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Discussion Starter #1
Hi

Nigel Calder is fairly convincing in arguing against using batteries in different physical locations in the same bank [eg Calder boatowner's mech & elec manual p22].

I am very inclined to take this advice and not "go boom", but have to admit that in my situation having two of three batteries about 3 feet away in a separate compartment connected with very large gauge wire is somewhat attractive and before i dismissed the idea entirely I thought i would solicit further opinions from Ye Olde Peanute Gallery

given the possible consequences, I doubt I would try this but curious if anyone has blowed themselves up doing this or done it without ill effects?
 

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It's done all the time. Never heard of a significant problem, providing the basic installation is correct.

On my boat, I have one large house battery bank consisting of six Trojan T-105 batteries. Two of these are under the nav seat on the starboard side, four are located under the berth in the owners cabin on the port side. The two banks are connected thru a hefty 1-2-BOTH-OFF switch which is left in the BOTH position.

The cables connecting the two banks are about 12 feet long, and are of heavy guage (1/O I believe). They probably should be larger, though.

Never had a problem in many years; everything works as it should.

That said, it's definitely preferable to co-locate all your house batteries, rather than separating them. But, if that's not possible, I don't see why you can't separate them if you do the proper engineering.

Bill
 

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with large guage wire so you do not have voltage drop i can't see what difference it would make. can anyone tell me why it would?
 

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The concern is voltage drop over a long length of wire. However, if you use large guage wire, 1/0 or 2/0 it should not be an issue. Again it is preferable to have them all together (all the weight is concentrated in one place and they are easier to service) but not absolutely necessary.
 

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Discussion Starter #6
thanks for the responses, particularly Bill, as nothing quite beats experience. sounds like it may be safely doable after all.

I'm not so concerned with any voltage drop, as sufficiently large gauge wire could be used (no offence, i personally am an awful speller most times, but gauge gets mispelled as guage so often) negating that.

Calder's concern was different temperatures for the different batteries in the same bank resulting in different discharge and recharging characteristics. i am extrapolating from your responses that you consider this to be a theoretical rather than practical risk.
 

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"with large guage wire so you do not have voltage drop "
With any wire, you have voltage drop. Even if it is a tenth of a volt, that will eventually age one battery more than the other and things will go downhill from there. You'd need to run the numbers for your cable size and length, and the amperage you are pushing, to see whether you really have "no" voltage drop or not.

But, if you arrange your cabling so that the total running footage to each battery is the same, the voltage drops are equal and then they are not an issue. That may mean having two or three or six feet of cable "wasted" here or there, but that's still a cheap price to balance the system.

Or, you could use arm-thick copper bus bars instead of cables. The voltage drop in those would be pretty insignificant.(G)
 

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The question for me is: When is a battery bank a battery bank?

I have my house bank, all geographically together and properly cabled up etc.

Then I have my starter battery and my windlass battery on the second "bank". Why the parenthesis? Well, the only connection between the two batteries is a pair of charge lines. The windlass is, as expected, in the bow and its battery is right alongside it. It gets its charge through a light-weight (comparitively) pair of wires that run through a temperature-sensitive switch that prevents the wires from overheating if the starter battery is down on cranking power.

When the charge system pts charge in, it does both batteries equally well, both on the engine driven alts and the Xantex mains charger. The Xantrex Link 20 also appears to read the batteries properly.

Am I likely to lose a battery prematurely? I don't know:confused:
 

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Thermal runaway is what Calder talks of. I suspect Bills two locations are of a similar temp. You might get closer to Calders scenerio if you have 2 batteries in the engine compartment and a 3rd in a cool locker.
Most modern charging systems have a temp sensor. Where would you put the temp sensor, on the 2 in the engine compartment or on the 3rd in the locker with a 30d temp difference?
Putting batteries in 2 lockers with a 5 degree difference is probably a lot different!

Andre
Sounds like your start battery and your windlass battery are 2 separate banks charged by the same system with 2 feeds
 

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Yes, Andre....exactly right! You beat me to it; I should have included that.

