This is Billy Joe Bob, welcome to Hillbilly RC. I know watcha thinkin, what do a hillbilly know about RC areioplanes. Y’all stick around and I’ll show you just how us hillbillies thank.
Today I wanna talk to y’all about BECs and how they work. I ain’t talkin’ bout Betty, Eleonor, and Clarice, I’m talkin bout, (Battery Eliminator Circuit). Dat’s some awful big words. So, fur I get started and my tung gets tangled round my eye-tooth, ima gonna ask my cuzen Lou to come on in and do the splanin.
Thank you, Billy Joe. As he was saying, today we will talk about BEC (Battery Eliminator Circuit) and how they operate. The one thing to remember about BECs, and how important they are to the safety of your aircraft is; they allow you to maintain control of your plane if you lose your ESC, (electronic speed controller).
Let’s try to understand how a BEC works. Think of a BEC as a transformer, it takes a higher voltage and drops it to a lower voltage. The higher voltage is used for your electric motor, and the lower voltage is used to power all your accessories (servos, retracts and so on). Most ESC have a built in BEC, unless you are talking about an OPTO (optocupler). That is a subject for another time.
Think of it this way. If you have an electric motor that requires a 16.8 volts @ 18 amps, and your accessories require 5 volts @ 2 amps, what would happen to your accessories if you supplied them 16.8 volts @ 18 amps? You guessed it; all your accessories would go up in smoke.
So, the BEC takes the battery voltage of 16.8 volts @18 amps and gives the motor what it needs, while at the same time transforms that same voltage to a lower voltage of 5 volts @ 2 amps to power up your accessories.
With that said, smaller aircraft are safe to fly with an ESC that has a built-in BEC, but what about larger aircraft which require more voltage? Here is where using a separate BEC is important.
There are two types of BECs you need to be familiar with:
- BEC – Linear Battery Eliminator Circuit
- SBEC – Switching Battery Eliminator Circuit
(Linear) BEC
Let’s use a 12-volt 1-amp battery and 5-volt 1-amp accessories for our example.
The way the LBEC works is by using a source, coupling capacitors, and a load. I’ll not get into the theory and operation of coupling capacitors, but we will discuss the source and load. For purpose of this article, we will keep it simple and not talk about ohm’s law. If you would like to learn more about ohm’s law you can go here: ohmlaw.com. Now let’s look at our BEC’s.
The 12-volt 1 amp battery is considered the (source), the 5-volt 1 amp accessories servo is the (load). The LBEC takes the source (battery voltage) of 12 volts 1 amp and regulates it to a lower voltage of 5 volts 1 amp for the (load). When this process takes place, there is unused voltage, and this voltage creates heat. In our case with the battery and servo there is 7 volts left over. To understand this better, let’s look at this equation.
12 Volts in – 5 Volts out = 7 Regulated Volts
1 Amp in = 1 Amp Out
7 Regulated Volts X 1 Amp Out = 7 Watts
So, if you took you 12 volts (voltage in) and subtracted your 5 volts (regulated voltage) you would have 7 volts remaining. This voltage is used up in heat. The formula would look like this.
12v-5v=7v, seven is the regulated voltage.
Now to figure the wattage or power, this is the formula you would need. You would take the regulated voltage (7 volts) and multiply it by the amps (1 amp). It would look like this.
7v x 1i = 7p, (v=power, i=amps, p=watts/power). This is the watts/power.
So, to figure the wattage used with any variation of batteries you would use this equation.
(input volts) – (output volts) = (regulated voltage) x (amps) = (watts/power)
12volts – 5 volts = 7 volts x 1amp = 7 watts. Or (12v-5v) x 1 amp = 7 Watts
12v – 5v =7v x 1i = 7i
In short, a LBEC is great for RC Aircraft that require low power to operate, and they are cheap. Remember, the greater the difference between the input and output voltages, the more heat it generates, and you know electronics do not like heat.
This should give you some idea of how a LBEC works without getting into all the technical data and confusing things. If you would like to get into the technical side of things, here is a link that will help you. Texas Instrument.
(Switching) SBEC
Like the LBEC, the SBEC is an electronic voltage regulator but handles it in a different way. The SBEC offers benefits the LBEC doesn’t. The SBEC does the following:
- Energy Efficient
- Require Fewer Batteries
- Allows for Higher Input Voltages
- Allows for a possible safe return for aircraft
Because of the complexity of the SBEC, we will not get into the details of how they are built. We, however, will try to explain them in a way that will help you understand.
How is an SBEC more efficient? The SBEC works by taking little bites of the input voltage (the battery) and moving it to the output voltage (the accessories). This is done by a switch and controller that regulates the rate the energy is transferred. By moving these small amounts of energy, it makes the SBEC 85% more efficient.
Try to think of it this way. If you have a bridge that is rated for 10 tons and you want to transfer 50 tons of material across it at one time what would happen? You guest it, it would collapse (LBEC overload). Now take that same bridge and transport the 50-ton load 500lb at a time, the bridge is able to handle the load with no structural compromise (SBEC safe).
The SBEC is not only efficient, but it allows for fewer batteries, electronics, and wiring saving space and weight. Let’s say you want to protect your aircraft by separating the motor from your accessories. To do this, you would need two receivers, two battery supplies, extra wiring and extra space. By using a SBEC you can accomplish both. What about higher input voltages? The SBEC allows you to use higher voltage battery packs to power the greater consuming electric motors and at the same time maintaining the proper voltage you need for all your accessories.
When it comes to your aircraft’s safe return to earth, the SBEC is instrumental in allowing you to do that. The SBEC isolates both systems (engine and accessories) from total failure. Should the ESC fail causing the motor to stop, the SBEC will still allow power to your accessories allowing you to possibly make a safe return home. It is important to remember, if the battery fails, all hope is lost.
I hope this gives you a better understanding LBEC’s and SBEC’s. Now I’ll turn it back to my cousin, Billy.
Woo-doggies, dat thar got my brain a hirt’en. Thank ya for sittin and bein a part of the family. C’mon and join us Nex time and we’ll pull us up a keg of nails and have us a driv’n good time talkn’ bout LiPo batteries. Y’all come back now ya hear.