Everyone has a different story and opinion.
I'd have to disagree strongly with any "never" as regards separating batteries. Noone on principle wants separate packs---it's always motivated by something else. Some folks believe that having separate strings and using them separately gives them at least psychological advantage in knowing they have that other pack. I'd guess that most folks who choose to not collocate the entire pack do so because of either weight balance concerns on the boat or logisitics in having space available for the batteries. Sure, there's definitely balance concerns with PbA battery chemistry that if you end up with short cables to one part of the pack and then there's a parallel pack forward with much longer cables. It was but one of the reasons I didn't locate any part of my PbA battery pack away from the main pack to the rear of the boat in 2003 thru 2014. Electric cars are informative here. From 1907 thru 1924, nearly every single electric vehicle manufacturer split their packs, opting for some portion in the front and some in the back. Cable lengths were long, but they needed the weight balance. And it wasn't as if the pack was always series-configured with the fore- and aft- half-packs. In several cases these half packs were paralleled up, even if just temporarily with 1st and 2nd speeds. Back to the 21st century: Many of us are using lithium now with its near non-existent Peukert effect and uber-low internal resistance for the cell sizes we use. In such cases, there's near zero risk, cost or impact in having part of your pack near the loads (and charger) and some (or most) of it located in more convenient locations. There's no out-gassing concern. There's not an issue with sharing---they'll balance later and as they go (and cells will get balanced with BMS).
Examples are useful: Just 1 of 10 of my lithium batteries can easily deliver more than max power to my ETEK motor with less than 0.5v droop impact at the battery. I have 6 of those relatively close by. Long cable lengths to the other 4 batteries? Not a big deal. In fact, I went overkill by using a much higher gauge cable than I needed---but there are good reasons for big cable (you want fuses to blow rather than cables to melt).
Anyway, your mileage may vary, but as long as I was accepting of any tradeoffs, I wouldn't hesitate to split the pack…it's been done for over 100 years now.
A West coast opinion-
-Myles Twete, Portland, Or.
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Wednesday, April 26, 2017 4:04 PM
To: electricboats@yahoogroups.com
Subject: RE: [Electric Boats] split location of battery bank
Mike,
It's never a good idea to separate the batteries and always have them as close together as possible. 5' isn't that big a deal but make sure he maximizes the cable size probably 2 sizes bigger than recommended for the amps. In most cases the A/B switch is farther away on a boat and I've seen wires way undersized going to them. Also the general maintenance of the battery wires that I've helped with on other boats can only be discribed as generaly poor when I got there. If anything I've learned to be very finicky about it.
Steve in Solomons MD
Lagoon 410 S2e
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Tuesday, April 25, 2017 11:24 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] split location of battery bank
Question about split location of a house bank: Is this a bad idea? How far apart is ok? I'm thinking it could affect the charging rates and the balance of the batteries. I'm helping a guy upgrade his house bank so this will be a fast charge, slow discharge situation. Any different from an electric drive situation?
It's an Islander 36. There's room for 2 each under the step, under the quarterberth, and under the nav station, so fairly close, maybe 5' runs.
Mike
Posted by: "Myles Twete" <matwete@comcast.net>
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