Electric Flight in Australia


What is BEC?

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BEC stands for Battery Eliminator Circuit. Some speed controllers are engineered so that the current to power the radio system in your aircraft is drawn from the flight pack (that also powers your motor). This saves weight because you do not have to carry a separate battery to power your radio.

Early attempts at BEC were fraught with problems. This has made old hands a little cautious about BEC, but like all things, the problems have been largely overcome and current BEC speed controllers are very reliable. Here is a summary of the difference between controllers without BEC, and controllers with BEC:

Without BEC you can have a speed controller in which the circuit for the radio, and the circuit for the motor power, are isolated from each other. The link between the two is achieved by an optical or light operated component. These controllers are said to be opto-isolated. This feature ensures that no electrical noise or interference can be passed on to the radio receiver by way of the controller.

With BEC, however, you cannot have opto-isolation. Early controllers with BEC were known to allow interference, especially when switching a motor on or off.

Another factor is that a BEC controller must keep the voltage that is being passed to the receiver within normal limits; not provide too much voltage, and not starve the receiver when high current is being drawn from the battery pack. It is normal to limit BEC to low voltage electric power systems. You will see that BEC contollers usually specify no more than 10-12 cells to be used. Voltage regulators have difficulty coping with higher voltages.

Finally, BEC controllers usually cut off the power to the motor when the flight battery is getting low, leaving enough power to sustain radio control for a period of time, sufficient to glide in and make a safe landing. This feature is called auto cut-off. Good quality controllers allow short bursts of low power after the cut-off operates so that you can make a safe landing - in case you are landing short, or need to clear a fence.

So, my advice is:

  • only use BEC controllers if using 4-12 cells
  • use BEC cautiously when drawing high current
  • buy a good quality BEC controller to minimise problems

Having said that, I have to admit that I am one of the old hands who is suspicious of BEC controllers. This has come from problems encountered flying Open Class F5B in the early days where interference problems were rife, and large cell counts were common. However, I have recently started using a modern BEC speed controller when drawing 50A with an Astro .05FAI in a 7-cell glider, and have not encountered any problems. I have also recently used a 40A BEC controller with aircraft powered by twin 400 motors, with no problems encountered. BEC is now common in all sports applications, and some competition applications!