PDA

View Full Version : What does BEC mean?


SBR_RV
12-06-2005, 12:26 PM
can someone explain to me what this term means. BEC?

Geoff_Gino
12-06-2005, 12:38 PM
can someone explain to me what this term means. BEC?

Hi

BEC stands for Battery Eliminating Circuit.
On lighter planes and set-ups that use less than 10 amps the BEC eliminates the need for a flight pack battery for the receiver.

The receiver is powered by the BEC, which plugs into the throttle channel of the receiver.

Geoff

Matt Kirsch
12-06-2005, 12:56 PM
You do have to be careful about how many servos you try to run with most BECs. The instructions will detail how many servos can be used safely, though people have been known to get away with using one more than what's recommended.

Unbalanced prop
12-06-2005, 01:48 PM
Not sure about other ESCs, but the BEC on my Phoenix 45s will allow me to run four servos (and receiver) with 10 round cells or 3S lipols and still pull over 40 amps. For higher battery counts you would have to go with a seperate UBEC or seperate flight pack to power the servos.

Doug

Harlan
12-06-2005, 05:27 PM
Hi

BEC stands for Battery Eliminating Circuit.
On lighter planes and set-ups that use less than 10 amps the BEC eliminates the need for a flight pack battery for the receiver.

The receiver is powered by the BEC, which plugs into the throttle channel of the receiver.

Geoff

I'm really new at this stuff, so bear with me if I'm asking for clarification that seems obvious to others.

If the BEC is a battery elimination circuit, where does the Rx get its power? Is there no on-board battery?

Harlan

Big_Bird
12-06-2005, 05:36 PM
I'm really new at this stuff, so bear with me if I'm asking for clarification that seems obvious to others.

If the BEC is a battery elimination circuit, where does the Rx get its power? Is there no on-board battery?

Harlan
As an example, I fly a GWS Corsair with a 3s (3 cells in series) Lipo 11.1 volt pack. There is no other battery in the plane. There is one connector (BEC) coming out of the ESC (electronic speed control) which is Futaba compatable and connects to the throttle channel on the receiver. This connector provides a regulated 5 volts to the receiver power buss and sends the throttle position signal back to the ESC.

Ken

slipstick
12-06-2005, 10:37 PM
If the BEC is a battery elimination circuit, where does the Rx get its power? Is there no on-board battery?

BEC only applies to electric powered models. It has eliminated the need for an ADDITIONAL SEPARATE battery for the radio and servos. They are driven by the BEC from the one motor battery.

Steve

SBR_RV
12-07-2005, 03:06 AM
BEC for up to 3 servos on 6-8 NiX/2-3 LiXX Cell, 2 servos if using higher voltage
Voltage Range: 6-12 Cell NiXX, 2-4 Cell LiXX (6-15V)



quoted above, says that two servos should be used if using a higher voltage. wouldnt the BEC be able to supply more power to servos if there is more power available?

Big_Bird
12-07-2005, 04:30 AM
quoted above, says that two servos should be used if using a higher voltage. wouldnt the BEC be able to supply more power to servos if there is more power available?

No. The reason that a BEC isn't able to supply more power at a higher voltage is this. With a 5 volt regulator the same current that is supplied to the receiver and servos must flow through the regulator. As an example lets use 100 ma (0.1 amps). With an 11.1 volt battery the 5 volt regulator (BEC) must do away the extra 6.1 volts. The regulator must dissipate 0.61 watts (6.1 volts x 0.1 amps). Now with a 7.4 volt battery, the regulator must do away with the extra 2.4 volts. That means that the regulator must dissipate 0.24 watts (2.4 volts x 0.1 amps). Quiet a difference. As you can see from this example the regulator has a lot more heat (watts) to dissipate on an 11.1 volt battery than it does on a 7.4 volt battery.

The number of servos that a BEC can drive is strictly limited by the amount of heat that it can dissipate. If the BEC gets too hot bad things happen. It's not a pretty sight. Some ESCs have 2 regulators in parallel and can drive more servos.

I hope this helps you understand what is going on.

