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External BEC installation
#1
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There was discussion today about external BEC's, so I thought I'd share this article I wrote for Crawl Australia/New Zealand. Even though it's based on surface application, the process and requirements are the same for rc aviation.

This is one method of installation, there is another (which is my preferred) that I will add later, in the next few days. The basics of that are:

All 3 control wires from the ESC go to the receiver. These power the receiver from the ESC's onboard BEC. I run the signal wires from my servos to the correct channel ports on the receiver, so they get their instructions the normal way. Then, I run the + & - power wires from my servos to the output wires on my 16 amp UBEC (which takes it's power from the battery plug that also feeds the ESC).

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History for you:

BEC stands for Battery Eliminator Circuit, and were first commercially introduced in the mid 80's.

Their purpose was to eliminate the need for the 4 AA (UM3) batteries needed to power the receiver and servos that were needed back in the day (and still are, or a battery of some description in nitro).

The drive battery was 7.2v ~ 8.4v and then, surface receivers could only take 6v max before they made the brown smell, so you could not just hook up a feed wire from the mechanical speed control (MSC) into the battery port on the receiver.

People started doing this with a diode pack or resistor inline, but found out that when the motor was under heavy load it would steal power away from the receiver and cause momentary loss of control.

Tamiya, Accoms and various other manufactures introduced a transistorised BEC that levelled out the power fluctuations and gave a constant 6v to the radio until the battery died, resulting in the servos sticking in their last position, which was normally full speed into something

1990ish on, BEC's were built into entry level receivers and standard inside ESC's (electronic speed controller). ESC's manage the power to the receiver to the point you could drive until the motor didn't have enough power to move the model but you still had control of the steering and throttle.

Now, modern BEC's.

The BEC in a ESC is normally capable of delivering 1.5 amps to 5 amps to the radio before it burns. This is fine for running one high performance servo in a race car or buggy.


Basic BEC installation


Piggyback the BEC power wires to your ESC's battery plug:

[Image: PA312527.jpg]

[Image: PA312529.jpg]

Remove the positive wire from the ECS's receiver plug. Most can be removed by lifting the little locking tab on the plug with a hobby knife blade.

[Image: PA312524.jpg]

[Image: PA312526.jpg]


Bind the loose plug to the other wires with insulation tape. This allows for quick reinstallation for programming with a Castlelink or Firewire if applicable. Now plug the ESC plug into the usual port on your receiver. Plug the receiver plug from the BEC into a spare port on your receiver (a channel, battery or bind port will work). If you don't have a spare port, you can use a y harness and share a port with one of your servos.

[Image: PA312530.jpg]

Done!

Signature overload. That list just got ridiculous. However, Funcubs are .... fun.
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#2

thanks steven , very educational thread .
i have a question .
isnt it better to buy an ESC with an onboard BEC , rather than add one , which adds more weight ?
I know a seperate BEC eliminates LIPO FAILURE , but what are the other benifits if any ?

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
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#3

Most ESC's (well everyone I have encountered) have an onboard BEC. But, this is ususally limited to 1 to 3 amps, depending on the size and application of the ESC. Your average 35A ESC is good for 4 HS55's etc, but when you are talking about big aerobatic models that run huge servos (or gangs of small ones) to pull hard and fast on large control surfaces, you can find your servos amp draw exceeding the capabilities of the ESC's BEC. This leads to current starvation to the receiver, a brown out and a stack.

External BEC's are available in a number of amp ratings, 8a and 16a are popular, so there is very little chance of a brown out through current drop under servo load.

You can't have two BEC's feeding a receiver, you get harmonic feedback between the two, and pop goes your onboards. That is why in the pictorial guide I instruct to remove the red wire from the ESC plug. Once you do that, all the current in comes form the external BEC, the ESC just receives throttle position commands.

I'm not aware of any BEC's with a low voltage cut off. Normally the ESC does that duty.

Signature overload. That list just got ridiculous. However, Funcubs are .... fun.
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#4

great. thanks for the info .

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
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#5

A couple more things to think about when choosing how to power your radio reciever and servos

Quite a lot of Higher power, aircraft type ESCs don't have an onboard BEC.

