BMS (Battery Management System) || DIY or Buy || Properly protecting Li-Ion/Li-Po Battery Packs

Summary

In this video, the creator discusses building a homemade lithium-ion battery pack and the importance of a Battery Management System (BMS) for safety. The pack consists of 4 cells in series and 2 in parallel, providing a range of 12-16.8V, 40A output, and 72Wh capacity. The creator explains the workings of commercial BMS units, their protection features, and walks through a DIY BMS project based on Stuart Pittaway's design. While DIY BMS offers more control and monitoring, it's more expensive and energy-consuming than commercial versions, with both having distinct advantages depending on the application.

Takeaways

• 🔬 The video discusses creating a homemade lithium-ion battery bank with a voltage range of 16.8 to 12 volts and a capacity of 5 amp-hours.
• ⚡ The battery pack is designed to output up to 40 amps continuously and has a nominal energy of 72 watt-hours, suitable for 12-volt devices after voltage adjustment.
• 🔋 The script highlights the importance of balancing the cells in a battery pack to prevent misalignments and potential damage due to overvoltage.
• 🛠️ The video suggests using a Battery Management System (BMS) for safety, offering protection against overcharge, overdischarge, short-circuits, and balancing charging.
• 💡 The presenter examines a commercial BMS, identifying its three functional groups and explaining how each component contributes to the overall protection of the battery pack.
• 🏭 The video contrasts commercial BMS with a DIY approach, introducing a BMS design by Stewart Pittaway that can be built at home for those who prefer not to purchase a commercial product.
• 🛒 The script mentions sourcing components for the DIY BMS from various suppliers, including JLCPCB for the PCBs and Mouser for other parts, with some special components from eBay.
• 🔧 The assembly process for the DIY BMS is detailed, including soldering SMD components, adding power resistors, and programming the microcontrollers.
• 🌐 The DIY BMS features online monitoring and balancing capabilities, which are improvements over some commercial BMS, providing real-time data through a web interface.
• 💰 The video concludes that both DIY and commercial BMS have their advantages, with the DIY option being more suitable for specific applications like solar-powered systems, while commercial BMS might be better for general use.

Q & A

What is the configuration of the homemade lithium-ion battery pack described in the video?

The battery pack consists of 4 cells in series with 2 cells in parallel, giving it a voltage range of 16.8 to 12 volts and an output capacity of 5 amp-hours.

What are some of the potential safety issues associated with this battery pack?

Safety issues include voltage misalignment among the cells due to different capacities, which can lead to overcharging or overvoltage, and the risk of damage in case of a short circuit.

How does a BMS (Battery Management System) help improve the safety of lithium-ion battery packs?

A BMS offers balanced charging, short-circuit protection, overcharge and discharge protection, which ensures that all cells charge uniformly and prevents dangerous conditions like overvoltage or short circuits.

What is the role of the DW01A IC in the BMS discussed in the video?

The DW01A IC protects each battery cell from overcharge, overdischarge, and overcurrent by controlling two transistors that disconnect the cell from the load when necessary.

What is the function of the HY2213 IC in the BMS?

The HY2213 IC is a lithium-ion balance charge IC that activates a transistor to discharge a cell through a resistor when its voltage exceeds a certain value, ensuring that all cells are balanced after charging.

How does the DIY BMS monitor battery cell voltage and temperature?

The DIY BMS uses an AT Tiny 85 microcontroller to sample the battery cell's voltage via a voltage divider and monitor its temperature using a thermistor. This data is then sent to an ESP8266 development board for online monitoring.

What are some of the key improvements offered by the DIY BMS compared to commercial versions?

The DIY BMS provides online monitoring and balancing capabilities that many commercial BMS systems lack. However, it is more expensive, time-consuming to assemble, and consumes more current.

How is the ESP8266 board connected and programmed in the DIY BMS?

The ESP8266 is connected to the battery monitoring system using a 4-pin JST connector and programmed by connecting it to a computer, uploading the provided code, and setting up the necessary communication and IP configurations.

What was one of the challenges encountered during the DIY BMS assembly process?

The creator accidentally ordered some component package sizes too large, which worked for the resistors but was not ideal for the capacitors. Despite this, the assembly was successful.

What is the final conclusion about choosing between a DIY BMS and a commercial BMS?

Both DIY and commercial BMS systems have their own advantages. The DIY BMS is ideal for applications like DIY power walls charged by solar power, while commercial BMS systems are better suited for battery packs that are not used as frequently.