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INFO - What's a BEC, and why it's REQUIRED!

Discussion in 'Master Parts List' started by lattu, Mar 5, 2009.

  1. RCPlattu

    RCPlattu Cadet

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    I've been asked about BECs (Battery Eliminator Circuit) so here's a little about them:

    BEC's purpose is to eliminate the need of separate receiver battery. It's connected between the lipo and the receiver. It lowers the lipo voltage, say 11.1 V, to about 5 V that receivers (and servos) use.

    Speed controllers (and sometimes even receivers) have integrated BECs and normally you don't have to worry about them. But if you use a higher voltage lipo (that is you need a larger voltage drop) or a lot of servos (meaning the servos draw a lot of amps), you may need a separate higher performance BEC.
  2. David393

    David393 Rookie

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    Re: Bec

    If a motor requires more than 7.4v how does this work if a BEC is incorporated?

    Based on the below, the BEC goes between the battery and the receiver in order to reduce the voltage to a safe level for the receiver and servos. How does the motor get the correct voltage if it connects to the receiver which is now getting a regulated voltage?
  3. F-111A John

    F-111A John Cadet

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    There are two ways to have a BEC, either a stand alone unit, or integrated into the motor's ESC.

    In the first case, the motor battery is wired to both the BEC and to the ESC in parallel. The BEC reduces the voltage to 5-6V, and this output is connected to the receiver. The ESC regulates the voltage sent to the motor based on throttle input from the receiver, and this voltage is sent to the motor.

    In the second case, the battery is wired just to the ESC, which has one regulated output for the motor, based on throttle input from the receiver, and also produces regulated 5-6V for use by the receiver and servos.

    With the integrated BEC/ESC, the power is sent to the receiver using the cord that is plugged into the receiver's trottle channel. With the stand alone BEC, it's regulated output is connected to the receiver's battery input, and the ESC is plugged into the throttle channel.

    Clear as mud?
  4. David393

    David393 Rookie

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    Re: Bec

    Claro como barro....

    I kind of understand what you're saying... but I still don't see how a motor that requires 11+ volts can get it if it is connected to the receiver and the receiver power input is being regulated.

    If possible can you provide some diagrams? A picture can be worth a thousand words....
  5. F-111A John

    F-111A John Cadet

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    Here's the best I can do. If it's still not clear, buy Dave's eBook on Power Systems, and all will be explained in much greater detail. (Plug for ya, Dave and Val!) :blushes:

    John

    Attached Files:

  6. RCPlattu

    RCPlattu Cadet

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    F-111A John has it right. The motor is never connected to the receiver or the BEC, it gets it's power from the ESC. A BEC (integrated or separate) delivers power only to the receiver which in turn delivers power to servos. Think an integrated BEC as a separate device inside an ESC, maybe that helps.
  7. kdknitro

    kdknitro Rookie

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    A bec question, please help me lol

    I have a corona reciever and i was wondering if im using at 11.1 lipo do i need a bec or can i just run it off of the speed controler, i dont know if the speed controler has a bec built in. I got the esc from grayson its 18 amp thats all i know about it. The reciever is a corona seinthesysed reciever.
  8. Jbirky

    Jbirky Airman

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    You can try to run the Corona Receiver from the ESC (Electronic Speed Controller). Either the receiver will power up or it will not depending on whether or not the ESC has an integrated BEC (Battery Elimination Circuit). Just make sure the brown or black part of the ESC wire is lined up with the negative (-) of your receiver, so you get the proper polarity.

    If you get no power to the receiver, then you have an ESC without a BEC. If you report what ESC you have, we can tell you if it has an integrated BEC or not. Another easy way to tell is by the number of wires on the ESC. Quite simply, an ESC will have two or three wires (in the lead that connects to the receiver) depending on if it is merely getting a signal from the receiver or if it is getting a signal from the receiver and providing a voltage feed to the receiver.

    ESC with 2 Wires: Does not have a BEC
    ESC with 3 Wires: Has an integrated BEC

    Everything plugs into a receiver (RX) and either provides it with a voltage feed or if it is a servo is provided with a voltage feed from the RX. The RX provides everything connected to it (every channel)with a signal such as a throttle position. You may think of a channel such as "Landing Gear" as defaulting to two positions 0% and 100% for up and down respectively. Other channels such as throttle you may think of as a scale of 0% to 100%. For example, if the receiver is spitting out a signal of say 57% on the throttle channel, the connected ESC will read 57% and know it needs to make the motor run at 57%. Likewise, you could put a servo on the throttle port and it would swing the throttle arm of a gas engine to 57% open throttle. Make sense? Clear as mud?

