A failure trifecta of poor design, worse maintenance and external forces out of my control
Last weekend I went to check on the boat and found, to my great disappointment, warm beer. My house batteries were way down, like 11 volts for both 2xGR31 banks (= 4 GR31 batteries total). It turned out my shore power cord plug had become dislodged at the dock box end, still partially in the twistlock receptacle but not making contact. Either a passerby stubbed his toe on the cord or maybe the strong winds jostling the boat in the slip did it but either way the result was the refrigeration drew down the batteries. No worries about low voltage damage to anything, of the few things I have on when away from the boat, the most vulnerable is the refrigeration and it has a low voltage cutoff feature that protects itself.
I thought I'd start the engine on the dedicated start battery that was isolated from the house loads, a design I've had since I rewired the boat 15 years ago, and let the 100 amp alternator do some serious work. No joy, that battery was dead too, now 5 dead batteries. OK, now I'm wondering if the engine start battery was indeed isolated. Dammit, I know it was so what is going on?
After very little checking I found the engine battery had dry plates. To my embarrassment I could not remember the last time I checked the water levels and to make matters worse, the engine battery was on one of two shore charger circuits 24/7 and it is a conventional lead-acid GR24 battery, not deep cycle. It was pretty clear lack of maintenance and constant charging cooked it but it was also clear its failure was unrelated to the dislodged shore power cord.
So how to make the system better?
I rewired the two shore charger circuits so each circuit goes to a house bank. No shore charging for the engine battery, it will now survive on alternator charging alone, same as a car. There are no sentinel circuits drawing off the engine battery so there are no losses at rest.
I replaced the engine battery and checked the water in the remaining 4 house batteries (all good, a couple of cells needed a minor top off), re-secured the shore power cable making sure it had an ample slack loop. If the deep cycle house batteries tolerated the deep cycle episode we should be good.
Last weekend I went to check on the boat and found, to my great disappointment, warm beer. My house batteries were way down, like 11 volts for both 2xGR31 banks (= 4 GR31 batteries total). It turned out my shore power cord plug had become dislodged at the dock box end, still partially in the twistlock receptacle but not making contact. Either a passerby stubbed his toe on the cord or maybe the strong winds jostling the boat in the slip did it but either way the result was the refrigeration drew down the batteries. No worries about low voltage damage to anything, of the few things I have on when away from the boat, the most vulnerable is the refrigeration and it has a low voltage cutoff feature that protects itself.
I thought I'd start the engine on the dedicated start battery that was isolated from the house loads, a design I've had since I rewired the boat 15 years ago, and let the 100 amp alternator do some serious work. No joy, that battery was dead too, now 5 dead batteries. OK, now I'm wondering if the engine start battery was indeed isolated. Dammit, I know it was so what is going on?
After very little checking I found the engine battery had dry plates. To my embarrassment I could not remember the last time I checked the water levels and to make matters worse, the engine battery was on one of two shore charger circuits 24/7 and it is a conventional lead-acid GR24 battery, not deep cycle. It was pretty clear lack of maintenance and constant charging cooked it but it was also clear its failure was unrelated to the dislodged shore power cord.
So how to make the system better?
I rewired the two shore charger circuits so each circuit goes to a house bank. No shore charging for the engine battery, it will now survive on alternator charging alone, same as a car. There are no sentinel circuits drawing off the engine battery so there are no losses at rest.
I replaced the engine battery and checked the water in the remaining 4 house batteries (all good, a couple of cells needed a minor top off), re-secured the shore power cable making sure it had an ample slack loop. If the deep cycle house batteries tolerated the deep cycle episode we should be good.
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