3 Battery Switch Installation

[Rrnman]

I purchased my 85 Sundancer 250 in November. I have a 3 battery on/off switch installation. Switch 1 starboard side to cranking battery, Switch 2 port side for 2 house batteries and Switch 3 in the engine compartment. All are charged by a Xantrex Multistage Battery Charger when shore power is connected. Based on the West Marine Battery Combiner document which came in the boat binder documentation I received Switch 3 appears to be a the Emergency Parallel switch. Can someone help tell me how these switches work? Below are my thoughts of how I think they work:

Switch 1 turn on for cranking boat and while cruising. Turn switch off when anchored.

Switch 2 turn on when anchored to run house loads. When leaving leave on so house batteries can charge while cruising to next location to charge the battery.

Switch 3 leave off at all times unless charging battery won't crank. Switch 3 can be turned on to combine both battery banks to start the boat in emergency. The West Marine document says if I leave switch 3 on to long then I may drain both battery banks.

When I'm on shore power and Xantrex is charging should all 3 switches be in off position? I would appreciate the input on how to manage these switches correctly and not find myself out of power on the water.

Thanks.

 

[Bt Doctur]

My personal opinion is NEVER charge the motor batteries, it can hide a bad battery and can boil out a battery if overcharging
I would dedicate 1 battery to each engine with a battery switch or emerg relay to combine both engine batteries to aid in starting.
I would only hook the charger to the house batteries ONLY and use a switch or relay to charge the house batteries while underway .
This setup leaves you with 2 dedicated batteries to start atleast 1 engine to use the engines charging system to charge both engine batteries.
You can afford to have the house battery go bad or go dead, but not the main engine batteries
Don't forget, you need batteries to power the emergency VHF call and your bilge pumps.

 

[Lazy Daze]

So, am I reading this correctly.... A PO installed 3 separate switches? I wonder why when a single (1-2-Both) switch would have done the job and make things MUCH simpler. Strange.

Is the alternator hooked up to your house batteries?

With a properly installed setup, switch "position" should not affect whether they are being charged by the onboard charger, or not. Follow the leads from the charger - where do they go/what are they hooked up to?

Me? I like all batteries hooked to the charger as it will make them last longer. With multiple batteries I wouldn't be worried about the possibility of, by chance, one battery having a surprise failure. Most times batteries die somewhat slowly. BUT, I can see why the Doc mentioned that and understand his reasoning.

 

[Bt Doctur]

I mention it because a friend has like a 31 or thereabout, 4 batts, 1 for each engine and 2 for house. Always had the shore power and charger running . Did a run from Lockwood marina to the Cove at Sandy Hook. 5 hours later was getting towed back in . All the batteries were dead and all had no electrolyte in them. Dead ,like no power to use the vhf either or the bilge pumps ,all had the plates exposed.
Granted no one bothered to check the fluid levels but being always on charge you didn't know that it was the last time the batteries were going to be able to start the motors. By not having them on constant charge you may catch that one slow, grinding start and know its time to replace that battery before your off shore waiting for a tow.
Quick battery test: remove the power to the ign sys or ground the coil tower lead. Crank to 20 seconds. Wait 5 minutes and again crank for 20 seconds. If you can do this the batteries are in reasonably good shape. If you cant do this, its time for replacement.
Do you plug your car in everynight, do you install a charger when you go on vacation for a week or two. Of course not and your call always start up.
Good batteries don't go dead, bad batteries do.