Ken

SBR_RV
12-07-2005, 05:59 AM
thanks, so no matter how many volts, the BEC will still only be able to supply X amount of power, correct?

from that reply i have another question. from the battery, does 11.1v go to the motor as well as going through the BEC to the servos?
also how do i know what size the BEC is, as it doesnt say on this webpage?
http://shop.eflypower.com/product_info.php?cPath=25_81&products_id=605

Vintauri
12-07-2005, 06:18 AM
thanks, so no matter how many volts, the BEC will still only be able to supply X amount of power, correct?

from that reply i have another question. from the battery, does 11.1v go to the motor as well as going through the BEC to the servos?
also how do i know what size the BEC is, as it doesnt say on this webpage?
http://shop.eflypower.com/product_info.php?cPath=25_81&products_id=605

The 11.1V or whatever the full voltage of the pack it goes to the motor through the ESC but the BEC always regulates the voltage to the RX and servos to 5V.

From your link it says this about the BEC "BEC for up to 3 servos on 6-8 NiX/2-3 LiXX Cell, 2 servos if using higher voltage"


Steve

Geoff_Gino
12-07-2005, 06:22 AM
Hi SBR RV

The BEC uses the battery voltage and steps it down to the required 5 volts for Rx. When the battery voltage gets low the ESC shuts down the voltage to the motor to ensure that Rx stays alive and will still operate the servos. In an 11,1 volt battery the cut off voltage on the ESC should be set to 9 volts (3,0 volts per cell) which would anyway be enough to supply the required 5 volts to the RX (or for a 2S pack 6,0 volts)

The reason for this is weight saving on small foamies which normally draw 10 amps of less. An added advantage is there is no need to charge the flight pack which isn't there.

Geoff

Harlan
12-07-2005, 06:39 PM
As an example, I fly a GWS Corsair with a 3s (3 cells in series) Lipo 11.1 volt pack. There is no other battery in the plane. There is one connector (BEC) coming out of the ESC (electronic speed control) which is Futaba compatable and connects to the throttle channel on the receiver. This connector provides a regulated 5 volts to the receiver power buss and sends the throttle position signal back to the ESC.

Ken

Thanks Ken. In summary, there is, of course, an on-board battery, so the BEC doesn't eliminate the battery, but, rather, allows battery sharing. In that sense it is a battery elimination circuit in that it eliminates the need for a second battery. Would that be correct?

Harlan

Big_Bird
12-07-2005, 09:58 PM
Harlan, that is 100% correct.

Ken

Bob_CO
12-07-2005, 10:07 PM
thanks, so no matter how many volts, the BEC will still only be able to supply X amount of power, correct?

from that reply i have another question. from the battery, does 11.1v go to the motor as well as going through the BEC to the servos?
also how do i know what size the BEC is, as it doesnt say on this webpage?

The BEC will supply a fixed voltage, 5v. The current or amps going through it is based on what is being consumed by the RX and servos. The higher the input voltage the fewer servos it can run because everything over 5v the BEC has to disipate as heat. So the BEC isa voltage regulator that takes any (any that we are dealing with) input voltage and converts it to the 5v the RX and servos want to see. The battery voltage goes through the ESC to the motor.



The reason for this is weight saving on small foamies which normally draw 10 amps of less. An added advantage is there is no need to charge the flight pack which isn't there.

Geoff

BECs don't really have anything to do with 10a or less systems. There are BECs built into 125a ESCs. It is just a matter of where you want to save 3-10oz on a plane. Not to mention the hassle of dealing with 2 batteries on one plane.

Thanks Ken. In summary, there is, of course, an on-board battery, so the BEC doesn't eliminate the battery, but, rather, allows battery sharing. In that sense it is a battery elimination circuit in that it eliminates the need for a second battery. Would that be correct?

Harlan

You have it Harlan.

SBR_RV
12-08-2005, 03:19 AM
so all BEC's supply 5v? (sorry for all the questions)

Bob_CO
12-08-2005, 04:01 AM
so all BEC's supply 5v? (sorry for all the questions)

Some supply 6v.

cyclops2
12-08-2005, 02:13 PM
Bring Extra Cash.

