BEC
Battery Eliminator Circuit.
On a nitro helicopter, there is a 4.8 volt "receiver pack" that powers the receiver, gyro,and
servos. On an electric helicopter, we already have a very large battery which powers the
main motor. However, the voltage of this main motor battery pack is typically more than 4.8
volts. So, the BEC will take the voltage of the main battery pack and regulate it down to 4.8
volts to power the receiver, gyro, and servos, This eliminates the need for a separate 4.8
volt receiver pack.
There are two types of BECs: linear BECs and switching BECs.
A linear BEC reduces the main battery voltage to about 4.8 volts by applying a resistive
load and wasting the excess power as heat. This has two important implications: First, the
current capacity of a linear BEC drops quickly as the input voltage rises. A typical 1 amp
linear BEC can dissipate about 3 watts, so it can handle a load of 1 amp at 8 volts, but can
only handle half this current, or 0.5 amps, at 11 volts. Second, a linear BEC is usually only
about 50% efficient (or less) since it discards excess power as heat. If a linear BEC becomes
too hot, it will thermal shutdown and you will lose control of the model.
A switching BEC functions by rapidly pulsing the main battery voltage to create an average
filtered output of 4.8 volts. This method of regulating voltage is more efficient than a linear
BEC, so a typical switching BEC is 80 to 90% efficient. Also, it can handle much higher input
voltages than a linear BEC (up to 35 volts or more), and the current capacity does not
drop at higher voltages.
Note: Most BECs are rated for 5 volts of output. The extra 0.2 volts will not harm the electronics
equipment. From an electronics point of view, a 5 volt regulator is easier to build
than a 4.8 volt regulator since the parts are more easily available, so most BECs output 5
volts instead.

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