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I am quite new to the science behind electronics (long time software guy), but here is my issue.

I have an Arduino UNO and an Ethernet shield attached to it, all powered by a 7.5VDC wall wart, rated at 1000mA. A multimeter shows that the wall wart is actually outputting around 10.6VDC, why is this?

When the unit is powered on, it immediately begins to heat up (near the power plug, is this called the voltage regulator?), eventually getting to the point of almost burning me.

Is this related to current being pumped into the Arduino? How can I fix it?

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This sounds like a case where you are using an unregulated power supply, and it is expected to provide 7.5V only at its rated 1000 mA. The Arduino Uno and Ethernet shield use less than 1000mA, so the power supply, being unregulated, is supplying too high a voltage.

An Arduino Uno has a 5V regulator near the DC power plug, and it should be capable of handling 6 to 20 V input.

The voltage regulator will get warm when it's converting excess power to heat, and indeed it may seem excessively hot. Given that the voltage you measured is 10.6, there must be a lot of current flowing in order for it to get so warm. (Otherwise it would remain cool.)

The excessive heat seems to indicate a problem such as a short or failed component. Does this problem happen with a different power supply? Have you measured the current use with the power supply you are using now?

Recommendations:

  • Power the Arduino and shield from a USB supply, it's regulated 5 volts and bypasses the Arduino's on-board voltage regulator.
  • Use a different power supply, preferably one that's regulated to the Arduino's input voltage range (recommended 6-12 on the product page).
  • To really know what's going on, you need to measure current, and I would also check the input and output voltage of the on-board regulator. However, continuing to use the power supply that causes excessive heat may permanently damage your device(s).
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  • \$\begingroup\$ I powered the board via USB and everything is fine. I do not have any regulated wall worts and all that I have are 9-12v with output anywhere from 12-15v, too much for my project. I'm not sure if I know how to measure the current? \$\endgroup\$ – lampwins Aug 14 '13 at 6:11
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    \$\begingroup\$ There may be a fault with the Arduino's on-board voltage regulator then. It should be capable of taking 6-20 volts and regulating it to 5V. It's hard to say if the heat it is generating is excessive without knowing the actual temperature. To measure current you need to insert your multimeter into the circuit, using the proper amperage range and moving the test leads to the appropriate positions on the unit. Sparkfun has a tutorial on this topic. \$\endgroup\$ – JYelton Aug 14 '13 at 6:21

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