Uno seems to be overheating when running on 12v

Could somebody tell me if I'm asking too much from my Uno...

I'm using a 12v (500mA) power supply, which is in fact giving me 17.6v, so I'm using a voltage regulator which give me a stable 11.94v.

Connected to the Uno I have: - SD card for data logging - 3 digital thermometers - LCD screen (2*16) running thru a shift register - clock - 12v relay to activate 2 pc fans. Those fan run directly from the voltage regulator - 120v relay to activate a bigger fan

When I'm running the Uno thru the USB port power, everything works fine (the LCD screen is a little dimmer) and no overheating (perfectly cold to the touch. But as soon as I modify the circuit and put the 11.94v in the Vin and GND, then the board start overheating (very hot to the touch).

Thanks for your help.

I don't think your meant to connect 12V to the Vin header. Put a little 2.1mm power plug on the 12V and plug it into the UNO power socket where it will get regulated down to the 5V arduino expects.

I don't think your meant to connect 12V to the Vin header.

Yes you can.

Basically you are drawing too much current. Also you supply is sagging hence the backlight going dimmer. Get a better supply with more current capability. And lower voltage if possible.

The Vin header connects to the input of the regulator and should be used with great caution as there is NO REVERSE protection at that point. Connecting there will allow the UNO to work fairly well on 6V in BUT be aware that the ALS1117 data sheet makes no mention of input reverse voltage protection so any misconnection (Reversing the wires) is likely to be A MAJOR ISSUE...


there is NO REVERSE protection

Yes but there is no reverse polarity protection on the 5V or on many other supplys.

While I am by no means advocating it the ATMEGA processor is rather good at withstanding reverse polarity if you don't apply it for too long. Especially if the power supply has some current limiting. I know, I was that stupid.

uno overheating problem solution

With 12v input, for every 1W your project consumes, the regulator has to dissipate 1.4W

The regulator is hardpressed to dissipate even 1W (they could have done better if they’d designed the board better, but they didn’t)

So at 12v in, you can get like ~0.7W out, which is ~140mA at 5v.

The uno itself can pull close to 40. The LCD screen is probably a couple hundred.

Wherein lies the problem.

If you had a lower voltage supply coming in - say 7v - you’d be in a much better place. 7v means regulator is dropping only 2v - you might be able to pull as much as 500mA sustained in this case… Can’t go much lower than 7v, though, as the regulator has a bit more than 1v of dropout.

yuksel19: uno overheating problem solution


A 5volt/3Amp open frame supply is overkill, since the Uno has a 500mA inline polyfuse. And could be dangerous because of the bare mains power connection. A 5volt >=500mA cellphone charger with USB plug/lead is much easier. Leo..

Power supply 5v 3A not meaning arduino pull up 3A from supply.İt is pull up how much necessary current itself.İf you want to safety for card you can 500 ma fuse between arduino and power supply.I am using arduino card + ethernet shild +sensors 5v 3A Power supply (connection polarity very important) no problem no card heating.My circuit is running 14 hours every day.

Sure, the Arduino pulls what it needs. Just saying that a 500mA cellphone charger the size of a matchbox can do the same job safer and more efficiently. An Uno and e.g. a W5100 Ethernet shield uses about 220mA. Leo..

Yes I am sure because I am using. You can test with ampermetter.Also I am using reset circuit for prevent locking first power on especially w5100 ethernet shild.

1 Like