After seeing several threads (like this one) I made a setup that powers a Photon directly via the 3V3 pin. I use a switch mode converter (Murata oki-78sr) to produce a clean 3.3V from the 12V input.
For some reason, the Photon got really hot, behaved erratically and then died. I measured all pins with a multimeter. Only 3V3, VIN, and the I2C lines read 3.3 volts. All other pins measure 0V. To me this looked perfectly fine, so I put in a new Photon and … it died too after a few seconds of operation.
The first time I had USB plugged in also, but the second time the USB wasn’t connected. I need this solved before plugging in another Photon, but I’m out of ideas as to why this happens. Could it be that there are issues with powering with 3.3V directly? Anyone?