If you're going to have batteries in different locations, it's best to have them in near-identical temperature settings. Mine are. Previously, several had been in the engine room; I moved them out for exactly that reason, and also to have easier access.

Bill
 

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HS's solution is similar to what I did on my friend's boat. The two sets of batteries are wired to a 1/2/Both switch that is located equidistant from both sets, and a heavier cable connects the battery switch's output to the main DC battery switch for the boat.
 

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Ah, different thermal environments. That would be something to be concerned with. To have a boat big enough for different microclimates, what a concept.(G)

Andre, do you really have one SLI starter battery and one deep cycle windlass battery combined in parallel as one bank?? I would expect the mixing of battery types, and the voltage drop from long cables, would create issues there. Possibly cooking the starter battery--and deep cycling it more than they should be--as the windlass battery sucks power through those long thin cables.
 

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Discussion Starter #14
thanks again for the responses. might actually change what i do in this case.

in addition to thermal runaway, which can happen apart from physically separate batteries in one bank and is pretty uncommon, Calder also implied that due to the different temperatures battery life would be reduced, i suspect almost like using different aged/sized/model batteries in the same bank.

cheers
 

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Andre, do you really have one SLI starter battery and one deep cycle windlass battery combined in parallel as one bank?? I would expect the mixing of battery types, and the voltage drop from long cables, would create issues there. Possibly cooking the starter battery--and deep cycling it more than they should be--as the windlass battery sucks power through those long thin cables.
Both my starter and windlass batteries are ordinary 12v lead acid batteries (not deep cycle) typically found in the average truck or bus. They are both 880CCA and each feeds its respective load via heavy duty battery cables to the starter and the windlass. The light weight wires to the windlass are only charge lines. There is no huge current flowing across them. These batteries release large current and recharge relatively quickly.

Just for my own interest, why would anyone use a deep cycle battery on a device that requires relatively short bursts of high current draw? Surely that's not a regime that favours deep cycle chemistry?

In fact as said earlier, I have a thermo switch on the charge lines that breaks the circuit if it gets hot and restores when it cools down. This stops the lines from overheating both under charge but more importantly, if the starter battery gets "soft", the thermo switch prevents the starter from drawing it's current along the light-weight lines from the windlass battery and vice versa.

Does that make better sense? It has been hooked up like that for nearly two years and appears to work just fine.
 

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I would have expected a deep cycle on the windlass, but that really is the kind of task/load that probably falls between the two types and can be met by either one, just depending on how much power the windlass takes, how long you run it, how big the battery is, etc.

The need for a thermal switch implies that the wires are expected to get hot from time to time--which is never a good thing. Thermal switches fail, like eveyrthing else (except maybe paperweights!) and that would leave you with a potential for fire. The switch, or a breaker, is still a good idea, but ideally the cables would be heavy enough so they would not overheat in normal use. If they are heating up at all, that indicates excess resistance for the current draw, which means you are wasting power whenever you charge that battery. Either running the alternator harder than it needs to be run, or more likely longer than it needs to be run.

But if you use the windlass infrequently, I can see that still being a reasonable tradeoff against the cost and bulk of "proper" heavy cabling running all the way forward.

Sounds like you have a "Group 79" battery, about the same capacity as a more common group 27 (in the US) but shaped a little differently, with about a 90AH capacity. Most SLI batteries are designed for something like a 5-10% discharge between recharges, so if that's all the power you are pulling out of it between charges (5-10AH) it should be perfectly happy.
 

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The need for a thermal switch implies that the wires are expected to get hot from time to time--which is never a good thing.
I'm sorry if I left that impression - it wasn't my plan:) . No, the thermal switch is not there because we're experiencing hot wires. It's really just a safety device that will cut the circuit if something goes wrong.

Typically with the windlass wired up locally (in the anchor locker), if the starter battery goes flat and you try to start the engine, the starter motor will draw a typical starter draw (say 35A) down two light weight wires and if there is no thermal protection, you have a bonfire. Our thermal switch has never had cause to do it's job so for all I know it might already be stuffed. Maybe I should find a way to test it.:p
 
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