Cutting +ve ESC lead on multi engines

[Dave Hopkin]

I know we should only have one live +ve supply to the RX when multiple ESC's are in use.......... but why?

It seems to me that the voltage would be in parallel as far as the RX is concerned so why would it cause a problem????

[onetenor]

Good question. There are probably other situations where this could apply though can't think of one right now.

[Simon Chaddock]

The advice is that with linear BECs it is quite safe to leave the +ve wires connected. Linear BECS tend to drop the voltage very slightly with load so all that happens is the one with the highest setting will carry most of the load. Just don't assume that 4x3 A linear BECs in parallel can manage 12 A!

I have several multis with linear BECS that have all their +Ve wires connected.

The situation is different with switching BECs as they can react to another BEC so only one +Ve must be connected.

If you not sure what type of BEC it is disconnect all but one +Ve wires.

[Dave Bran]

And if you are going to disconnect, free the tab and extract the pin from the plug, then fold it back and insulate to the other wires, then you can refit easily later if the ESC gets a different model to play with.

[Trevor]

If the model has retracts and/or flaps, I like to use the second BEC to power those. This reduces the load on the BEC which is powering the Rx and primary flight controls and also provides some degree of protection from any retract malfunction resulting in excess power demands.

Its easy to do: Extract the red pin from the second ESC plug as Dave describes. Do the same for the flap and retract plugs, then join all these extracted red leads together and apply a bit of heat shrink.

Trevor

[Dave Hopkin]

I know full well how to do it, that wasnt the question, to rephrase it the +ve is a common rail within the RX so connecting addition +ve supplies to it will not raise the overall voltage so as far as I an see there is no risk to the RX, but would there be any effect on the operation of the ESC's

[John Lee]

Posted by Dave Hopkin on 12/08/2016 16:06:22:

but would there be any effect on the operation of the ESC's

well magic smoke came out of one of mine when I inadvertently omitted to remove the +ve

[gangster]

It has to one of the situations where. If you have to ask the question the answer is don't do it. The natural belief is that parrelleling them give a greater current capacity and an element of redundancy. Well yes sometimes but as already explained it might be ok with linear regulators but some regulators could start to interfere with each other. And as we see someone on the thread has learnt the hard way

[pete taylor]

Just for the sake of throwing a curved ball in, why not dispense with the BEC altogether by isolating all of them and using a separate receiver battery?
Safer than little black boxes and able to handle appreciable loads.
Most multi-engined models are more than capable of carrying the extra weight.

[Dave Hopkin]

Actually it works perfectly as Simon suggested....

4 EDFs 4 ESC, each edf in a separate channel on the RX, each with the +ve connected and it works perfectly with some Taranis mixing to replicate the throttle channel onto three others

 

No smoke whatsoever

Edited By Dave Hopkin on 12/08/2016 20:47:53

[onetenor]

Doesn't disconnecting the becs and using a seperate battery defeat the object of having BECS in the first place ? I'm now confused .

John

[Simon Chaddock]

The object of BECs was to save the weight of a separate power supply and to power Rx & servos from a battery that cannot run out before the supply to the flight motor. Quite a valuable asset for a plane.

[Allan Bennett]

First of all, the reason that one cannot normally connect switching BECs in parallel is because they achieve the voltage reduction by rapidly switching the power on and off so that the receiver and servos only see 5v or whatever the output's meant to be. Because of this switching, they could interfere with each other if connected.

Parallel may indeed work with some brands due to better/different electronics, but with others it results in smoke. So not worth risking in my view.

A separate battery for the receiver might run out before you're finished flying, if you don't monitor it. A BEC will undoubtedly be lighter than a receiver battery and, so long as your main power supply is 2S or more, it will reliably supply power to the receiver even when the battery voltage is so low that the motor's stopped.

Edited By Allan Bennett on 14/08/2016 10:56:01

[Martin Harris - Moderator]

Conversely, a fault in the ESC/BEC can lose supply to the receiver which is arguably less likely with a well monitored battery. It happened recently while I was flying a friend's model (well tested powertrain) which developed a fault in the ESC - lost the motor, dead sticked it and on the ground run lost all communication. When we got to it, we found the battery feed wires had unsoldered themselves from the ESC!

[pete taylor]

With rx batteries being in the order of 2500mAh these days and costing comparatively little, it's most unlikely that they'll expire during the course of a flying session.
Also, when you consider that we're discussing multi-engined models that are more than capable of carrying the extra weight it's a simple insurance policy to have.
I've been making a point of using a separate rx battery for a long time now without a problem and have witnessed several models lost due to esc or bec issues.
You pays your money and takes your pick I guess!