What is a Battery Eliminator Circuit?

by FliteTest | August 14, 2018 | (6) Posted in Tips

What is a BEC? What is a UBEC? What on earth is an SBEC? This article will uncover the mysteries of the Battery Eliminator Circuit. 

A battery eliminator circuit is a voltage regulator. It is designed to drop a big voltage down to a smaller voltage. As modern RC airplanes use high voltage batteries, it allows you to run your receiver, servos and other accessories from your main battery without using a seperate lower voltage one. There are lots of types, so let's jump  right in. 

An ESC with a built-in BEC

Do ESCs have them? 

Yes! Most Electronic Speed Controllers have in-built Battery eliminator circuits. This means you really don't have to worry about much; all you have to do is plug your BEC lead into the receiver and you'll have the required power fed to it. Usually, this is 5 volts. Sometimes, though, you might still require a dedicated BEC for higher powered models. 

Are there different types of BECs?

Yes, there are quite a few. 

BEC - Linear Battery Eliminator Circuit

SBEC - Switching Battery Eliminator Circuit

UBEC - Universal Battery Eliminator Circuit

Let's look into this in more detail. 

(Linear) BEC

A simple battery eliminator circuit does what it says on the tin. It steps down power, but in doing this it's actually quite wasteful. This is because, when you get rid of power like this, you turn your energy into heat. So, although a simple BEC is easy to use, it is inefficient and expends useful power. 

In addition to this, BECs can't really be used with bigger batteries with higher voltages. This is because the higher voltage would make the BEC far too hot and it would fail (electronics don't like heat). They are, therefore, only usable in the small stuff. 

(Switching) SBEC

An SBEC is little more complex than the humble BEC, but it means that you can often power high powered models through one. It works by using a switching, alternating current to step down your battery voltage to a safe 5v for your RC gear. Virtually no power wasted by the SBEC and you can still run large amounts of power through it. A capacitor and coil smooth out the average of the switching current and allow the RC gear to run on a consistent voltage. 

(Universal) UBEC

A universal battery eliminator circuit, for all intents and purposes, is the same thing as an SBEC. It uses a switching regulator to control the voltage to your vital electronics. Confusingly, both terms (UBEC and SBEC) are used as some brands one or the other. Increasingly, UBEC is being used as the standard term.

An ESC with a built-in SBEC

So which should I use?

It really depends on what power system you're thinking of using. For most applications, you can get away with using a simple ESC which handles everything for you. You can find ESCs like this in all of our Power Packs on the FT Store. Occasionally, if you need a lot more power and want to run batteries that are over 4 cells, you might want to consider using a UBEC/SBEC ESC or a seperate UBEC. 

If you have any questions, or anything to add to this article, comment below!

Article by James Whomsley

Editor of FliteTest.com





The-One-Who-Never-Crashes on August 16, 2018
It's important to remember that a UBEC or SBEC produces electrical noise when it switches. This can be an issue on FPV builds, as most vtxs and cameras are quite sensitive to such noise. If you don't have a very high voltage to step down and can provide cooling for the BEC, I would suggest using a linear BEC on an FPV build.
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randyrls on August 24, 2018
On multi engine air-frames, Only connect one BEC to supply power to the receiver and servos. Pull the power lead from the other ones. A BEC can operate with both connected if they are identical, but multiple UBEC or SBEC connected will not work. Remove the Power lead (red?) from the BEC connector and insulate it so you can reconnect it if ever needed.
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What is a Battery Eliminator Circuit?