BEC Voltage Regulator – What is a BEC or voltage regulator’s purpose?
Gas guys will go by the term voltage regulator. Electric Modelers will refer to this unit as a BEC unit as this is the name given by many ESC manufcatures. These names will be used interchangeably throughout this article. One of the most commonly used accessory for the radio system in RC is the BEC (Battery Elimination Circuit) unit or Voltage Regular. This is common in Radio Control Airplanes, Radio Control Boats, and in some cases Radio Control Cars. In an electric model, the motor LiPo battery pack is typically between 7.4v (2 cell) and 37v. (10 cell) The receiver operates at nominal voltages between 4.5v and 6.2v. A BEC Unit / Voltage Regulator serves the main purpose of dropping the voltage of the motor battery pack on an electric model down to the proper voltage required by the Receiver. In other cases a Voltage Regular or BEC unit is used in Gas or Nitro models in combination with a LiPo Receiver Battery. In this case it would drop the 7.4v voltage to the required receiver voltage. Pay close attention to the specs on your unit to be certain it will work with the desired setup and voltage input level.
Switching BEC vs Linear BEC
The difference between these two types of voltage regulators is dictated by the method used to provide the end result.
Most stand alone BECs or voltage regulators use the more superior switching method
The switching method can be explained in a simplified way by saying the BEC unit acts like a high speed switch constanly turning off and on in order to provide a steady and accurate output voltage. This method is very efficient and will also be very accurate with varying levels of input voltages. You will find the current and voltage specification in your manual received with the unit. A switching BEC may be found in higher end ESC’s, or new ESC’s. A switching BEC is also found in many stand alone units.
It is common for older or inexpensive ESC’s to use a linear style BEC. ESC’s that have a Linear style BEC will tend to operate between 2 and 6 LiPo cells in series. These ESCs often provide specs for the built in BEC unit. They may be similar to 3 amps at 5.5 volts. What is often not explained is how this actually works in terms of those provided specs.
A Linear BEC works by turning the excess voltage in to heat. So what does that mean? Well, if you plug in a 7.4v LiPo battery into the ESC with a linear BEC, the BEC unit must remove about 2 volts in order to provide 5.5 volts to the receiver. That doesn’t sound too bad. Now what if it were a 3 cell LiPo? The linear BEC must remove about 5.5 volts in order to provide 5.5v to the receiver. That’s quite a jump. As you increase in cell count, the linear BEC must work harder to remove the unwanted extra voltage. Since all this extra voltage translates in to heat, this further increases the amount of heat in your ESC’s BEC unit. The additional heat for every extra LiPo cell will then reduce the actual amount of current the BEC unit may supply. The 3A current we were talking about earlier, may only be 2A when a 3 cell LiPo is connected to it. As you increase the ESC input voltage, the amount of continuous current to the servos generally decrease.
When is a Linear BEC safest?
This is a difficult question to answer. Often on an ESC there is also a maximum recommended amount of servos. Following this rule is also very important. Generally, a 2-3 cell LiPo running with a linear BEC may be safe when operating at the maximum recommended amout of servos. As you increase the ESC input voltage to 4 cells or higher, this is where the trouble may begin. Using 4 cells may be touch and go for many models. In some cases boats and cars may be the safest running only one light duty steering servo. In a plane it is generally not recommended. More than 4 LiPo cells in series is not recommended for any linear BEC unless otherwise noted.
Recommended BEC Voltage Regulators
What can go wrong in the event a linear BEC fails?
In a plane? You don’t want to go there! All servos most likely will be starved for power. If the servos are starved for power, the receiver also does not have power. With no RX power available, a plane is going to go most likely down. Not the best ending. As for a car or boat, in most cases it takes an approximate 2 seconds or so for the ESC to recognize and shut down from a lack of receiver signal. If you are lucky enough, you may end up with a dead boat in fail safe mode out on the water or same scenario with a car.
It is also important to understand that 2.4GHz systems tend to be more voltage sensitive. If you are using a 2.4 system, it is in your best interest to provide the most steady flow of RX power to your receiver and servos.
Reliability a Concern?
If reliability is of a concern, select the best option that will provide you with the most reliability. If reliability is a huge concern, it may be a great idea to run 2 LiPo receiver packs with a BEC or voltage regulator units in parallel to 2 different channels on your RX. This will ensure your RX gets the proper amount of power and will also double the amount of current your system can draw.
Installation of a BEC unit
Installation of a BEC voltage regulator is quite simple. Power from your battery enters the input leads of the BEC unit. The output side of the BEC unit goes to your receiver. On some BEC units, there may be a connector port for the ESC’s radio lead. You may use this for your ESC and then the BEC units output wire would be connected to the throttle channel. If there is not an ESC lead port, the BEC units output lead may be placed in any channel on the receiver. The ESC’s lead will then need to have the center red wire pushed out. Pushing the lead out of the connector will allow it to be replaced later if need be. Then simply plug your ESC in to the throttle channel.