Unmanned aerial vehicles and drones come in all sizes—from hand-launched micro-UAVs to large-scale versions with jet propulsions, electric motors, and internal combustion engines.
Batteries are the life force of these drones. Understanding how the batteries work will help your drone fly high. Drone batteries come with many different energy storages like hydrogen fuel cells, lithium-ion (Li-ion, lithium polymer (Li-po), nickel-metal hydride, etc.
The most popular method to power them is lithium battery configurations when it comes to smaller versions of UAVs or drones. This is because they are lightweight, inexpensive, and are readily available in multiple sizes, capacities, and voltages, and they have high current rates. They also have high energy densities that work for smaller endurance drones and fixed-wing designs.
All drones are susceptible to multiple fault and failure conditions—from merely annoying to catastrophic. This makes robust electrical protection essential.
If you choose the right battery management system for your drone, it will help improve performance and increase its lifetime. In this article, we will discuss the know-how of LiPo batteries in drones and the importance of battery management systems.
What are LiPo batteries?
Lithium polymer batteries are the most common batteries used in drones. It is composed of a lithium-based cathode and anode separated by a polymer electrolyte.
They’re more commonly used for drones because they are smaller and possess high energy density.
LiPo Batteries and Drones
LiPo batteries can easily lead to “thermal events” like smoking or catching fire if not charged or used correctly. However, many circuit protection options are available to help protect LiPo drone batteries. It protects against over-current and over-temperature conditions that lead to thermal events.
Thermal events in LiPo batteries are because of their internal chemistry. When the battery is operated at or beyond its limits, it accumulates oxygen atoms and the build-up of lithium oxide (Li2O.) This creates more excellent internal resistance, leading to more heat and the beginning of the thermal runaway cycle.
Once the battery pack starts to swell, it is a good indication that the battery is damaged beyond repair or has reached the end of its life cycle.
Using a battery at the above mentioned condition beyond this will further increase its temperature and can potentially lead to a fire. Over-discharge and overcharge both can cause problems in batteries:
At the time of over-discharge, if the cell voltage drops lower than 1.5V, gas will start getting produced at the anode. When the voltage drops to less than 1V, copper from the current collector starts to dissolve. This causes internal shorting of the cell, and hence, under-voltage protection becomes essential.
When cell voltage reaches 4.6V, the heat starts building up at the cathode. Cylindrical cells are internally protected from the pressure with the help of:
- Activated CIDs (current interrupt devices)
- Internal PTCs (positive temperature coefficient discs) increase the resistance when heated.
LiPo cells, however, do not have internal CIDs and PTCs. Therefore, external overvoltage, over-gas, and over-temperature protection for lithium polymer cells are especially critical.
This is where the need for circuit protection and battery management systems comes into the picture. Multiple circuit protection options help guard drone batteries against high temperature and over-current conditions. This includes:
- Metal Hybrid PPTC with thermal activation (MHP-TA) devices
- PolySwitch PPTC devices, ultra-low resistance devices
- Surface-mount fuses
- TVS Diode Arrays
Drone Circuit Protection Options
Here are some circuit protection options to consider:
1. MHP-TA Devices
MHP-TA devices offer low thermal cut-off temperatures, high hold-current ratings, and are compact—all these provide invaluable protection to the LiPo batteries.
The latest MHP-TA devices offer a 9V DC rating and a higher current than typical thermal cutoff (TCO) devices.
These devices can handle voltages and high-capacity battery charge rates in LiPo cells. In addition, it provides resettable and accurate over-temperature protection. Its compact footprint also simplifies circuit protection in ultra-thin battery pack designs.
2. Polyswitch PPTC Devices
Polyswitch PPTC devices offer better solutions for batteries like:
- Lithium-Ion (Li-Ion)
- Nickel metal hydride (NiMH)
- nickel-cadmium (NiCd)
These devices are compatible with high-volume electronics. In addition, their UL, CSA, and TÜV agency recognition makes it easier to meet regulatory requirements.
The low resistance helps increase battery operating time and enhances over-temperature protection from thermal events.
Surface mount resettable PPTCs suit well for protecting Lithium battery packs. It provides over-temperature prevention with low internal resistance and power dissipation.
3. Surface Mount Fuses
Polyfuse LoRho Surface Mount Resettable PPTCs are better suited for protection circuit modules for Li-ion and LiPo battery packs. It provides fast protection from over-temperature and over-current, ultra-low internal resistance, voltage drop, and power dissipation.
They’re a low maintenance alternative to one-time fuses as they reset automatically and offer over-current protection. In addition, they can be mounted within an electronic protection module on the board and simplifies the assembly process.
Although fuses and PTCs are both over-current protection devices, you can reset PTCs automatically. Traditional fuses will need replacement after they are tripped. A fuse will completely stop the current flow (which may be desirable in critical applications). Still, after most similar over-current events, PTCs continue to enable the equipment to function, except in extreme cases.
4. TVS diode arrays
Electrostatic discharge is also a significant concern for multiple drones. In addition, it is a concern for I/O ports on the flight controllers. As the data rate on the signal port increases, you need to consider the capacitance of the chosen suppressor so that it doesn’t introduce any signal integrity issues into the system.
For example, circuits in this port running at low speeds can be protected with higher capacitance arrays. Multiple protection options are available for the same, such as:
- Polymer ESD Suppressors (PGB or XGD)
- Transient Voltage Suppressor (TVS) diodes
A battery management system for lithium-ion batteries is crucial for assuring your drones’ safety, protection, reliability, and longevity in sustaining driving operations. Make sure you partner with reliable battery management system companies. Our smart battery management technology at Oakter optimizes the life of the battery pack through continuous monitoring and effective cell balancing. It also determines the accurate state of charge and state of health of the battery packs. For more information, reach out to us here.