Separating retract power from Rx battery...will this work - RC Groups
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Aug 02, 2012, 03:15 PM
Registered User

Separating retract power from Rx battery...will this work

Hi everyone

Getting back into flying after about 16 years away. Flew nitro then, decided to try electric now.

I got a Durafly P51, Spektrum dx6i, OrangeRx 6 ch rx. When I flew back then, just plug in a battery to receiver. This is my first electric. I've searched and read alot on ESC, BEC set-ups, useing separate bec for like retracts. But I'm still a bit confused on the wiring and such.

I would like to put the receiver on its own battery and run the aileron, rudder, elevator, and flaps on it. I was thinking of having the retracts on the esc/bec,motor battery. I plan on upgrading the esc to a 45 or 50A. For now I was going to use 3s 2200 or 2650 lipos. Maybe try some 4s later.

Will this work? (the highlighted area). If so, can I use NiCD or NiMH battery for the rx if the esc/motor/retract battery is lipo or does it need to be a lipo?

Thanks for any help
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Aug 02, 2012, 03:20 PM
Endlesslag's Avatar
Yes, that will work just fine Good idea too, in case the retracts get stuck or something.

Also, welcome to RCGroups
Aug 02, 2012, 03:31 PM
Registered User
Your wiring diagram looks fine. That's basically the way I (and many others) do it, so that the receiver won't be starved of power if a retract stalls.

Your receiver supply can be any type of battery, or it could be another BEC, taking its power from the main battery.
Aug 02, 2012, 04:07 PM
Registered User
Thanks guys.
Aug 02, 2012, 11:22 PM
Registered User
Wintr's Avatar
The only issue I see is, if a retract stalls, it will pull lots of power from the BEC on the ESC, possibly making the ESC heat up, especially if the main battery is 3S or higher volts. If the ESC has a switch mode BEC, this is less of a problem.

For one of my aircraft, I use a 1800mah 3S LiPo and two switching BECs, one for the receiver and servos, the other for the retracts. I disabled the one in the ESC, which runs from a larger, 4S battery.
Aug 02, 2012, 11:50 PM
St. Louis
Foambird's Avatar
What retracts are you using? I did not go with this set-up since the E-Flite retracts have a protection circuit that kicks out in a jam. Resets so you can cycle the gear.

Otherwise I think your set-up is good insurance.
Aug 03, 2012, 08:56 AM
Registered User
It's the esc/bec that comes with the plane. I can't tell what it is, other than what Hobbyking has on their site. I'm going to replace it with a 45 -50A that does have a switching BEC.

Where would you wire in the separate BEC?

The retracts too are the ones that came on the plane, so I'm don't know the brand.

I really appreciate everyone's help.
Aug 03, 2012, 03:21 PM
Registered User
The power leads for the separate BEC are usually soldered to the ESC's main battery plug, so the ESC (and its built-in BEC) and the separate BEC both power up when you plug the main battery in, and power down when you unplug.

The 5v (or whatever) output from the separate BEC goes into the battery slot or any spare slot in your receiver.

Just in case you're wondering which BEC to use for the receiver, and which for the retracts; I would always use the stand-alone BEC for the receiver because there's always a slight risk of the ESC failing and taking its built-in BEC with it. If that happens, you've lost power to the retracts but you've still got control of the aircraft if the receiver is powered by the stand-alone BEC.
Aug 03, 2012, 03:41 PM
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7oneWo1f's Avatar
Nice job on your diagram. If you want to take it as far as you can go, putting bypass caps between power and ground, at the Y between section 5 and section 6, as well as the Y between section 2 and 4, will reduce noise and susceptibility by providing a path for high to low switching return currents (to your receiver). Small .1 uF capacitors should be sufficient. The receiver likely alread had bypass caps, but putting an additional .1 uF for your retract and throttle wouldn't hurt.

Also, if this is a larger plane, twisting your servo wires (2 or 3 wire servo wires) will help with EMI/glitches/crosstalk, as well as using a Ferite ring between your ESC and the section 5/6 Y.
May 05, 2013, 12:35 PM
Registered User
Recce's Avatar
I posted this question in 1100mm Durafly p-47 thread, but here it would probably get more views. I would like to do a reverse on my model: power the rx together with flight controls from the BEC and retracts, flaps and navigation lights from a separate battery. I found information about how to do it: Also found a lot of info from Google and this forum, but I would like to get some info about the following:
Does it work if I use a low voltage battery to bring down the retract operation speed? If control power came from the BEC and drive power from say 3,0V. The retracts themselves probably need 4,8v to operate, does that mean control power only, or both? The retract resembles this one:

Would the overload protection work with lower voltage?

I plan on doing my own tests, but not any time soon. So I`m looking for your opinions and experience.

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