I’m trying to decide on a charging technology that will automatically charge all my battery banks when a charging source is present. Right now I’m trying to choose between the respected Blue Sea SI 120 ACR and the newish Sterling Battery-to-Battery Charger. I like the simplicity and reputation of the ACR, but I like the fact that the Sterling Charger can do multistage charging appropriate to each individual isolated battery bank. I also like that the Sterling can do a targeted desulfation charge.
You'd need the bigger B2B from Sterling if your charge sources are up to it. It is a nice piece of gear, as is the very simple ACR..
I’m concerned that the ACR would cause the charged bank to get a voltage that is higher than it needs and the discharged bank to get a voltage that is lower than it needs (Calder, p40). This is why I’m looking into the Sterling battery-to-battery charger.
This physically can not happen with combined batteries and should be filed under "urban myth".. The voltage across all battery banks becomes the same and each bank will take the current it needs from the charge source. You can not over or under charge "combined" batteries as they charge at the same voltage and reach an equilibrium.
The echo charger probably has too small a capacity for charging the large banks I have.
The Echo is the wrong fit for this application and far too small.
Since I’ve owned her (until the past month) the boat has been run with the two sets of house batteries joined together in a single house bank. But as I contemplate buying new batteries, I’m coming face-to-face with what I’ve already known and have been trying to ignore, Nigel Calder’s cautions about mixing different battery types in a single bank, and especially the dangers of mixing batteries in the wildly different temperature environments between the engine room and the companionway area (in general, though, Calder strongly advocates single large house battery banks). Charlie Wing, on the other hand, advocates an older practice using half-sized and alternated banks that has turned out to have been essential to me in analyzing the health of my various different batteries.
Any thoughts you can share?
As you already discovered the engine room is a TERRIBLE location for any battery bank, but of you must keep them there your "charge source" should monitor temp of the hottest bank and reduce voltage accordingly. This means your battery charger and alternator regulator should have temp sensing capabilities.
Charlie's statements are based on the old model of a boat with equal sized battery banks and a 1/2/BOTH. You have three banks 2 house 1 start. Most boats today use a single larger house bank, this allows for shallower discharges and longer life, and then a single starting battery. Alternating house banks usually results in deeper discharges to each bank and thus a shorter cycle life. If the new bank can be fit so all the batteries are the same then you might consider making them one big bank. If you feel more comfortable you can put a safety switch in that keeps them with the potential to be isolated but normally they would remain as one bank..
For the engine room issue alone the Sterling B2B makes a lot more sense than the ACR IF you can deal with a max of 45A charging output. If you need more than the 45A capability then an ACR with temp sensing on the engine room bank can work though the cooler bank will be charging a tad slower due to the lower voltage/pressure.
The B2B has the ability to BOOST the voltage going to the second bank while the hot bank is seeing a lower voltage or you could use the B2B to feed the hot bank and it does its own temp sensing..
Sterling B2B Charger