3-bank charging characteristics

[F51]

I did a search for this but came up empty, so I am asking the forum members.

Quoting from the Xantrex True Charge 2 manual that came with my charger:
It says the charger has *up to three full current rated outputs.*

The note below that goes on to say *each output can charge different batteries that have the same chemistry or can tolerate the same charge sequence and voltage/current ratings.*

I interpret that to mean that all three outputs will have a common bulk/absorption/float routine. I have a 900ah house bank of T-105s and a start bank of 2 group 27s. Will the charger top off the house bank and cook the start bank. Seems as though it would if it follows the same profile for all three outputs. Maybe someone on the forum knows the reality? Thanks.

[djmarchand]

You might think that is the case: cooking the starting battery. But in practice it isn't a problem.

The reason is that the period of high voltage necessary to push the amps into the house batteries (14-14.5) doesn't last long enough to damage the starting batteries. In my case with a 600 AH house bank with a Group 24 starting battery, the high voltage lasted only a couple of hours.

David

[belizesailor]

I've used a Xantrex charger with multiple banks before with no problems. I have not stuck a multimeter to this and watched, but I assume it is smart enough to vary the charge output to each bank, but that the charge profile (gel, flooded, etc) must be the same. Otherwise something would likely get cooked or undercharged.

Xantrex could probably answer this question in more specific detail.

[Stu Jackson]

Overcharging Batteries with a Combiner or ACR

Shouldn't be any different with a charger.

[belizesailor]

Yes, my boat is set-up with a combiner system for house + two starts. When charging all battery banks are combined and, as your link points out, the juice just flows where it is needed...as long as you don't overcharge the house bank (and thus nowhere for juice to go) then this works fine (the charger should prevent this from occurring).

With multi-bank chargers (where there is a direct connect from charger to batteries for each bank) I am not sure if they actually monitor different charge levels for each bank or if they are effectively combining banks with relays internal to the charger.

The Xantrex units I have used in the past have separate connections for each bank.

[PEACETIME]

I have a 3 bank Xantrex 40 that determines how much each bank needs. I find this problematic in that I only have a total of 40 amps available. I have found the charger will divert about 10 amps as a float charge to each of the 2 banks and then only have 20 amps for the bank that was in need of recharging. I have installed fuses for each of the three legs. With this I can then pull fuses from the banks that are not needing to be charged and direct the full output to the bank that needs all it can get. The charger has always worked fine but, it is now hardly ever used due to the solar system. Still keep it for use with the generator, which created a new problem due to generator sizing. I suggest you use an amp meter on each of your banks to see what is really going on.