In this article we will discuss what ESC, BEC and UBEC are, what the advantages are using UBEC, and linear VS switching.
Check out this post about how to choose ESC for quadcopters.
What are ESC, BEC, UBEC?
ESC stands for Electronic Speed Controller. It converts the PWM signal from the flight controller or radio receiver, and drives the brushless motor by providing the appropriate level of electrical power.
BEC stands for Battery Elimination Circuit. It’s just a fancy name for voltage regulator, which converts main LiPo battery pack voltage to a lower voltage (e.g. 2S 7.4V, 3S 11.1V or 4S 14.8V to 5V). BEC is usually built into ESC, and as the name suggests, it eliminates the need for a separate battery to power the 5V electronic devices.
UBEC stands for universal BEC or sometimes ultimate BEC. It’s used when ESC doesn’t have built-in BEC, or standalone power system is required. They generally are more efficient, more reliable and able to provide more current than BEC. The UBEC is connected directly to the main battery of the multicopter, the same way as an ESC.
You might sometimes also see “LBEC” and “SBEC”. LBEC stands for Linear BEC, and SBEC stands for Switching BEC. I will explain what they are in the last section in this article.
Why Use UBEC over ESC BEC?
In layman’s terms, UBEC has the following advantages over ESC built-in BEC:
- UBEC are more power efficient
- BEC tends to overheat with large input/output voltage difference, or large load; UBEC doesn’t have this problem and thus more reliable
- UBEC generally can provide more current safely
The reason behind these are due to the way how voltage is regulated. Most BEC are linear type, and UBEC are switching type. For a more technical insight, please carry on to the next section: Linear BEC VS Switching BEC.
If your ESC don’t have BEC, you can use an external UBEC to power your FC and RX. The UBEC’s input cable should be connected to the LiPo battery, and the output cable to the RX and FC. No change is required in the ESC connection.
But if you want to power your FC and RX with an UBEC, while your ESCs have built-in BECs, those BECs first needs to be disabled/disconnected from your system. Simply remove the red wire (5V) from the output servo lead of the ESC.
Linear BEC vs Switching BEC
There are two types of BEC; linear and switching. They are basically the two type of voltage regulators: linear and switching voltage regulators , which have been covered before, but here is the summary of differences.
They are sometimes also referred to as LBEC and SBEC.
Most ESC’s built-in BECs are Linear type.
Linear BEC reduces the voltage from the main Lipo to 5V by converting the excess voltage into heat. This is not a very efficient way of voltage converting as you can imagine.
As input voltage gets higher, or current draw gets larger, more power will be wasted and converted into heat. That’s why this type of voltage regulator is not ideal for high input/output voltage difference or high current application. It’s generally only used on 3S or below (some works on 4S, but very rarely recommended)
Overheated BEC will enter thermal-shutdown, and cause loss of power to the flight controller and radio receiver, and eventually a crash.
When the main battery pack is fairly low (e.g. 7.4v 2S), wasted power is relatively small because there is not much voltage difference, so efficiency is better. But as you use higher cell count lipo efficiency drops right down. Lots of power is wasted and converted into heat.
This is something you should bear in mind, but I just want to assure you that I have been running 4S on my Blue series ESC (rated 2S to 4S by manufacturer), and using the built-in BEC to power my FC and RX, I have not had a single problem with it. Although it gets a bit warm, it still runs reliably with good good amount of air flow. This leads to another argument, where to mount your ESC on quadcopter frame?
Switching BECs reduce the output voltage by switching the supply on and off several thousand times per second. They don’t heat up like linear BEC, and they generally handle higher input voltages and higher current much better.
They have a very consistent efficiency across a wide range of input/output voltages, which is around 85%. This is also the choice for running on 4S or above system if you are after reliability.
One drawback with switching regulators is the noise they produce due to the nature of voltage regulation, that’s why they are not used on ESC’s. Some people put a LC filter at the output and it seems to clean up the power pretty well.