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Discussion Starter · #1 ·
I purchased a 2004 RX-8 donor of opportunity and have also purchased six Tesla S modules, which are arriving. I understand that it would be good to distribute the weight throughout the vehicle (over front and back axles) for traction and steering on this RWD vehicle.

However, the trunk of this car is loaded with space, if I can stack these modules four high, directly over the rear axle. Very convenient and accessible, it will keep everything dry, and the trunk still has plenty of space left for storage.
My questions are:
1. Is it a big concern having 360 pounds over the back axle? I removed the gas tank and the exhaust system but that is probably 120 pounds max.
2. Can I stack these battery modules 4 high? If so, should I use insulating separators other than just the plastic shields that comes on the modules?
Batteries in trunk.jpg
 

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I purchased a 2004 RX-8 donor of opportunity and have also purchased six Tesla S modules, which are arriving. I understand that it would be good to distribute the weight throughout the vehicle (over front and back axles) for traction and steering on this RWD vehicle.

However, the trunk of this car is loaded with space, if I can stack these modules four high, directly over the rear axle. Very convenient and accessible, it will keep everything dry, and the trunk still has plenty of space left for storage.
My questions are:
1. Is it a big concern having 360 pounds over the back axle? I removed the gas tank and the exhaust system but that is probably 120 pounds max.
2. Can I stack these battery modules 4 high? If so, should I use insulating separators other than just the plastic shields that comes on the modules?
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1. I'd recommend looking at the car's GVWR to figure out if it's an issue. Typically there is a separate rating for the front and rear axle. This is often printed on the sticker normally located somewhere on or near the driver's door.

2. Yes you can, and most people do. You can get bus bars that are made to work perfectly in that configuration. Just make sure that the modules don't bounce around and that the positive and negative contacts on the one end don't hit anything conductive they're not supposed to (like the side of a battery box).
 

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Discussion Starter · #3 ·
Excellent!, Can I stack the modules as-is (with plastic insulator shields from Tesla) or should I add an insulator between modules? Will this effect the fit of the bus bars? I am purchasing positive to negative busbars.
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You can place the modules above each other; Tesla does that with the two modules at the front of the 16-module packs. But you can't just stack them on top of each other in a vehicle (although people do that when storing them - each module needs structural support, and cannot rest on another module.
 

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Discussion Starter · #5 ·
OK.
So I need to build racks to stack them on inside the trunk:
-Is there any particular kind of shielding needed between modules or will metal racks work.
-Any suppliers that provide DYI rack kits?
Just thinking out loud here but if you have any suggestion, they are welcome.

I will look on the internet and have some ideas with tool I have on-hand.
 

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Check out a model S battery tear-down video if you have not done so already. Its hard to tell if the modules are sitting on the floor of the box, or if the weight is being carried by the rails on the sides. The tesla module box i have was lined with some sort of aluminized particle board esque material - anyone know what that stuff is called? It looks like the S uses the same stuff.

With the plastic covers, I would not think you would have any problem with using steel shelves - but if the rails on the side are the structural part anyway, you might not even need them to be resting on anything. You could just have them slide into a rack like oven racks (the best analogy I could think of).

I would definitely hold off on designing the system until you have those bus bars on hand - they will likely dictate what space you will have to conform to.

Anyway, looking forward to seeing it come together!
 

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OK.
So I need to build racks to stack them on inside the trunk:
-Is there any particular kind of shielding needed between modules or will metal racks work.
-Any suppliers that provide DYI rack kits?
Just thinking out loud here but if you have any suggestion, they are welcome.

I will look on the internet and have some ideas with tool I have on-hand.
These premade boxes are available, but they're ludicrously expensive.

One suggestion: instead of stacking them vertically, put them side by side horizontally. This video shows someone who did just that. For a trunk, you'll probably be able to fit more this way than any other way.

When you say shielding do you mean covers for the contacts on the modules?
 

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Hi JHart,

I have an 2004 BMW convertible E46 3-series converted also using 6 Tesla S battery modules. For weight distribution and space reasons, I went with 4 under the hood in a 2 wide x 2 high configuration and 2 in the trunk in a 1 wide x 2 high configuration. (See the pics.) They are all stacked with just the stock plastic packaging around them, and it has worked great. I think you'll find most people do this, especially when using the bus-bars you noted, which you'll see I also used. I know these Tesla modules may not necessarily have been designed to stack, but they are very structurally solid and rigid, so I really don't think there is much of a concern. Do note however, that is assuming your Tesla plastic shields have no damage or anything like that, and that your modules are well secured which is very important for a lot of reasons. BTW - securing these modules can be a little challenging as they don't have much in the way of mechanical attachment points. In the end, I went with an approach of strapping them in (again, see pics) which has worked great. There would definitely be a point where stacking these would not be a good idea, and maybe 4 high is past that point, but with almost 2 years of real-world usage, I can tell you if done right, 2 high is no problem.

In terms of weight distribution, obviously what you want is to have it be as close to stock as possible. It is very likely that in the end your conversion will weigh more than what you started with, but again, the distribution of that weight is what is most important. The most precise way to go about figuring this out is with "corner" scales to weight your car under each of its four wheels before you start and then play around with different configurations with all of your components. Most race and high performance shops have these, and usually they'll do that weighing for you for a nominal cost. (If you happen to be near Denver, Colorado, I'd be happy to do it for you.) There are home/hobbyist mechanic versions of these starting for about $1,000, which is obviously not cheap, but just so you know. If you Google and such, you'll see a number of folks that have come up with some hacked ways of doing this on the cheap with bathroom scales and such. (Not sure I'd recommend that.) In any case, I cannot say for sure, but my gut tells me that your plan for 4 modules in the trunk will definitely change the dynamics of that car significantly. By too much? Tough to tell without trying, but I'd definitely make sure you play around with it before committing to it.

C.J.

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