Understanding BEC in FPV Drone Flight Controllers and ESC

In this article, we’ll delve into the roles and benefits of BEC in FPV drone flight controllers and ESC, with a focus on the advantages of using a BEC, and the differences between linear and switching BECs.

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If you’re selecting an ESC for your FPV drone, you might find this accompanying post helpful: https://oscarliang.com/esc/

What is a BEC?

A Battery Elimination Circuit (BEC) is essentially a voltage regulator that steps down the voltage from the main LiPo battery pack (e.g., from 4S 14.8V or 6S 22.2V) to a lower voltage like 5V or 9V. Commonly integrated within the flight controller or ESC, the BEC eliminates the need for a separate battery to power your electronics.

Further Reading: What does “S” mean in “2S, 3S, 4S and 6S batteries”?

A “UBEC” stands for Universal or Ultimate BEC. It’s used when an ESC doesn’t have a built-in BEC, or when a standalone power system is needed. Known for their efficiency and reliability, UBECs can also provide higher currents than typical BECs. They connect directly to the main battery, much like an ESC.

Why Opt for a UBEC Over an ESC’s Built-In BEC?

Choosing a UBEC over a built-in BEC in your ESC offers several benefits:

• UBECs are more power-efficient.
• Unlike BECs, UBECs don’t overheat under high voltage differences or loads, enhancing their reliability.
• UBECs typically support higher current outputs safely.

These advantages are due to the different methods each system uses to regulate voltage. Most integrated BECs are linear, while UBECs use a switching method.

If your ESC lacks a BEC, an external UBEC can be used to power your electronics. Simply connect the UBEC’s input cable to the LiPo battery and its output to your receiver and flight controller, without altering the ESC connection.

However, if you’re integrating a UBEC in a setup where your ESCs already have built-in BECs, you’ll need to disable those by disconnecting the red wire (5V) from the ESC’s servo lead.

Linear BEC vs. Switching BEC

BECs can be either linear or switching. Linear BECs, often found in ESCs, dissipate excess voltage as heat to step down the LiPo voltage to 5V. This is not particularly efficient, especially at higher voltages or with significant current draws, as it can lead to wasted power and overheating: https://oscarliang.com/linear-regulator-vs-switching-regulator/)

Switching BECs, on the other hand, toggle the power supply on and off to manage voltage reduction, avoiding the overheating issue common with linear BECs. They maintain about 85% efficiency across higher voltages and currents, making them preferable for setups above 4S.

From personal experience, I’ve run a 4S setup on my Blue series ESC with its built-in BEC to power my flight controller and receiver without any issues, though the ESC does get warm. Proper airflow is essential in such configurations.

Conclusion

Whether you choose a UBEC, a BEC, or an ESC with an integrated BEC, understanding these components’ functions and limitations is crucial for developing a reliable and efficient power system for your drone.