Looking for reliable simple overcurrent/reverse polarity protection

Thread Starter

bigjoncoop

Joined Feb 1, 2019
108
hey guys,

I'm trying to make a circuit to protect against short circuits.... Using this for drone / quad copter building. Alot of people use 12v automotive light bulbs or u can buy simple boards with a ptc resettable fuse circuit...

I'm trying to create a circuit to do the same thing but without using light bulbs to limit current or ptc resettable fuses. I do have a bunch of different size poly fuses but it seems they do not trip fast enough. Can i just use a Schottky Diode? I came across some basic circuit that just use some mosfet to accomplish this but unsure if this is a feasible method. Also I need to be able to use either 12.6v or 14.8. Or both...

Here is one example I found. Put not sure what value of components to use. And how does this circuit protect from reverse polarity ?

Smoke_stopper_example.JPGSmoke_stopper_example.JPG

if anyone has a better circuit to accomplish this or ideas please let me know. Thanks. Don't want to use relays also.
 
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MisterBill2

Joined Jan 23, 2018
6,070
A very simple means of reverse polarity protection is simply a series diode. Mostly, devices tend to not draw excess current unless the polarity is reversed, and so that covers the rest of the problem. The downside of using a series diode is the forward voltage drop, so that from a 12 volt source you only get 11.3 volts, nominally.
For current limiting during development and build stages you can purchase power supplies with adjustable current limiting functions. Once the drone is built short circuits should not be an issue, unless sloppy construction is a problem.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
108
@MisterBill2. Yeah I was thinking I could just use a diode. Me personally I use my power supply for current limiting when building new quadcopters etc...

I'm trying to make this simple device that doesn't cost hardly anything to give to my flying Buddies so they can stop blowing up their new builds LOL.

So if I put a shottkey diode in series with the Positive wire, that will protect the electronics when being powered up if there is a short circuit or something similar? That will limit or stop the current?

If all I need to use as a diode that would be great. I could just take 2 XT60 connectors wire them together with the diode and make a small simple adapter.

Just so we're clear, I'm looking for something to limit current in case of a short circuit or reverse polarity.
 

Papabravo

Joined Feb 24, 2006
13,726
@MisterBill2. Yeah I was thinking I could just use a diode. Me personally I use my power supply for current limiting when building new quadcopters etc...

I'm trying to make this simple device that doesn't cost hardly anything to give to my flying Buddies so they can stop blowing up their new builds LOL.

So if I put a shottkey diode in series with the Positive wire, that will protect the electronics when being powered up if there is a short circuit or something similar? That will limit or stop the current?

If all I need to use as a diode that would be great. I could just take 2 XT60 connectors wire them together with the diode and make a small simple adapter.

Just so we're clear, I'm looking for something to limit current in case of a short circuit or reverse polarity.
We used a resettable PTC fuse.

https://www.littelfuse.com/products/polyswitch-resettable-ptcs.aspx
 

crutschow

Joined Mar 14, 2008
24,966
So if I put a shottkey diode in series with the Positive wire, that will protect the electronics when being powered up if there is a short circuit or something similar? That will limit or stop the current?
No.

Reverse polarity protection and short-circuit protection are two different functions, and generally require two different circuits.

For example, a diode will protect against reverse polarity, but do nothing to limit the current in the normal direction.

And the circuits referenced by Albert protect against over-current in the normal direction, but do not protect against reverse voltage (at last for anything above about 5V).
 
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