A Battery Eliminator Circuit, or BEC, allows you to have a lower voltage voltage output such as 5 volts DC from a battery at a higher voltage. In robotic a common scenario is the need to run motors at 12 volts DC or higher and at the same time needing to supply 5 volts DC for microcontrollers or RC receivers. With a BEC you can achieve this while only using one battery.
What the BEC Does
The RoboClaw motor controller has a built-in Battery Eliminator Circuit, otherwise known as a “BEC”. The RoboClaw’s BEC is a high efficiency switching voltage regulator. A voltage regulator, like the on on the RoboClaw, takes a higher voltage a outputs a regulated source of a lower voltage. This means that the RoboClaw has two voltages onboard: the voltage provided by the battery powering the RoboClaw and the 5V output of the onboard BEC.
The 5V output of the RoboClaw’s BEC is used to power the logic side of the RoboClaw while also providing a 5V power source to power external components such as microcontrollers, RC receivers and encoders. Almost anything on your robot that needs a 5V power source can utilize the BEC as long as you don’t exceed the current rating of the BEC.
Using the BEC
The 5V power is available at several locations on the RoboClaw. On RoboClaw boards with headers 5V power is available at the positive (+) pins of the S1-S5 headers as well as the encoder power headers. On RoboClaw boards with screw terminals there is a single 5V terminal powered from the BEC. Be aware that some components will also need to share a common ground with the RoboClaw and this can be accessed at the negative (-) pins of the headers you’ve used to get power from; screw terminal boards have a single ground pin that can be used for the same purpose.
Figure 1: Logic battery input and locations of 5V power on the RoboClaw header.
The regulator used in the RoboClaw is a switching type regulator and has a dropout voltage of 0.5 volts. This means that the input voltage to the BEC must be a minimum of 5.5V to ensure that the BEC can provide a stable 5V output. The BEC current rating for all RobClaw models is listed below. Also note that the RoboClaw itself may have a separate and different minimum voltage to operate.
|RoboClaw Model||BEC Rating||Minimum Battery Voltage|
|RoboClaw Solo 30A||1.2A||6V|
|RoboClaw Solo 60A||1.2A||6V|
|RoboClaw 2x60AHV 60VDC||1.2A||6V|
|RoboClaw 2x60AHV 80VDC||1.2A||6V|
|RoboClaw 2x120A 60VDC||3A||10V|
|RoboClaw 2x160A 60VDC||3A||10V|
|RoboClaw 2x200AHV 60VDC||3A||10V|
Logic Battery as BEC Source
While we’ve discussed that a BEC allows for the use of a single battery in a robot, the RoboClaw can also utilize a second battery, known as a logic battery. A logic battery provides an independent source of power for the onboard BEC. It ensures that the RoboClaw logic and accessories will always have a stable source of power and not suffer from brownouts and other power interruptions. Brownouts can occur when motor driven by the RoboClaw are under heavy load or when motors make sudden direction changes at high speed. A logic battery is recommended when the primary power source for the board will be heavily loaded down by the motors. On the RoboClaw board there is a pin header for connecting the logic battery. The same voltage ratings that apply for the primary power source also apply to the logic battery.
|RoboClaw Model||BEC Rating||Logic Battery Minimum||Logic Battery Maximum|
|RoboClaw Solo 30A||1.2A||6V||34V|
|RoboClaw Solo 60A||1.2A||6V||34V|
|RoboClaw 2x60AHV 60VDC||1.2A||6V||30V|
|RoboClaw 2x60AHV 80VDC||1.2A||6V||30V|
|RoboClaw 2x120A 60VDC||3A||6V||14V|
|RoboClaw 2x160A 60VDC||3A||6V||14V|
|RoboClaw 2x200AHV 60VDC||3A||6V||14V|
There are several precautions and things to look out for when using the onboard BEC, with or without a logic battery. As we discussed earlier a separate logic battery is suggested when the RoboClaw will be driving heavy loads. Also, be sure to not exceed the current rating of the BEC or else the RoboClaw may behave erratically. Finally, note that electrically noisy components connected to the BEC, such as some encoders will cause problems with the proper operation of the RoboClaw.
Thumbnail photo by Mataresephotos / Wikipedia Commons