Battery eliminator circuit
Encyclopedia
A battery eliminator circuit (BEC) is an electronic circuit
designed to deliver electrical power
to other circuitry without the need for a battery
. Historically the expression was sometimes used to describe devices used to power battery-driven equipment from mains electricity. This is still the case in many products offered in retail electronic supply stores.
-mounted cameras in photography studio
s are often use a BEC to avoid having to interrupt lengthy shooting sessions to replace batteries. The use of the tripod can also interfere with access to the battery hatch.
(ESC). BEC allows such a model to carry only one battery
(the motive power battery) instead of two (motive power, and a separate battery to operate the R/C equipment). A BEC-equipped ESC meant for airplane use often incorporates a low-voltage-cutoff (LVC) circuit which can sense the voltage drop caused when the battery has little charge left in it. It then cuts the power to the 'drive' motor
in order to provide the 'steering' servo
(s) with enough power to be able to bring the model safely back to the operator. The power to the propeller would be cut but the operation of the control surfaces would be maintained in order to perform a dead-stick landing. Without this feature, all control would be lost when the battery expired, probably resulting in the destruction of the model. In some cases, the BEC is part of the radio control receiver, instead of being part of the ESC.
R/C BECs in their simplest form use a linear fixed voltage regulator
with its standard circuit suggested in the manufacturers datasheet - usually the power supply of the receiver needs 5 V. Low drop types are preferred - especially for batteries with only a few cells. For small models 1.5 to 2 A
are enough, for mid-size models a 3A type needs to be considered. BEC's for large models have to provide current of 5A or more. Here a more complicated switched mode regulator should be used, as the BEC has to deal with losses. These Losses are proportional to the difference of the target voltage
of 5 volts and the voltage
of the main battery, as well as they are proportional to the provided current. For example a 10 cell (NiMh) accumulator with a normal voltage of 12 volts. With a peak current of 5A the BEC will have losses of (12V-5V)*5A = 35W. With a linear regulator these 35W will be converted to heat and so require a large heat sink. In all cases it is a good idea to mount some large capacitor
s to buffer the regulated output. In large plane or ship models another possibility is to buffer the power supply
with a further capacitor
near the actuators (Servos).
and ATV
applications to reduce the weight penalty involved in carrying a battery. The battery is typically replaced by one or more large but light-weight capacitor
s which smooth out the fluctuating electrical pulses coming from the alternator
, without themselves generating power. As there is no electrical power source, electrical starters cannot be used.
Electronic circuit
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...
designed to deliver electrical power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
to other circuitry without the need for a battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
. Historically the expression was sometimes used to describe devices used to power battery-driven equipment from mains electricity. This is still the case in many products offered in retail electronic supply stores.
Studio photography
TripodTripod
A tripod is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object. The word comes from the Greek tripous, meaning "three feet". A tripod provides stability against downward forces, horizontal forces and moments about the...
-mounted cameras in photography studio
Photographic studio
A photographic studio is both a workspace and a corporate body. As a workspace it is much like an artist’s studio, but providing space to take, develop, print and duplicate photographs. Photographic training and the display of finished photographs may also be accommodated in a photographic studio...
s are often use a BEC to avoid having to interrupt lengthy shooting sessions to replace batteries. The use of the tripod can also interfere with access to the battery hatch.
Radio-controlled (R/C) models
In an electric-powered radio controlled model, the BEC is typically part of the electronic speed controlElectronic speed control
An electronic speed control or ESC is an electronic circuit with the purpose to vary an electric motor's speed, its direction and possibly also to act as a dynamic brake...
(ESC). BEC allows such a model to carry only one battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
(the motive power battery) instead of two (motive power, and a separate battery to operate the R/C equipment). A BEC-equipped ESC meant for airplane use often incorporates a low-voltage-cutoff (LVC) circuit which can sense the voltage drop caused when the battery has little charge left in it. It then cuts the power to the 'drive' motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
in order to provide the 'steering' servo
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
(s) with enough power to be able to bring the model safely back to the operator. The power to the propeller would be cut but the operation of the control surfaces would be maintained in order to perform a dead-stick landing. Without this feature, all control would be lost when the battery expired, probably resulting in the destruction of the model. In some cases, the BEC is part of the radio control receiver, instead of being part of the ESC.
R/C BECs in their simplest form use a linear fixed voltage regulator
Voltage regulator
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...
with its standard circuit suggested in the manufacturers datasheet - usually the power supply of the receiver needs 5 V. Low drop types are preferred - especially for batteries with only a few cells. For small models 1.5 to 2 A
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
are enough, for mid-size models a 3A type needs to be considered. BEC's for large models have to provide current of 5A or more. Here a more complicated switched mode regulator should be used, as the BEC has to deal with losses. These Losses are proportional to the difference of the target voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
of 5 volts and the voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
of the main battery, as well as they are proportional to the provided current. For example a 10 cell (NiMh) accumulator with a normal voltage of 12 volts. With a peak current of 5A the BEC will have losses of (12V-5V)*5A = 35W. With a linear regulator these 35W will be converted to heat and so require a large heat sink. In all cases it is a good idea to mount some large capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s to buffer the regulated output. In large plane or ship models another possibility is to buffer the power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
with a further capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
near the actuators (Servos).
Vehicles
BECs are also used in some motorcycleMotorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
and ATV
All-terrain vehicle
An all-terrain vehicle , also known as a quad, quad bike, three wheeler, or four wheeler, is defined by the American National Standards Institute as a vehicle that travels on low pressure tires, with a seat that is straddled by the operator, along with handlebars for steering control...
applications to reduce the weight penalty involved in carrying a battery. The battery is typically replaced by one or more large but light-weight capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s which smooth out the fluctuating electrical pulses coming from the alternator
Alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
, without themselves generating power. As there is no electrical power source, electrical starters cannot be used.