Power Supply Problems (12V)

I am busy building a aquarium controller using the Arduino Mega. I have purchased a 12V 2 Amp AC-DC converter which is connected directly to the Vin pin (Have measured it to be exactly 12V). I chose to use this one as I will also be using it to power the dosing pumps.

When running from the USB everything runs smoothly, however when I use the 12V connected to the Vin pin the board heats up to a point where you can almost not touch it, and that is with it running only the touch screen connected and nothing else. Also when running from the Vin pin the touch screen does not run as it should either (either just shows a white screen, or sometimes when it starts up does not react to touching it).

Unfortunately I am more of a programmer and not all clued up when it comes to the circuit design. Am I missing something here?

When you run from the USB the controller is using 5V directly from the PC.
When you use 12V to Vin, you are using the controller's on board 5V regulator.
It has to drop 12V to 5V and in doing so dissipates heat due to the 7V volt drop and the current flowing through the regulator.
Apart from the controller, what other things do you have using the controllers 5V pin.

12V is considered by many, including me, too high for the Vin or DC socket, 9V is more suitable.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png, including power supply?

And if possible a picture of your project.

Thanks.. Tom... :slight_smile:


Attached is the rough sketch of everything that will be connected. As mentioned though it is currently only the Mega and the touch screen that is connected. All other components have not yet been added to the circuit.

The idea behind using the 12V was so that I would only need one source for all components in the circuit as the dosing pumps run off 12V. Should have probably tested everything before I went and fitted it neatly into the project box (which is already very cramped, doubt I will be able to fit in another 9V converter).

It is just strange that when using the 12V that the screen does not function correctly. I have had problems like that before, but usually when there is insufficient power supplied to the Arduino. Would it be possible to build a small circuit with resistors to lower the voltage? However then the resistor would probably just end up dissipating heat?

Also some picture of the setup. You can see what I mean with the project box is packed quite tightly. However I did get everything to fit




Nice, like the installation.
Not sure how much current the display draws, but as the regulator heats up it drops its output voltage to try and survive, so your display may be reacting to the regulator shutting down.

You can adjust those SMPS too, that trim pot near the output terminals is the fine adjust, see if you can lower it and get a compromise with the temp.

Tom..... :slight_smile:

I have tried tweaking the voltage. Lowest I could get it was around 10.8V. When set on 10.8V the display does come on, but the function of the touch screen remains a problem. The Arduino still heats up quite heavily (cant really tell the difference). On 12V the screen remains blank. Will see if I can find a 9V and see if it makes a difference.

I measured the current draw of the Arduino and screen together and measured about 0.3 mA (can that be correct).

300mA * (12-5)= .3 * 7 = 2.1W, you would need a heatsink to dissipate that amount of energy from a SMD linear reg.
Have you got a specon the display, also the two input devices, are they on the arduino 5V pin?

Tom.... :slight_smile:

Hi, See Info on power limitations HERE

Measured it again now, came in at 4.5 mA, thus 0.0045*12 = .054 Watts.

Something does not seem right though, 4.5mA seems a bit low while running code and powering the touch screen. Will need to sit down this weekend and see where I am going wrong