    Okay, so you have only three wires yet two are needed for a signal, and two are needed to provide power. Well, the black/brown (-) is a common shared wire. Red (+) to Black (-) is 5 volts DC.

    Here are several prevalent color combinations:

    Castle Creations, JR, Spectrum:
    Orange (Signal)
    Red + (The voltage Feed)
    Brown - (Shared)

    HiTec:
    Yellow (Signal)
    Red + (Voltage Feed)
    Black - (Shared)

    ESky, Futaba:
    White (Signal)
    Red+ (Voltage Feed)
    Black - (Shared)

    I hope this helps.

    If your ESC has three signal wires going to the RX, it should power it up.

    If your ESC has two wires going to the RX, you need a power source such as a BEC or a receiver pack.


    Notes:
    DO NOT connect two or more power sources whether the be ESC /w BEC, Standalone BEC, or receiver packs. Use only one power source or you will probably be regretful.

    ESCs with three output wires are for Brushless motors
    ESCs with two output wires are for brushed motors
  9. herbalicious

    herbalicious Rookie

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    hehe alright Lattu ...i might add that ..the speed control has two sections a high voltage high amperage side and a low voltage low amperage side powering the Rx ..
    and its not a high performance BEC ...its a voltage regulator ..and i have yet to see a electronic speed control that delivers the same battery voltage to the receiver ..when BEC was introduced into receivers ESC's had not been invented yet ..so when you put that 7 cell nicad in your rc it only powered the motor ..and thats alll so you had to have 4.8 volts to the Rx ..even the very first novak SC required no voltage regulation to the Rx ..meaning that it was already handled
  10. Tooombucket

    Tooombucket Cadet

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    If an Esc has 3 wires doesn't that just mean its brushless? Doesn't neccesarily mean it has an integreated BEC?

    I want to fly my glider using a 7.4V lipo, I am using a Ar6100 and HXT900s. What rating of BEC do I need?
  11. kdknitro, I have the same esc as you do and yes it has a built in BEC and it will power what you have just make sure you have the connector in properly.

    Tooombucket, Yes and no lol. The ESC will have 2 wire's for the battery and 3 wire's for the motor. 2 wire's on a brushed. and of course you have the 3 small wire's for the receiver, which power's the receiver.

    I haven't been into the rc plane aspect of this very long, but I have had hobby class car's and truck's for that last 15 year's and as long as I can remember ESC's have alway's had integrated BEC's. I might be wrong, but as long as I can remember.
  12. Threedee

    Threedee Cadet

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    I think, as long as it could feed your reciever with more than 3.5v then your good.
  13. herbalicious

    herbalicious Rookie

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    Toombucket

    its not a BEC its called a voltage regulator and your local hobby shop should have one or more from different companys the one that im using has a output of 5volt 2.5 amps also make sure you put the regulator in between the on/off switch and the receiver ..i made the mistake of putting it between the battery and the on/off switch and it drained my lipo {puffed} (__(____(((~~~ it
    evidently it draws power even without a load .. good luck Toom..:D
  14. ok herb don't confuse him.

    A battery eliminator circuit (BEC) eliminates the need for a separate receiver battery in an electric model aircraft (or car or boat). Instead, the receiver and servos draw their power from the same battery that powers the motor (unfortunately, no one has yet come up with a circuit that will eliminate the motor battery too). The BEC is usually part of the electronic speed control (ESC), although it would be possible to construct a stand-alone BEC that is connected between the motor battery and ESC.

    In an electric powered radio controlled model, the BEC is typically part of the electronic speed control (ESC). BEC allows such a model to carry only one battery (the motive power battery) instead of two (motive power, and a separate battery to operate the R/C equipment). A BEC-equipped ESC meant for airplane use often incorporates a low-voltage-cutoff (LVC) circuit which can sense the voltage drop caused when the battery has little charge left in it. It then cuts the power to the 'drive' motor in order to provide the 'steering' servo(s) with enough power to be able to bring the model safely back to the operator. The power to the propeller would be cut but the operation of the control surfaces would be maintained in order to perform a 'dead-stick' landing. Without this feature, all control would be lost when the battery expired, probably resulting in the destruction of the model. In some cases, the BEC is part of the radio control receiver, instead of being part of the ESC.

