Repairing the lightning damage
Phil May and Andrea Twigg
Tue 4 Nov 2014 04:22
The main damage from the lightning, apart from various fuses being blown, was that three of our power distribution boards were fried. The boards are no longer in production (I believe the company that made them has shut down) and so Catana could not easily supply replacements. I decided to try and repair the boards.
They are fairly simple relay control circuits built from standard electronic components. I picked up all the components I thought I would need on my last trip to the UK. The main challenge was that the failing chip got so hot that it burned a hole right through the circuit boards. These are three layered boards, with a set of copper tracks on each side of the board and another set sandwiched in the middle. The tracks in the burned out area were a real mess.
I started by replacing the chip on the least damaged board and that one worked first time. On the second board I failed to clean away all the debris, leaving a voltage leak between two of the pins of the chip, which was incorrectly triggering a relay. That problem took the most part of a day to resolve. I took more care with the final board and this one also worked first time.
The final task was to replace some burned out LEDs on the central console. This was unexpected and I did not have replacement LEDs, but surprisingly found a Radio Shack on Curacao where I could buy them.
We now have central control of our boat systems again!
We were not struck directly I have been wondering why a nearby strike would cause such damage. I think it is because we are a catamaran and are therefore more susceptible to voltages through the water, for the same reason that you are more likely to survive a nearby lightning strike if you are standing on one leg. (Do boy scouts really practise standing on one leg in a storm?)
With two hulls in the water, the voltage from a strike nearby will find a nice low-resistance path up through the ground in one hull and out of the ground in the other hull. Meanwhile the boat systems are subjected to hundreds/thousands of volts of reverse polarity. Why aren’t catamaran electrical systems designed with all the grounding routed through just one of the hulls?
The failing chip got very hot...
...and burned right through the circuit board, fusing the pins and tracks
The fix involved replacing the burned out chip plus some failed resistors and capacitors
The majority of the tracks to the chip had to be rewired