Polarity Protection for Turnigy 9x Tx

http://www.sparkfun.com/datasheets/Components/General/FQP27P06.pdf

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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Comments

Russell B. Sutton June 3, 2011 at 4:50pm

I have posted both N & P wiring diagrams.
Yiangos Yiangou June 3, 2011 at 4:27pm

Russel i agree with simon, the first diagram was correct :) you need to change the mosfet in ur diagram , it should be a Nfet
Russell B. Sutton June 3, 2011 at 4:06pm

LOL and WA LA it just works and I'm not burning up another Tx. It works just test your setup before using to make sure you have it connected and wired right.
Simon June 3, 2011 at 4:05pm

@Russell

Sorry but I think you still have the wrong diagram. Take a look at this TI application note . Maybe this will help with all the confusion.

MOSFETS are a good way to add reverse battery protection because the operating voltage drop is very low - c. 80mV versus 600mV for a common diode or 300mV for a Schottky.
Yiangos Yiangou June 3, 2011 at 3:45pm

the forward diode voltage is -4V therefore at ~-11 volts the conductivity is near negligible
I.S. June 3, 2011 at 3:20pm

@Yiangos

Yes, agree, BUT n reverse the built in diode should conduct spoiling the protection.
Yiangos Yiangou June 3, 2011 at 3:15pm

IS this works because in order for drain and source to conduct the voltage at the gate must be grater than the gate threshold voltage. so in the correct polarity , in the gate you will have ~11v far grater than the threshold (-2v). When in reverse mode the gate voltage is ~-11v which is less than the threshold so no conduction between the drain and source :)
I.S. June 3, 2011 at 2:58pm

Ok, seeing the vdo it looks like it works. However the connections doesn't look solid and the exact FET model is not displayed.

So good for you, but can you explain us why it works, despite of the reverse diode?
Yiangos Yiangou June 3, 2011 at 2:56pm

Russell i just did a try with an IRF4905 and the 1st diagram worked, the 2nd was opposite (the way to burn it :P)
Russell B. Sutton June 3, 2011 at 2:52pm

@ Melih LED's are not good for testing this curcuit because they only work one way. If you connect the led the wrong way how r u to tell whats wrong. The electric motor displays that the curcuit is working correctly. It shows that if connected the correct way it will spin. connected the wrong way and it will not spin and does not spin in reverse.

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