two fxr's two 3amp bec's why run an external
 

I have been in r/c for 20+ years and I have 2 fxr's in my xr10 and I don't see any need for another bec, the 2 onboard bec's put out 3amps ea so why would I need to add another bec. I haven't experienced any issues running them like this so what am I missing?

Re: two fxr's two 3amp bec's why run an external
 

Simply put, if you're running a "power hungry" servo, it can probably pull more than the 3 amps when you stall it out. Just cause there are 2x 3 amp BEC, doesn't give you 6 amps to use. Just what my brain is telling me, feel free to correct me if needed. "thumbsup"

Re: two fxr's two 3amp bec's why run an external
 

no it will give you 6 amps of bec power. just like if you had two 5 amp power supplies you could charge at 10amps. I am thinking people are just doing as they have always done, lol

I have a degree in electronics, so I am 100% sure on my logic. But there might be some real world expieriances that show me something different, lol

Re: two fxr's two 3amp bec's why run an external
 

Pretty much all manuals for all ESC's state to remove one red ESC/RX wire (when running dual ESC's) since you are NOT supposed to run 2+ BEC outputs into a single RX. You WILL eventually burn something out or up. If you run an external BEC into the RX, you need to pull all ESC red wires from the RX.

Now, you are back to a single 3A BEC which can be fine up to ~200inoz steering servo.

Either use smaller output servos or run an external BEC. Your choice.

PS, I've been in RC for many years as well. It was not until I got into crawlers that I had a need for more amps than what the ESC BEC could provide.

Re: two fxr's two 3amp bec's why run an external
 

Fixed it.

Re: two fxr's two 3amp bec's why run an external
 

So this would explain why my buddies FXR LED temp goes to being fully lit after a few minutes? Also his power cuts in and out. He is running a Savox 1256 20kg servo.

I am running something fairly crap in mine (probably 7kg) with the FXR and i don't have any issues and temp is @ 1 led.

Re: two fxr's two 3amp bec's why run an external
 

lol, it is a wierd setup for sure, I run a external bec on most my cars, but man it is making my head spin on why i would need one with two bec's, lol

and thanks for the response duuude, I could be 100% wrong but still 100% sure, lol iff I was 99% sure I still would have no idea, like the beer commercials, lol

Maybe someone from tekin or novak could chime in on this

This is a joke right?

Edit: Sorry for not following along...

Only 2 3amp bec's? I've got 2 castle 10amp bec's set at 12v plugged into my rx...

Re: two fxr's two 3amp bec's why run an external
 

I am no electrical engineer so I wont use any fancy terms but the problem is something about them being switching voltage regulators (I think that is the correct term) and they will fight one another if there is more than one powering the same device.

Re: two fxr's two 3amp bec's why run an external
 

If you running a 3 cell lipo you need a castle BEC.

Re: two fxr's two 3amp bec's why run an external
 

You are 100% wrong.

Two 3a power supplies are still only good for 3a's total.

Are you sure you aren't confusing your electronics degree for a math degree?

Re: two fxr's two 3amp bec's why run an external
 

how do you come up with that, if you have two 3a power sources hooked in parallel then your total capacity for current draw is 6amps, sorry duuuuuuude but you are just plain wrong go back to electronics 101.

I can't believe how backwards some people are on here about electronics.

Also it is a regulated power source so no external bec is needed for 3s. I run 4s with speedo's in my boats with no external bec.

Just put a bec on everything, don't worry about it.

There obviously is not much manufacturer support on this site. I have a message into the president of tekin, I am sure I can get a legit answer from him I will post it up on here when I am get a reply.

Please don't clog up my thread, your opinion are on here. Hopefully someone who actually works for the company can post a good reply.

Re: two fxr's two 3amp bec's why run an external
 

If it were possible, it would be done, but its not. But hey, I don't have a fancy degree so wtf do I (and many, many, many other people here) know?

Go ahead, hook your two internal bec's together and see how wonderfully they work in harmony.

Connecting power sources in parallel is not the same as connecting batteries in parallel.

