I am not sure if anyone has ever experienced what just happened to me, but I think it is important info for everyone out there. My battery compartment exploded early yesterday morning. No one is certain exactly what happened, and no one who has investigated the accident has ever seen this occur. I am still up on the hard in Annapolis trying to get my new engine installation completed - that was a subject of a previous thread, and I will update everyone who followed that thread separately once I get my new engine running.
The explosion was quite severe and apparently set off my smoke detector which everyone in the yard heard. There was no fire. Oddly no one claims they heard the explosion itself, as it may have happened before the contractors started to come in for work. It blew the lid completely off of the passageway berth and into the ceiling, jamming it between the wall of the aft closet and the wall near the nav station closet. Fortunately no one was on the boat at the time, but if someone had been in the passageway between the main saloon and the aft cabin, they would have been seriously injured or even killed. I do not want to even speculate what would have happened if someone had been sleeping on the berth. I had some parts and tools sitting on the berth cushion and they were either shredded, melted, or survived depending on the material. It was a scary situation.
I am working with my insurance company and they hired a local surveyor to assess the situation. They, as I do, want to know the reason for the explosion. Beyond the damage to the compartment lid/berth and the surrounding woodwork, here are the facts:
- At least 2 of the AGM batteries had been breached with cracks in the tops. None of the VRLA valves had popped.
- A few of the batteries were bulged out at the sides. Not clear if that happened initially or as a result of the explosion. Ultimately about half of the 12 on the 24-volt side were "bad."
- My shore power connections were off. The only charging source would have been wind and solar. Both of those systems have been working correctly for a long time, and early in the morning there was no wind and not much sun. We do not think it was an overcharge issue. I have multiple monitoring systems including the Xantrex that came with the boat, plus a Maretron monitor and Blue Sea meters. All were nominal when I left the boat before the explosion. Voltage was about 27.5 and there was a small load of maybe 3 or 4 amps DC, easily absorbed with the solar panels.
- The batteries are a little over 4 years old and came with the boat. I have never had a problem with them, and the charging systems have never pushed above 28 volts.
- The battery setup was reworked last winter by a very good contractor here in the yard. They added fuses to all the loads, and it has worked very well for months now. I find it hard to believe that there was no primary battery fusing on the boat at all, but that is still another topic for review. However, the explosion would not have been related to current flow and hence the fusing was not an issue one way or the other.
- I have 12 Intimidator AGM batteries in the battery area with a 12V starting battery.
- Testing them after the accident revealed about half of them to be unserviceable (either electrically or physically).
It is clear to the investigators that the explosion was the result of hydrogen gas buildup in the battery compartment. The problem they observed is that (while there is a vent at the forward part of the battery compartment, Amel seals the compartment completely). Normally the vent is OK, as any residual hydrogen will escape out the vent.. But the Amel setup prevents any makeup air from entering the compartment. Normally AGM batteries do not vent externally, as the hydrogen sulfide normally released in a flooded battery is actually recombined in an AGM setup. There are valves in a VRLA battery, which are supposed to open if the internal pressure gets too high. However, if the casing is breached, gasses will release immediately, which is what happened here. What no one knows yet is why the batteries cracked open. The bottom line is that the vent could not release the gas fast enough, and the hydrogen gas exploded as it built up in the sealed compartment.
I am going to modify the configuration by adding ventilation to the front of the battery compartment. I am also going to install 13 new Lifeline batteries (12 31-XT and 1 31T battery for starting). Good quality batteries with a modified install should prevent a recurrence. What a mess.................
All I can say is thank goodness no one was hurt.
s/v Phantom Amel 54 #044