    R/C BECs in their simplest form use a linear fixed voltage regulator with its standard circuit suggested in the manufacturers datasheet - usually the power supply of the receiver needs 5 V. Low drop types are preferred - especially for batteries with only a few cells. For small models 1.5 to 2 A are enough, for mid-size models a 3A type needs to be considered. BEC's for large models have to provide current of 5A or more. Here a more complicated switched mode regulator should be used, as the BEC has to deal with losses. These Losses are proportional to the difference of the target voltage of 5 volts and the voltage of the main battery, as well as they are proportional to the provided current. For example a 10 cell (NiMh) accumulator with a normal voltage of 12 volts. With a peak current of 5A the BEC will have losses of (12V-5V)*5A = 35W. With a linear regulator these 35W will be converted to heat and so require a large heat sink. In all cases it is a good idea to mount some large capacitors to buffer the regulated output. In large plane or ship models another possibility is to buffer the power supply with a further capacitor near the actuators (Servos).

    R/C BECs in their simplest form USE a linear fixed voltage regulator.
  15. Tony

    Tony Airman

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    kudos...very nice
  16. ScottLott

    ScottLott Administrator

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    What the Heck is a BEC?

    Hey guys! I've gotten this question alot so I just wanted to address it for everyone at once. Before I get started, you can pick up a good BEC that I recommend from Grayson Hobby here:
    http://www.graysonhobby.com/catalog/product_info.php?cPath=52&products_id=876&affiliate_banner_id=5

    First off, BEC stands for Battery Elimination Circuit. Essentially, its purpose is to power the servos and receiver using the power from your main battery(the one that mostly powers your motor) without the need for a separate receiver battery.

    Most Electronic Speed Controllers (ESCs) that are around 40 amps or less come with a BEC on the speed controller. How can you test this? Plug your battery into your ESC and plug the ESC into the receiver's throttle port. If it powers up, your ESC has BEC. If it doesn't power up, no BEC. Normally, the higher amperage(50 amps plus) ESC's do not have an onboard BEC.

    There are limitations on the BEC, though, so you need to be careful. Most ESCs come with a 3 Amp BEC. This is enough to power about 3-4 standard servos without much of an issue. However, if you are using digital servos or doing something with your servos that keep them under constant pressure, that number drops to 2 or 3. So if you need to use more servos or want an insurance policy for your electric airplane, getting an external BEC is the way to go.

    Now that we've established a need for the BEC, I will show you how to wire it. There are 20 thousand different ways to do this, but this is my way and I found it works quite well.
    You'll need to purchase a deans female and male connector and solder them together, then solder the BEC onto the deans connectors where you soldered them together, like this:
    [​IMG]
    Then, you've got a couple options. First off, let me say in all cases you will need to check if your ESC has an onboard BEC before plugging in your separate BEC. If your ESC DOES have an onboard BEC you need to disconnect or cut the RED wire that runs from your ESC to your receiver. If your ESC DOES NOT have an onboard BEC, you can skip that part. Also, the BEC will plug into your reciever's BATTERY port and the ESC will plug in where it normally goes, the THROTTLE port of the reciever.

    The first way you can plug all this up is to set up the BEC so it runs off the same battery as your ESC by just plugging it through, like this:
    [​IMG]

    Or, if you would prefer to run 2 separate batteries you can plug it in like this:
    [​IMG]
    Keep in mind when you do this setup the battery plugged into the BEC doesn't need to be much more than a 10C 500 mah 2-cell li-po.

    In either cause, the 5 AMP BEC will help act as a safeguard against loss of power and allow you to add many more servos to your parkjet without worry. Thanks guys!

    Couple Q & A just to cover the rest of the bases:
    Q: What if my ESC comes with a 5 amp BEC instead of a 3 amp BEC?
    A: In this very rare case, you probably won't NEED an external BEC, but its still a good idea.

    Q: Will my XXXX ESC work with the Grayson Hobby BEC?
    A: There should be no issues with any brushless ESC, but you should always bench test your setup before trying to fly with it.

