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Topic: Reverse polarity protection? (Read 3937 times) previous topic - next topic


I recently blew up a motor shield made by a third party because I attached the power leads the wrong way around. Lots of heat, smoke then a nice pop! Ok it was a cheap shield from HK, maybe it's karma. I since bought the kosher rev 3.0 board which is much better anyway.

I decided to put a reverse polarity protection circuit between the battery and the my project. I'm not sure whether it's absolutely necessary, but for a quid it's worth it I think.

Not sure if most Arduino hardware already has this. I guess (maybe wrongly) that if the hardware has a voltage regulator, it is protected, but I also note that many shields and other pieces rely on the regulator on the Main board, so if you power it directly (as in a motor shield) you can possibly fry it!

My circuit works, but not sure if it is a good circuit. Could someone with please offer advice?

Many thanks
Craig Turner, blog: http://gampageek.blogspot.co.uk/ It helps with my learning if I write things down, esp. for others to follow (constructive comments welcomed to improve)


Aug 10, 2012, 03:29 pm Last Edit: Aug 10, 2012, 03:32 pm by HugoPT Reason: 1
Another idea is use bridge rectifier.(4 diodes).
If you connect a bridge in a dc pure dc circuit you can swap the pins on the ~ input pins like you want.This is because the bridge only 2 diodes can work at a time and the outup + and - will be always right.
This provide a mistake protection against reverse polarity in the input.
See this page : http://highfields-arc.co.uk/constructors/other/revpolepro.htm
Arduino Mega 2560
Arduino Nano
Arduino Duemilanove
MAC OS Montain Lion
Raspberry PI Model B


Nice little you-tube video on reverse polarity protection here  http://www.youtube.com/watch?v=IrB-FPcv1Dc


In high-current applications a "crowbar" can be a useful low cost reverse polarity protection.  Include a fuse and a cheap large current rectifier that conducts if you power things the wrong way.  If you connect the supplies the wring way the fuse just blows.  When operating normally there is no voltage drop or power dissipation from rectifiers and no expensive mosfets.


This is a known technique and I have see a very similar circuit that does work, thought I'd saved it but can find it right now.

Try Googling "FET used for reverser polarity detection" or some such.

I've used bridge rectifiers in the past, it's a simple method if you can afford the two diode drops.

Rob Gray aka the GRAYnomad www.robgray.com


Aug 11, 2012, 11:59 am Last Edit: Aug 11, 2012, 02:09 pm by trendski Reason: 1
Thanks people for the input. I feel more confident now and I'll stick with the Mosfet as it is very efficient for my project.

Could this be a suggestion for enhancing arduino shields and allied boards, ie to add a simple low power circuit that protects it from reverse polarity mistakes? MOSFETs only cost a few cents, which seems a good investment to save maybe tens of dollars.


PS really liked the You-tube tutorials
Craig Turner, blog: http://gampageek.blogspot.co.uk/ It helps with my learning if I write things down, esp. for others to follow (constructive comments welcomed to improve)

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