Need to understand BECs better

[Captain Midnight]

I have a Venom Creeper with a Rooster 2s ESC.
I read that Jake Wright didn't run a BEC so I figured ok that works for me, I'm not running a BEC either. Im only running a Hitec 645 servo, but after seeing what a difference more torque makes I want to run a stronger servo, the CS 170 or hitec 7950 or 7954.
That one will probably draw more power which brings me back to needing to understand BECs again.
I get what BECs are supposed to do, but how do they do it?
Is it basically a capacitor that stores power to ensure the right voltage goes to my servo?
I keep reading about people smoking BECs all the time. What causes that to happen?
How much does the BEC and all its wiring weigh?
The reason I'm asking all that is cause I'm was thinking that a small dedicated 2s lipo might be a way to go.
The roosters instructions advise you can run that way, just don't turn the speedo on and power it with the external battery.

• Benefits - Only one lead going into the receiver and no rats nest of wires to contend with and no programming to deal with.
• Drawbacks - weight and finding a home for the extra lipo.

Has anyone looked at the weight penalty and or the run time that a small 2s would provide?
I admit I just hate having a rats nest of wires in my RC Cars and a Value simple (to me) over complex solutions so I have not embraced BECs, YET.
Can you help me to get why they are so necessary?

 

[Stew]

BEC's of course take power from the main battery and regulate it down to the voltage your receiver requires. Back in the day when 6v packs were common there was no need for circuitry since the voltage was the same with the main battery and the receiver battery, all you needed was a connector coming off the main battery that plugged in to the receivers 'batt' connector.

Now a days with main batterys coming in 7.2v, 8.4v, and higher you need to bring that voltage down to 6v for the receiver, and receivers can accept the incoming power through servo ports, you do not need a separate connector for the 'batt' port.

When you say people are smoking BECs all the time, do you mean ESCs? The BEC is an integrated component of the ESC, they are not separate. It would not be a capacitor that handles this function, a capacitor is used to store electricity, it is a voltage regulator circuit.

You would need to read the spec's of the ESC to see what the max power rating it can provide to the receiver, then get the spec's for all your servos and make sure you are not exceeding the power rating for the BEC circuit in the ESC.

 

[JeremyH]

The BEC is an integrated component of the ESC, they are not separate.

He is probably talking about an external BEC.....separate from the ESC.

And CM, you I have read of folks running the servo straight from their 2S lipo.....just make sure that your servo will handle the 8.4V peak that comes out of them. "thumbsup"

 

[Captain Midnight]

Yes I was talking about external BECs like the CC BEC.

 

[Narly1]

Check out these 2 links.

At the heart of your CCBEC is a switching regulator circuit.

http://en.wikipedia.org/wiki/Voltage_regulator#Switching_regulators

http://en.wikipedia.org/wiki/Voltage_regulator#Comparing_linear_vs._switching_regulators

Narly1

 

[Captain Midnight]

"such as a 5V microprocessor often in "sleep" mode fed from a 6V battery, if the complexity of the switching circuit and the junction capacitance charging current means a high quiescent current in the switching regulator)."

HUH?

Is there a dumbed down version?

 

[Chi Town]

The reason you run a bec is this:

If your esc and servo are wanting the same amount of volts, the esc will win. Your servo will be under powered thus making less torque and less effective.

I have been to enough crawling comps to have never seen someone power a servo thru an external bec and separate battery.

I run a 7955tg with a ccbec set at 6.5v and have not had a single issue in over a year. I also run the same setup on my scaler, no issues there either.

I think those that burning up BECs are running the volts to high.

I think if you look thru build threads you will find people run a bec, but not a separate battery.

 

[Narly1]

"such as a 5V microprocessor often in "sleep" mode fed from a 6V battery, if the complexity of the switching circuit and the junction capacitance charging current means a high quiescent current in the switching regulator)."

HUH?

Is there a dumbed down version?

Try this (from http://www.dimensionengineering.com/switchingregulators.htm ):

"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."


Narly1

 

[Digger]

I am guessing here, but running a TS170, cs170 or 7955 servo, 2s goat 18.5 and LNC lights would warrant adding a CC BEC to the setup? Up until now I have been running a 5645 hitec without an external BEC and everything has been working pretty well, but I need to upgrade the servo to something with more power, so I suppose I have to feed it more power, too...