# Battery Management System Hardware Concepts: An Overview
## 3 Topologies of BMS
### Real-World Examples
A comparison of the PCB found in the battery pack and the specifications of bq76 PL536A, however, showed that the used product is at least very similar to bq76 PL536A, which is also built into the Tesla Model-S battery that was available for analysis (see below). Each of the three PCBs contains six monitoring ICs and one microcontroller with a galvanically isolated connection to the rest of the system (most likely CAN). TI's bq76 PL536A can be daisy-chained in order to need only one communication connection to the system, which can also be observed here. For cell voltage measurement, there are connections of flexible PCB between the cells' terminals and the BMS PCBs located between the terminals. In addition, several temperature sensors can be observed. A module that seems to be the BMS master (Bosch) can be found next to the pack's communication signal connector. The main contactors and a fuse are placed next to the power connector. This battery showed the highest integration efforts of all specimens examined in this work's context. The whole BMS is located in the battery's case, it is built very space efficient and uses few cables. Altogether, it appears to be designed holistically, having the complete system in mind, as opposed to the next example. Example (3) VW e-Up  
Another battery pack that has been disassembled originates from the _Volkswagen e-Up_ (2013, initial registration: February 2014). It is shown in Figure 4b. The pack contains 17 serially connected modules (Figure 5b), each consisting of six serially connected pairs of two prismatic cells. The e-Up battery does not have a cooling system or a service disconnect, dividing the battery into two halves. The BMS modules are centralized, and the white box on the left side of Figure 4b) contains the measurement ICs (or BMS slave) for the whole battery pack. To the right of it, below a black cover, the contactors, fuse and current measurement can be found. The other white box contains some kind of BMS master. A large amount of voltage measurement wires connects the individual cells to the slave module, where Maxim's MAX11068 [3] is used for the measurement and balancing tasks with MAX11081 [8] as a secondary protection device. A closer look at the PCB shows that nine MAX11068 (12 voltage measurement channels each) are daisy-chained via I2C, which is also used to connect the last IC to the rest of the system. There is no microcontroller converting to a more robust field bus, like e.g., CAN. Apart from that, the slave's PCB is filled with a large amount of balancing resistors taking up most of the space. Example (4) Tesla Model-S  
An exception among the named examples is the Tesla Model-S battery. Here, only one module was available for analysis (see Figure 5a). According to [29], the whole battery consists of 7104 single 18,650 cells, divided into 16 modules in a 96s74p configuration, which means that each module contains a series connection of 6 \(\times\) 74 parallel cells. The individual cells are connected via bond-wires, which also act as fuses. The nominal voltage is 355 V and a liquid cooling system exists. For the BMS' cell-monitoring functions, TI's bq76 PL536A-Q1 is used, which is placed on a PCB mounted to one side of the module. The cell voltage measurement is performed using wires welded to the connecting plates of the parallel connections. Comparing the different battery packs shown here, it can be determined that there are significant differences in the construction, especially regarding the level of integration observed. While the _smart ed_ pack features large scale integration, the batteries of _VW e-Up_ and _Mitsubishi i-MiEV_ show only very moderate integration efforts. The former pack contains comparatively little cabling. The cell monitoring ICs are mounted on oblong PCBs on top of the battery modules in a very space saving manner, while the BMS-master is also located inside the pack, next to the signal connector to the car.