Battery eliminator circuit

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A battery eliminator circuit (or BEC) is a device found on electric-powered models and supplies power to the receiver, servos and gyro from the main battery (that also powers the main electric motor), thus eliminating the need for a separate receiver battery and thereby saving weight. Usually, these are equipped with built-in voltage regulation circuitry to convert the main battery's voltage to a level compatible with the receiver and servos, regardless of the main battery's voltage (within given limits). Often the BEC is combined with the electronic speed controller.

There are two main ways that battery eliminator circuits reduce the voltage from that of the main battery to the 5 to 6 Volts suitable for the flight electronics:

  • Linear BEC
Drops the voltage with a resistive divider, with the excess power essentially being dissipated as heat. As well as not being very efficient, it also means that as the main battery voltage increases, the battery eliminator circuit is capable of delivering less power to the electronics. However, a linear BEC (or linear regulator) generates little or no electrical noise ("EMI") since there is no high frequency switching going on and can be built from a much simpler electronic circuit.
  • Ultimate BEC (uBEC)
Drops the voltage via a small switched-mode power supply; this is much more efficient, and does not lose performance as the input voltage rises. Potentially, however, it can cause additional Electromagnetic Interference (EMI), interfering with the receiver electronics; this is usually mitigated with a ferrite ring on the power output leads.

Most BECs are optimistic about how much voltage the helicopter control electronics can take. A few items, such a digital servos and a few gyros can be damaged by operation at higher voltages; a voltage regulator can be used to drop the voltage to 5V for those devices that need it.

See also

Please note, output from the passive resistor divider type BEC only drops as battery voltage decreases (not increases - as detailed in orginal text of this article) Also substitute the word 'decreases' in appropriate place for active 'switch-mode' BEC circuit.

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