After working with my Arduino Boards for a little over a month now. (Mega and Nano) I have noticed the board seem to get very warm when using the external power in instead of the USB port when powering the units. Especially the MEGA. I have checked the voltage coming from the Power supply and it reads 9.17 VDC which is well within the acceptable voltage range. I also checked the Voltage output of the boards and they are reading 4.98 VDC for the 5V output on the board. The Power supply itself is rated at 9 VDC / 1A.
My question is how hot are these boards suppose to get? To me they seem a little warm for my liking. Especially the Arduino Mega.
As near to 7volts is the best for arduino, especially if you are going to use an Ethernet shield.
It is the shield that is using the extra current which makes the regulator get hot.
Normally this is not too much of a problem because if it gets too hot it will automatically shut down.
It can get too hot to touch and still be fine although a rule of thumb says use a heat sink when it is too hot to touch.
So either reduce the voltage or add a heat sink or stop worrying about it.
It is good to know there is a thermal shutdown, sounds like the heat sink is the way to go though. Did a little research on the web and cane up with a solution. However It brings up another question. When adding components to the Arduino what is the rule of thumb for current draw that the Arduino can handle and if that threshold is met is there a external power source for the 5 VDC that can exceed that threshold?
Not sure what you mean exactly. The Arduino Uno regulator has a series diode in the external regulator input line and that is rated at 1A as is the regulator so that sets the limit for an external supply. You only have half that when powering of USB. If you have a project that exceeds that then you need an externally regulated 5V.
Note there is a limit on the current the arduino processor chip can supply at 40mA per pin with a total of 200mA in all. It is best to run under these limits. The arduino board when not powering anything else consumes about 35mA. Note that applies tot he processor chip you can get more from the 5V supply line. You need to differentiate between current supplied by the processor’s pins and current from the 5V pin.
Maybe this will help you:-
200mA for 328, 800mA for 2560.
USB 500mA, on board regulator 800mA.
Thank you very much. Your information has been very helpful and I now have some basic guidelines to follow as to what circuits can be added to my project.
A powerhungry shield might have a powerregulator onboard. Maybe it's better to use this regulator and feed the arduinoboard from that one?!
I have noticed the board seem to get very warm when using the external power in instead of the USB port when powering the units.
This is normal.
it reads 9.17 VDC which is well within the acceptable voltage range
The presence of heat doesn't indicate a problem. The acceptable voltage range is stated as up to 12V, even though the regulator can support voltages of at least 20V. The practical limit of the heat sink provided by the PCB the regulator is attached to, limits the usable voltage.
Vregulator - Voutput = 9V - 5V = 4V Drop across the regulator.
Since you compare to USB, say you draw the maximum current USB allows, which is 500mA. This means the regulator is now dissipating 4V * 0.5A = 2Watts. That's a lot of power when the PCB it is attached to is the only heat sink.
Also realize, that what you consider "hot", components do not. They can tolerate more heat than you can.
I'm also having this problem. I'm using a stepper motor paired with an H-bridge and whenever the USB cable is plugged in and connected to the computer, the code and hardware work fine with the board and H-bridge heating up just above ambient temperatures.
However, when I plug in a 9V battery into the Arduino, the code stops working properly and the arduino board (I'm using an Uno) heats up (HOT) as well as the H-bridge after a few seconds.
I tried putting capacitors where the Vin comes into the H-bridge (Pin 8) to negate the power surge on the H-bridge, but the arduino still gets HOT and the stepper motor skips steps, performs too many steps, or pauses all together.
What can I do to fix this problem? I need to have an isolated system that does not plug into the wall and it needs to last a full week without any changes.
Swapped a cheap Uno for a real one and the overheating went away ... the problem (on the cheap one) appears to be excess current flowing from the power plug to the USB. My cheap Uno draws 25mA at 12V without the USB cable connected. That jumps to 258mA as soon as the USB cable connects to a computer. My old true Uno (with ATMEGA 328-P DIP) draws 50mA at 12V with or without USB. There's more difference between these boards than just the FDDI chip ... Heating is evident on the components between power and USB sockets, parts labeled Q1, R14, ... just don't have time to trace the parts against the schematic ...
Summary: this is a real problem with some of the knock-off arduinos that aren't properly isolating external power from usb power -- its not a daughterboard problem.
Swapped a cheap Uno for a real one and the overheating went away ... the problem (on the cheap one) appears to be excess current flowing from the power plug to the USB. My cheap Uno draws 25mA at 12V without the USB cable connected. That jumps to 258mA as soon as the USB cable connects to a computer. My old true Uno (with ATMEGA 328-P DIP) draws 50mA at 12V with or without USB. There's more difference between these boards than just the FDDI chip ...
Tracing some voltages on the two boards: U1, a LM358 compares 3.3V with (Vin-0.6V)/2. With external power, the real Arduino U1-1 = 5V, cheap Arduino U1-1 = 3.74V, probably not quite shutting off the FET T1 (labeled Q1 on the cheap board). U1-8 = 5V on both, so either the op-amp isn't putting out enough voltage or the FET is drawing too much current. On both boards, this FET is a small 3 pin chip on the edge between the power and USB sockets, and although I don't have an IR sensor, I believe its absorbing the power.
Summary: this is a real problem with some knock-off arduinos that aren't properly isolating external power from usb power -- its not a daughterboard problem. I've seen it with several cheap Unos.