In this blog, we will introduce the structure of the master-slave BMS, how to match the slave board according to your own needs, what is needed to install the master-slave board BMS, the functions of each module, and installation tutorials.
Master-slave board BMS
The main role of the BMS is to protect the cells inside the battery pack from operating outside of their operating range and to optimize their cycle life by accurately monitoring them (temperature and voltage) while controlling the balancing, charging and discharging process according to the user's requirements Predefined.
For most DIY projects like e-bike or e-scooters that require less than 5 kW of peak power, there are several BMS on the market that are "good enough" most of the time. When an application requires more than 5 kW of power, those "inexpensive" BMS are becoming insufficient at protecting the pack due to the facts that they do not allow their parameters to be adjusted (Fixed voltage, fixed balancing thresholds, no temperature monitoring & fixed current limits) and are using a solid state switch to disconnect the load from the battery pack in case of an emergency. The main problem with solid state switches is related to their nature of failing "closed" instead of failing "open" like relays or contactors.
Master-slave board BMS is oriented toward high-power applications where the battery pack's long-term performance is critical. Master-slave board BMS is integrated with EVC500 main contactors directly bolted onto the main board and is equipped with a heavy-duty PCB soldered current sensor good up to 500A continuous. Integrating all components on the same board reduces the amount of cabling required and simplifies the installation process. Master-slave board BMS has a large set of parameters that can be precisely tuned by the user depending on the application. For instance, users can choose to limit the soft discharge and recharge voltages, thus improving cells' durability. Other parameters such as MIN/MAX operating temperatures, balancing threshold value, current limits, and more options can be defined by the user through the app.
The advantages of the master-slave board BMS: high channel utilization, flexibility of system configuration, adapting to modules and battery packs of different capacities and specifications
Slaves boards are offered in three different versions : LTC6811-12S, LTC6812-15S & LTC6813-18S. All three slave boards share the same built-in functionalities and have the same physical dimensions with similar pins layout. All versions are supported by the master board firmware and uneven cell numbers connected in series is possible. The choice of which version to use will depend of the pack physical layout and/or the internal modules arrangement.
MKBMS is based on the modular BMS of LTC68XX and STM32 MCU, and is connected to one or more slave boards and integrated integrated boards of different sizes through the ISOSPI interface. The modular BMS can be configured for various applications with battery voltages within 150V.
How to choose a suitable slave board
The easiest way, send your needs to our mailbox: firstname.lastname@example.org, our staff will recommend the best match for you.
Rationale for picking slave boards: For uneven cell count in series, only the last slave board in the daisy-chained loop should have one cell less connected than the other slaves. Ex: 39S= 10S+ 10S+ 10S+9S
Let's take a look at a few common collocations, and you will have a better understanding of the collocation of slave boards:
What is required for installation
In addition to the main board, the installation of the split board also requires a relay, a 12V step-down module,power cables and a slave board corresponding to the number of strings.
The relay is quite an "automatic switch" that uses a small current to control the operation of a large current, (equivalent to an overcurrent judgment switch, when it detects that the current is too large, use this relay to turn off the power output.)
The function of the 12V step-down module is to provide the relay with a 12V working voltage. The operation of the master-slave board BMS requires at least one external 12V power supply to be connected to the 12V connector input. The power supply must be powerful enough to provide the peak power required to close the main contactor and prevent short circuits.
Power cable: BAT+ & LOAD+ must obviously be connected to the main contactor terminals. The BMS needs to be connected as well to those terminals, but only for monitoring battery pack & load voltages. As mentioned earlier, Master-Slave Board BMS Master board is designed around the main contactor and should normally be bolted directly over the main contactors terminals & over the cable lugs.
User can also choose to install the main contactor remotely. In this case, the contactor terminals must be connected to the board with small cables & round terminals connected in their respective mounting holes for enabling the battery pack & load voltage monitoring processes. Keep in mind, the main positive current path does not run through the BMS, but through the main contactor.
On the other hand, the main negative current path must run through BAT- & LOAD- in order to monitor the current going out of the battery pack. The large current shunt resistor is soldered directly underneath the PCB. M8 cable lugs + M8 bolts are required and must be connected directly to the shunt resistor from below.
(Warning: Do not short-circuit the contactor coil outputs. Use contactor with built-in economizer.)
How to install
In the next blog, we will explain the operation details such as how to wire multiple slave boards and the connection instructions of other accessories.
The installation video of the master-slave board BMS is in production. After the editing is completed, we will embed the blog and upload it to social media synchronously. Please follow https://www.youtube.com/c/MAXKGO