AS3935 Lightning Detector: The Sequel

“Look aloft!” cried Starbuck. “The corpusants! the corpusants!"

 "The lightning flashes through my skull; mine eyeballs ache ... " - Captain Ahab

The rainy season came late and in its very first acid test, the AS3935 detected the oncoming storm and disconnected the ADSL modem in good time. However a really close strike after that took out the AS3935's relay module; the lightning must have arced over the open relay contacts into the 5V line. I had unwisely left my laptop connected to it to collect the debug messages, so the lightning took out my laptop as well as its power module, and plunging the neighborhood into darkness.

And to prove it was no fluke, repeated strikes on the now-unpowered system produced white arcs on a twitching relay board, a real sight to behold in the darkness. "The corpusants", like Starbuck said in Melville's 'Moby Dick'. This is probably very risky, so do proceed with caution if you ever have the misfortune to encounter this.

Scorch marks on the relay module

The over-current on the 5V line is such the heat lifted the copper trace right off the PCB.

The surge must have arced over to the nearby 5V pin on its way to the USB power line

And welded the USB connector to the hub.

The USB hub socket was welded to the cable. Note the melted contact on the left.

The ESP-12E had no obvious signs of damage but was unresponsive. Happily the AS3935 was undamaged.

Burst mains 'Live' wire in the power extension cable

The 'Live' wire in the mains power extension (to laptop power adapter) open-circuited, although the 13A fuze was intact. The 3A 230V fuze in the laptop adapter blew. This calls for a rethink:
  1. the relay contacts need to be a lot better isolated from each other
  2. more isolation is needed between the relay module and the ESP-12E
  3. the power modules need to be better isolated

(Update 2020-01-22): The lightning strike propagated along the 5V rail and damaged the LM1117-3.3 regulator in the ESP-12E. It also seemed to have slightly damaged the AS3935 (which also takes 5V directly to the IC) and although its registers read normal and it can be calibrated, it no longer classified 'disturber' events as lightning, no matter how near. New parts have been ordered - this is not over!

(Update 2020-02-15): Dismantled my laptop, an Asus X751L. 

Asus X751L disassembled - one of the worst things about laptop repair is the disassembly. There are myriad flimsy plastic tabs to break and also various irreplaceable flexible cables to rip off by accident

As suspected, the fuses had blown:

Blown fuses, middle, just beside the 6-pin 19V power adapter connector. The power MOS QM3024M3 are the square 8-pin IC just to the left

The fuses lead to the drain of a QM3024M power MOSFET rated at 30V and a stonking 46A. The source is connected to a second QM3024M3, and this second MOSFET has a short-circuit from drain to source. Ouch.

The first MOSFET is likely used to turn on 19V from power adapter to the mainboard power supply unit, and the other MOSFET to connect the battery when there is no mains supply. The short-circuit means that the lightning strike short-circuited the 19V adapter output and battery output simultaneously to 0V. Indeed the battery was completely drained. Looks like I have a dead power MOSFET as well. 

Dead bug: QM3024M3 upside down. On removal the mainboard is no longer shorted

I confirmed this by de-soldering it from the mainboard.

Watch this space. Happy Trails.

"... I will do my endeavor. I try all things; I achieve what I can" - Ishmael,  'Moby Dick' by Herman Melville