Reverse polarity protection.

[Drac0]

Looking to add some reverse polarity protection for my gear but being very much an electronics n00b I'm looking for a simple solution. I want to use a MOSFET setup - I understand how it works but knowing exactly what I need & how to put it all together is another thing.

So I'm after some recommendations for an already setup board that I can just plug in the 12v power & the output & have it work. Looking at putting it in a small box on the mount to support both the mount & accessories, so probably 15A capacity?

12V input ---- protection circuit ---- output to mount/accessories.

Any recommendations or suggestions? I see all these ones for solar etc, but not sure if they would work, so after input from the more experienced.

Cheers,
Mark

[sharkbite]

Hi Mark....

The best way to do this (in my view) is use a bridge rectifier...

as long as you wire up the output of the rectifier correctly to start with, it does not matter which way you connect the battery.

These are really cheap - i don't know why they are not on the input stage of any dc device....
especially on things like my scope, which will blow the control board if it goes on the wrong way....

the next simplest is just a diode on the +ve side....if you connect the battery the wrong way it will simply not flow any current at all...
In fact thats exactly how my ciggie lighter socket power supply works...

15A is probably overkill, but there is not much difference in price between devices, so take your pick!

[Drac0]

Isn't a bridge rectifier more for AC to DC conversion? Know nothing about these so that's just from a quick search. I did look at using just a diode, but decided to go with the MOSFET solution. AS for the amperage, just want to be sure I cover everything - mount, cooled camera/guide camera, couple of dew heaters etc. Never sat down & worked out the full draw.

Cheers,
Mark

[sharkbite]

Correct - they are used for ac to dc conversion....and the way that they do this is to 'rectify' the input - i.e route the -ve going signal to a +ve output.

Not really sure what you mean by going the 'Mosfet' solution - since mosfets are transistors, any solution would be more complex than a rectifier or a diode...

[floyd_2]

What a great topic. I read up on using diodes a little bit here: https://www.allaboutcircuits.com/technical-articles/how-to-protect-your-circuits-using-only-a-diode/ Schottky diodes look like a great way to protect battery powered setups from reverse polarity connections. It's of less use to a 240v setup like mine where the cables can only connect one way, but when you're on battery power it could be super important because of the initial battery connection. Those Schottky diodes look like they would be a very easy solution.

[Drac0]

This is the type of thing I've been looking at, but really have no idea if it's suitable for what I want to do.

[sharkbite]

Hi Mark - this looks like it can control the voltage as well...

so say you had something like a 20vdc source, and you wanted to
reliably reduce it to 12...
(the verbage implies it can be adjusted between 3-20v)
I cant tell if it actually does what you want though...(and i'm pretty sure the -ve is common - so likely it wont)

If all you want to to is make it impossible to blow up a device by connecting it the wrong way - then the two original options i suggested are the easiest.

1 diode will basically stop any reverse current, and you would have to re-connect the battery properly before it works.

A bridge rectifier will work regardless of how you connect the battery.

you might lose ~1 volt across a diode- but using my scope as an example - it doesn't seem to affect performance.

In my ciggie lighter supply, there is a single 1N1004 diode and it easily runs the scope.

[dikman]

That device is basically an electronic switch controlled by an input signal, so not really what you need. Whatever you use has to be permanently connected at the input of your device (mount, camera etc) i.e. on the equipment itself and before you plug in your power cord. As Sharkbite said, wiring a bridge rectifier across the equipment side of the socket will work but putting it on the power supply itself won't stop you accidentally connecting reverse polarity.

If you're using polarised connectors, however, I don't see how you could accidentally connect it wrong? What am I missing here?

[bojan]

People, don't complicate things unnecessarily..

Bridge is a good idea.. but there is a bit of voltage drop (1.4 V)

Or just one single Schottky diode (lower voltage drop, 0.3-0.5V) in series with positive wire will do as well.

[Outcast]

This may not suit all but, there is a very, very simple way to do this & it is the method I use...

I have a 'permanent' pigtail swinging off my battery, two ring connections bolted to the terminals with two Anderson 15A powerpole connectors on the other end of the pigtail.. one red, one black that connect together...

On the battery end of my 12v cable, I have another pair of Anderson 15A powerpole connectors, again one red, one black that similarly connect together.

In this configuration, unless I remove the pigtail I've attached to the battery or, connected the pigtail incorrectly it is pretty much impossible to connect your mount in reverse polarity.. I say pretty much because, it's astounding what humans are capable of stuffing up but, essentially, when the two powerpole are connected to each other (they slide together) I cannot see any way to then plug the 12v cable incorrectly to the pigtail because the plugs simply will not go into each other...

The only catch is to be absolutely certain that positive to positive & negative to negative all the way to the 12v pin connection... This is really very simple & all you need to do is double check that you fitted them correctly. Wiring can be either soldered or crimped in place... I crimped because my soldering sucks...

For me this is foolproof because, the only way that I would undo the battery pigtail is if the battery is completely dead & being replaced otherwise, the pigtail is never touched...

It doesn't matter that you can't distinguish the red anderson from the black under red light because you simply cannot connect the two sets of anderson plugs on your leads together except correctly...

This is the simplest solution I know of & involves little to no technical skills..

I did this because I was paranoid about frying my mounts... I've been using this setup for about 5 years now with zero problems & in my opinion pretty much zero risk of frying a mount due to incorrect polarity.

Hope this helps

Edit: Meant to add pictures, added now.. these are available at Jaycar