PDA

View Full Version : How to build simple BEC?

Ceeray
Apr 24, 2005, 04:46 AM
I am making a plane which needs 3 micro servos, 1 retract servo and 2 sub micro servos. So I need other BEC than whats in my CC25. So how to build one? 3S lipos in use.

My friend can make it , hes trained for that but if you people here have some ideas I can use it would be appreciated!

Thanks!
Bruce Abbott
Apr 24, 2005, 07:38 AM
A BEC is just a voltage regulator. Any standard 5V linear regulator IC that can pass at least 2A should work, eg. L78S05, LT1085-5, KA78T05. A good sized heatsink will be required to keep it cool.

Make Your Own BEC (http://ann-neil.supanet.com/BEC.pdf)
Ceeray
Apr 24, 2005, 07:54 AM
Thanks , that was just what my friend thought too! How about taking some power from ESCīs BEC and then powering some servos from separate BEC?

Or putting 2 chips parallel, could I get about 4 A max?
jperch
Apr 24, 2005, 10:33 AM
I wouldn't recommend connecting two regulator chips in parallel. Slight variations in the two chips will cause one to try to pump current into the other. They don't generally like that.

You could work up a circuit that would power some servos from your ESC's BEC and the others from the one you make. But that is going to make for a somewhat complicated wiring setup. I suggest you just build or buy a BEC that can handle the entire load. Also make sure you disable the BEC from your ESC when you do this.

Joe
vintage1
Apr 24, 2005, 07:06 PM
Thanks , that was just what my friend thought too! How about taking some power from ESCīs BEC and then powering some servos from separate BEC?

Or putting 2 chips parallel, could I get about 4 A max?

Ther are some regulatots that will do 4A. As long as its not for very long (heat) but off hand I don't have part numbers.
KnimRod
Apr 24, 2005, 09:41 PM
Don't forget power dissipation.. Linear voltage regulators control the voltage by effectively adding "resistance" in a series circuit. The current in a series circuit will be the same everywhere so the regulator's power dissipation will be (Vin-Vout)*I watts. In this case, that's 14 watts for 2A and 32 watts for 4A (all worst case). Keep that in mind when designing around a linear regulator. This is the beauty of the switch mode regulators like the UBEC.