Weber and I have been investigating Leaf drive systems, so Graeme kindly asked if we'd like to take one and do a quick disassembly. How could we refuse?
The PCB inside the ECU-like box:
The connectors along the bottom all go to individual cells. So this is not a cell-top BMS, it's the other kind, where the management/monitoring happens away from the actual cells. As most readers of this forum will know, Leaf battery cells are packaged into 2S2P "cans" with three screw terminals. There is a nifty flexible orange plastic harness arrangement that screws to the cells, making the interconnections (from memory, maybe that's not right) but also the connections to the BMS.
The twelve chips all in a row in the bottom half of the board are ASICS (Application Specific Integrated Circuits, i.e. custom silicon) with the part number D15110. There isn't a manufacturer's logo that we could find. Each chip handles four cells. There are another 12 of these, with all the associated components, under the board. Here is a close-up of one such channel:
Note the four larger resistors (0805 size, about 2 mm x 1.25 mm, still pretty small), marked "431". These are 430 ohm resistors, and would appear to be the only possible bypass resistors. If so, these would have a maximum of about 4.3/430 = 0.01 A or 10 mA of bypass current. This is about a tenth of the current of the next lowest BMS bypass capability, so maybe they're not bypass resistors at all. If these are bypass resistors, bypass capability is extremely weak. Power dissipation would be around 43 mW; these resistors are generally rated at 125 mW with adequate heatsinking. So they are sized about right for taking around 4.3 V (the approximate potential of one Leaf cell near full charge).
Near the middle top of the board is a CPU, I believe it's a Renesas chip similar to the one in the VCM (Vehicle Control Module, the main ECU). Maybe that "pacman" symbol (sorry, not visible in these reduced-size photos) is the same as the one on the ASICs; the logos (if that's what they are) on the latter look more like dots. It's presumably the BMS master, and seems to also control the main and pre-charge contactors. That's what's in the second box, attached to the BMS box by a cable:
The two rectangular black boxes with the Panasonic labels are the main contactors (breaking the positive and negative ends of the pack, by the looks). The coloured wires go to a smaller contactor, which must be the pre-charge contactor. It is associated with a ~ 20 W resistor under the contactor unit. This unit oozes quality; all the quick-connect connectors have plastic boots; every place where battery (circa 400 V) potential exists in a small space has a substantial plastic barrier separating the terminals; the bus bars are a work of art, and so on.
So: will these battery monitoring (and possibly very weak management) units be usable by converters? Well, the contactor box is pretty neat, if your conversion doesn't need a heap of current. The BMS ECU... well, it's designed for a 96S (~ 365 V nominal) pack, and I don't think it would take too kindly to a bunch of cells being missing. However, if your pack had a multiple of 4 cells in series (i.e. an even number of cans), then you would not be using half a channel, so it may be possible to ignore or bypass the unused channels. The ASICs appear to communicate to each other digitally, and there are opto-couplers at end ends of the pack. There are more details, including a schematic, here: My Nissan Leaf article "BMS details" . So you could perhaps intercept the digital stream on its way to the BMS master, which you might be able to ignore, but then you'd have to figure out what the digital stream meant. That might be easier than trying to figure out the CAN bus packets that the vehicle normally uses to communicate with the BMS master. So: a fair bit of work.
7 Cirkles of Tua
