What type of BEC meets your needs?
Greg Gimlick [email protected]
BEC
A BEC is a Battery Eliminator Circuit—plain and simple. Rather than using a separate 4.8‑volt or 6.0‑volt battery to power a radio receiver, a BEC provides power to the airborne radio.
The BEC pulls power from the motor battery, steps it down to the appropriate voltage, and uses it to power the receiver and servos. Most of the time the BEC is part of your Electronic Speed Control (ESC), but there are stand‑alone units, too. Which one is best depends on your application.
Linear or Switching?
This confuses many people. Most smaller ESCs tend to use linear regulators because they are cheaper to produce and work well for low‑power setups drawing little current.
The voltage is stepped down through a simple resistance method and the waste product is heat. Linear is only appropriate up to approximately 12 volts, and at most three analog servos, unless the manufacturer indicates otherwise.
A switching BEC operates much like a tiny speed control, switching power on and off at high frequency to step the voltage down to a safe level for your receiver and servos. The switched output is then filtered to provide steady voltage with little ripple. There is minimal waste and consequently little heat is generated. The significant benefit is more stable power with the ability to stand up to higher demands. Some switching BECs can handle 20 amps or more of surge without failing, whereas a linear regulator will go into safety shutdown because of heat. Switching BECs can also use a much larger input battery without danger of overheating. Some stand‑alone BECs can be used with packs up to 12S. Although BECs are rated in amps, be aware that watts are the limiting factor.
Why Not Just Use a Receiver Battery?
Weight is a precious commodity when flying electrics—the smaller the airplane, the more important it becomes. Using a BEC—even a stand‑alone version—saves some of that weight for other things such as a larger‑capacity motor battery or scale detailing.
Equally important is that you know you’re going to take off with a freshly charged motor battery and you won’t have to worry about the state of your receiver battery. If you’re coming from a glow‑engine background, how many times have you forgotten to charge the receiver battery until you were ready to leave for the field? Problem solved.
Have High Demands?
If you require a large motor battery and you are using several servos, you might benefit from a stand‑alone BEC unit such as the Castle Creations BEC Pro. These can be wired to handle a 12S pack and programmed to provide your choice of voltage to the radio. Best of all, they will handle a momentary surge of as much as 20 amps. You don’t want to plan for that level, but it’s a great safety net, and the unit only weighs roughly an ounce. Most separate BECs can be programmed for the output voltage; the Castle BEC Pro is programmable from 4.8 to 12.5 volts.
Helicopter Considerations
Be sure to check the allowable voltage for your gyro/tail‑servo combination before programming your BEC output voltage. Most servos will handle 6 volts, but many gyro combinations won’t.
Throttle Hold
Helicopter pilots are accustomed to this, but most fixed‑wing fliers are not. If you aren't familiar with what it does: very simply, with the flip of a switch you can kill the throttle and, regardless of what you do with the throttle stick, the motor stays dead.
For electric‑powered airplane pilots it's a huge safety feature. You can arm your airplane and, by using the switch, add the safety of disabling your throttle stick.
My Spektrum DX7S makes this option available for both helicopter and fixed‑wing programming, but most radios don't. Because each transmitter is different, it's impossible to walk you through specific steps to enable it.
Check which switch on your radio is used for helicopter throttle hold/cut and define a mix so that the switch will move the throttle to zero when activated. Test it without your propeller attached to be sure it works properly. This extra safety step should be standard.
Taking Off
I hope I cleared up some questions if you are unfamiliar with BECs and how they are used. Next time I'll look at some upgrades for electric ducted fans that I've been playing with.
SOURCES
- Castle Creations (913) 390‑6939 www.castlecreations.com
- Spektrum RC (800) 338‑4639 www.spektrumrc.com
Transcribed from original scans by AI. Minor OCR errors may remain.
