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I am putting together a quadcopter, and one of the things I've stumbled across that I don't quite understand is Battery Elimination Circuits (BECs).

The Flight Controller on my quadcopter is a modded Arduino board with some motor pins and other sensors integrated into it. The Flight Controller is capable of being fed anything from 12V to 5V. I have been feeding it 12V straight out of my LiPo battery, which it regulates down to 5V and continues merrily on its way.

Now, the Electronic Speed Controllers (ESCs) that drive the motors each contain an integrated BEC. From a post on this site under the "Discussions" tab, one guy claims that the most common thing to do is use the BEC to power the Flight Controller.

So it seems to me like the BEC is kicking 5V back to the flight controller. Is that good enough? Do I need to worry about low current or low voltage conditions? It's pretty important the Flight Controller say running.

I have read a few links about BEC's:

From this link, I think I understand that the voltage regulators in BEC's are generally linear, which is going to use more power than a switching power supply, but then in the comments, the guy who asked the question said "thanks... I'll go with a BEC." I'm not sure what I'm missing there.

So I currently have four ESCs, each with three pins (Signal, V, GND) connecting to my Flight Controller. I also have 12V straight from the battery connecting to my Flight Controller board, which is regulated down to 5V.

Is this wasteful? Wise? Should I remove the (V, GND) pins to the ESCs and only keep the signal pins? I'm spinning my wheels here because I'm obviously missing something.

What is best power and weight-wise?

Any advice is appreciated. I didn't know BECs existed in the not-too-distant past.

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  • \$\begingroup\$ The BEC is used at relatively low power out. As long as its load is a small % of total copter load then linear is fine as well as heatsinking is adequate. IF you drive higher power loads via a BEC you will waste significant power. Most servos and certainly high power ones are not good BEC power candidates in you want to fly long & prosper. Flight motors absolutely must not be powered via a BEC. \$\endgroup\$ – Russell McMahon Jan 19 '14 at 10:04
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If your flight controller already have its own DC/DC converter you should go for it, because it is probably designed for this particular use.

Most speed controllers with BEC are based on linear regulators. Basically these regulators turn excess voltage into heat, the more current you will draw the hotter they will be. If, for some reason, they become too hot they will go into protection mode, and stop to work.

To disable a speed controller BEC just disconnect the red wire from the from servo plug, unless your flight controller board already have a system allowing to choose the power source.

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Q1. To power the FC, stick to the regulator provided on the flight controller (FC) as it is designed specifically for use with the peripherals present on the FC. Having two regulators is just wastage of power and linearly regulating 12v to 5v is not a very good idea. However, if you are well versed with electronics, you can tweak the circuits to work the way you want, i.e. you can make the whole system to work on a single regulator. However, mod/hack the FC and ESC only if you are well known with regulators and related concepts.

Q.2 Should you disconnect V,Gnd pins to the ESC and keep only the signal connection? Well, without Vdd line, how will you power the receiver? Since the entire system has a common ground, your signal levels will be sensed properly. But if there is no supply voltage to the Rx, it wont power up! Unless you don't know the exact specifications of the regulator present on the FC, do not use the FC's 5v regulator to power up every new 5v device you get. I would suggest you stick with the BEC powering the Rx and let the FC's 5v reg do its job. If you are fluent with electronics concepts, you can eliminate one regulator and run all the 5v devices using a single 5v regulator.

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