 |
| "The drama's done. Why then here does any one step forth? — Because one did survive the wreck" - Herman Melville, 'Moby Dick' |
It's been a strange dry season - there wasn't one. Instead of the choking haze from the fires of Indonesia, August and September brought only rain and thunderstorms. The AS3935 survived them all, until now. As usual the AS3935 detector flagged the oncoming storm. Since the lightning appears to come from the phone copper lines, esp8266 relay modules were used to disconnect the phone line from the ADSL modem. The modem is powered from a float-charged NS60 12V automotive battery. The battery charger, too was disconnected from the mains, both Live and Neutral, so as to deny the strike a path to Earth.
In order to reconnect after the storm an esp8266 4-channel module itself is powered from the same battery, but a separate 2-channel esp8266 relay module is used to disconnect the ADSL phone lines. The ADSL relay module itself is also disconnected from its 5V power supply, as previous strikes tended to jump from the relay contacts to the 5V/GND lines powering the relay coils.
The esp8266 and as3935 modules are wirelessly linked via MQTT server.
On Thursday Sep 24, a nearby strike came in via the ADSL line, and flashed over the open relay contacts. This destroyed the 2-channel relay module (including the attached esp8266) and propagated along the 5V power line over to the 4-channel relay contacts. There it flashed over the open relay contacts to the 12V-5V buck converter and damaged it. This resulted in a short-circuit across the 12V battery and also damaged the 13.8V CC CV module used to float-charge the battery. There is no direct connection to Live, Neutral or Earth (the 4-channel relays were off).
The 4-channel relay is the only component along the strike path which survived.
 |
| From right: lightning strike along the ADSL line flashed over the relay contacts to the 5V power lines. Insulating tape was used to reduce severity of flashover |
 |
| Note the burn mark along the 5V power PCB trace |
 |
| Burned area: relay coil 5V pin near relay contact connected the surge to the 5V power system and spread via the LM1117 to the ESP8266 via the 3.3V output. It also propagated to the 12V-5V buck converter |
 |
| 12V-5V buck converter had shorted output schottky diode SS34 |
 |
| 13.8V CC CV float charge module takes unregulated 18Vdc and puts out 13V8 constant current constant voltage. Its output schottky diode SS54 was shorted, effectively shorting the battery |
 |
| Sole survivor: 4-channel relay module used to disconnect power to battery charger and to ADSL relay module |
The lightning strike must have been really close because it also took out my autogate controller and damaged lights a few houses down the street. Unlike Captain Ahab, this is where I concede defeat. After 25 years, the lightning won and I disconnected the ADSL system.
Henceforth the future is fiber-optic. In fact it was operating concurrently with the ADSL modem when the lightning struck and it survived unscathed. At least I had Netflix.
Happy Trails.
"And I only am escaped alone to tell thee." -- Job
No comments:
Post a Comment