Overheating Uno(s) with system hardware?

Hello! I'm creating a system in which I have a few inputs and a few items being powered by the system. I supplied the arduino with 12v 3a as well as 9v 1a. The program was working fine and replicable - everything was right until I got a computer error message.. A little while later I'm here. Bear with me as it's a lot of info, I've tried a lot so far..

I have overheated any/all arduinos (at least 3) hooked up. I burnt myself at one point.. it's not just warm. Heat is around power section of board. I tested each with power supply, nothing connected. It didn't overheat in the test which makes me think it's not the problem. However one board started overheating after using it for this project. I think it got fried... All boards are genuine. I tried the uno with just the screw shield and that didn't cause the heat either.

When overheating they've gotten hot, triggered a warning on my computer (macbook pro, said usb device using too much power), some have gone non-responsive, even to reset button on board, no computer communication, etc.

Details about the system -
A 3.3v multicolor led has one color lit up via relay signal when triggered. The program requires a few things to be completed. Once done, the first relay disconnects power to the first color and a second relay connects power to a different color to indicate completion.

These are my sensors and other items connecting to the uno via the shield.

  • 1 momentary button (gnd/digital pin)
  • 1 5v light
  • 3 5v relays (one is two on a board)
  • 3 plugs - when plugged in connects gnd/digital pin
  • 2 knob switches (gnd/digital pin)
  • 3 5v led toggle switches (gnd, 5v to toggle, when 'on' connects to 5.1k resistor then digital pin to reduce chance of short)
  • 1 3.3v multicolor led

Everything except one (later saw it was disconnected) showed a change on the serial monitor/reacted as it should, though now I'm having some issues with things not being read properly. I rewired everything to be more secure by using an ethernet head breakout board - I only had 2, so the last one is a tad different. Point being it was all working well prior, then overheating happened and now I'm stuck.

I tested all power things (light, 3 toggle switches, led) by connecting those directly to the board power pins and nothing caused it to overheat or even get warm within a minute or two. The board only overheats when I connect the screw shield and it's pretty quick.. (I don't have spare shields to test).

The system worked in the past so I don't see the need to post the code. It's really just checking if they're in the right position and changing the color of a bulb. Simple.

Am I crazy or did I miss something? I'm going crazy and running out of boards..

No Arduino board is a power supply. Any higher current (>100mA) loads, like relay coils and maybe your LEDs should have external power supply. If powering by USB the limit is around 500mA.

Be careful when using the power plug or Vin. Powering through Vin or the power jack means that the Arduino and all peripherals that are on the 5V rail are powered by the onboard 5V regulator. The on board 5V regulator is not heat sinked so will supply limited current before it overheats and shuts down. The amount of current depends on the voltage input to Vin or the power jack. The higher the voltage the less current can by supplied. I would use a buck converter to drop the 12V or 9V to 5V and connect that to the 5V on the Arduino, bypassing the, weak, 5V regulator. Then the rated current of the DC DC converter is available on the 5V line.

Not sure where I mentioned that, I probably typed wrong or I may not quite understand - I used an external supply that's 9v 1a and a 12v 3a. I have a 5v 2a but opted for a 9v as we use it with a few other systems and it works well. I felt there was a bit more things so a 9v would work better, not sure that's right but it happened.

I used the 3.3 and 5v pins from the arduino to the leds/etc. I'm less familiar with the Vin option.

Not sure what you mean regarding the power plug/jack? Isn't that what I plug into to power the arduino ?

I've run systems with 3-4 relays and more LEDs so I'm having a hard time with this. Some systems I've used a mega, not sure if that's the right move but I'm open to it.

I think I get what you're saying - the arduino has a 5v regulator to keep it around 5v as it can handle that best? like the board itself steps it down to process it or something like that?

I'll test it with a 5v supply and let you know, thanks!


The community section is the wrong place for technical questions about your project so I moved it into a more appropriate section.

Overheating like this is because you are using the power jack. The Arduino’s built in regulator has very little in the way of heat singing and so gets hot with anything more that 100mA or so of current t drawn.


Do not power a UNO(, Mega 2560, Leonardo, Nano, Pro Mini) by the "Barrel Jack" or "Vin" if you propose to connect any other devices to it.

Definitely not. :roll_eyes:

You need a regulated 5 V supply, connect it to the "5V" pin and ground, but disconnect the "5V" pin while you have it plugged into a PC via the USB socket. On a Nano, you do not have to disconnect it.

So don't use the barrel jack, but connect a power supply to power the arduino by plugging it in to the 5v jumper pin on the board? That outputs 5v to my relays and other things, how could it be something the arduino accepts power from..?

It said my post was similar to others in a community section or something, I wasn't sure where honestly. There's a lot of places, haha. Thanks!

Sidenote is there a place or somewhere to reference on what to post/where? Deciding where to put a post can sometimes be ambiguous .. at least since I'm new to the forum :sweat_smile:

What else could it be? :roll_eyes: It is the supply connection to the logic chips. We constantly have to keep repeating this simple explanation: The Arduino is not a power supply. It does not "provide" power, it uses power.

As you have in fact found for yourself - the "5V" pin does not "output 5v to your relays and other things". That is not its purpose. :upside_down_face:

The description at the start of each section is a good guide.

A lot of posts are misplaced. But the name "Community" should give you the clue. Community is about people, teaching, running courses, meetings, showing off what you have done and so on.

Most of the technical stuff goes on in the "Using Arduino" section. With a section for each major type of Arduino use.

Then there are specialised sections devoted to specific and unique boards and board types. This is in the confusing named "Hardware" section. I maintain this is due to the people who set up the section not actually being native English speakers.

Then there are sections devoted to specific languages.

Yes I know it can be difficult to sort it all out, so thanks so taking it in the sprit it was given.

Hi, @professionalpanicker
Welcome to the forum.

Can you post a circuit diagram, showing power supplies and hardware with with labels?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

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