Battery combiner question

[tmac]

Here's an electrical question I haven't seen answered in the archives. Assume you have two battery banks, one for house and one for starting, connected by an ACR combiner. Also assume the alternator is directly connected to the house bank.    If using a 1-2-Both switch, is there any problem with having that switch set to "Both" while charging from the Alternator?  Seems to me that there would be a dual concurrent path to the Starting battery – one through the combiner and one through the switch.  I do a lot of residential wiring, and having two concurrent paths for a circuit would be very wrong.  But of course we don't have combiners in residential wiring...

[Stu Jackson]

Tom,

The reason it doesn't come up is that those who have actually installed combiners understand how they work and why they were installed in the first place. 

Those of us that have simply don't use the B position, there is no need to do so.  If done inadvertently, I don't think there would be an issue, it's just a different path for the same current to flow and, then, only when charging sources are present and the combiner is closed.  (There may be  differences between DC and AC and can understand why there shouldn't be in 120V sources, which would include the danger of a live point when something "appears" to be off when the second source is actually present.  I don't think that is an issue in boat charging systems.)

And, from the Elec Systems 101 topic: "And if your echo charger or ACR breaks, then simply use the B position on the switch but ONLY when charging sources are present! !  Backup, backup, backup."

[tmac]

Stu, that's kinda what I had assumed, but I wanted to make sure that there wasn't something else that I wasn't considering.   I agree that I would personally, in this arrangement, never use the Both setting, but when you have young grandkids on board, you never know what might happen, despite giving them stern instructions about leaving stuff alone. 

When you're stuck inside all winter eagerly awaiting your chance to finally get working on the boat you just bought and had to immediately wrap up for winter - you sit around imagining all kinds of theoretical situations...

[LogoFreak]

I've eliminated the 1-2-B-off switch on my boat all together, I just have and on-off switch.

[Stu Jackson]

I've eliminated the 1-2-B-off switch on my boat all together, I just have and on-off switch.

There are probably a half dozen different ways to wire/switch two battery banks, shown quite clearly in the Electrical Systems 101 topic.  If one has employed a battery combiner (or ARS or duo charge or echo charge or any other automatic relay system that connects the secondary non-house bank when charging sources are present), then the concept applies.

Some have deliberately chosen to employ "jumper cables" to do so in the event that the skipper determines is necessary to connect two banks of batteries that are not wired with a switch to easily do so.  Your boat, your choice. 

Just as a reminder, though, connecting a dead bank to a good one is not a good idea, because the dead one will only serve to pull the good one down.  Unless one is thoroughly familiar with the DP+ switch, it is one of its inherent drawbacks, as discussed by Maine Sail in the "Darn AGMs and Dual Circuit" thread in ES101.