On the power connection page, it is suggested that we use zener diode for protection when using back up power supply. The connection suggested is to connect zener across the +5v and GND of the servo rails directly.

http://plane.ardupilot.com/wiki/common-pixhawk-wiring-and-quick-start/

 

   However when I read about zener diode, then the circuit to control voltage is suggested as follows.

 

  Notice the resistor in series with the zener.  I understand that this resistor will consume the voltage which is excess to the required voltage. However in the connection suggested for PXHawk, there is no resistor.  In this case how is it able to regulate the voltage? My knowledge of electronics is limited, so I would appreciate an explanation of this.

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On the RSSI, use only a single wire from the DragonLink RSSI pin to the SBUS signal pin on the Pixhawk.
Iskess,
I think I could not expressed myself well enough. Let me correct it.I use only one cable from pixhawk sbus to uhf rssi. The other cable I meant is from ppm to pixhawk rc in.
Thank you.
So just to confirm, you have 4 wires total. 3 are on the PPM cable, and a single wire, signal only, on the RSSI.
I'm really just wanting to make sure you don't have the +5v middle wire connected on the RSSI cable.
OK I got it. Sorry for the language barrier :)
Thank you.

Onur

Just to be clear. The zener diode and capacitor should be wired in parallel. Therefore the zener-capacitor combo are wired in reverse to the BEC correct?  I am using this youtube video as a reference where the guy wires the zener and capacitor to the BEC.

https://www.youtube.com/watch?v=e6jDSCXQHAc

Thanks

The zener + should be connected to the servo rail +. 

Chris said:

Just to be clear. The zener diode and capacitor should be wired in parallel. Therefore the zener-capacitor combo are wired in reverse to the BEC correct?  I am using this youtube video as a reference where the guy wires the zener and capacitor to the BEC.

https://www.youtube.com/watch?v=e6jDSCXQHAc

Thanks

No, as I understand it the zener must be reversed.
That's what it shows in the official http://ardupilot.org/plane/docs/common-powering-the-pixhawk.html#co...

And I also researched elsewhere on the net as i wasn't sure about it.

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