Rugar
12-08-2005, 02:30 PM
http://www.hobby-lobby.com/ubec.htm

cyclops2
12-08-2005, 10:12 PM
$43 dollars for a 3 amp I C voltage regulator. It is worth $ .05 in any volume. PCB is $ .10 . No wonder all hobbies are showing poor young peoples interest. Rich old seniors only need apply. :(

Bob_CO
12-09-2005, 12:13 AM
There is always this guy.

http://www.dimensionengineering.com/ParkBEC.htm

SBR_RV
12-09-2005, 04:10 AM
No wonder all hobbies are showing poor young peoples interest. Rich old seniors only need apply. :(

i see what you mean. im 17 with a part time job still at school, and paying $10AU for a peice of rubber to deflect fuel exhaust on nitro models is starting to bug me. (can make my own for $0.50)

SBR_RV
12-09-2005, 04:11 AM
thanks for all your help and replys. i think im fairly right on what BEC is all
thanks.

slipstick
12-10-2005, 10:23 AM
$43 dollars for a 3 amp I C voltage regulator. It is worth $ .05 in any volume. PCB is $ .10 . No wonder all hobbies are showing poor young peoples interest. Rich old seniors only need apply. :(
Come on then, don't be shy. Where can I get all the components needed for a 5A switched mode regulator for 5 cents ? I'll sell them cheaper than $43 if you can source all the components including PCB for me for 15 cents as you claim ;).

Steve

Bob_CO
12-10-2005, 08:32 PM
Come on then, don't be shy. Where can I get all the components needed for a 5A switched mode regulator for 5 cents ? I'll sell them cheaper than $43 if you can source all the components including PCB for me for 15 cents as you claim ;).

Steve

QFE

40 cents is about as cheap as you can go on a 5a IC voltage regulator and that is just for the 1 chip.

But at the end of the day it doesn't matter if it costs 15 cents, 15 dollars or 30 dollars to make an item, it is worth what the market is willing to pay. I promise you cyclops, if someone could make money by making these and selling them for less they would be doing it.

Also consider that a 5a BEC isn't going into a cheap airplane with just a few servos (unless it is overkill) running a 3s1p pack. You are probably looking at several hundred dollars in a ship that flies that BEC. Heck it may even be several hundred dollars just for the battery. So I don't see how a high-end BEC is the limiting factor one who or what age group gets to buy one.

Big_Bird
12-10-2005, 09:58 PM
$43 dollars for a 3 amp I C voltage regulator. It is worth $ .05 in any volume. PCB is $ .10 . No wonder all hobbies are showing poor young peoples interest. Rich old seniors only need apply. :(

If you will send me a working prototype switching BEC (none of that linear stuff, it has to dissipate too much heat) I'll be glad to send you a dollar and thoroughly test it. Fair enough? None of this RC stuff is cheap, but what hobby is now days.

Ken

Clangador
03-14-2009, 06:54 PM
So where are these things located in a airplane? I have two foamies and have not noticed anything like a BEC.

Big_Bird
03-14-2009, 11:29 PM
So where are these things located in a airplane? I have two foamies and have not noticed anything like a BEC.
On this photo the BEC is the white colored module connected by 3 wires behind the motor. Some motors have a built in BEC.

Red Scholefield
03-15-2009, 12:44 AM
On this photo the BEC is the white colored module connected by 3 wires behind the motor. Some motors have a built in BEC.

I think we may be confusing some. The component you point out is an ESC (Electronic Speed Controller). Most of these used on planes drawing up to 60 amps have as part of their circuitry a BEC (Battery Elimination Circuit) which is used to power the radio so that a separate battery is not required. In the case where the ESC (such as an Opto controller) has no BEC, a separate BEC can be used in place of a receiver/servo battery pack.

Big_Bird
03-15-2009, 12:53 AM
Red, you are totally correct. I failed to mention that a BEC is quite often contained in the same module as the ESC.

Clangador
03-15-2009, 05:30 PM
Ah so those capacitors in the ESC might be it?

kyleservicetech
03-15-2009, 10:27 PM
Add to this confusion, the Switching Power supply type of BEC units, such as the Common Sense and Castle Creations units. I've been using both brands in my 6S2P A123 models with very good success.

