Battery project during winter doldrums

[SalishAire]

PROBLEM: Hyacinth (A25) came to us with 2 - 12V deep cycle batteries in good condition but we always felt we needed to only use one at a time for "house" duties as we needed to keep the second in reserve for engine starting. ALSO: After living on a boat with 2 massive battery banks (and an engine start battery) and then a trailer all with flooded batteries we (OK primary keeper of the batteries Clarice) was just tired of accessing and watering batteries. On Hyacinth the process involved removing the main bench seat, lifting the floor board, lifting the battery cover, and so on.

PLAN: Install a house bank of 2 - 6V deep cycle commercial grade (we chose Trojan brand) AGM batteries for the house bank and a separate AGM start battery with a charging system that gave priority to the start battery.

This is what was installed (and came out very nicely!):

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[DesertAlbin736]

Norman, you're thinking along the same lines as I did with my 'add a larger holding tank' project in which I had to relocate my batteries to make room for the larger holding tank. I went with AGM's only because mounting them inside the starboard bench seat lazarette locker (which meant reinforcing the floor panel to handle the extra weight) made access to add battery water more difficult. AGM's "convenience" factor comes at a cost in addition to just the higher price. That of course is the need for a "smart" charging profile with a regulator (and onboard charger) capable of cycling between constant current, constant voltage, and 13.4V "float" mode. Otherwise overcharging with 14.1V all the time even when the batteries are already at full charge can over time deplete electrolyte that can't be replaced thereby shortening battery life.


Personally if you had easier access than this to your batteries I would stick with FLA. One the other hand, AGM's are more convenient to deal with.

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So I added a Mark Grasser solid state external reg for the engine which does have an AGM charging mode as well as a manual 13.4V "forced to float" option. And I installed a Blue Sea Systems "Add A Battery" main switch with SI/ACR relay that automatically keeps house & start banks separate when the engine isn't running. The "SI" function is "Start Isolation", meaning when the starter is actually cranking the engine the house circuits including your electronics are kept isolated from the momentary voltage drop caused by heavy amp draw of the starter motor. When the engine is running & alternator is putting out a charging voltage the relay closes and charges both banks through a separate fused circuit. So you don't have to worry about running the start battery down because you forgot to switch from "Both" while on the hook for several days.

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Here's my wiring diagram

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SI-ACR charging relay

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12V distribution inside the head compartment showing SI connections

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[LopezMike]

Just in case anyone besides me is a bit intimidated by such complexity, I offer my 'dumb' solution.

I have two banks. A pair of golf cart cells for a house bank and a G27 for cranking. A disconnect switch at each bank for emergencies. I bought an extra oil pressure switch that operates backwards, i.e., the contacts close when the pressure comes up after starting the engine. This is plumbed to the same place on the engine as the existing oil pressure switch that feeds the warning light.

I have no "1 - 2 - all" battery switch which means that I have reduced the probability of my doing something dumb like running both banks down!

When the engine is running, both banks are in parallel. When the engine stops and the oil pressure drops, the two banks are separated.

So far, so good.

Mike

[DesertAlbin736]

Mike, that's a very innovative solution!. I didn't mention the 20 watt solar panel trickle charger mounted between the opening hatches on the hard top roof over the helm station. It runs thru a 'smart' controller & on/off toggle switch direct to the batteries. The controller also incorporates a digital voltmeter that shows minimum, maximum, and actual real time voltage of each battery bank and output voltage plus max & actual amps of the panel. It ranges from a recorded max of 1.7 amps to a range of 0.5 to 1.5 amps. It also can allocate varied splits of output between banks, which I have set to 30% start/70% house, since where I park the boat I don't have access to AC shore power to otherwise keep the batteries topped up.