Onboard RX batt kept charged with BEC?

[DeaninMilwaukee]

I'm in the planing stages of doing a 1/2 scale Stits fly baby: http://www.airventuremuseum.org/collection/aircraft/Stits%20Sky%20Baby.asp that I will be powering with a123's and started thinking about what would be the most reliable RX power source possible.

After finding out that the CC bec is programable at 0.1v increments, I came up with the idea of setting it right at the voltage a full rx battery would be, ( 5.4v?) for the purpose of keeping the rx batt " topped up" at all times.

Done this way, you'd have the " always charged " convenience of a bec only system, with the safety of a built in backup battery taking over seamlessly if the bec or main flight battery should ever fail, or the the other way around with the BEC taking over if the on/off switch or rx battery would fail in the rx batt half of the system.

Wiring would be very simple, ( y harness), and the only real downside seems to be the small weight penalty of the RX battery.

So what do you guys think? Am I missing a good reason that this is a bad idea?

Dean in Milwaukee

[rebell]

This sounds like a good idea. I am not an electronics expert, but the only thing I can think of is: what will happen if the main flight battery fail, will the power from the RX battery not drain excessively fast through the BEC? OK, you only need the power for a short time for landing, so high drain will not be a big problem. Better that and have backup power. I guess you will have to try it on the ground.

[DeaninMilwaukee]

I'm fairly certain that juice can only flow on way through a switching bec, so that scenario should'nt be possible, but I'm going to look into it to be sure. Thanks.

Anybody else?

Dean in Milwaukee

[Carl Petersen]

A general solution would be to use a diode in series with the BEC output to block any reverse current flow. You'll have to raise the BEC voltage slightly to compensate for the diode forward voltage drop. This would work for any BEC circuit design.

Another advantage could be that the battery can smooth out the high current spikes seen when say all the servos are moving at once under load.

Interesting...

[karl k]

I'm fairly certain that juice can only flow on way through a switching bec, so that scenario should'nt be possible, but I'm going to look into it to be sure. Thanks.

Anybody else?

Dean in Milwaukee

To make sure you won't back feed and cause problems with the BEC, you could install a diode in the BEC wiring and raise the voltage 0.7v to compensate for the forward voltage drop of a silicon diode.

Karl

[Carl Petersen]

A Schottky diode would be a better choice.