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Discussion Starter · #1 · (Edited)
I was hoping someone could sanity check my wiring diagram for the Orion BMS 2 (48-S) cell taps. I am running 5 Tesla Model S batteries (6 cells each) and StealthEV BMS boards for each battery. My battery packs are split with three in the front and two in the rear, with a fuse between packs. The Orion BMS came with two loomed connectors, each pre-wired with 2 Groups (12 Orange, 12 Red) and 2 negative wires.

My plan is below based on the information I was able to find. One question I had was whether the second battery in a group (pins 7-12) actually doesn't need a ground (black wire) connection to the battery board.

Connector 1
  • Battery 1: 1- and wires for cells 1-6 to the furthermost negative battery (in rear)
  • Battery 2: Cells 7-12 connected, no ground connected
  • Remainder of wires (all of red Group 2 and 13- negative) unused
Connector 2
  • Battery 3: 1- and pins 1-6 (cells 13-18)
  • Battery 4: Pins 7-12 connected, no ground connected
  • Battery 5: 13-, and 13-18, 18-24 joined together


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Unfortunately you’ll need larger Orion 2, eg 60 cell configuration. But don’t take my word for it - read their docs thoroughly to make sure your wiring matches your intention. (https://www.orionbms.com/manuals/pdf/orionbms2_wiring_manual.pdf)
Again read through it, but you’ll need one ‘black’ wire per Tesla battery board to satisfy their requirements for interconnects, fuses etc. Their system expects cells in groups of 12, and Tesla batteries are in groups of 6, so you tie taps 6 through 12 together, and so on. Fuses are supposed to be groups of 36 taps. Page 50 gives you a high level idea to start, but yes, start on page 1! 😉
Good luck and keep us posted. What is your project car anyway?
 

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Disagree about needing a larger BMS.

You should not run non-isolated BMS wires wild like your diagram implies...they are HOT, unfused, and being over 60V, a major safety hazard.

The right way to do this for multiple battery boxes is each battery box has a satellite BMS and its sense wires are all inside a battery box that then links to a master BMS through a galvanically-isolated link.
 

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Discussion Starter · #4 ·
It's a 1973 VW Thing conversion. I also think the larger BMS is not warranted. The cell tap connectors that came with the BMS were pre-wired with 24 wires and 2 grounds (two cell groups each), but there's room to add a third cell group if I wanted (total of 36 taps per connector). From the manual,
"If safety disconnects and fuses are used and cannot be located on multiples of 36 cells, cell positions on the BMS must be left unpopulated such that the safety disconnects fall between a multiple of 36 cells on the BMS."
. Since the first pack (rear) has 12 taps used and 13-36 un-used, I think it addresses this issue.
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Remy, I think I understand the point you're trying to make, but just to clarify: The cell tap wires are running through the car in heat-shrink, but each wire carries a sensing load from each cell in the battery module. I have one BMS board for each battery module (5 total). Each battery module is 22.8V nominal, and each module is divided into 6 cells. So my thought was that each cell tap should be carrying less than 5v back to the BMS. Also, this is from the Orion manual,
"The pre-wired cell tap harnesses available with the BMS come in various lengths and use 22AWG UL style 11028 wire. The wire is rated for 600V and -40 to +105 degrees C. Because of the mppe style insulation, it is physically thinner than comparably rated PVC wire and has about 10x the abrasion resistance of standard PVC wire"
.

Also, below is my more detailed wiring diagram. The BMS is connected to the 3.3kw charger, which is in turn connected to the HV side of the battery modules.

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The wire is rated for 600V....

Yes, the sense is 5V or less with respect to the negative side of a cell. The top sense wire will be sitting at roughly 120V and it is likely not fused.

In your setup, you may be able to stay below 60V by housing most of the 120V components in your diagram inside the front pack's battery box.

In theory, each BMS sense lead needs a fuse or limiting resistor before it exits a pack's box.

You also have nothing protecting the cable that runs from the front pack to the contactor. It may not be needed, depending on where that contactor is (it should be inside the battery box(es)).

I would also put the disconnect in the high current cable running between the two packs.
 

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In theory, each BMS sense lead needs a fuse or limiting resistor before it exits a pack's box.
That and not having a battery box containing the wires, where copper BMS wires are vibrating in the literal breeze, work hardening, cracking, then breaking, meant this was eventually going to happen:


He got lucky, as he had noted, that it didn't burn to the ground. He was blessed with the chance to redo one of the most beautiful Beemer models, hopefully without shortcuts, or "fix it later", this time.
 

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That and not having a battery box containing the wires, where copper BMS wires are vibrating in the literal breeze, work hardening, cracking, then breaking, meant this was eventually going to happen:


He got lucky, as he had noted, that it didn't burn to the ground. He was blessed with the chance to redo one of the most beautiful Beemer models, hopefully without shortcuts, or "fix it later", this time.
From what I can tell, it looks like those modules have the "stock" Chevy Volt BMS & harnesses.
...& for ALL of that to happen & the module (or whole pack) didn't "catch" on fire too (I'm impressed) :)

So, what actually caused the fire? (a short in the BMS lead wires?) (or caused by wires he added?)
 
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