Alternator Output and Battery Switch Wiring

[Stu Jackson]

In my continuing "In Defense of the Simple 1-2-B Switch" ramblings, I've discussed many different issues.  The most recent one was a discussion with a fellow skipper who was interested in Jim Moe's wiring diagram.  Please see Reply #31  here:  http://c34.org/bbs/index.php/topic,4787.30.html 

What this topic did was to explain how to modify Jim's two switch diagram to my simple 1-2-B switch wiring.

There are other "angles" on this concept of alternator output wiring and the 1-2-B switches.

[Edited, 5/05/09 - Stu]  Also see Reply #11, Alternators & Batteries topic: http://c34.org/bbs/index.php/topic,4949.msg30101.html  This post includes simple wiring diagrams showing the 1-2-B switch to the alternator and starter.  This suggestion only works if you have two separate wires FROM to the C post of the switch: one each from the alternator and to the starter.  If you only have one wire from the switch to the alternator and the little wire connecting the alternator and the starter, this won't work, because in switch position 2 the starter would not be energized.

One of the things I discussed in my November 2006 Alternator Regulator installation article was the rerouting of the alternator output from the 1-2-B switch directly to the house bank. 

There are two ways to do this.  Directly from the alternator to the house bank, or using the house bank connection post on the 1-2-B switch.

In 1998, when we first bought our boat, I installed a new charger (a Freedom 15 Inverter Charger), and a battery combiner.  As an interim step to get the alternator output OFF the "C" (or "Both") post of the 1-2-B switch, I simply MOVED the alternator output FROM the "C" post of the switch TO the house bank post of the switch.  Electrically, this is the same a completely rerouting the alternator output directly to the house bank.  We had two separate wires from the C post of the switch (in addition to the DP wire: one to the starter and a separate one to the alternators.  Many boats only have one.  This concept works fine with the OEM small internally regulated alternators meager output and the factory OEM #4 wiring (both from the alternator to the switch in the electrical panel and the same sized wiring from the switch in the panel to the house bank).

[Ed. - Stu ] Some boats only have one wire to both the alternator and starter, with a little wire between the alternator and the starter.  This will not work with that arrangement.  Our boat had two wires from the switch - separate ones each to the alternator and the starter.  I moved only the alternator wire to the house bank post on the switch.  The starter wire remained on the C post.  See Figures 1 to 3 in the Alternator & Battery topic linked above.

Alt. Output Choice: IF the alternator output now goes to the "C" post of switch, you could, very simply, just move your alternator output from there to the #1 (house bank) post of the switch - it's simpler than completely rewiring the alternator output to the house bank if you don't have the time or want to bother, and is electrically exactly the same: think about it to understand this simple idea that I used for many years before I installed our high output alternator and rewired directly from the alt. to the house bank. But check the wire size from the switch to the bank to make sure it's adequate; it's usually #4 wire on Catalinas, so if you still have the OEM alternator, it should be just fine. If and when you get a high output alternator, then you can and will need to change the alternator output directly to the house bank because the #4 wire will be too small for the current it needs to carry over that distance. If you do this simple change now, you'll still need "a means of charging your reserve bank with an echo charger, relay, combiner, or a simple on/off switch - your choice."

I highly recommend this simple change, highly, get it? Get the danged alternator output OFF of the C post and you'll sleep a lot better, knowing your switch cannot ever harm to the alternator EVEN IF YOU TURN THE SWITCH TO OFF WHEN THE ENGINE IS RUNNING!!! That's because the alternator output always has a route to the house bank. It's easy to do, and in most cases the wire from the alternator (unfortunately) is already there - just move it from the wrong C post (which boat factories continue to do!!!) to the right (house bank) post.

To see this whole thread from co.com, see: http://forums.catalina.sailboatowners.com/showthread.php?p=620765#post620765

[Ron Hill]

Stu & readers : I guess that my idea back in 1991 wasn't all that bad.

I reasoned (as I wrote in the Mainsheet - way back then), "What I wanted to charge were the batteries not the Battery Selector switch !"  So I took my dual output Balmar and ran a #4 + (positive) line directly to each + battery bank (bypassing the battery selector switch).  Then I also ran a #4 - (negative) wire from the alternator case to the furthest negative (-) battery post.  I crimped and soldered all connections!  Each + positive wire run was fused at each battery bank because the connection length was about 5 feet.

I'm by no means an electrician, but I am a pretty good plumber and reasoned that electrons flow much like water.  My thinking has not let me down in the past 25 years.  A thought

[Stu Jackson]

Ron's right.  See Replies #8 through #10 on this topic, Updating Electrical Systems & the 1-2-B Switch:  http://c34.org/bbs/index.php/topic,4623.0.html