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| JP checks the damages: all lights, radars and antennas blown! |
or The Big Surge Protectors
September 8, 2012
Portobelo (Panama)
Already three months since a direct lightning strike in the San Blas Islands devastated our electronic suite, and the controversy still rages on. To have or not to have a marine lightning protection system?
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| Some of the John Deere sensors: unprotected from a surge, the JD electronic boxes and sensors were blown. |
We are strong proponents of Dr. Ewen Thomson’s Marine Lightning Protection System. Other cruisers are of the opinion that the more you do to protect your boat from lighting, the more you elevate the level of the water to the top of your mast, the more likely you are to get hit. I’ll let you debate the issue and will only concentrate on what we learned from the strike.
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| JP made his new home inside the electronics cabinet! |
Dr. Thomson is yet to give us his final analysis, including a likely path of destruction and I look forward to his scientific dissection of the event. Meanwhile, here is our point of view.
Why bother with marine lightning protection in the first place? Because DOMINO is a large power catamaran and, as such, at much higher risk than a sailing monohull. We trust statistics and probabilities. Statistically, sailing cats are twice as likely to get hit by lightning and, when hit, they sustain more damage. Being large, we typically anchor well away from other yachts, thereby increasing our probability of sustaining a strike. So, we took the approach of not “if”, but “when” we get another strike, and we improved on DOMINO’s protection system.
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| Domino in Belize - See the size of the VHF antenna on port side, way taller than our central lightning rod. |
Our main error,it seems, was to install a 16’ VHF antenna. The size of the antenna was not the problem in itself. But the fact that the tip of the antenna was higher than our lightning rod, therefore was not protected by the “umbrella” provided by the lightning rod. From our observations, the discharged went not only though the lightning rod, but also through the antenna, blowing it away.
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| TVS diodes |
Our second errorwas to not have protected the electronic equipment against a voltage surge. The concept of Groundingis explained in details in Dr. Thomson’s website and I’m not about to discuss that topic. On DOMINO, the lightning ground and the general ground are interconnected. While most of the strike energy was dispersed by the large lightning grounding plates under the hulls, voltage spikes ran up the negative circuit and damaged most of the equipment connected to ground.
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| 15KPA17A TVS diodes |
To prevent this in the future, JP is installing arrestors and preventers on all major electronics. This is a very tedious but very indispensable task. Note that none of the Free-standing equipment was damaged (computers, phones, iPad) which in my opinion validates the concept of Faraday Cage as designed on DOMINO!
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| 15KPA diode. The silver band connects to the Pos. side. |
This week, JP is into TVS or “Transient-Voltage-Suppression” diodes. Right, it’s a new one on me! So what are these ¼” long little buggers, what do they do and you do you install them? I Googled “Wikipedia” to the rescue!
These little electronic units also known as “Little Fuses” are designed to protect electronic instruments from intense but short voltage spikes induced into electrical wires during events such as a lightning strike. They are able to absorb high intensity power for a very short time. Once the peak power has passed, the unit resets itself.
“A transient-voltage-suppression diode can respond to over-voltages faster than other common over-voltage protection components such as varistors or gas discharge tubes. The actual clamping occurs in roughly one picosecond, but in a practical circuit the inductance of the wires leading to the device imposes a higher limit. This makes transient-voltage-suppression diodes useful for protection against very fast and often damaging voltage transients. These fast over-voltage transients are present on all distribution networks and can be caused by either internal or external events, such as lightning or motor arcing.” (http://en.wikipedia.org)
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| Ready to fabricate |
Relatively inexpensive ($2.50 to $20 depending on the models) TVS diodes are available from DigiKeyand Little Fuse, the latter providing an Selection Process and Guide.)
JP came up with a shopping list of TVS diodes and that’s what he installed so far:
24V 15KPA33A - AIS (Furuno FA-50)
Fish finder (Furuno DFF3)
Sat compass (Furuno SC50)
30KPA33A - Radar (Furuno DSR12)
Autopilot (Simrad AC12)
Electronics breaker panel
Main 24V breaker panel
12V 5KPA17A - VHF radio (ICOM M604)
15KP17A - Both Engines (John Deere 6081 AFM)
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| Connecting to Pos. |
Then, he went to work! Not terribly difficult, really, as long as you remember to place the silver band side of the diode on the positive (red) side of the circuit.
A little crimping, a little heat shrink, some terminators (ooop… sorry, JP informs me that these little buggers are called “ring terminals”), and your surge protection is ready to be installed.
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| This "Little Fuse" connection might save our engine electronics some day! |
Connected between the Pos. and Neg. the little diode is ready to protect the circuit from electrical surge. MAKE SURE YOUR CIRCUIT IS PROPERLY FUSED!
Voila! There are other kinds of surge protectors, but that’s a story for another day!
Until then,
dominomarie
