ESC's and BEC's

[Raften]

I have a slight understanding of these things. As I understand it a good quality ESC will have a built in BEC and the function of the BEC is to supply a constant voltage to things that need power other than the motor, like servos and such. A stand alone BEC will do the same but perhaps a more reliable job since it is not part of the ESC.

I have been reading that people are starting to connect brown outs on 2.4 systems to a failure of the built in BEC. And the fix for that may be installing a stand alone BEC. The amp rating of the BEC is dependent on the number of devices the plane has and the higher the number the higher the AMP rating of the BEC ???

Am I anywhere close to correct in my limited understanding of all this?

I also have a question as to where in the system a BEC goes, does it connect directly to the battery or into the Rx?
Thanks, Jim

[Pete Lane]

Hello Jim.

You are correct in your understanding of the function of a BEC. Castle Creations makes a 10 amp BEC, thats very good,runs up to 6 full size servos, and is the one I use.
The BEC gets soldered into the outgoing battery leads and plugs into the battery port on your recever, the ESC goes into the channel three port.Some require you to snip the red wire on the ESC to disable its BEC, dont snip the wire, just depress the pin and pull out the prong and tape it up so you can use it again.
Their are other devices such as a battery share, and a UBEC that I use in my 20-35 volt Jets also.


Pete Lane

[7rider]

Another trick to disconnecting the red wire of the ESC is to use a short extension between the ESC and the receiver. Just remove the red wire with the extension, and the ESC is untouched.

Some higher end ESCs also have switching vs. linear BECs. Dimension Engineering has a nice article on the differences between the two:

http://www.dimensionengineering.com/swi ... lators.htm

The standalone BECs that Dimension Engineering and Castle Creations sells are switching regulators.

One other thing to remember is that if you add a battery with more cells, it's going to decrease the amount of amps a linear regulator can handle. So an ESC that was running fine on 3S might be overloaded with a 4S battery.

[7sp]

Sometimes a pic is worth the proverbial 1000 words....

cc_bec_wiring_diagram.jpg (143.91 KiB) Viewed 209 times

7SP

[Raften]

Thanks for the picture, helps to see the layout. I am considering adding a BEC since I had a suspected 2.4 glitch very high and out over a lake last week. My Radian would not have taken kindly to a swim. I should be able to get by with a 3 amp BEC for that plane (R/E) should I not?
Thanks, Jim

[7sp]

Assuming that your running a 3cell pack. A 3-AMP switching BEC (also called a UBEC) should be more then enough for 2 standard mini servos. The normal 2-3 cell ESC with a built in linear(non switching) BEC was around 1.5 Amps and that was OK for up to 3 micro servos with a 3cell pack and 4 micro servos on a 2cell pack. The problem became more apparent once digital servos and more power sensitive 2.4Ghz receivers hit the market. Keep in mind that the AMP capability of the linear BEC is a function of the number of battery cells. The more cells the higher the voltage. The higher the voltage the harder the BEC has to work to reduce that down to a voltage that is usable by the receiver and servos. The harder the BEC has to work the less AMPS it can deliver.

7SP

[Raften]

Switching BEC means you can select the output voltage instead of a single fixed voltage?

[7sp]

Switching BEC means you can select the output voltage instead of a single fixed voltage?

NO. Without getting to deep into electronics. There is two types of circuits "Linear" and "Switching" used by the R/C manufactures to take one voltage and reduce it to a lower voltage. "Linear" being the old and not so efficient method and "Switching" being the newer and much more efficient design. The better efficiency is that it wastes less of your battery as heat, by the use of a Very high speed switch. You can think of it as flipping a light switch on/off so fast that the light can never fully come on. So in this case, switching so fast that the full voltage is never reached and there by lowering the output voltage from say, 11 volts to 4 volts.

7SP