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Nov 06, 2017, 05:53 PM
Non Fragosus
jackcutrone's Avatar
Discussion

Internal BEC v separate BEC?


I guess the question is what is the advantage of a stand-alone BEC rather than an internal BEC in the ESC?

I know that if you hit LVC the ESC will cut power to the motor. Will it also brownout the receiver if you hit LVC on the flight battery where it is an internal BEC? If so, if you are running a separate BEC off the flight battery won't that also do the same?

Is the only way to be safe to run a separate battery and separate BEC (at least assuming those don't fail) or a Scorpion backup battery type system?

Thanks,
Jack
Last edited by jackcutrone; Nov 06, 2017 at 08:07 PM.
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Nov 06, 2017, 10:19 PM
Registered User
vollrathd's Avatar
Quote:
Originally Posted by jackcutrone
I guess the question is what is the advantage of a stand-alone BEC rather than an internal BEC in the ESC?

I know that if you hit LVC the ESC will cut power to the motor. Will it also brownout the receiver if you hit LVC on the flight battery where it is an internal BEC? If so, if you are running a separate BEC off the flight battery won't that also do the same?

Is the only way to be safe to run a separate battery and separate BEC (at least assuming those don't fail) or a Scorpion backup battery type system?

Thanks,
Jack
I use only the Castle Creations ESC's in my dozen electric models. They range from around 400 watts to 4500 Watts. The "smaller" models, 1100 Watts or lower use a separate CC 10 Amp BEC. My larger models, running 2200 Watts, 2800 Watts, and 4500 Watts are using the Castle Creations Talon ESC's with their built in 10 Amp BEC.

But, IMHO, for these larger models, it's a good idea to provide a backup receiver battery, just in case. Just to many $$$$ involved. Attached is a drawing on how I did it.
Nov 06, 2017, 11:40 PM
Registered User
Wintr's Avatar
I know of no ESCs with built-in BECs that shut the BEC down when the motor is shut down at LVC. The 'standard' LVC is 3.3V per cell (too low, IMO, with today's batteries), but the BEC draws so little power that it should continue operating well after the motor shuts down.
Last edited by Wintr; Nov 07, 2017 at 02:00 PM.
Nov 07, 2017, 04:39 AM
An itch?. Scratch build.
eflightray's Avatar
Probably the main, and biggest advantage of a built in to the ESC BEC is you don't have to figure out how and where to connect it, that's all done for you.

Having a separate BEC does allow you more freedom on type and output, but still comes back to the, you have to fit it.

Whatever you choose, switching BEC is good, linear BEC is not so good --

Slightly dated thread --- Sbec, ubec, bec whats the difference?

Ray.
Nov 07, 2017, 10:46 AM
Non Fragosus
jackcutrone's Avatar
Quote:
Originally Posted by eflightray
Probably the main, and biggest advantage of a built in to the ESC BEC is you don't have to figure out how and where to connect it, that's all done for you.

Having a separate BEC does allow you more freedom on type and output, but still comes back to the, you have to fit it.

Whatever you choose, switching BEC is good, linear BEC is not so good --

Slightly dated thread --- Sbec, ubec, bec whats the difference?

Ray.
Eflightray's answer took me to a thread where there was a good explaanation copied from a mfr's website which seems to explain things, though it might be a little dated. Quoting from the answer and with the disclaimer that it contains some advertising from a mfr that I am not familiar with:

http://www.dimensionengineering.com/info/bec



Dimension Engineering's BEC FAQ
What is a BEC?
BEC stands for Battery Eliminator Circuit. In the old days of electric
flight you had to use a separate 4.8V battery pack to power your receiver
and servos. As the hobby evolved, speed controls started to include Battery
Eliminator Circuits to power your receiver and servos, allowing you to get
rid of the extra receiver battery pack.

How does a BEC work?
A BEC is basically a step down voltage regulator. It will take your main
battery voltage (e.g. 11.1 Volts) and reduce it down to ~5 Volts to safely
power your receiver and servos.

What are the advantages of a BEC?
If you are flying electric, a BEC is better than a battery pack in nearly
all cases. On average, the BEC will weigh 10-20 times less than a receiver
battery pack! Then you have to take into account the hassle of charging the
receiver pack. It is another battery you have to carry around along with
another charger. Did you remember to charge it after the last time you flew?
Uh-oh might want to double check that!
With a BEC, you only have to worry about charging your main flight pack and
then you are guaranteed to have a safe flight.
Glow planes usually need a receiver pack, but the vast majority of electric
planes out there are better off with a BEC.

I have a 3A BEC in my speed control - is that enough?
What is a switching BEC?
It is very common for speed controls to have BECs rated at 2 or 3A.
However, what the manufacturers do not tell you is that this rating is only
true for an input voltage of 6V. The BEC on your speed control is what
engineers call a 'linear voltage regulator'. It works by burning up excess
voltage and turning it into heat. The higher the input voltage, the more
heat gets produced. If there is too much heat, then the BEC will either fry,
or shut down! The result of this is that in real world situations, if you
are running a 3S lithium battery pack, your ESC's BEC will only be able to
provide about 0.5A before it overheats. At 4S, most ESC manufacturers don't
recommend you use the BEC at all, or at best power two small servos.
Dimension Engineering's BECs are a different type of voltage regulator - a
switching voltage regulator. They do not care very much about what the input
voltage is, and as such can provide your servos with their full current
rating all the way up to 8S or more. For more information on the principles
of a switching BEC, please visit our beginner's guide to switching
regulators.

