charging two batteries

[dmarkvid2]

I have a 28' Bayliner Cierra Sun Bridge with a 460 King Cobra. I have two batteries. My question is, when I am cruising, and charging on the altinator, or when I am charging with shore power, should I have my battery switch set on "BOTH" for charging? I know one battery is for the engine, and the other is for the accesories. Does it need to be on "BOTH" to charge them both. If I had the switch set on "ONE" would both batteries still get charged?

 

[Boatist]

Re: charging two batteries

The alternator will charge the battery the switch is set on.
If 1 it will start off 1 and charge 1.
if 2 it will start off 2 and charge 2.
If both will start off both and charge both, but if one battery is low it will draw current from the charged one.

Be aware that turning the switch with the motor running can blow up your alternator. If you turn it thru off with the motor running then check your alternator before making any long trips. Also if switch is not a make before break then turning it with the motor running will likely blow the alternator.

I would add a battery isolator so you can charge both batteries anywhere the switch is set. It also protects your alternator because you always have both batteries connected.

 

[ricksrster]

Re: charging two batteries

dmarkvid2, I'm not trying to steal your post, but I have a question for Boatist and I think it applies to this topic.
Could a trickle charger be connected to the Alt. post of an isolator to keep both batteries topped off? Wouldn't that have the same result as the alternator charging the batteries?

 

[bruceb58]

Re: charging two batteries

You wouldn't want to have the trickle charger go through the isolator because of the voltage drop.

I prefer a battery combiner to an isolator. It connects the two batteries together when the charge voltage on either battery reaches a set level.

 

[Boatist]

Re: charging two batteries

I would not use a trickle charger either. Most are not regulated and can over charge. Better to use a 10 to 15 amp automatic charger. Charger will drop to 0 amps when the battery is fully charged.
Also with a big battery like like a trolling motor battery it can take a week to recharge and all that time the battery is being damaged.

Yes the charger can be connected to the alternator post on the isolator.
Mine is connected that way and I have never had a battery that did not last at least 6 years. I hooked up to a plug on the bow of the boat and modified my charger for an adapter that will plug into that plug.
Also have a 12 volt line to the trailer from my truck and can charge the boat battery from my truck's alternator while going down the road.

With batteries most important thing is to recharge as soon as possible. When a battery is discharged damage to the battery starts and the longer it is left discharged the more damage it does.

If you have a battery switch an isolator will protect your alternator better than a battery combiner as the load of both batteries is always felt reguardless of where the switch is. You would have to disconnect the cable to both batteries at the same time to blow your alternator.

 

[ricksrster]

Re: charging two batteries

Boatist, Send me a picture of your set up for the plug on the bow and trailer. richard.palmer2@earthlink.net I have an automatic charger 2A/8a/12A. There is also a switch for regular battery and deep cycle. I have both on my boat with a switch and an isolator. The wire from the rectifier to the starter solenoid is disconnected and a new wire run from the rectifier to the isolator to protect the charging system on the boat in case of a switch off situation.