EDF rx for 6s lipos to solve BEC problems

[RMatteson]

Any one know with all the 6s EDF jets out there, why isn't there a rx that could handle 25 volts from a 6s and distribute a workable voltage to servos and retracts, with out a BEC? Many of the threads go into flyers putting a separate battery for rx. With weight concerns, wouldn't a larger amp BEC do just as well? What kind of batteries are being used? I have just got a FW T-45 and have read some flyers are having crashes with brown outs, which is blamed on BEC. so what's the story on this. Pushing too long a flight or is the 8 amp BEC not large enough? I see CC has a larger BEC that is programable to 20 amps. I don't care if all I get is a 2-3 minute flight, but what I do care about is crashing a plane with a voltage problem. I'm hoping some of the jets jocks with time on a lot of different jets could reply to my questions.
Thanks for your time, RICK

[PikeStaff]

Understand that a brown-out is not automatically a failure of the BEC - there are other sources that can cause one, like bad or broken solder joints, bad battery connections, etc. If something in the power circuit causes voltage to drop below the minimum the receiver will operate at, you have a brown-out.

The BEC in most ESC’s is usually adequate to its task; being integral to the ESC does expose it to heat generated by the ESC. Heat is an enemy of any electronic device, and contributes to increased circuit resistance....which, in turn, can reduce voltage from the BEC.

Folks turn to discrete BECs as a way of getting around that - no added heat input from other sources. Plus, the separate BEC can be picked for its voltage and/or amperage output, something not typically available from the built-in BEC. And since the discrete BEC gets its power separately from the ESC, it isn’t subject to losing power should something happen to the ESC....like melting down or having capacitors erupt due to power draws. It happens. :(

Running a separate battery essentially does the same thing as running a separate BEC; it isolates the power supply from the ESC. Two ways to skin a cat.

The weight penalties for either option aren’t too big - in the case of a discrete BEC, typically less than 20 grams. A 500 or 600 mA battery (2 cells) adds a little more, somewhere in the range of 100 g or so. Not monumental, and can be a good aid toward getting some planes balanced. Truly, not enough to cause any kind of real concern in a typical EDF.

A lot of us have lost a plane or 2 to power system failures; doing a post-mortem on the jet can help determine just what failed. While I have had what I believed to be spotty BECs in some instances, it usually turned out to be failed/intermittent connections. The ones where there was no doubt, however, were when destruction of the ESC took all power out with it. And as a consequence of those, all my planes carry discrete BECs now. Small, easy peace of mind.

[fhhuber]

Spektrum Brown Out is by definition : Inadequate power to the RX.

From there you need to find out WHY you have inadequate power.

Excess servo load due to servo binding can do it. A single HS 55 servo can draw almost 2 amps when "stalled" (gets hot fast and the case will start to melt if stalled too long)

Intermittent connection between supplying battery and RX. That can be a bad solder joint or some failure in the ESC's BEC section (or failure of a stand-alone BEC) or broken wire...

Too many servos (or servos that are too large) for the power source.
I have a model that just by "stirring the sticks" can pull RX voltage down to 3.9V using a pair of 5 cell NiCd Sub C 3200 mah packs via 2 switch harnesses to supply the RX (that's 15 amps of RX/servo system power...). I changed that plane to using a "Powersafe" RX that has a pair of 12 gauge power input leads and a pair of 3200 mah 2S LiFe.

The list of why you might not have adequate power to the RX is long... The important thing i to note that you have a problem and you need to find what it is, then solve it before flight.

ALL of my models using >4S LiPo power systems use separate LiFe pack(s) to supply the RX.

[fhhuber]

Note that Spektrum RXs can accept 2S LiPo direct and there are servos that can handle that voltage now.

If you need the HV servos.. you need to supply the RX and servos separately (not using BEC from the main battery) from the ESC/ motor power system.

[mongo]

just a real quick throttle change could wreak havok with a direct 6s lipo rx power system...

[RMatteson]

Thanks for the replies, it give me some things to check over before I take up my FW T-45. I've been flying the bigger 1600, 1700 and a 2000mm span war birds this summer, after leaving the big gas planes, because of noise. I hope to get as much jet time as I can.

[RMatteson]

Sure wish they wouldn't call some one new to the forum Student Pilot, as I feel it gives the impression that you are new to RC planes. I have been flying for over 45 years, but new to electric power. Hope to use the jet jocks knowledge again when some comes up.
Rick

[Rcjunkey]

Sure wish they wouldn't call some one new to the forum Student Pilot, as I feel it gives the impression that you are new to RC planes. I have been flying for over 45 years, but new to electric power. Hope to use the jet jocks knowledge again when some comes up.
Rick

That is a generic fill in when someone signs up for the first time, you can go to your personal settings and change it to anything you want

[seaviper]

Thanks for the replies, it give me some things to check over before I take up my FW T-45. I've been flying the bigger 1600, 1700 and a 2000mm span war birds this summer, after leaving the big gas planes, because of noise. I hope to get as much jet time as I can.

You will love the T-45. It's a great jet trainer