As many advised here in the forum I'm using a 5v 3A UBEC to power my Raspberry Pi Zero W:
https://www.dx.com/p/hobbywing-5v-6v-3a ... ubec-15149
The UBEC input is drawing from a 12V 230A lawnmower battery.
The output is directly into the 5v and GND pins. There are a few devices pulling power from the Pi's 3V:
two I2C devices (ADC and LSM303), a UART device (I moved the bluetooth UART to the mini-UART) and 2 4-channel relay boards (one is a DPDT relay board). For the relays I've disconnected the JD-VCC jumper and they are pulling 5V in parallel to the PI to power the relay, while the input signals and the regular VCC comes off the PI's 3V. In total I don't think these pull more than 3A, and none of the relays were switched on at the time of the problem.
All connections are made through a breadboard, but I'd like to move to something more permanent as soon as I'm confident that the power setup is working and I stop burning up pis.
I've burnt out two Pis now with this configuration, they appear to work for a while then poof. In the most recent time the Pi had been in use with no wiring changes for about 20 hours. It had been running for about 3 hours contiguously while I was debugging a program on it over SSH. The Pi was essentially idle (except for an active Wifi connection) and I went to copy some new code over winSCP and the Pi froze - green activity light was still on and solid green. I disconnected the power (jumper clips) and reconnected it to reboot the Pi, the power light didn't come back on. I pulled the pi out of the breadboard and tried connecting via a normal power supply from adafruit and sure enough it's toast.
Is it the UBEC that's killing my Pis or is it possible something else is awry like overheating? Perhaps somehow when I connect the high amp battery it's pulling more than it should for a split-second? Is there a more reliable way I can supply power than this UBEC?