A little confused with BECs

[davidq19]

So I've done some reading up on BECs and I kind of understand it for rc planes but I'm a bit confused when it comes to rc cars. I have a tekin rs and the on board bec says it outputs 6 volts. I also have a hitech 645 servo and it says that it can take 6 volts. So if run a 3s lipo why will I need to install a BEC? What am I missing?

[warriorsimi]

from what i understand the esc only puts out so much voltage for the servo ,even though it can handle 11.1 volts .so it must have some sort or regulator so it won't burn up your servo the castle bec can be programmed for higher voltage for servos that can handle the higher voltage with the programming cable.

[Solitaire]

It's not the voltage, but the amperage the ESC can handle. Most users running 3S LiPo's and super strong servos use 10 amp BEC's to handle the load. Many ESC's can only handle 5 or 6 amps.

[davidq19]

Originally Posted by warriorsimi

from what i understand the esc only puts out so much voltage for the servo ,even though it can handle 11.1 volts .so it must have some sort or regulator so it won't burn up your servo the castle bec can be programmed for higher voltage for servos that can handle the higher voltage with the programming cable.

So the tekin rs says it has a 3amp bec 6 volts. it shouldnt put out anything higher to my hitec 645 servo right? I would need a BEC if I want my servo to get more volts, through programing it?

[fknfastintegra]

Originally Posted by davidq19

So the tekin rs says it has a 3amp bec 6 volts. it shouldnt put out anything higher to my hitec 645 servo right? I would need a BEC if I want my servo to get more volts, through programing it?

I dont have a tekin, in theory Yes your stock bec volt shouldnt exceed 6v. If you want to get more volts thru your servo then yes you would need an external bec, via programming it.

[GrimJeeper91]

The magic question here is how many amps do servo's draw? This data is never published in servo spec's. I emailed both JR and Hitech and received no response. I've spent quite a bit of time Googling this and never found anything definitive. Does anyone have any published data that documents this?

[The Violator]

Since I have never spoke on this subject I will weigh in. Why are you fighting it? $23 for a bec. They are like prison sex, you can fight as hard as you want, in the end its gonna happen. My advice is to try it without. BUT do not post all the stupid questions about why your car goes nuts when you turn, why it loses power, why it burned up the esc and servo. Just do it and prove everyone else wrong on why they added a BEC and did not have issues without one.

Or you could just add one because the stock bec inside all esc's was meant to power a 60 ounce servo in an on road car with a 3" tires. Unless thats what you have an external power source would be a great idea to power your servos.

[Harley]

Unless you want to get into the physics of how going up in voltage drops the power of the internal BEC just buy the stupid thing.

I'm also moving this out of the Wraith forum. This is an ELECTRONICS question that has nothing specific to do with a wraith.

[crawlhog]

HEY DAVIDQ19 if you dont think you need one then dont get a BEC, apparently you have all the answers and you know what works and what dosent. youve got threads all over asking the same stupid stuff. several people have answered your questions allready but you still seem to know better.

[Charlie-III]

David, sorry, we get a bit wound at times since this is a common question.

Yes your ESC BEC can supply 6vdc to the servo.
Yes, your ESC BEC can supply some amount of amps to your servo.

When you jam the tires between rocks and what to turn your tires, or, you did not set the steering EPA's correctly, even a low torque can draw quite a few amps.
My general rule of thumb, up to ~200inoz rated servos can work OK just off the ESC BEC. After that, you run out of amp supply which WILL cause a RX "brownout". This means the rig may stop, the rig may glitch, you may burn out the servo or ESC.

Above ~200inoz, you WILL need an external BEC (unless you run a Holmes Hobbies BRXL ESC) to get maximum use out of your servo dollars spent as well as save the rest of your electronics.

Your choice.
Have a nice day.
PS, search in the electronics forum for "brownout" to see what people describe and what the solution is.

[Meatwad]

Originally Posted by The Violator

Since I have never spoke on this subject I will weigh in....

Lol

To the op: if you were running 2s you could *probably* get away without a bec, although still not healthy for the electronics. But since your esc has to kick down the voltage about half (12.6 to 6) for the internal bec, not only does the amperage spec go down its working too hard. Just get one and sleep more soundly at night. You will never even thank anyone that your stuff is still working, it'll just keep working.

[Charlie-III]

Originally Posted by The Violator

Since I have never spoke on this subject I will weigh in.

Now I understand........(just got caught up in the forum....)

[davidq19]

Got it, thanks for all the info. Sorry for posting similar threads just new to all this and just trying to get some info and oppinions.

[Harley]

Originally Posted by davidq19

Got it, thanks for all the info. Sorry for posting similar threads just new to all this and just trying to get some info and oppinions.

Limit it to one thread per topic, or search first because most all the answers are all readily available.

[Grizzly4x4]

Originally Posted by Harley

Unless you want to get into the physics of how going up in voltage drops the power of the internal BEC just buy the stupid thing.

It's all about power, P=IV (power = current x voltage). The internal BEC can only handle a certain amount of power so the higher the voltage drop across the BEC the less current it can handle.

Back before there were external BECs I posted this about running a voltage regulator.

Originally Posted by Grizzly4x4

The instructions say that it is designed for 5 cell NiCd/NiMH and 2 cell LIon RX packs but MPI told me that as long as the 20 watts is not exceeded the regulator will be fine.

So what does 20 watts mean?
With an input of 7.2V, and an output of 6.0V; it can handle 16.6 amps of current draw from the servos.
With an input of 11.1V and an output of 6V; it can handle 3.9 amps of current draw.
To calculate this you need to know the voltage drop across the regulator. That is found by subtracting the output voltage from the input voltage [input(V) - output(V)], then divide 20 by that number.
Current(amps) = 20(watts) / voltage drop(V)
For my setup: voltage drop = (11.1 - 7) = 4.1V then current = 20 / 4.1 = 4.88 amps
If I want to draw more current I have to raise the output voltage to be closer to the input voltage. However, the output voltage must always be at least 1V less than the input.

[D-Ride]

Im so confused....Im just gonna go order one..

[Charlie-III]

Originally Posted by Grizzly4x4

It's all about power, P=IV (power = current x voltage). The internal BEC can only handle a certain amount of power so the higher the voltage drop across the BEC the less current it can handle.

Back before there were external BECs I posted this about running a voltage regulator.

Very nice write-up Griz!

[Grizzly4x4]

Originally Posted by Charlie-III

Very nice write-up Griz!

Thanks Charlie.

[GrimJeeper91]

Originally Posted by GrimJeeper91

The magic question here is how many amps do servo's draw? This data is never published in servo spec's. I emailed both JR and Hitech and received no response. I've spent quite a bit of time Googling this and never found anything definitive. Does anyone have any published data that documents this?

So does anyone actually know how many amps these these are drawing? Not just speculation, looking for published data.

[Rig Rocker]

This is such an interesting and informative tech thread! I think I need to go buy one of these so called bec thingies