What are the pros and cons of internal BECs and external BECs?
Most speed controls nowadays have an internal 5V linear BEC. It is a nice
cheap, simple solution that works very well at low voltages like 2S lithium
and 6 cell NiCd packs. If you are flying a 2S lithium aircraft, stick with
the internal linear BEC on your speed control because it will be cheaper. 3S
lithium and above is where a switching BEC starts to pay off. Since the
external switching BEC will work efficiently at higher voltages you will
immediately notice your speed control running cooler. You will be able to
run more and more powerful servos. You will be guaranteeing reliable power
to your receiver and servos. If you have ever suddenly lost power to your
receiver in flight, then an external switching BEC may be the answer to your
problems.

Are there any other reasons to get an external BEC?
Some of the new Spektrum receivers draw significantly more current than a
normal receiver, and are particularly sensitive to voltage fluctuations. An
external switching BEC can help ensure your new receiver gets reliably
powered. Our switching BECs also allow you to have a choice of output
voltage - 5 volts or 6 volts.

I'm not using a speed control. Can I still use the BEC to give me a steady
voltage?
By all means! Dimension Engineering BECs maintain all their specifications
without a speed control attached. Be sure to cover or clip the BEC's ESC
pins so they don't electrically contact anything.

5V or 6V?
One of the great things about an external switching BEC is that it allows
you to choose your voltage output. Running at 5V gives you standard servo
response. Running at 6V means more power will be delivered to your servos,
so you will get more speed and torque. Running at 5V or 6V will depend on
what you are flying, and how you personally like to fly. A simple parkflyer
that isn't doing any complicated maneuvers will probably feel best at 5V. If
you are doing complicated 3D aerobatics with sharp turns, you will probably
appreciate the response 6V gives you. Helicopter flyers especially like the
response 6V gives them on a tail servo. If you decide you want to run at 6V,
make sure your servos can handle it. Most servos can, but some really tiny
ones like the Hitec HS-50 will burn up at 6V.

How will a switching BEC affect my flight time?
Actually, it will barely make a difference to your flight time. Compared to
your main motor, your receiver and servos barely draw much power at all. On
a typical flight you can expect to have ~10 seconds less flying time if you
have been using a receiver pack. If you have been using a speed control's
linear BEC, then a switching BEC might get you ~10 seconds more flight time.
Nothing really noticeable.

I heard that switching BECs can put out harmful radio interference, causing
reduced range. Is this true?
This is true for a lot of the switching BECs on the market. This is because
it is relatively easy to make a switching BEC that gives you 5V and powers
your servos, but it is not easy to come up with a design that is free of
radio interference. This takes hundreds of man hours, dozens of design
revisions, expensive test equipment and extensive beta testing. At Dimension
Engineering, we put the time, money and effort into developing BECs that do
not radiate. As long as you keep the BEC at least 2 inches away from your
receiver, antenna and other electronics, you will not experience any
glitching. We guarantee it.
Nov 07, 2017, 04:20 PM
Registered User
Just to allay your fears about receiver brown-out when the main battery drops down to lvc: So long as you're using 2S or more, when your ESC's lvc shuts down the motor the battery voltage will be at least 3 volts x the number of cells, so 6 volts if it's a 2S pack. That's plenty of voltage to allow the built-in BEC to continue supplying a regulated 5v to the receiver.

Having said that, it's good practice to time your flights, or use telemetry to monitor battery voltage, so that you never run the battery down to lvc. Then you won't have the excitement of having to do a "dead stick" landing.
Nov 08, 2017, 08:55 AM
I'd rather be Flying
davecee's Avatar
Receiver power sources that I've personally had fail.
4 cell NiCd pack, factory weld failure
4 cell NiCd pack, wire fatigue and failure at a factory soldered cell to wire joint
Internal BEC failure doe to my error, 10 cell NiCd pack on a linear BEC rated for 7 cells
Main flight pack failure that was supplying a BEC. Failure of a cell to cell solder joint that I had made. Due to physical stress on a large 24 cell NiMh pack that was not properly supported within the airframe, which allowed the pack to flex
I've never had a failure of any other BEC, either internal or external. I prefer to keep things simple. I use the internal BEC appropriately and use an external BEC only when necessary, eg perhaps the ESC does not have an internal one.
Nov 08, 2017, 09:18 AM
I miss President Reagan
KMK001's Avatar
Quote:
Originally Posted by jackcutrone
I guess the question is what is the advantage of a stand-alone BEC rather than an internal BEC in the ESC?
.................................................. .......
As long as everything works as it should, I see very little advantage one way or another. I personally prefer the stand alone BEC but that's because I'm an old radio tech who likes to be able to address the individual components of a system.

Internal I would think costs slightly less. But maybe not. Takes less room in the model and has fewer connections to deal with, check and fail. Down side is should one part of it fail, BEC or ESC, you have to replace the whole thing which could mean greater expense in the long run.

Stand alone has no real advantage other than should it fail, you replace only that one part. But being separate, cooling might be less of an issue for both the ESC and BEC. You may prefer placing the BEC closer to the Rx while the ESC is by the motor?

But I suspect in not too many years you won't be able to find a stand alone BEC.

But again, as long as everything is working as it should......................................


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