    Q: Why is my battery getting warm now that I installed the BEC?
    A: If you are running the BEC and the ESC off the same battery, you have to remember that there are now 5 additional amps being pulled from your battery. So if you have a 20 amp ESC with a 20C battery and you plug up the 5 amp BEC, you're now pulling a combined 25 amps from your battery, causing it to exceed the 20C rating. This can be solved by getting a higher C rating battery, not flying at full throttle the whole time, or using a separate, smaller battery for your BEC.

    If anybody has any more questions regarding this topic, feel free to ask below!
  17. herbalicious

    herbalicious Rookie

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    mobackwudsflyer

    ok if your a electrical engineer please raise your hand ,,,that way we know who to ask for help :D bec's seem to be misunderstood ...from what im seeing in some of the posts ,,and i hope we have actually helped people understand ..my opinion is that the name they gave this circuit is confusing ...if i create a new circuit can i name it whatever i want ??? Herb's circuit !!! motorbattery eliminator circuit ...lmao no batterys needed .. :rolleyes:
  18. 12860682321

    12860682321 Cadet

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    B.E.C

    if you have more then 7 or even five servos you need a B.E.C that stands for Battery Eliminating Circuit. if you don't have a B.E.C than you have a 50 to 85 percent chance to heat up of fry your E.S.C or you 2.4 Ghz Reciver or my your battery if thats even possible. the repair cost of a new E.S.C or a 2.4 Ghz is around 100 dollers 50 dolllers for a good E.S.C and 50 dollers for a gool 2.4Ghz reciver heres a link or a good E.S.C and recivers and B.E.C.

    B.E.C http://www.graysonhobby.com/catalog/index.php?cPath=52&osCsid=cbdd04442fe0dcaa6c763bfd37e2a22e

    E.S.C http://www.graysonhobby.com/catalog/index.php?cPath=6

    and recivers http://www.graysonhobby.com/catalog/index.php?cPath=17

    and another one http://www.pmhobbycraft.ca/store/category/7/44/AIRCRAFT-Systems-%26-
  19. Jbirky

    Jbirky Airman

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    Well that is not often the case. Typically, the problem is more complicated than that. If you have too many servos, you will not know it unless you do stunts or something in the air. What is most likely to happen is a brownout of your receiver, which may cause your RC Plane's electronics to reboot. This creates a lock-out and may result in a crash. In the best-case scenario, you notice nothing but a blinking receiver indicating you had some holds.

    That is the most likely thing to happen. There is not, necessarily, a specific number of servos where bad things happen, but rather everything appears fine until you are in flight and something mysteriously gives out causing you to loose control. I.e. Just because 8 servos works in ground testing does not mean it will work in flight.

    Note: I am not saying stuff will not burn out. I am just saying that you are more likely to crash than burn out an ESC/BEC. Receiver is less likely to burn out, and the battery will almost definitely not burn out from too many servos.


    To know what you are using, you need to a meter, anyway, for diagnostic purposes. Like Grayson's Documents indicate, most BECs are 3 Amps to 5 Amps.

    In my setup, it appears that a Corona Digital Metal-Gear servo takes up to 3 Watts in operation as measured from the battery lead. Now, 3 Watts @ 12 volts is a lot less amperage then 3 Watts @ 5 volts given the formula P=IE. In other words, Power (Watts) is equal to the Amperage (current) multiplied by E (Voltage).

    In my tests the system uses 3 Watts as in 3=P, and it is a 5V BEC; I have

    P=IE ; 3=I*5 ==> I= .6 Amps (per servo)

    How many of my servos can I have with a 3 Amp BEC???
    .6* n = 3 ; n= 5 servos

    How many of these servos can I have with a 5 Amp BEC?
    .6n = 5 ; n = 8.3 Servos ;-)

    Regardless, subtract at least 1 servo because you should NEVER assume your system will perform perfect. I.e. A 3 Amp BEC might not be good to a full 3 Amps and you should NOT risk it. With that said, I believe manufactures should add some wiggle-room. I.e. If they say 3 Amps, I think they should be good for more than 3 Amps, but you should assume they are good for a little less than 3 Amps...

    I might buy some BECs and evaluate their claims.
  20. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

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    Hmm... I think we should be giving more pictures / how-to on this topic.

    It's quite important, and we should also say which BECs perform well, and which are not so good.
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