BECs

[Toothpick]

Hello first of all i don't own my own crawler (yet!), but have been seeing the term BEC thrown around quite a bit. I can not find anywhere (yes I did search for about an hour to no avail) what a BEC is really used for/why it is needed. I think it work with provide power to things other than the motor?? Any help/redirection is greatly appreciated!

As for my rc experience I own a Traxxas Slash, and I have driven comp crawlers and scalers before just waiting for the right moment to spring on one for myself!

[Lentsnh2012]

A BEC is essentially a voltage regulator and keeps from your receiver browning out due to a high power servo. A Castle Creations BEC is the best because you can adjust it with the Castle Link, as well as it being super small.

[crockins]

What he said ^
It allows you to supply controlled voltages to different components. If you're running a high power servo it's good, as stated above, for preventing brown out. Also in the case of high voltage batteries (3s or higher), your esc might be able to handle the voltage but it might fry your receiver. wiring the BEC as in the castle instructions will supply a given voltage (say 6 volts for example) to the receiver and servo (and lights or whatever you want) while supplying the higher voltage to the esc.

[Toothpick]

Thanks guys that really helped clear up my confusion!

[Olle P]

BEC = Battery Eliminator Circuit

• It was born out of need when the trend for main batteries was to deliver more voltage than the receivers (Rx) could handle. Instead of adding an extra lower voltage battery for the Rx (and servo) a simple solution was to reduce the battery voltage.
• There are two general BEC designs, linear and PWM.
  • The linear design is older and can be seen as a variable resistor in series with the output. It regulates the output voltage by simple voltage division.
    • The advantage of this design is that the output really is a steady voltage as long as the input voltage is high enough and the BEC temperature is within limits.
    • The disadvantage is that the reduction in voltage is done by "burning off" power, which means:
      • the BEC gets warm and thus can only be used for smallish voltage reductions and/or low currents.
      • The BEC itself can use up quite a bit of the battery's energy.
  • The PWM design is newer, and today the most common. (Often referred to as UBEC or SBEC.)
    • The advantage of this design is that virtually no power is used to reduce the voltage. The control electronics do use a small amount of power, and there's a little internal impedance, but it's almost negligible. This means:
      • Can reduce the voltage quite a bit.
      • Can deliver a fair amount of current.
    • The disadvantages of PWM are:
      • The output voltage is a wave with the desired value as the average (RMS). Capacitors are used to reduce the difference between peak and average voltage.
      • The PWM frequency might interfere with the radio (Rx) and the Electronic Speed Controller (ESC) control circuitry.
• BECs are made as stand-alone units as well as built into most ESCs.
  • The answers in the postings above relate to stand-alone BECs.
  • Built-in BECs are typically more limited in use because of thermal properties. Both the BEC and the ESC circuitries develop heat that mess with the performance.
    They're good for feeding the Rx and a low power servo.
    What typically happens when too much power is drawn from the BEC (and ESC) is that the BEC voltage drops, causing the Rx to misbehave. This can/will then cause the steering and/or speed control to behave erratic.

[Axial Rose]

I've looked at the CC BEC diagram --> LINK

If I want 6V to go to my Hitec HS-7954SH servo, do I connect the 6V output from the CC BEC to go directly to the servo and then get power to the receiver from the BEC built into my ESC?

This servo can run on 7.4V in order to obtain ~400 oz/in of torque so I reckon I need to connect my CC BEC to the computer and set it to the closest voltage?

I'm not embarrassed to ask questions - a couple years ago someone told me it was okay to connect 3S to the ESC I told him I was using . . . I still have that fried piece of junk hanging on pegboard at my work bench as a reminder to get good advice before proceeding.

Thank you

[k7zpj]

Originally Posted by Axial Rose

I've looked at the CC BEC diagram --> LINK

If I want 6V to go to my Hitec HS-7954SH servo, do I connect the 6V output from the CC BEC to go directly to the servo and then get power to the receiver from the BEC built into my ESC?

This servo can run on 7.4V in order to obtain ~400 oz/in of torque so I reckon I need to connect my CC BEC to the computer and set it to the closest voltage?

I'm not embarrassed to ask questions - a couple years ago someone told me it was okay to connect 3S to the ESC I told him I was using . . . I still have that fried piece of junk hanging on pegboard at my work bench as a reminder to get good advice before proceeding.

Thank you

With the HS-7954SH servo, I would wire the BEC to power the servo directly as in this diagram and set the BEC for 7.4V output. The receiver still gets power from the ESC.

Taken from Definitive wiring diagrams for BECs Rx Servos Motors etc.

You can do this by making your own wiring harness, using a Y-cable and pulling the red wire at the receiver or use a RX-bypass adapter like in the link below.
Holmes Hobbies LLC

[Axial Rose]

Originally Posted by k7zpj

You can do this by making your own wiring harness, using a Y-cable and pulling the red wire at the receiver or use a RX-bypass adapter like in the link below.

Thanks

[crockins]

I'm still a little confused about the reason for running it directly to the servo rather than running through the receiver as the CC diagram shows. Unless you're using a real monster, almost all the servos that people commonly use don't need higher than 7.4 v for peak torque/speed and most receivers can handle that voltage so why wire it direct to the servo? Seems like wiring it according to the CC diagram allows the ESC to feed just the motor while the BEC gives an appropriate voltage to everything else. A 10 amp BEC like the CC one should be plenty to supply the receiver and a high torque servo with no problem. Is the idea just to limit the amp draw through the receiver and if so is that really necessary? I'm not saying it's wrong by any means! I'm just trying to understand the pros and cons of each way. I've seen lots of people suggest one way or the other but I've never seen a good explanation of why!

[Olle P]

Originally Posted by Axial Rose

If I want 6V to go to my Hitec HS-7954SH servo, do I connect the 6V output from the CC BEC to go directly to the servo and then get power to the receiver from the BEC built into my ESC?

That's the best way, in my opinion.
Do also have the black cable connected to both BEC and Rx to make sure the control signal is correct.

Originally Posted by Axial Rose

This servo can run on 7.4V in order to obtain ~400 oz/in of torque so I reckon I need to connect my CC BEC to the computer and set it to the closest voltage?

It's actually closer to 8.4V (a fully charged 7.4V battery, which the servo is designed for) required to get that torque.
You probably don't need that much torque in reality though. I run my servo of that very same model on 6.0V and have no issues with "low torque".

The CC BEC comes set to 5.1V by default, so some upward adjustment is advisable.

Originally Posted by crockins

I'm still a little confused about the reason for running it directly to the servo rather than running through the receiver as the CC diagram shows.
... 7.4 v for peak torque/speed and most receivers can handle that voltage so why wire it direct to the servo? ... Is the idea just to limit the amp draw through the receiver and if so is that really necessary?

I give you three reasons:
1. Reliability. Differentiating the power supply to two sources make sure that the power drawn from the servo won't influence the Rx functionality.
2. Amp draw through the Rx. Those connectors and wiring aren't designed for high current and it provides an unnecessary voltage drop.
3. Voltage differentiation. Even if an Rx can handle 7.4V (which all by no means are guaranteed to do) there might be other devices attached to the Rx that can't. Lighting, sound, winch, etc...
I prefer having the option to use different voltages on servo and Rx for optimisation purposes.

[Axial Rose]

Mega-thanks Olle P

I'm going to run 3S with both trucks, and each has brushed motors

For the first time ever yesterday I used the Castle Link software (?) to set my CC BEC and my CC ESC - this was incredibly fast and easy!

I'll never go back to counting beeps again.

Never!


My test runs yesterday were trouble free - everything worked exactly as it was supposed to - awesomeness!