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Old 01-02-2020, 02:33 PM   #7
Baker
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City: League City, Tx
Vessel Name: Floatsome & Jetsome
Vessel Model: Meridian 411
Join Date: Oct 2007
Posts: 7,332
Quote:
Originally Posted by rslifkin View Post
It can be. But some electronics also have a fairly high cut-out threshold and will drop out if you get a dip down to 10.5 volts or so. Unless you've got a massive battery bank, starting a decent size engine with the house bank drained to 60% can easily cause a second or 2 of voltage down to that range (even more so if there are other loads being powered). It's not necessarily a big concern, but for me, it's reason enough that if there's going to be more than 1 battery bank on board, the house should only be a backup for starting, not the primary source of engine starting power.
I guess that is what we are talking about to some degree....a MASSIVE battery banks. I am not saying to keep your modest sized house bank and eleminate your start banks. I am saying keep your modest sized house bank and add your start batteries to it.....equals a fairly large combined bank. I once screwed up and had my inverter on when I thought I was on shorepower. I have my inverter programmed to cut out at 40% battery power. Of course after the surprise of all AC loads shutting down, I thought to myself.....hmmmm....I wonder if my engines will start on this depleted battery state. I didn't notice any sort of depleted performance from the starters. The engines fired right up....granted I did not have any electronics on as I didn't not think to add them to my impromptu test. I Also have AGM batteries...not sure what their performance curve is on a fairly discharged battery....if they stay level and drop off rapidly or if it is a gradual slope.

I will also echo what was said above. A 40amp charger is WAY too small for a boat that big. Just get you another one(bigger is better) and they can both charge the same bank as long as more than 40amps is needed. Once it gets below that the lesser charger will kick off. It is very possible a boat that size can be burning more amps than the battery charger can keep up with. I have a friend that is a marine electrician. He called on a boat that had an electrical "problem". It was a Carver 53 with a 40amp charger. He went around the boat and counted all of the amps that were being used....50 amps with a 40amp charger. THAT was the problem! AGM batteries also desulfate by rate of charge. They like a good hard fast charge. To give you an idea, Odyssey(maker of the batteries on my boat) recommends a charger that is half the size of the bank!!!!! So a 600amp bank would require 300amps of charging. That is what they call optimum...obviously that is tough to fulfill. But the bigger the better.
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