A Battery Eliminator Circuit, or BEC, allows a system to have more than one voltage available for components while using a single power source. 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 an RC receiver. A BEC eliminates the need for multiple power sources at different voltages.

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 input and supplies a lower voltage output. 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.

The 5V power is available at several locations on the RoboClaw. On RoboClaw boards with pin 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.

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 2x7A	1.2A	6V
RoboClaw 2x15A	3A	6V
RoboCLaw 2x30A	3A	6V
RoboClaw 2x45A	3A	6V
RoboClaw 2x60A	3A	6V
RoboClaw 2x60AHV 60VDC	1.2A	6V
RoboClaw 2x60AHV 80VDC	1.2A	6V
RoboClaw 2x120A 60VDC	3A	10V
RoboClaw 2x160A	3A	10V
RoboClaw 2x160A 60VDC	3A	10V
RoboClaw 2x200AHV 60VDC	3A	10V

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 motors 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 2x7A	1.2A	6V	34V
RoboClaw 2x15A	3A	6V	34V
RoboCLaw 2x30A	3A	6V	34V
RoboClaw 2x45A	3A	6V	34V
RoboClaw 2x60A	3A	6V	34V
RoboClaw 2x60AHV 60VDC	1.2A	6V	30V
RoboClaw 2x60AHV 80VDC	1.2A	6V	30V
RoboClaw 2x120A 60VDC	3A	6V	14V
RoboClaw 2x160A	3A	6V	14V
RoboClaw 2x160A 60VDC	3A	6V	14V
RoboClaw 2x200AHV 60VDC	3A	6V	14V

There are several 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