There are a couple of reasons for this. Once you start getting into high power stuff say 800W plus
the ESCs/motor combination can generate quite a lot of electrical noise. it's because they are very quickly switching high currents. For a plane that's bad, noise can interfear with your reciever and greatly reduce the range at wich it works reliably.

Noise is the mortal enemy of a good RC link!! One way to beat this kind of noise is to run seperate power supplys for your drive motor and for you radio link & servos. It's much safer to do this when your machines runs on 10S or 12S lipos. Infact it's realy the only way to go for anything over 6S I reckon. For 3S - 6S set ups it's not so critical.

If you look at the specs of some ESCs that don't have an internal BEC, you will see that they say opto only or something similar. This means that they are opto coupled to the reciever. What happines is that the signal is delivered opticaly to The ESC so there is no way wire bourne electrical noise can get accross into the RX (reciever) This type of ESC will need all of the three wires going to the reciever plug. You only want to disconect the red wire if your using an external BEC with an ESC that has it's own built in BEC.

Why would you use an external BEC if you have one already built in your ESC??
The answer is to get enough power to run fast and power hungry digital servos with out the risk of brown out. You should bare in mind that the load on the BEC is variable, it depends on how many servos are working and how hard they are working. A problem might not show up on the ground at all and only become an issue in the air when things are working much harder.

Most internal BECs don't have a great power out put. If you over load the internal BEC it will drop the voltage to you radio's reciever and once it goes below a certain threshold the reciever will reboot and youll loose control untill it either comes back on line or crashes. ie you will suffer a "brown out"

There are two types of BECs.
Liniar regulators and Switch mode supplies. As you might expect there are pros and cons for both.

Liniar regulators are very low noise and are very reliable devices. They have an advantage in that they will supply much greater power than their rated out put for a short time with no problem at all. However they are not efficient when the difference between the input and output voltages is great. So they work very well for dropping the voltage from a seperate 2S (8.4 V Max) lipo down to 6V, to power the radio link and servos. You would not even think of using a liniar regulator to drop the voltage of a 10S pack (42V Max) down to 6V for your RC link. It just won't cut the mustard used in that way.

Switch mode supplies (switching BECs) Can effeciently cope with large differences between the input and out put voltages. you could use one to go from a 10S lipo pack down to 6V and it will work well. (Allways read the speck of the BEC some are only rated to 8S some for 12S etc) Unlike a liniar reg, they are not good at going over their rated current output even for a short time. If you exceed the Max current rating you'll start to pull the output voltage down and if you exceed it by enough, it will brown out your RX. The other thing with switch mode supplies is they can be noisy. This is because they work in a different way to a liniar regulator. Switch mode type BECs should have a ferite ring and the reciever lead should be wrapped around this a few times. The more the better. Never remove the ferite ring to make the lead longer to reach a distant RX. They are there especially to filter the noise off the lead that goes to your RX and are there for good reason!!

So for use with a 4s to 6S system a switching BEC running powered from the main pack with a good ferite and an opto type ESC is a good set up. Of course the usual range checks need to be done with motor running ect ect.

For a large model with a 6S-12S set up I'd be looking at using a seperate 2S 800-1300 mAh lipo with a liniar BEC to power the radio gear and an opto type ESC and large capasity Lipos pack to run the drive motor. This system is going to be the safest and most reliable. It can still be improved on tho'

For the ultimate in reliability you can use two liniar Regs and two seperate lipo packs to power your RC gear. If you do this you must put a shotkey diode in the posative lead of each 6V out put.
The negatives can be joined together. The diode acts like a one way gate and prevents the regulators fighting one another. It also means that if one reg or lipo pack fails the other one will continue to seamlessly run the radio link. The diode prevents the current from flowing back towards the other reg in the case of a dead short as well. With most diodes you get a 0.6V drop across it, so if the regs are set for 6V then the supply will become 5.4V which is a very happy voltage to run most radio gear on.

Hope this is of some help

“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
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#6

very interesting stuff , i will keep this post in my memory banks for future reference jason . cheers .

