View source for Battery eliminator circuit (BEC)

A '''battery eliminator circuit''' (BEC) accepts battery voltage and provides a lower voltage for other circuits, such as the receiver (Rx) or the [[Servos]]. It is so named because it eliminates the need to have a second battery (often called the "receiver battery") of a different voltage.

=How it works=
For several decades, most digital electronic circuits were made to operate using a steady 5 volt (5V) supply of power. There are very few batteries, or combinations of cells, that equal exactly 5V, so in radio-control systems you may see fairly forgiving radio receivers (Rx) and servos that are supposed to be operated with 5 volts, but which work just fine on as little as 4V or as much as 6.5V.

Unfortunately these circuits can be damaged by higher voltages, and the LiPo batteries used in combat robotics are usually a minimum of 7.4V, with larger battery packs much higher. A BEC is a small voltage regulator circuit connected to the full voltage of the battery, which delivers a steady voltage so that the digital electronics operate correctly.

=BECs built into ESCs=
Many [[ESCs|electronic speed controllers]], such as the RobotPower Wasp and the FingerTech TinyESC, include a BEC circuit that feeds 5 volts back to the receiver. The amount of power provided should run any modern Rx, but it might not be enough to also run servos connected to the Rx.

=Standalone BECs=
There are several small and light BECs on the market that will provide 5 volts with enough current to run multiple servos and receivers. If you use one of these, be sure to disable the BEC in your ESCs (if any) by using the disable feature or by disconnecting the 5 volt wire from the ESC to the Rx.

=Troubleshooting the BEC=
*If your Rx is not powered at all (no lights, for instance), make sure there is at least one BEC connected and providing power.
*Avoid connecting multiple BECs to the same Rx, unless they are designed to operate that way. Disconnect all but one 5V supply wire to the Rx. Don't disconnect Ground wires; they are still needed. Also, don't disconnect the 5V wires that provide power from the Rx to servo(s).
*If the Rx lights are on, but its behavior is erratic, use a voltmeter to measure the voltage across 5V and Ground terminals on the Rx. (Many Rx will also report their voltage back to the transmitter, which can display it on a screen.)
*If the Rx is working correctly, but the servo(s) are not, the voltage may be just low enough (below 4.8V) that most servos will not operate. Consider adding a standalone BEC, or using a servo that can run on a higher voltage, and therefore get its power directly from the battery.