user50081: Problem with my arduino is when I check voltage of 3.3 volt pin using multimeter , voltage varries a lot from 1.5v upto 5v. Due to which esp8266 wifi module connected to this 3.3v pin gets very hot. 
Is the arduino is faulty or can me made to produce steady 3.3 v . Kindly suggest .
Thank you.

user37622: I am sure the voltage is stable without load. Voltage fluctuations are sign of not enough current available.
If you look into the Uno specs, you will find out that the 3.3 V pin can supply max 50 mA.
If you look into esp8266 datasheet in power section you will find out that it needs far more current than 50 mA.
Power the esp8266 from 5V pin over a voltage converter.

user4143: The Arduino cannot power an ESP8266 directly.
A genuine Arduino has the LP2985 which can provide up to 150mA (about a quarter of what you need for an ESP8266) and will go into "thermal shutdown" when it gets overloaded. 
However, a Chinese (or other cheap) clone could use something even less powerful, with or without thermal protection.  In this case overloading the 3.3V pin could irreversibly damage the 3.3V regulator (which may be internal to the USB chip, killing the USB connection in the process) and thus render it unable to regulate the voltage down to 3.3V properly.
If the latter is the case then it is also possible that the higher voltage passed through by the failed regulator could have also killed the ESP8266 chip.

50081: <p>Problem with my arduino is when I check voltage of 3.3 volt pin using multimeter , voltage varries a lot from 1.5v upto 5v. Due to which esp8266 wifi module connected to this 3.3v pin gets very hot. </p>

<p>Is the arduino is faulty or can me made to produce steady 3.3 v . Kindly suggest .</p>

<p>Thank you.</p>
 37622: <p>I am sure the voltage is stable without load. Voltage fluctuations are sign of not enough current available.</p>

<p>If you look into the Uno specs, you will find out that the 3.3 V pin can supply max 50 mA.</p>

<p>If you look into esp8266 datasheet in power section you will find out that it needs far more current than 50 mA.</p>

<p>Power the esp8266 from 5V pin over a voltage converter.</p>
 4143: <p>The Arduino cannot power an ESP8266 directly.</p>

<p>A genuine Arduino has the LP2985 which can provide up to 150mA (about a quarter of what you need for an ESP8266) and will go into "thermal shutdown" when it gets overloaded. </p>

<p>However, a Chinese (or other cheap) clone could use something even less powerful, with or without thermal protection.  In this case overloading the 3.3V pin could irreversibly damage the 3.3V regulator (which may be internal to the USB chip, killing the USB connection in the process) and thus render it unable to regulate the voltage down to 3.3V properly.</p>

<p>If the latter is the case then it is also possible that the higher voltage passed through by the failed regulator could have also killed the ESP8266 chip.</p>
