EV not universally smiled upon (and that's still the opinion for many guys long-term) but I'd also never restored an E9. Of course I had Brett and Tyler's invaluable help with metal and fabrication that I could never have done on my own.

Mostly I just thank you for the type of comments about the build. We took a lot of time to do this car right. This car should really have been parted out for the very few usable items on it. But now that it's done it is a very tight, very clean car. I only hope I can do it justice on the trim and interior :)

It has also been great to see a good handful reach out desiring to also convert to EV. Jeff came along and now his car is a few months away from driving as well. Bo needs to jump in too! Others here and on Instagram have asked if we can help convert their E9, E24, E28, E30 and more. I am not looking for a new career, but it is great to see such interest. While the collector market generally requires pure originality, if converting classics to EVs means seeing more on the road then that is certainly a good thing. Hopefully you will be seeing me on the road very soon!
 

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We got the hood on yesterday. She looks a lot more like a proper car now that the hood and decklid are there! We had to notch into the frame of the hood just a tad to fit around the battery box. We designed the box knowing this was required. It's a little notch into the frame on two sections.

We also got the Brembo/Tesla electric parking brake calipers functioning. It is remarkable to have a parking brake that actually stops your car. I've never experienced it with any car I've owned. Now I have to build in plenty of failsafes, as these worm drive brakes will lock the rears up without regard. I'd be going backwards in a hurry if it happened at speed :)

Coupe.jpg
Hood.JPG
B416C846-C389-4F46-B69A-C0869F7DBCC2.JPG
7AEB10C1-CAA2-4FE8-93EE-0AA1A0D59997.JPG
 
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