batteries in different physical locations, same bank

[ArgleBargle]

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?

[btrayfors]

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

[captbillc]

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?

[camaraderie]

I would say 3 feet away with proper wiring is NO issue.

[peikenberry]

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.

[ArgleBargle]

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.

[hellosailor]

"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)

[Omatako]

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

[xort]

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

[btrayfors]

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