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
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#7

What is really interesting is that the best ESC's that money can buy... Kontronic... build ESC's for up to 12S and come with built in BEC's, I know some of the best pilots that use Kontronic and they never use stand alone BEC's.
The only problem is Kontronic ESC's start from about $250 for 4S and go up to $$800 for 12S...
Inteseting eh?

Parkzone Stryker 27 Evolution
E flite Ultra Stick , T 28 Carbon Z
Skyartec Skyfun Scorpion,Skyfun 90 EDF
Hobbyking Voltigeur, Funfighter T28, Mirage 2000, Minimoa 2.4m Glider
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Don't ever let the fear of landing keep you from taking off!
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#8

yes interesting and contradicting at the same time Gary . I would be interested in finding out why these guys use these esc 's over the theory behind using separate bec's .

patience !!Biggrin paaatience !!Paranoid paaaaaatience Tounge paaaaaaatieeence Lol dooooohhhh !!! Upset


DANGER WIFE CAN READ FORUMS . love you darling . sig changed .
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#9

Yes me to mate, but there must be a reason for it... what sort of technology are Kontronic using that gives them the edge in reliability... you certainly pay for it, I've been looking at an 80amp ESC they make for my next big plane because they keep it simple and also keep the weight down but it costs $369.

Parkzone Stryker 27 Evolution
E flite Ultra Stick , T 28 Carbon Z
Skyartec Skyfun Scorpion,Skyfun 90 EDF
Hobbyking Voltigeur, Funfighter T28, Mirage 2000, Minimoa 2.4m Glider
Jet Teng L-39 HPAT Stumax 90
Pheonix Tiger 50
FliteWork Extra 300 LPX 2.6M
Spectrum DX9i , DX6

Don't ever let the fear of landing keep you from taking off!
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#10

No real answer to this one. Just different perspectives.

I use a Kontronic Jive 80A HV ESC in the Logo and not a separate supply. The Jive ESC has a completely independent BEC supply internally with no shared electronics at all for the radio/sevos yet comes in a singe package. This means the ESC can fail and I still have power to the RX, flybarless controller and the servos. The rating of the BEC is 15A and has two power leads (needed to move 15A through servo stye leads as the connectors can't cope with this sort of current on a single lead - plus gives redundancy in power lead connections). The Logo has large powerful servos on the cyclic and it is not uncommon to move 4 servos simultaneously in the heli therefore demanding compared to planes however I doubt whether I would draw more than 3A.

The Kontronic unit works flawlessly. Only an ESC fire or battery power lead failure would stop it which is possible - but very unlikely.

I didn't go for an external supply due to more weight, more wiring, more complexity, and more to go wrong - but in the knowledge I was using Kontronic - but ouch on the price.

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#11


It's the old story of you get what you pay for. That set up of yours Dave is super nice and super reliable too!! Sure the Ktronic ESCs are great gear!! An internal BEC makes them nice and simple to set up. I'll bet London to a bric that it's using a switch mode type BEC and I'll bet it's noise performance is excellent as well. It's not a trivial thing to achieve. I reckon they have really good engineers developing their products and they know just what is required, they probably do a lot of testing and would use only the best components they can buy. I'll bet those ESCs are not heavy either concidering their power rating. All this adds to the cost but for my humble budget the price is still a bit steep.

With a seperate lipo pack for the RC link you do have to remember to charge it as well. I use telemetry to monitor this packs voltage and I can safely get 6 flights out of the dual 850 mAh packs in my Yellow Yak. After that they are still above 4V per cell.

I look at setting up a whole 12S powered plane, Airframe, power system, servos, the lot for under 600 dollars. And I reckon I can get a pretty reliable machine for that as well. Call me a cheap ar$e but my planes don't fall out of the sky very often...................touch wood. Smile

PS I would secretly like to be able to afford the really nice stuff Wink




“The knack of flying is learning how to throw your machine at the ground and miss.”

"When once you have tasted flight, you will forever walk the earth with your thoughts turned skyward, for there you have been, and there you will always long to return."  ~Leonardo Da Vinci
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#12

Yes, switch-mode (5S to 12S) input.
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