Comment by Andrew Radford on June 3, 2011 at 11:29am

So this means the stock Turnigy 9x has no polarity protection? Cripes... Not disputing it's a good value Tx but you wonder what else it is missing!

Comment by Russell B. Sutton on June 3, 2011 at 11:37am

By the time you get done doing all the mod's you end up with a really nice radio.  All in all it's worth it.  I just don't want anybody else to have to go through the pain of burning up a new radio like i did.

Comment by Ross Kerley on June 3, 2011 at 12:00pm

My stock FlySky has built-in polarity protection.  It merely has a series diode on the positive battery input.  

 

I don't think your circuit will protect it from anything.  The body diode of your MOSFET will allow current to travel if the battery is connected in reverse.  Your MOSFET is upside-down, but you might as well just use a diode to block reverse voltage.  Please correct me if I'm wrong though, I'm a bit rusty on my circuit components.  

 

Comment by Darren on June 3, 2011 at 12:02pm

is that something that can be made into each lipo conector? ie, would that help in the same reversal on an esc connector? ive done that too :(

Comment by Amilcar Lucas on June 3, 2011 at 12:21pm

Yeap the mosfet body diode will conduct when the batery is reversed.

It will not work, just use a simple diode instead.

 

Comment by Russell B. Sutton on June 3, 2011 at 1:07pm

I tested my curcuit with a 11.1v LiPo, P ch Mosfet, and an electric brushed motor.  If i connect my battery the correct way the motor spins.  if i connect the battery the wrong way "reverse" the motor does not spin.  To me that is working correct.

@ darren  I would not use this with high current.   

@ amilcar Look again,  The diode drains almost .75v and you still need a  .33 amp  fuse.  I never tested with the "N" ch- Mosfet,  I was told in the sparksFun forum about this and to stay under 750ma  rated curcuits.

Comment by Ross Kerley on June 3, 2011 at 1:13pm

I'm curious now, maybe you have Drain and Source swapped? If you disconnect the Gate altogether, does it still work correctly?

Comment by Russell B. Sutton on June 3, 2011 at 1:25pm

@ Ross I don't have it swapped

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

 

Get a P ch-Mosfet and try it with a DC brushed motor and a voltmeter.

Comment by Russell B. Sutton on June 3, 2011 at 2:07pm

Sorry guys I was wrong.  Ross I had to check my self, I did have it backwards, thanks for the look out.  I have changed the wiring diagraim up top I have also added a video.

 

Comment by I.S. on June 3, 2011 at 2:28pm

This circuit was discussed weeks ago.

As we mentioned, the "built in reverse diode" of that certain FET spoils all protection.

Just think about other one without it.

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