My third Orange Pi Zero came last week, yesterday I plugged it and had heating issues... So I started reading, learning and testing....
Setup:
OPiZ-1: 256 MB, no SPI flash - Has extension board plugged - for comparison
OPiZ-2: 512 MB, with SPI flash
OPiZ-3: 256 MB, with SPI flash (new one with problem)
Test conditions:
All with (newish) Sandisk Ultra 16 GB Class 10
All new formatted (SD Formatter) and burned/validated (Etcher v1.0.0) with Armbian_5.25_Orangepizero_Debian_jessie_default_3.4.113.img
All on my desk - side by side, ambient temperature 25.0-25.1 C (20 cm from boards, no air flow)
No case, no passive/active cooling
Power supply 7 port 5V 36W total, 2.4A per port (wait, wait, I tried others, separated etc - I'm testing them with USB V/A/W tester - 5.2-5.3V / 0.260-0.350 A)
First install done, rebooted, apt-get update && apt-get upgrade'd, rebooted, tested