Experentia Docet

As it says, experience teaches.  Experience in the sense that repetition leads to mental muscle memory. But a bad experience can also teach, and we just had one.

While we were away from the boat, the temperature sensor for the battery charger failed in such a way as to report to the charging computer the batteries were roughly 1 deg F. Batteries this cold can accept a full volt more that batteries at 90 degrees (which is what these were).

Batteries at 90 degrees, when charged a full volt higher than appropriate, do not respond well. Actually they start by giving off hydrogen gas, then they boil sulphuric acid, and eventually short. Such shorting may or may not lead to a fire. But fire or not this is usually a death knell for very expensive batteries.

In this case, one 135# battery definitely died a bloated, boiling death. Fortunately, in doing so it may have protected the other two such that we can operate until spring albeit at reduced amp-hourage.

Running the charger with manual temperature settings demonstrated the charger had not failed — just the $10 temperature sensor they charge $50 for.

So a $10 failure has destroyed $1500+ of AGM batteries.

To add injury to injury, the acid fumes followed the wiring looms through the boat and sank into the bilge. So all red wires are now brown. All white wires are now lighter brown. The Horseshoe buoy and Lifesling (stored below) are now brown. And all copper and bronze are now black.

I posted a warning of this failure mode on the SSCA Discussion Board and got the usual holier than thou lecture from non-members with nothing better to do. But hopefully it will alert some one.

Going forward we are going to reconfigure our charging concept, and I am looking into a DC voltage sensing relay that will shut the charger off if it senses voltage higher than we deem acceptable. I know, more technology to fail, but relays are a bit more robust than a diode and a resistor.

Perhaps the insulting part (aside from the SSCA DB) was a fellow on our dock was sufficiently put out by our high voltage alarm sounding (yes, we have one, and it worked), he threatened to break into the boat and shut the d**n thing off. But did he tell the marina office so they could call us, and we could tell them what to do? Noooooo. Modern America strikes again.

Glad this happened before I hooked up the solar panels, or I might have thought that they were involved.

And as usual, the fine fellow who wired the boat in 2004 devoted a substantial amount of his time to helping me sort this all out.  Thanks, Jonathan.

More blistering hot weather this coming week and the prospect Tropical Storm Earl could become a hurricane and deliver a direct or glancing blow. Seems like this Bermuda High would keep it east of us. Let’s hope.

2 responses to “Experentia Docet

  1. Pingback: Sneaky Amps | Periodically Peregrine

  2. Pingback: AC Voltage Management | Periodically Peregrine

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