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Possibly a dumb question but what happened to the intumescent goo? Was it never in production packs or only in earlier/later versions?
Missed this almost...
The 18650 cells are bare, no label or anything. So the entire casing, including the negative end, is negative. So you're looking at the negative end of the cell. The bus plate sits on top of a piece of plastic with cut outs for each individual cell. The cutout in the plastic with it's raised walls around the hole (to protect the small fuse) are what you're seeing on top of the negative end of the cell. The cell level fuse then connects from the bus plate to the cell itself through this opening in the plastic.
The same for the positive side, except the positive end of the cell has a triangle-like positive terminal that is insulated from the negative casing.
Note that the plastic protective cover is in place on the modules in most of my pictures, also.
More cool info.
This sounds like it was a gallon or so per module, not the whole pack, right?
U4 - Silabs isolator (http://uk.mouser.com/ProductDetail/Silicon-Labs/Si8642ED-B-IS/?qs=NVLsoTRMv1oBDPBFWNUX/g==) for the interface back to the BMS board
Dang!
I hate SiLabs parts. Tesla used them in the fob as well.
No rear surprise on the degree of isolation as the modules are at vastly different potentials.
You can balance at any SOC, but if you want the absolute max capacity out of your pack, balancing at 100% SOC (or close) is going to give you the highest number.Ok, so the excess electricity is wasted as heat, right? Sounds to me that balancing can occur at any SOC regardless of whether or not the car is charging. So does this bust the long standing TMC theory that pack balancing only occurs on a max range charge?
So, any thoughts about what that small shunt board attached to the bus bars is?
The one thing I haven't been able to figure out is how the coolant actually flows through the modules to cool the individual cells. Is that grey rubber-like material shown on the last picture related to the cooling?
Expanding on that, the BMS could at most draw about 42W from the pack if all 96 bleeders were active at once... which would take 84 days to bring the pack (85kWh) from 100% to 0%, lol.
I think most imbalances would be a few 10s of mV, which should be only a couple hours of bleeding probably.
It is a current monitoring board for the BMS to know how much energy is flowing in or out of the pack as a whole. The shunt is a piece of metal with an accurate and known resistance, and the voltage drop across it at various current draws is directly proportional to the amount of current flowing through it. The small board reads this and calculates the power flow and reports it to the main BMS board.
The grey rubber like material is actually thermally conductive material (like thermal pad material), and it presses against the coolant loop and every cell. The coolant loop goes into the module, flattens out, then weaves around all of the cells conducting heat through the thermal material.
- - - Updated - - -
I'll also note for completeness that the presence of the isolation IC on the BMS module board rules out any inter-module active balancing.
Changing the target balance voltage for one module to be different than others (based on small V/Ah differences between modules) would still result in passive balancing -- as the pack charges, some modules' bleed resistors would be used before others. As others have posted, I don't see any way to do inter-module active balancing with the circuitry shown.Inter-module active balancing is done by shuttling during charging but this shuttling is not done in the traditional dangerous way. Balancing is done by increasing the voltage not only bleeding. Bleeding is not an efficient way of balancing as it just creates heat. Virtual shuttling is done by continuously changing the target balance voltage which will in effect shift charge through the whole pack