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Topic: Nano, Can I wire 5volts to the 5 volt pin and 12v to the vin at the same time? (Read 217 times) previous topic - next topic


Hello, I bought a fixed 5 volt regulator off of Amazon and I plan to wire that to my 12 volt power source and then to my 5 volt in along with plugging in the 12 volt power source to the vin on my nano. This is for a vehicle application using analog inputs and pwm outputs.


Why would you want to put two power supplies?  What's the point?  Just use one of them. 
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I'm guessing the 5V source may be battery?  The 12V from the car?  It's not a good idea... you need a way to switch it... a comparator circuit that senses 12V at Vin should work. 

I've done something simlilar before and it's doesn't work well and can drain the 5V source and if that's battery it's not a good thing.
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No, can't do that. And i everything i powered from the same source (even when using regulators with the exception of isolated regulators) you don't need to.

If you want to have some kind of fail save you can add a diode to the 5V input. Same trick the USB uses. But this will drop Vcc a bit. Depending on the application this isn't a problem.
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there's nothing in the schematic that stops you from doing that... it acts like a parallel 5V supply.  It's just not a great idea... things can go wrong.

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Thanks for the replies everyone. I guess i'll just hook up a 5v source to the nano.
I was asking because I already soldered a 12v source but I'm afraid I'm afraid I might be over working the regulator so I also wanted to add a fixed volt regulator to the 5 volt source. I had a problem with my nano restarting and the L led light flashing rapidly which turned out to be a bug with the watchdog timer and the Chinese nano's. I burned an UNO bootloader to the nano which seems to have fixed it but my nano will cut off momentarily here and there as it is controlling my fuel pumps. I just tried plugging in a 5v usb power bank and tested that without 12v power input and it seems to be working with no interruptions unless I just got lucky in those 2 min. lol. Hopefully this will fix my issues.
Thanks again guys.


Doing that is fine - it's silly, but it works fine.

Powering a nano off 12v and expecting the regulator to handle it, not fine - you get basically no current out of that.

Wiring the 12v from an automotive power system to the Vin pin of an arduino, not fine. Automotive power is notorious for being very noisy, and full of high voltage spikes.
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The spec for the Arduino Uno Rev3 says "Input Voltage (limit) 6-20V"  so running it directly from the car supply should be fine.

However car supply positive is typically up to 14V, and youre regulating it down to 5 so dropping 9V.

If you are drawing a lot of current from the Arduino then the regulator will run hot, especially if its in an enclosed or hot environment (like a car).

So my favoured option would be to use a 5V 1A regulator to the 5V input, and not connect to the DC Vin


Many reports here of Nanos blowing up on 12volt supplies.
Especially in combination with 5volt (USB) supply.
The reason is not always clear,

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