Hamilton Electric Bikes

What is a “BMS” Battery Management System and why does it matter?

You may be tempted to purchase a cheap battery online or from a friend but there is usually a reason and a potentially very dangerous reason why it is so cheap. It’s much faster and cheaper to make an ebike battery without a BMS. But without a proper functioning BMS your deal of the century battery runs the risk of overheating and catastrophic failure.

The battery’s internal management system, often referred to as a Battery Management System (BMS), plays a crucial role in maintaining the battery’s health, safety, and efficiency and can affect the charging speed in several ways.

Here’s a brief list of what your BMS is doing for you behind the scene why this is important:

  1. Temperature Regulation: The BMS monitors the temperature of the battery cells and can reduce the charging current if the temperature goes beyond safe limits. Overheating can damage the battery, so charging might be slowed down to keep temperatures in check.
  2. Cell Balancing: Lithium-ion batteries are made up of multiple cells, and the BMS ensures that all cells charge evenly. If some cells are at a higher voltage than others, the BMS might slow down the charging to allow the lower-voltage cells to catch up, ensuring all cells reach full capacity at about the same time.
  3. Voltage Monitoring: The BMS constantly monitors the voltage of the battery cells. As the cells approach their maximum voltage, the BMS may reduce the charging current to prevent overvoltage, which can be harmful to the cells.
  4. Charge Rate Control: To prolong the life of the battery, the BMS may limit the charge current as the battery approaches full capacity. This is often seen in the final 10-20% of the charging process, where the charge rate is reduced (a process known as “tapering charge”) to prevent overcharging and reduce wear on the battery.
  5. State of Health (SoH) Management: The BMS might adjust the charging speed based on the battery’s overall state of health. As batteries age and their capacity diminishes, the BMS might alter charging parameters to best suit the condition of the battery cells.
  6. Safety Protocols: If the BMS detects any fault conditions, such as a short circuit or a cell anomaly, it may stop charging altogether to prevent damage or unsafe operation.
  7. Communication with the Charger: Some BMSs can communicate with the charger to control the charging process more precisely. They can request a specific voltage or current level based on real-time assessments of the battery’s condition.

Because of these and other BMS functions, the actual charging time can be longer than the theoretical time calculated by simply dividing the battery capacity by the charger’s output current. The BMS ensures that the charging process is safe and as efficient as possible, while also maximizing the lifespan of the battery.

So at the end of the day it is always safest to purchase your ebike from a reputable dealer and stay away from third party websites or stores selling cheap Chinese knockoffs and never intermix chargers and batteries, only use the charger and battery that came with your ebike. If you are ever unsure give us a call and we can help guide you down the safest path.

Happy riding and remember to always look for excuses to get out and ride!!



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