Reverse polarity protection for battery | ZMK | Page 1

dawn rover Dec 15, 2025, 4:22 PM

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Hey! So I want to implement some simple reverse polarity protection on my battery connection, since I accidentally fried one of my microcontrollers because I like a dumb dumb didn't check polarity on a battery I bought. Would something like this work, using a P-Channel mosfet?

MCBat+ goes to the B+ pin on a Nice Nano V2 and MCBat- goes to GND on the Nice Nano V2

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I had thought of just using a simple diode, but the voltage drop that would include doesn't make me comfortable lol

minor beacon Dec 15, 2025, 7:08 PM

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Do you intend to support charging the battery as well? If so, using a simple diode will prevent current going back the other way to charge the battery.

My investigations into reverse polarity protection circuits that support charging just led me to a never-ending series of increasingly complicated circuits which each fixed some issue with the previous one but added new issues of their own. At that point, I just gave up and decided to use keyed connectors and silkscreen text so you can check that the battery is wired correctly.

dawn rover Dec 15, 2025, 8:51 PM

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minor beacon Do you intend to support charging the battery as well? If so, using a simple dio...

Yeah charging the battery is going to be supported too. If adding a diode is perfectly fine and the voltage drop isn't a problem, then I would much rather like to go that way

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Or well, in the current method charging the battery is supported just by using the nice nano v2, since it has battery mangement. BUT it doesn't seem to have reverse polarity protection lmao, at least I don't think the clones do then - since I fried one by plugging the battery in the wrong way around and having it try to charge lol

minor beacon Dec 15, 2025, 9:01 PM

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Adding a diode is not perfectly fine for charging. That means current can only come out of the battery and never back into it.

dawn rover Dec 15, 2025, 9:05 PM

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True yeah, I misread what you wrote :) I was a lil confused. I've done some research and it seems like one of the best options is a p channel mosfet. But I've also just contemplated doing the silk screen and keyed connectors lol

minor beacon Dec 15, 2025, 11:57 PM

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https://www.ti.com/lit/an/slvae57b/slvae57b.pdf has some info that may be useful to you in section 4.

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You would want reverse polarity protection but not reverse current protection, since reverse current is a feature here. Probably a good idea to breadboard a circuit that you want to use and test that

With a simple load connected (a high value resistor or something else that you don't care about blowing up if your circuit doesn't work), you get the expected voltage with correct polarity and no voltage with reverse polarity.
With the battery in the correct orientation and connected to your charger, the charger is able to charge it.

Also, not a bad idea to use the smallest battery you can and keep a sand bucket on hand whenever experimenting with lithium batteries...

#Reverse polarity protection for battery