Battery switch during shore charging?

[gypsyrecs]

I was wondering if I need to have the master DC battery switch on "ALL" or "OFF" when hooked up to shore power and charging. The Newmar charger leads go directly to the batteries (it even says right on the case to do this) so I wouldn't think it matters where the switch is. I Googled it and found two different views. Any suggestions?

Here is what I found on-line:

From US Sailing:

When connecting to shore power, have the power switch set to "AC" or "Shore Power", the battery charger turned on and the battery switch (center dial in picture below) set to "ALL". Most sailboats will charge both batteries when the shore power is plugged in and the battery charger turned on, regardless of the setting of the battery switch.

From a charter company:
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When on shore power (120 volt AC), the three batteries (one starting and two house) can be charged if needed by the charging system. This system brings the batteries up to full charge in phases and maintains the batteries in a fully charged condition when connected to shore power. It is permissible to leave the charger on for extended periods (such as while sleeping), but with regular use of the engine this should not be necessary. In addition, some 12V devices (including light bulbs) may be harmed by long-term exposure to the above-normal voltages created during charging. For this reason we ask that you turn off the battery master switch before turning on the battery charger.
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[u079721]

I would agree with you that it doesn't matter, IF the charger is hooked up directly to the batteries as usually recommended.

My charger was also rigged to the batteries directly, and the bilge pump too (with its own fuse), so I always turned the batteries OFF when leaving the boat. I also agree with the charter company about turning off sensitive electronics during charging in case there is too much overvoltage. I don't get the US Sailing suggestion at all unless it dates from a time or practice of running the battery charter circuits to the battery switch and not the batteries directly.

 

[jmpirate]

Turn it off

I has been my experience that chargers are almost always set to charge regardless of the position of the battery selector switch. As a rule, I very rarely put the selector switch to "both." I have seen too many batteries rendered useless before their time due to its companion failing. When this happens, the good battery is perpetually trying to keep the charge up on the bad one, thereby killing both.

 

[Tom Metzger]

I'm not sure I believe this

I also agree with the charter company about turning off sensitive electronics during charging in case there is too much over voltage.

I'm not sure I believe this. Is someone suggesting that they turn off their radar, GPS, chartplotter, and VHF when they are powering in a foggy shipping channel? Right!!! The alternator is likely to put out higher voltage at the batteries than the shore power charger because of it's larger capacity and larger wire.

The voltage put out by the charger is not a problem unless you are equalizing, and then, probably, only for the incandescent lights. Modern electronics are not affected by high voltage and typically have a 10 - 16 volt or higher input range.

 

[newgringo]

My 2 bits

From sunny MX. Most important is my automatic bilge pumps are powered only with a battery turned ON, any or ALL. So worst case if I get a leak I want the pumps to have all the electricity they need to keep it afloat. Oh, the alternator charges to 14.3 which does the final charge from time to time. My shore power charger peaks at 13.400 vdc with batteries ON, OFF or whatever. Enough to keep charged but not over charge.

 

[Second Star]

When I charge when motoring, the alternator feeds the batteries thru an isolator/balance device that electronicaly chooses how much current to sent to my two battery banks; the 1-2-BOTH switch doesn't matter. When I shore charge, I set up my system so I can choose which battery I want to charge using a simple single pole switch; if I choose BOTH on the main, my shore charge goes to both banks. A simple way to see how any system is charging is to use a meter and see what the voltage is at each battery when you move between 1-2-BOTH.