PCM and BMS, what is the difference?

​What is a PCM (Protection Circuit Module)?
  • A PMC is a stand-alone protective circuit.
  • It is purely analogical, this means there is no software integrated into it.
  • There is no possibility to switch-on or to switch-off the battery pack.
  • There is no possibility to get a precise status update about the charging level of the battery pack.
  • It cannot steer a charging unit or a consuming unit (electric motor, etc.).
  • A PCM only rarely surveys the temperature level.
  • It equalizes only in a very basic manner the different elements of an application.
  • It is usually a low-cost product, produced in Asia.
Typical applications which make use a PCM: low-cost products like certain electrically assisted bikes or small electric tools.

What is a BMS (Battery Management System)?
  • A BMS is an electronic board which is a lot more advanced than a PCM. A BMS contains a microcontroller with intelligent software integrated into it.
  • It calculates and interprets different types of measurements like the SOC (state of charge) or the SOH (state of health).
  • It offers a different level of protection (for example: it can distinguish between a normal and an abnormal event with regard to time).
  • It contains a communication bus (I2C, CAN, MODBUS, …), allowing for the transfer of information.
  • It has the facility of being steered by a main application.
  • It has the capability to communicate with other BMS in order to form a battery of much larger capacity, whereby it adapts itself automatically to the different needs.
  • It can go into standby mode in order to optimize its energy consumption.
  • A BMS possesses an intelligent algorithm to equalize the different elements of an application.
  • Via its communication bus, a BMS can steer chargers and/or consuming units (usually a motor) in order to optimize the utilization of the batteries and the behavior of the system.
  • It offers the possibility to execute a complete diagnosis of the battery at any given moment.
  • It can keep record of the battery life (counting errors, counting usage and storage time,)
Typical applications which make use a BMS: advanced products like robots, drones, electric bikes, electric vehicles, etc.
RELECTRO typically uses PCM's in its batteries.  The reasons for this include, inter alia:
  • Most electric bikes do not require the sophistication of a BMS
  • The cost of a PCM is significantly lower than that of a BMS - this cost is passed on to the customer
  • RELECTRO uses only top quality Samsung and Panasonic cells, which are typically spec'd to be within 0,5% of each other, so the requirement for cell balancing does not really exist
  • Those electric bikes whose batteries are supplied with BMSs (an extremely low percentage) rather than PCMs have differently designed and non-compatible BMSs, which means the we could not stock spares in anticipation of those batteries with failed BMSs being sent to us for repair