Arduino Nano burns with ESP-01 in parallel So I have an Arduino Nano powered in parallel with an ESP-01 (for the ESP there is an extra LM1117-5.0 voltage regulator in series).

+12V ---------+---------+
              |         |
             Reg        |
              |        NANO
             ESP        |
              |         |
 GND ---------+---------+


My problem is that after a while, the Nano burns (my guess is the difference in current that both devices draw).

In any case, what could be the reason and what could I do to fix it?

Thanks!
Use the 5v regulator to power both the ESP and the Nano. Those onboard regulators have minimal heat dissipation and if they burn out you lose the whole Nano. Check how hot your external regulator gets and mount it on a heat sink if it gets too hot to touch. 
NB Connect the regulator output to the Nano 5v pin directly