Battery Switch Position while Running

[BruceK]

The Manual for my twin engined boat says don`t run with the battery switch set to "All" or "Both". The marine electrician who did my boat delivery said the same when he provided a schematic of the battery set up. But why?
Today I spoke with the electrician about something else and quizzed him on "why". He says if you set to "ALL" the alternators see the batteries as fully charged and won`t put out amps.
I try to alternate between setting to "1" and to "2" while running but at anchor,I set to "All". I know there is a "make one house and the other start" thinking on a 2 battery bank set up,but I figure I`d rather drain both batts moderately than drain the heck out of one while preserving the "start" one 100%. Of course you need to know you`ll have enough amps for starting, in my case I know from experience I will. And in the unlikely event that`s not so, there`s the genset and charger to provide amps, with its own dedicated start battery.

 

[jwag956]

I think the electrician is right - when in 'All' both batteries and alternators are all cross-connected. Depending on the alternator this could cause confusion and either one or the other alternator might not output anything - or they both might and cause some battery issues. On our GB - when we got it - it was on 'All' - which was hiding the fact that one alternator wasn't working at all (even the engine surveyor missed this). The GB bible says specifically to have it on '1' or '2' - suggesting even/odd days. 'All' can be used if you need a bit extra oommph to start the engines or one alternator is bad etc.

If you switch back and forth every day or so - one battery shouldn't be drained too much and you'll feel confident that both are charging and up to the task.

 

[tiltrider1]

Mid read the question

 

[O C Diver]

That's to much to think about. I have one alternator for the engine and one for the house bank. Unless an alternator or a battery dies, no need to combine or worry which one got charged.

Ted

 

[Mac G]

This discussion is enlightening because I come from a single engine two battery background.
I always set selector switch to All or Both while steaming so both batteries would charge when underway.
But then at night while at anchor I would pick one or the other to run the house lights leaving the other untouched and fully charged for starting the engine again the next day.
Are you folks saying with twin engines that is incorrect thinking?
Please clarify and advise.
Thank you

 

[twistedtree]

Gotta have a wiring diagram. Without it, everyone is just guessing based on how they imagine the boat is wired. Anyone could be right, and anyone could be wrong.

 

[jwag956]

I'll agree with @twistedtree - boats seems to be notoriously different in this area and seem to get modified a lot as well. For our 89 GB - factory wiring - the recommendation is to use one one at a time unless needed for starting. Alternate frequently to verify both banks are operational.
There also seems to be a lot of 'difference of opinion' on whether cross-connecting will confuse the alternators while underway or not - I suspect this also is a factor of type of alternators and precise wiring.

 

[BruceK]

My electrician/boat mover`s advice came as part of the wiring diagram he sent me by text/SMS during delivery prep.
I disagree with drawing all house power overnight while anchored from one bank. It has the potential to overdraw the selected bank when you could draw on both to a moderate extent.
The problem with alternating between 1 and 2 while cruising is remembering to do it and which was selected last time. Maybe a notepad at the helm, or in a log.

 

[SteveK]

I only have one house bank, so do not need to remember to switch.

Don't understand why micro manage this. Determine an average need for Ah and build one bank able to handle more than that need. Recharge and start over.

 

[koliver]

I only have one house bank, so do not need to remember to switch.

Don't understand why micro manage this. Determine an average need for Ah and build one bank able to handle more than that need. Recharge and start over.

Like Steve, I don't see much of an issue here.
My boat began life with three battery banks, one for two "house - #1", one for two "house #2" and one for "start".
It also had a totally inadequate charging system, dependent upon a 40 amp AC charger, fed from either shore power or a 4kw genset, and a pair of low output, internally regulated alternators. All that still seemed to work, and the 1-2-ALL switch was actively rotated. As things aged out and got replaced, the system changed to a quad of GC batteries comprising the "house", a single small "Start" battery, solar, a 160 amp alternator, externally regulated, a 100 amp charger and the single holdover, an original internally regulated small alternator connected to the start battery. The 1-2-All hasn't been rotated since those changes and lives happily undisturbed, at "1".
I typically get over 10 years out of each of my batteries, so they seem to be happy. My voltage rises with the sun, to 13.xx, when it used to rise with charging to something <13.

 

[Trawlerman]

It seems to me that the statement -- "if you set to "ALL" the alternators see the batteries as fully charged and won`t put out amps." -- does not make logical electrical sense. Assuming that the two DC systems batteries share a common ground (as they should) and assuming that the positive lead from each of the two systems is taken to the switch, then if both alternators are "seeing" 13.2 volts, then in fact the batteries ARE charged and the alternators need do nothing more at that time than provide the existing current drain. Alternators charge (or don't) based on their DC sense terminal, and if you start out prior to switching to "both" with (as example) one battery low (say 11.7 volts) and the other battery charged (say 13.2 volts) -- then the minute you switch to "BOTH" -- the fully charged battery will begin to donate current try to raise the low battery up, and if the engine(s) is/are running then the alternators will also chime in with with current till their respective sense terminals rise to the set point of 13.2 volts. Albeit, in a twin engine setup, the setpoints of the two alternators are rarely exactly the same 13.2 volts and even if they are the losses in the battery-to-alternator wiring will be slightly different even in a good installation, -- so as a result one alternator will likely work a BIT harder than the other, but both will be charging. The more likely use of the switch is to separate the batteries when NOT running so as to ensure there is at least one charged battery when you go to start, and switch to BOTH when actually running so that the engine aternator that is charging the house bank that got run down due to its being used for house loads while anchored does not have to do the whole recharge on its own. The only caveat in this logic is that each battery bank must have an independently sensed battery charger feed wire when on shore power so as to NOT be pumping current into a battery that is fully charged.

 

[BruceK]

I readily understand the "when drawing, engines off" setting advice, though I prefer to draw both moderately than one heavily, and have not experienced starting issues.
On the 'engines running alternators charging" advice, I see the reasoning but remain troubled by the coinciding advice of the marine electrician and the boat manufacturer, ie," Don`t run on "ALL"."
With conflicting advice, it remains unresolved. Another of life`s little mysteries.
Can we try another approach? Is there a negative to running on "!" and "2" alternate days?

 

[Greg QS]

Just remember . Never switch the battery switch while the engine is running. Sudden death for an alternator

 

[Action]

Just remember . Never switch the battery switch while the engine is running. Sudden death for an alternator

Maybe. Depends on the switch.
Never switch to off.

If the switch controls two battery banks and has a make before break design, switching between “1” “All” and “2” will not cause any electrical damage. Because there is no electrical disconnect (OFF) between those positions.

 

[rslifkin]

Correct switch position depends a lot on what you have for a battery layout.

I have 3 banks on my boat (and 4 switches). Banks are labelled 1, 2, and House. Normally the engine and generator switches stay on Port=1, Stbd=2, Gen=2 (so stbd and gen share a start battery normally). House switch stays "on". The only time the switches get moved is to de-power something for maintenance or if a start battery fails and I need to start something from the other start battery. There's no switching required in normal use.

 

[Iggy]

Gotta have a wiring diagram. Without it, everyone is just guessing based on how they imagine the boat is wired. Anyone could be right, and anyone could be wrong.

I agree, there could be a combiner/s and/or a ACR/s installed. I have one engine and 3 banks. With three battery switches that all charge up automatically. This is not counting the genset battery and switch. Without knowing the wiring and setup, its almost imposable to know how to set the switches.