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

Melih Karakelle June 3, 2011 at 2:44pm

Just use a Schottky diode, voltage drops only ~0.3 volt and it protects your circuit. If you can find a FET without internal diode, your circuit works.
PS: Use a LED or multimeter for testing your circuit. It is better than a motor.

http://works.PS/
Russell B. Sutton June 3, 2011 at 2:40pm

Added a video to blog. It's working great
Russell B. Sutton 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.
Russell B. Sutton 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.
Ross Kerley 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?
Russell B. Sutton 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.
Amilcar Lucas 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.
Darren 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 :(
Ross Kerley 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.
Russell B. Sutton 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.

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