Sbec, ubec, bec whats the difference?
I know what a BEC (battery eliminator circuit) is for. I think? To cut battery power to the motor while conserving enough power for operating the servos as well as allowing us to use the motor battery to power the receiver and servos. But what is a UBEC or SBEC? Could someone please enlighten me.
UBEC was the original name for a stand-alone BEC produced by Kool as the "Ultimate BEC".
SBEC comes from "Smart BEC"
The various stand-alones like the Castle Creations 10A BEC are often simply referred to, probably incorrectly but who cares, as UBEC.
Just like "Kleenex" for any brand of tissue!
UBEC (Ultimate BEC) is/was the trade name of one of the first add on bec's that allowed you to use more servos at higher pack voltages and produced by Kool Flight (Jeff Myers, SEFF organizer) It now has seemed to morph into "Universal" bec because a bunch of the Chinese stand alone bec's are referred to as UBECs.
SBEC stand for Switching BEC vs the built in linear bec which was limited to 3 or 4 servos and 3 or 4 lipo cells. The new lines of Switching BEC speed controls basically incorporate a "UBEC" into the esc itself instead of having to use a stand alone system.
Letchworth, Great Britain (UK)
Joined Jul 2004
The BEC is the part that drops the battery pack voltage (7.4v, 11.1v, or whatever) down to 5v or 6v for use by the receiver and servos. It's called a battery eliminator circuit because it eliminates the requirement for you to use a separate 4-cell NiCd or NiMh receiver battery to power them.
The BEC is usually incorporated into the ESC, so that simply plugging the ESC into the receiver is all you need to supply power to it. But often the built-in BECs are insufficient to deal with all the servos you have, or the high voltage of a 4S and upwards LiPo pack, so you can get a stand-alone BEC to do the job.
Stand-alone BECs are usually the switching kind, so they can deal with higher voltage and current than the linear kind which are usually built into the ESCs. SBEC, UBEC, and other terms have become generic terms for, usually, switching BECs. But it's always wise to check the BEC's specs, irrespective of what the manufacturer calls it, to make sure it is switching if you want high-power and/or high-voltage use.
This newbie needs to know whether a Red Brick 10A ESC with UBEC rating 5v/1a will work with 2S 20C lipos, in conjunction with 3/4x SuperMicro linear servos rated at 3-4.2v, and an Orange R415 Rx?
Don't understand much about this techology at the moment, but learning as fast as I can, so any help appreciated...
Nonetheless, on 2S, most basic ESCs with built in BEC will be OK for 3-4 servos. (but NOT on 3S). However, the voltage rating on your servos is less than the 5V output of the BEC, so you would risk cooking a servo. You might need to look for an external BEC with lower than normal output. Sorry, didn't find one on a quick search.
I have a 10A ESC that has a BEC built in ... so that is possible.
The problem as you identified and I think the questioner quite rightly is concerned about is the low voltage super-micro servos.
IM AM NOT TRYING TO SELL ANYTHING FROM THAT WEBSITE OR WORK WITH THEM OR TELL THEY HAVE THE BEST PRODUC. I HAVE NEVER TRY ANYTHING FROM THEM BUT THE INFO GIVEN IS VERY GOOD.
This will help
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
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
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
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.
What is wrong with a linear regulator?
Linear regulators are great for powering very low powered devices. They are easy to use and cheap, and therefore are very popular. However, due to the way they work, they are extremely inefficient.
A linear regulator works by taking the difference between the input and output voltages, and just burning it up as waste heat. The larger the difference between the input and output voltage, the more heat is produced. In most cases, a linear regulator wastes more power stepping down the voltage than it actually ends up delivering to the target device!
With typical efficiencies of 40%, and reaching as low as 14%, linear voltage regulation generates a lot of waste heat which must be dissipated with bulky and expensive heatsinks. This also means reduced battery life for your projects.
Even the new LDO (low drop-out) regulators are still inefficient linear regulators - they just give you more flexibility with input voltage drops.
How is a switching regulator better?
A switching regulator works by taking small chunks of energy, bit by bit, from the input voltage source, and moving them to the output. This is accomplished with the help of an electrical switch and a controller which regulates the rate at which energy is transferred to the output (hence the term “switching regulator”).
The energy losses involved in moving chunks of energy around in this way are relatively small, and the result is that a switching regulator can typically have 85% efficiency. Since their efficiency is less dependent on input voltage, they can power useful loads from higher voltage sources.
Switch-mode regulators are used in devices like portable phones, video game platforms, robots, digital cameras, and your computer.
