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Battery select

Dec 18, 2016
41
Hunter 306 ft lauderdale
i have a 2003 Hunter 306. Noticed that no matter what battery i place the selector to 1 or 2 the motor will start start. I had thought it was set up as batt 1 for house and batt 2 for start. i know there is batteries set as series and parallel. i believe the current set up was the cause of two prior stranding events after a long sail. fortunately i carry a battery jump kit that saved me from a tow. any ideas as to how to separate the batteries please.
 
Jan 19, 2010
8,816
Hunter 26 Charleston
Track down the wiring. It sounds like you have them tied together. Most likely parallel or you would have other problems as well. My first guess is that the positive leads from the battery switch go to a common buss. At that point they are essentially the same circuit and your switch is not really doing anything at all. You have a simple circuit that has twice the amp-hours as a single battery would have.
 
Jul 7, 2004
6,975
Hunter 30T Cheney, KS
The switch may be wired to switch which battery gets charged while both are connected to the load. Not the way it's done.
 
Sep 25, 2008
5,848
Alden 50 Sarasota, Florida
Or the difference between which is your “start” battery may be determined by the position of the battery switch - none of us can know how your boat is wired.
 
Feb 26, 2004
21,270
Catalina 34 224 Maple Bay, BC, Canada
The skippersd' answers are right. These may help you understand what you have once you get into it:

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

1-2-B Considerations (New 2020 - Rodd finally got around to diagramming what I had done in the above link in 2009 :) )
1/2/BOTH Switch Considerations

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings

This is a newer primer for boat system wiring design with a thorough digram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation
 
Oct 26, 2008
4,517
Catalina 320 Barnegat, NJ
Oh Boy … you're in for a whole new world now! There is so much to learn! The simple answer would seem to be that you aren't charging your batteries. There will be a logical reason for this failure, but you will have to learn more about how your boat is set up and wired and describe it to us before we can really help. When I bought my boat years ago, I had 2 batteries and one was dead. Because I didn't know anything, I soon killed the other one, too. Then I had to figure out what I needed to do. The links that Stu provided were the start of my education!
 
  • Ha
Likes: jssailem

arf145

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Nov 4, 2010
403
Beneteau 331 Deale, MD
So, on 1 or 2 your engine *will* start? My last boat was set up that way, and I thought many/most boats were. Whether I thought of one of them as "Start" and one as "House", whichever one the switch was set on, that battery would supply power for everything, starting and house. The problem came at the 1+2 setting where they were combined.
 
Oct 26, 2008
4,517
Catalina 320 Barnegat, NJ
Everything is a WAG without a sketch.
And without knowing how @tom.p.brown is actually using the switch. His hint is that he considers 1 to be House and 2 to be start. But the switch doesn't actually work that way. We don't know what position he uses predominantly, or if he puts the switch into the "BOTH" position. My guess would be that he has one dead battery that won't charge and he may have one battery that isn't being charged because the switch is in the wrong position, or he is using the "BOTH" position and he is draining a charged battery into a dead battery.
 
Feb 26, 2004
21,270
Catalina 34 224 Maple Bay, BC, Canada
Very good analysis, @Scott T-Bird . Also glad to be of help to you over the years, and that it worked for you. @tom.p.brown is going to have to answer the questions that have been raised before anyone can venture any further guesses.
 
Last edited:

higgs

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Aug 24, 2005
3,455
Nassau 34 Olcott, NY
My boat came with a battery isolator that keeps the starting battery off the same curcuit as the house batteries. The starting battery has its own switch, as well. This is a nice setup, as even if the house batteries go dead, it does not effect the starting battery.
 
May 24, 2004
6,510
CC 30 South Florida
The 1,2, both, off switch has positions for two batteries. It does not matter how many individual batteries you may have as long as they are connected and grouped into two. The Negative cables go to a common ground but the positives, one goes to #1 and the other to #2. Each battery group will be isolated from the other unless you combine them by switching into "both". The switch will determine which group battery feeds the loads and receives charge from the alternator. Some use one position for the House Batteries and the other position for a dedicated starter battery. This requires remembering to manipulate the switch from both to house after a few minutes after starting the engine. Make sure your switch is equipped to "make before break" . This refer to the transfer of active electrical contact before leaving the prior circuit, to protect the diodes in the alternator. There are more sophysticated ways combining and isolating batteries and different ways of utilizing the Switch it just depends on the degree of complexity required. Connections to the battery charger are just another topic.
 
Feb 26, 2004
21,270
Catalina 34 224 Maple Bay, BC, Canada
The switch will determine which group battery feeds the loads and receives charge from the alternator.
Benny, I know you know this, but wanted (needed?) to clarify this for folks reading these electrical threads)
This is the way most boats are wired OEM.
IMPORTANT: One has to understand why and what improvements CAN be made and what other owners can do (and may already have done).

Like this:

OEM 1-2-B Switch Wiring History
Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams