79 replies to this topic

[cbr6fs]

I have been asked to start a thread on fitting a BEC to surface vehicles, so will try me best.


Thought the best format would be a question and answer type layout.

Q/ What is a BEC?

A/ BEC stands for "Battery Eliminator Circuit"
Traditionally most RC products run off 7.2v and higher, this is great for the motor and Esc, but most Rx's and servo's run off 6v.
So rather than run a separate 6v battery supply for the Rx and servo manufacturers started incorporating and BEC into their Esc's.


Q/ Doesn't my Esc already have a BEC

A/ Chances are it has yes


Q/ So why do i need another?

A/ Most manufacturers use very poor BEC's in their Esc's, these tend to work out for cheaper servo's but once we start to upgrade to faster stronger servo's they really start to show their weakness in providing good solid amps to both the Rx and servo.


Q/ How do i know if i need a BEC?

A/ In my opinion, if your paying £30+ on a servo then £10 on a BEC is an extremely wise investment.
Not only will your stock servo run better (so you might not need the upgraded servo) because your now supplying good consistent clean power to the Esc, this will also run better.


Q/ Any downside to running a BEC?

A/ Only real downsides are:
1/ Your wallet will be just over £10 lighter
2/ There are more wires knocking around your chassis
3/ Fitting it


Q/ What are my BEC options?

A/ There are many many BEC out there, it really depends on what servo/servo's your running and what voltage you want to run them at.
For 99% of our surface vehicles something like the Castle Creations BEC will be more than adequate.



It operates up to 6S input voltage and outputs from 4.8v up to 9v.
As it outputs up to 10 amps, it's enough for all but the wildest servos and applications.

If you want more there is also the Castle Creations BEC Pro



This operates up to 12S and outputs from 4.8v to 12.5v with 20 amps peak output.

There are many many more BEC's out there from the likes of Futaba, Hobbyking etc etc but these are the 2 examples i'm most familiar with.






Cheers
Mark

Edited by cbr6fs, 25 March 2011 - 10:07 AM.

[cbr6fs]

Q/ How do i connect the BEC?

A/ Obviously you need to connect the + and - input wires of the BEC to the battery.
For the BEC's output though you have 2 options here:

Option #1
Connect the BEC to the Rx.
This will power the Rx then the servo from the Rx



This will only work if you have a 3 channel or more Rx, or the Rx has a power input (as used by Nitro's) like on say the Hitec Rx's.

As standard your Esc provides power to your Rx (then to the servo) via the connector the Esc connects to the Rx with.
This is the 3 wire cable with the servo type connector at the end.

Now because we are now powering the Rx via our BEC we no longer need the Esc's power input, so we MUST remove the red wire as illustrated in the diagram above.

Word of caution though, most Esc's today use this connector to program our Esc's.
If you cut the red wire then the programming card or castlelink will NOT work.

For this reason i highly recommend that you buy a short "servo extension cable"



You will then remove the red pins by prying open the connector like so:



Then gently pulling the pin out.
Once both ends are removed, either tape the up out the way, or just remove the red wire entirely.






Cheers
Mark

[cbr6fs]

Option #1 is probably the easiest way.


Problem is though, if for some reason you get your servo's into a bind and pulls more current than the BEC can supply your Rx will brown out, or loose connection with the Tx.

The other thing is, if you have a high voltage servo and you Rx only works up to 6v that means that your lovely expensive servo is working no where near it's potential and the potential you've paid for as your Rx supply is restricting it to only 6v.

In these cases the best method to connect the BEC is straight to the servo, bypassing the Rx altogether.


Option #2



To clarify you have 3 wires coming from your servo, the colours vary but for the sake of simplicity we will use the wire colours shown in the above diagram.
Yellow = Signal wire
Red = + wire
Black = - wire

The signal to operate the servo still needs to come from the Rx, so this wire still needs to connect to the Rx.

For the - and + wires though we will wire straight from the BEC.

Again rather than cutting up Esc and servo wires i would strongly advise to buy a short servo Y-harness.


Just like the Esc, for some BEC's like the Castle Creation ones, to program the BEC you will NEED all 3 wires from the BEC to connect the Castlelink to.
So i would highly recommend leaving the BEC harness alone and cutting up the Y-harness.

You want 1 wire to the Rx (yellow in this case)
2 wires from the BEC (red and black)
All 3 wires congregating into the servo input, like below.



Personally i much prefer option #2 as it frees up the Esc to supply power to the Rx, so unless your Esc burns out you know you have Rx power.
Plus even if the Esc does burn out, you know you still have steering.




Cheers
Mark

Edited by cbr6fs, 25 March 2011 - 01:10 AM.

[R46]

nice write up mark i see it as if more then 3s running bec wise investment

deserves sticky +1

Edited by R46, 25 March 2011 - 01:14 AM.

[cbr6fs]

Q/ What about after i'm connected do i need to do anything else?

A/ Before or after you sort out the connections on most you will need to program the BEC to your desired output voltage.
With the Castle Creations BEC's you will need to plug in your CastleLink to the BEC's 3 wire output and start the CastleLink software.

Once connected and the software started you should see this window.



I've not yet seen any BEC software upgrades, so you should be good to go to the "Basic" tab to set the voltage.



As you can see from the asterisk, from the factory the standard CC BEC comes configured to 5.1v.
You need to check with your servo manufacturer as to what voltage you need to set it to, on my Hitec 7980 i'm running at 8v.
My Turnigy HV300 runs up to 12v so as the basic BEC only ran to 9v i ran this servo at 9v.

Find out your servo's recommend voltage, set it to that, press the "update" button to send the change to the BEC and your good to go


That's about it really.


I can't recommend using a BEC highly enough, the BEC's used in both MMP and MMM in particular are extremely poor, i'm able to brown out my Rx with both these Esc's supplying the Rx even with relatively mild servo's.
For just over £10 i honestly believe they're a great investment, as i say only downside is the extra wiring knocking around your chassis


Hope this helps, i'm by no means any expert, but i've wired up a few BEC's now so if i know the answer i'll happily answer any questions.



Cheers
Mark

Edited by cbr6fs, 25 March 2011 - 01:26 AM.

[Guns]

Didnt know I could connect my BEC to my CAstle Link, Spose I better do that next lol

Do I just plug the BEC into the Castle link I use for my MMM?

Thanks

[78.8]

Guns, on 25 March 2011 - 07:50 AM, said:

Didnt know I could connect my BEC to my CAstle Link, Spose I better do that next lol

Do I just plug the BEC into the Castle link I use for my MMM?

Thanks

Yes, use the same link

BEC will have a little green light to show its on

[Guns]

Cheers, any one know what Voltage the Savox 1256 is best used at?

[notfast]

what is BEC??

[zebrevo]

Battery Eliminator Circuit

Uses the running batteries in an electric car to power the servos, rather than having a seperate 4xAA pack, or hump pack.

Most ESC will have one built in - but if running high voltage batteries, they tend to be inefficient and an external BEC can be used, offering advantages as described above.

http://en.wikipedia....minator_circuit

[notfast]

Thanks

[cbr6fs]

notfast, on 25 March 2011 - 09:26 AM, said:

what is BEC??

Great question, added to the first post

[cbr6fs]

Guns, on 25 March 2011 - 07:56 AM, said:

Cheers, any one know what Voltage the Savox 1256 is best used at?

6v
http://www.savoxtech...ile/SC-1256.pdf

[sonik]

excellent thread , much needed, agreed with R46 sticky is needed , i use a Y-harness though to connect my bec rx connector to one end and esc rx connector to other then into the rx itself , still trying to get my head round how to do it with just a servo extention ? where would both the esc and BEC leads go ? 1 would be left out ?

just re-read the thread and you already explained that excellent write up

Edited by sonik, 25 March 2011 - 12:05 PM.

[carmst74]

So by yoiur theory, if i run my ace in my lightning, i should fit a BEC???