Switching regulators are complex circuits to design, and as a result they aren’t very popular with hobbyists. However Dimension Engineering creates switching regulators that are even easier to use than linear regulators, because they use the same 3 pin form factor, but don’t require any external capacitors.
What can switching regulators do that linear regulators can't?
With high input voltages, driving loads over 200mA with a linear regulator becomes extremely impractical. Most people use a separate battery pack in these situations, so they have one battery pack for high voltage devices and one for low voltage devices. This means you have twice as many batteries to remember to charge, and twice the hassle! A switching regulator can easily power heavy loads from a high voltage, and save you from splurging on an additional battery pack.
Certain kinds of switching regulators can also step up voltage. Linear regulators cannot do this. Ever.
How do I tell if I need a switching regulator?
As a general rule of thumb, if your linear voltage regulation solution is wasting less than 0.5 watts of power, a switching regulator would be overkill for your project. If your linear regulator is wasting several watts of power, you most certainly want to replace it with a switcher! Here is how to calculate power losses:
The equation for wasted power in a linear regulator is:
Power wasted = (input voltage – output voltage) * load current
For example, let’s say you have a 12V lead-acid battery and you want to power a microcontroller that draws 5mA, and an ultrasonic rangefinder that draws 50mA. Both the microcontroller and the ultrasonic rangefinder run off of 5V. You use an LM7805 (a very common linear regulator) to get the voltage down to 5V from 12V.
Power wasted = (12V – 5V) * (0.050A + 0.005A) = 0.385W
0.385W is not too bad for power losses. The LM7805 can handle this without a big heatsink. You could get more battery life if you used a switching regulator, but in this case the power consumption is so low that the battery life will be very long anyway.
Now let’s expand on this example, and add two servos that draw an average of 0.375A each, and also run off of the 5V supply. How much power is wasted in a linear regulator now?
Power wasted = (12V – 5V) * (0.050A + 0.005A + 0.375A + 0.375A) = 5.635W
5.6 Watts is a lot of waste heat! Without a large heatsink the LM7805 would get so hot it would desolder itself or melt your breadboard or defeat Iceman. Even with the heatsink, 5.6W is also a lot of life to suck out of your battery for no reason. A switching regulator such as a DE-SW050 would be very useful in this case, and would reduce power losses to around 0.5W.
Is a switching regulator really worth 10+ bucks?
The final thing to consider is of course, cost. If your project is cheap and simple enough that a switching regulator would triple the cost of the entire project, then a switching regulator may be hard to justify. However if you are building a more advanced robot, airplane etc. and a switching regulator adds 15% to your cost, but gives you 35% more battery life, then it is a good deal right?
The servos mentioned in post 8 are made to run on a single cell batt. Using a 2 cell with a ESC with a bec works fine if you use a diode between the ESC and the rcvr to drop the voltage.
Joined Nov 2003
Using a resistor to drop the voltage is a bad idea since the voltage will then fluctuate wildly depending on what current the RX and servos are drawing at the time.
It may be practical to use a diode in the line to drop 5V to around 4.2V (depending on exactly what diode you use). At least diodes have a fairly constant volt drop.
USA, ME, Ellsworth
Joined May 2008
A recent discussion in another thread inspired me to test a CC Thunderbird 18 (one of my most used ESCs, I own a number of them) to see exactly how much heat the internal BEC was generating with and without any servos attached. And I was surprised at the results.
I used my eLogger V3 and put to temp sensors on the ESC, one in between the rows in the MOSFET field and the other in the area of the BEC IC and caps on the other side of the PCB. It was connected to a rewound D4023-850 motor and run up to the 18-20A region using a CCPM servo tester for throttle control.
I estimate that the servo tester is about a 400 mA (0.40A) or so load on the BEC.
In the images the the current is brown and the two temp traces are gray and yellow. And all are labelled.
As you can see, with the TB18's BEC powering only a servo tester the temp quickly climbed to above 150F in both areas.
When I pulled the red lead out of the throttle/BEC lead and powered the servo tester up with an external BEC and repeated the test, the MOSFET field temp stayed about the same (the ESC was loaded to it's rated max) but the temp in the BEC IC and capacitor area only climbed to about 97F
I have been flying numerous TB18's for several years now without using external BEC's and with two or three 9 gram servos and a small Berg receiver on the BEC. I have not once burned one up or had one fail on me. But I have not been testing how hot they were getting.
It looks to me like the TB18 temperatures can get well up into the 100F range and even push 200F without any problem as long as they are well ventilated. But I'm going to pay more attention to the heat build up on them than I used to.
CC has said that the Thunderbirds are OK on 3S and with 3 servos and my usage of them has born that out numerous times.
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