Is UBEC required?

Why do we need UBEC ?

Adding UBEC to your electrical system might save you model from an unexpected outcome which may lead to uncontrolled plunge and crash into the ground.

In the basic electrical system setup of model, the ESC has a built-in BEC. The Li-Po battery is connected to the ESC which will power-up the brushless motor, the radio Rx/receiver and all the servos. Most of the built-in BEC have a limited ability to supply power to the radio Rx/receiver and servos without overheating/glitch. When overheating / glitch occurs, the Rx receiver tends to reboot (restart) itself, leaving you unable to control until the reboot process is completed; usually almost 2 seconds. Sometimes during the reboot process, the servos turn to their max travel and then return to neutral position before you can gain control. This will cause your model to maneuver randomly. Your model is still save when the overheating/glitch happens at high altitude, but you will never know when will it happened.

Besides the limited ability to supply power, a built-in BEC is commonly a linear type. A switch-mode BEC has a much higher efficiency than a linear type BEC, when using Li-Po battery pack with 4S or more.

• Linear BEC: a 4S Li-Po battery has a typical voltage of 14.8V, in order to produce BEC output of 5V/1A, the current flow into the BEC is at least 1A, therefore the power on BEC is (14.8V x 1A) = 14.8W. But the useful output power is only (5V x 1A) = 5W, so the efficiency of the BEC is just (5W / 14.8W) x 100% = 33.8%; the remaining power of (14.8W – 5W) = 9.8W is converted to heat energy. This makes the BEC hot and may caused overheating.
• Switch mode BEC: to produce BEC output of 5V/1A, the current flow into BEC is only 0.38A (actual test data from EMAX UBEC manual). The power on BEC is (14.8V x 0.38A) = 5.6W, therefore the efficiency of the BEC is (5W / 5.6W) x 100% = 89.3%.

Therefore, adding UBEC with switch-mode BEC to your system will improve the reliability and performance of the model. There are 2 condition of installing UBEC to the system:

1.  The ESC has no built-in BEC.

The UBEC’s input cable is connected to the battery and the output cable to the radio Rx/receiver (batt channel). No change is required in the ESC connection.

2.  The ESC has a built-in BEC.

The built-in BEC of the ESC needs to be disabled; remove the red wire from the output cable of the ESC (the three-colours-cable which is connected to the Rx receiver). The UBEC’s input cable can be connected to the same Li-Po batt which is used to power up the ESC. This can be done by connecting the UBEC to the Li-Po batt’s balance plug. The header of the UBEC’s input cable is required to be changed to the proper Li-Po batt’s balance plug header.

Adding UBEC only adds a couple of grams in weight; in this case EMAX 3A UBEC weights 11 g.

Be safe and confident at your flight.

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