Re: two fxr's two 3amp bec's why run an external
 

Even if 2 3a in parallel made 6a which I believe only series would do that, 6 amps isn't enough for most high end servos. The castle bec I run is 10 amp. And I was told, the higher your battery voltage the less amps your bec is, I am not electrons wiz just trying to help.

Re: two fxr's two 3amp bec's why run an external
 

Parallel double the amp capacity, series doubles the voltage. Theoretically. It doesn't always work out that way in the real world.

Re: two fxr's two 3amp bec's why run an external
 

See I told you I don't know much :oops:, but I found this out on the web and this guy seems to know his stuff.


"The feedback circuit of the regulator with the lower rated voltage (IC1) would simply turn of it's output stage. So the regulator with the higher rated voltage (IC2) does now the voltage regulation and provides all current.

If the load current increases beyound the current limitation of IC2 the voltage starts sagging as the typically linear regulator goes into constant current mode. When the voltage sags below the rated voltage of IC1 this regulator will open the output stage and maintain it's rated voltage.

Provided that the designers of the regulator did their job well this is a piece of cake and is quite offten used in applications to stage regulators.
Most dual lab-power supplies allow this parallised mode as well.
I've seen quite a few commercial ESCs using two linear regulators on the board.
So it does work.

To summarise it: Trouble with paralleling linear[!] regulators is a urban myth derived from suppliers just telling you this mode is outside their guarantees.
So it's not a technical but a legal issue.

Switching mode supplies are a different category.

The trouble is your expectation. You WON'T get twice the current and one regulator will see the full load and hence the higher temperature.
So eigher make shure one ESC can provide the Rx and servo power or split the output among the servos.
But "disabling" one BEC in a twin is rather useless. You won't get less trouble than with both parallel. "

Re: two fxr's two 3amp bec's why run an external
 

wow why even clog the thread with all the useless posts

and duuuuuude you obviously know what I am saying since you know parallel multiplies the capacity.

What are the other factors that make it a bad Idea, I am running one battery for both speedo's so I don't see your thing about harmony. I am pretty sure people are just hooking up external's because that is what the guy before him did. If I burn it up then I guess I learned, but I think it will be fine.

Re: two fxr's two 3amp bec's why run an external
 

Yes and no...in the perfect world doubling up to vr's will double the current handling capability. However in the real world, issues occur. Basically VR's have a feedback loop (basically monitors output voltage), as the output voltage fluxuates it will cause the vr to increase or decrease the output voltage so it stays as constant as possible. The slightest difference of voltage (millivolts) seen on the output pin (between the two vr's) will cause one voltage regulator to take on the entire current load till it can't keep up then the 2nd vr will start taking the rest load so the output voltage doesn't continue dropping. Working the BEC in one esc at 100% all the time and the other only picks up the lag will cause serious heat issues in one of the esc's, burning up its BEC, then you're out an esc. It may also cause issues on the esc's normal operations because the internal BEC actually is what powers its brain, so if that voltage isn't very constant/steady/where it needs to be, then you'll get funny business out of it.

Now, circuits can be designed so two can be doubled and balance a load, but i'm confident that our esc's weren't designed to have their internal BEC's paired up with another...

Bottom line, get an external bec

Re: two fxr's two 3amp bec's why run an external
 

And if you don't want to run an external bec, use your esc bec to power the rx, then run your servo direct off the lipo....

Re: two fxr's two 3amp bec's why run an external
 

Its also important to note that the amp rating of a BEC changes with the input voltage, higher the voltage the lower the amp output the BEC is capable of.

A CC 10A BEC is rated at 7a with a 12v input (roughly operational voltage of a 3s lipo). I dont want to know what a 3 or 5a BEC would actually put out when running a 3s pack, this is the reason why there is a need for a better BEC when you increase input voltage.

The reason why your boat is fine running on 4s with the internal BEC is because there is a lot less load on the servo. When is the last time your rudder got stuck between two rocks and you had to wiggle it free?