The CC unit does have a lot more electrical noise on its receiver output, as shown on my Tektronix 2236 Oscilloscope, but this noise has absolutely no effect on my Spectrum radios.

The Common Sense unit has an absolutely clean DC output. Both units handle switched 4 ampere loads with absolutely NO dipping of voltage below 5 VDC.

Something to consider for the larger models. Plus, you have no receiver batteries to worry about. (On a good day for flying, Geez did I charge that receiver battery???)

slipstick
03-15-2009, 10:58 PM
Ah so those capacitors in the ESC might be it?
No, capacitors are never voltage regulators. More probably one of the things that look like a FET or maybe a transistor is it ;).

Steve

Clangador
03-15-2009, 11:10 PM
Ok okay.

Dr Kiwi
03-16-2009, 01:28 AM
The CC unit does have a lot more electrical noise on its receiver output, as shown on my Tektronis 2236 Oscilloscope, but this noise has absolutely no effect on my Spectrum radios.

Totally off-topic, but your comment may explain the non-zero rpm (with no motor running) I see with my Eagle Tree RPM sensor when I use a Castle Creations ESC. Dualsky and Motrolfly ESCs always read zero, but each different Castle ESC (PH10, PH25, PH45) gives a different and definitely non-zero (~2000-~7000rpm) reading at rest. Once the motor is running, the RPM are recorded correctly even at a few 100rpm.

kyleservicetech
03-16-2009, 04:20 AM
Dr Kiwi
Noted your response, it might also help others.

The CC converter operates without a linear downline DC regulator as is used in the Common Sense regulators. And, switching power supplies are well known for a lot of noise in their outputs. I'm certain Castle Creations has tested them on all brands of 72 Mhz radios, but personal opinion, I won't use them on 72 Mhz radios. At any rate, all of my recievers are Spektrum 2.4 Ghz anyhow.

These switching power supplies usually have an "Upper and Lower" voltage threshold where the switching circuitry turns on at the lower voltage, and back off at the upper voltage. In the CC converter, this upper/voltage differential voltage is on the order of 50 millivolts or so, depending on the load. (I measured this a year ago!) This CC converter voltage swing has a frequency in the ultrasonic range. And, no, you can't just hang a big capacitor across the output of the CC BEC. That would just change the frequency of the noise on its output.


Question:
How much current does your Eagle Tree monitor circuitry pull? If its a few milliamperes, you might be able to "clean up" the CC output to your Eagle Tree monitor circuit with maybe a dollars worth of parts from Radio Shack.

Let me know about the current pulled by the monitor. This would involve a simple resistor/capacitor to filter out the noise. Once I know the Eagle Tree current requirements, I can suggest resistor and capacitor values to try. (They would be on the order of a 33 ohm resistor and 270 Microfarads. The resistor in series with the 5 volt red wire to the Eagle Tree unit, the capacitor wired directly across the input to the Eagle Tree unit. Watch polarity on the capacitor. They are marked with a minus on their negative side. If the Eagle Tree unit pulls 10 milliamperes or so, that would give a voltage loss of 33 ohms multipled by 0.01 Amperes or about 1/3 volt loss. It would be a good idea to add a 0.1 uF ceramic capacitor directly across the 270 Microfarad cap just in case the 270 uFd cap has problems with high frequency. I can provide a photograph on how this modification will look. And no, it will not have any effect on the warranty for your Eagle Tree monitor. Just make damn certain you don't reverse plus and minus to the monitor!)

DO NOT use a resistor capacitor circuit between the CC converter and the radio receiver!!!. That series resistor would result in so much voltage drop the receiver would quit when servos are actuated.

kyleservicetech
03-16-2009, 04:44 AM
Clangadore
Ah so those capacitors in the ESC might be it?Ah so those capacitors in the ESC might be it?

These ESC's generate a lot of electrical noise from switching the high currents that go to your brushless motor. (These ESC's generate three phase power to drive what amounts to a three phase brushless motor!)

But, these switched high currents generate high voltage transients that can also cause damage to the switching Field Effect Transistors (FETs) if you are not careful. The large capacitors you see on the inputs of just about all brushless ESC's are there to knock off these voltage transients.

Clangador
03-16-2009, 09:18 AM
Okay.