Polarity Protection for Turnigy 9x Tx










I'm currently waiting for my new Tx in the mail and will be doing a video. 


 You can use either a "P" or "N" channel Mosfet will work.  This curcuit works better than the Crowbar curcuit because it doesn't need a fuse, and with  less of a voltage drop.  "N" channel Mosfets are more common to find and be to used.   I have decieded to just make a reverse polarity connector instead of Modding the radio for a now.  I removed the charge port connector from the radio to use as passage way for my wiring.



I used a balance connector to connect to the 11.1v Lipo.






















I removed the Tx charge connector and enlarged a whole for the wiring to pass through.























Finished it up with some Velcro to hold the battery.  I have already noticed with a 1600mAh 11.1 LiPo my battery life has increased by 2 to 3 or more hrs.  SWEET!


Even better protection using both a mosfet and a charge pump IC.


You can find the Charge Pump IC's online.

   Here:    Charge Pump IC











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  • Sure,

    First thinks first, you need to cut the traces that connect the power pin to the rest of the board. You can see that on the pic that i posted. (+ve pin is the middle one) just use a paper cutter or smthing

    there is also another trace u need to cut on the other side of the board .


    Then if ur using a P fet put a wire from the middle pin (+ve) to the source pin of the fet, a wire from any ground ( i used the right pin ) to the gate of the fet and 2 more wires from where the +ve trace was going to the drain of the fet :)

  • Distributor

    I would really like more details on this Yiangos... maybe more pictures or steps to take to do this... 

    Russell, if you are doing it, please post detail pictures, I want to do the same soon... I will do the battery mod this weekend so why not doing this as well while there!

  • Sure :)

    First I cut the trace from the +ve pin (there are 2 traces, one which leads to the bottom pin and one on the other side of the pcb which leads to the smaller perpendicular pcb thouse are connected together probalby to withstand more current as the traces are small ) most left or right pin in the battery pins is ground so it goes to gate, middle is +ve so it goes to source(3rd pin on the FET) and the drain goes to where the pcb used to go before i cut it :)

  • @  Yiangos Yiangou      Can u explain your wiring in your pic.
  • @Russell

    How are you using the diode ? In series with the current, or between plus and minus ?


    1) When diodes are reversed polarized they only let a very small "leakage current" flow.

    Your diode will NOT get hot in this conditions, because it simply does not dissipate any power.

    2) The diode will not get damaged when reverse polarized unless you apply more voltage than the "reverse avalanche voltage" for a long period of time with a lot of current. This is also known as the diode voltage rating, for 12V applications, a 60V diode is more than enough. And there are a LOT of 60V diodes out there.


    Yes, it will "burn" more than 0,3V  when direct polarized (connected in series).


    You will only need the fuse if you connect it between plus and minus. But then:

    -The fuse will only pop when then battery is inverse connected.

    -There will be no dissipation on the diode when coreectly connected, not even the 0,3 V that I told abou above.

    -The diode must have a rating of around twice the "normal current". i.e. if TGY X9 needs 250mA, the fuse should be 500mA.

    -The fuse must be a fast burning fuse.

    -The diode must have at least a 20V rating 1A.

    The diode will not get warm when inverse polariyed, simply because the diode will pop really fast, before the diode even had time to get warm.


    I hope this helps to sed some light on the matter.


  • 3692218971?profile=original

    Here is a picture of my mod with an irf 4905 :)

  • The circuit diagrams labelled figure 2 and figure 3 are correct.  In both cases the FET is being enhanced, and thus the current is being passed through the FET, rather than the body diode.  If you measure the voltage across the FET's drain and source you will find it is much less than what you would measure across a conducting diode.


    The FET reverse polarity circuit is a far superior to a Schottky diode, which for any decent current (above a few Amps) will drop a lot more than 0.3V - more like 0.5 or 0.6V.  The FET solution will be 20mOhms or so, depending on the device chosen.


    As an aside, the symbol for an N-channel FET is incorrect in the first diagram, right at the top of the page.  N-channel FETs have the arrow pointing inwards.



  • @Melih

    Thanks for clarifying. That post really make sense.


    This is what we keep saying various time because of the "inverse diode"


    I think you can do a test for confirming Melih's hipothesis that you swaped gates and is just disconnecting the gate pin. If your circuit just works the same. You definetely are just using the FET's diode.

  • @ Melih    When i use a diode  1.) it gets hot when connected wrong.  2.) it needs a fuse so that it doesn't PoP the diode or smoke the curcuit board wiring.  The Mosfet doesn't get hot when connected wrong.  ?  How are the GSD connected wrong?  if I swap the "S" & "D" the motor sipns if the battery is connnected either way.    
  • Current diagram works, BUT :)
    You are using FET as a "diode" in this diagrams, because internal diode polarity same with your battery and GSD connections wrong. If you want to use it, just use any diode. It is same thing.

    PS: I know the LED is a diode, because i have 24 years electronic experience. If you need to use it in other direction, Just turn it around. But a multimeter(on ampermeter mode) will be better.
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