#7 · How Does a BMS Protect a Battery Pack?
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- A BMS (battery management system) is a protection system that monitors voltage, current, temperature and more, and prevents overcharge and over-discharge so that the battery pack is used safely.
- The three main protection functions are overcharge, over-discharge and overcurrent protection, together with short-circuit and over-temperature protection and cell balancing, which keeps the cells at an even voltage.
- If the BMS protection has cut off, the battery has left its normal range. To prevent accidents, find the cause of the cut-off before using the pack again.
Article #6 covered the rules the user should follow to use a battery pack safely. This article covers the device that keeps the pack safe from the inside: what a BMS actually does.
1. What does a BMS watch?
A BMS continuously monitors the battery's condition, including voltage, current and temperature. When a reading leaves its set range, the BMS controls charging or discharging to protect both the battery and the machine.
2. Three main protection functions
- Overcharge protection — keeps the voltage from going above the upper limit during charging. Overcharge can lead to safety incidents caused by heat and swelling.
- Over-discharge protection — keeps the cell voltage from dropping below the lower limit during discharge. An over-discharged cell can be damaged beyond reuse or repair.
- Overcurrent protection — keeps a current larger than the operating range from flowing. The difference between the brief peak current a machine draws and the current drawn continuously is covered in article #4.
Other built-in protection functions, such as short-circuit protection and over-temperature cut-off, also help prevent safety incidents.
3. Cell balancing — keeping the cells in step
Even the cells that make up the same pack can drift slightly apart in voltage during use. As the gap widens, the highest cell reaches the upper limit first, charging stops early, and the usable capacity shrinks. Cell balancing is a management function that narrows the voltage gap between cells so that the whole pack is used evenly. Balancing methods (active and passive) will be covered separately in a later guide.
4. A proven BMS is essential
A robotics battery pack needs a BMS with monitoring that covers everything from machine operation to storage and standby, along with precise data output. To optimize a robot's drive efficiency, choose a battery pack fitted with a BMS that has been thoroughly proven in industrial settings.
For safe use, the monitoring and control functions of a BMS also need to be built in several layers rather than one. Safe use is possible only when second and third layers are designed to keep monitoring and controlling the battery if the first one fails.
POWERCRAFT has developed BMS in-house alongside its battery packs. From high-performance industrial BMS to ultra-compact BMS for heavy-duty and humanoid robots, design starts from an understanding of the environment in which a robot actually operates, and the company has developed BMS with a multi-layer safety design.
- A BMS is the protection system of a battery pack that monitors voltage, current and temperature, and controls charging and discharging when they leave the set range.
- The main protection functions are overcharge, over-discharge and overcurrent protection, together with short-circuit and over-temperature protection and cell balancing.
- If a protection cut-off has occurred, the battery has left its normal range, so find the cause before using the pack again.
- When choosing a battery pack, check that the BMS is proven in industrial settings and designed with protection in several layers.
— the BMS protection functions of all 49 standard packs are listed on each product's spec sheet. If the machine needs a BMS matched to its current, communication or operating environment, browse the POWERCRAFT custom build projects and fill in the specification request. POWERCRAFT will quote to suit the machine.