Tesla BMS

Header bms

Rechargeable batteries are a phenomenon of modern times. The most commonly used are Li-Ion batteries. They can be found practically everywhere - mobile phones, hand tools, large energy storage for photovoltaic power plants, and in electric cars.

However, these batteries are very sensitive to the conditions in which they are operated, necessitating the use of BMS (Battery Management System) protection electronics; this safely disconnects the battery if one of the parameters is exceeded. At Tesla, we have been developing protections for 15 years for batteries used in hand tools (drills, saws, grinders, breakers, etc.) Thanks to our own development and the flexibility we can provide, in the future we would also welcome cooperation in other areas of battery use, e.g. small means of transport - electric bicycles, scooters, etc., small work machines, etc.


We can design and manufacture protective electronics (BMS) for charging Li-Ion batteries with the following characteristics:

  • Charging 3 - 16 cells
  • Setting of nominal and maximum discharge/charge currents
  • Setting temperature limits
  • Balancing: passive – balancing currents typically up to 100 mA, or according to your needs
  • Pre-charge, pre-discharge option
  • Communication: UART, RS232, HDQ, SMBUS, I2C
  • Signaling: state of charge (SoC), number of charging cycles, error states, etc.
  • Electronics consumption (typical) - operation/idle/disconnect: 2 mA/ 100 uA/ 10 uA
  • We meet the following standards: EN 62133-2, IEC 62368-1, IEC 61000-6-1, IEC 61000-6-3, IEC 61000 -4-2, UL 62133-2, UL 2054, UN 38.3, RoHS, etc.


In order for a battery to be truly and safely disconnected, our electronics are controlled by a microprocessor, for which we create our own software according to the customer's requirements. Using our BMS protection, the battery is protected several times during operation by monitoring its condition.

Standard monitored statuses include battery overcharging, battery operating temperature monitoring, exceeding the permitted current (for both charging and discharging), and balancing. Safe disconnection of the battery is ensured in the event of a short circuit on the battery terminals, low voltage for operation (i.e. battery discharge below the permissible value of the cell voltage), or when the maximum charging current is exceeded.

Thanks to our design, the BMS can be very quickly and easily adapted to the customer's requirements, both parameters and dimensions of the PCB, built-in, etc. Currently, our BMS are designed for 3-16 Li-Ion cells in series (10.8 to 57.6V) and nominal currents of 50A and more.

BMS can have output communication such as SMBUS, HDQ, UART, RS232, I2C for communication with a superior device such as a charger.


Overcharge protection


Overcurrent protection


Protection against overheating


Optimizes battery capacity

Why is cell balancing important?


Cell balancing is one of the most important features of BMS electronics. In battery blocks where multiple cells are connected in series, different cells are charged differently during the charge/discharge operating cycles. These small differences are caused by the different properties of the individual cells, as no two cells are exactly the same. The result is a gradual divergence of the terminal voltages on the cells. Over time, these different voltages result in the cells being only partially charged, so the cells use their entire voltage range which is usually from 3.0 V to 4.2 V for the Li-Ion type. Finally, some of the cells work in the range of, for example, 3.1 - 3.7 V and some 3.9 - 4.2 V. The more cells there are in series, the greater the possibility of gradually unbalancing the accumulator.


Balancing increases the capacity of the battery; all cells are fully charged and resume working in their entire voltage range. Most importantly, the lifetime of the entire accumulator is extended.

The passive balancer monitors the voltage on the battery cells during charging. In case of a difference between individual cells, the balancer starts to load the cells with the highest voltage (less current flows into more charged cells, more current flows into less charged cells) and thus compares the voltage on the cells. As a result of passive balancing, the cells are charged to the same voltage, but there are higher losses during charging. Passive balancing is not effective, as redundant energy turns into heat on the load.

Active balancing is controlled by the processor during charging and discharging. Every cell is monitored, and bad ones are discarded. Energy is actively transported between cells from one charged cell to the entire battery or from the entire battery to one less charged cell. Energy transfer is then between adjacent cells or cells in one series branch or in cells between branches. This results in a shortening of the battery charge, an extension of its life, and an extension of the operating time of the battery pack.

The role of the BMS is to guard, monitor, communicate and restrict.


  • voltage
  • current
  • temperature
  • charging
  • discharging
  • battery health


  • voltage during charging and discharging
  • current during charging and discharging
  • internal impedance of cells
  • stored energy
  • released energy
  • total operating time
  • number of charging cycles


  • HDQ
  • UART
  • RS232
  • I2C


  • spikes from appliances
  • excessive discharge
  • overheating and hypothermia
  • surge during charging
  • undervoltage during discharge
  • cell overcharging