Complicating Battery Matters

Posted: December 1, 2012  |  Tag: 

By: Grid Michal

I know I’m losing my mind. I just bought a small trawler with a battery switch that only controls the engine. When I viewed the boat and the owner tried to start it, apparently No. 1 battery was “dead.” He switched to ALL, and the engine started fine. I’ve left it that way for the last month, as I had other work to do. I finally put a load tester on No. 1, and it tested great. So did No. 2. But there was no power coming from the No. 1 position, so I bought another battery selector switch, removed the three cables from the old switch, making sure to label each with the position on the back of the switch, and installed them on the new switch. Congratulate me! I now have no power at No. 2 or ALL, but there is power at No. 1. Now, if I turn on my AC main with the battery charger, I have power at 1, 2 and ALL.
The first thing you need to do is stop complicating the situation. I believe you’ve innocently created a problem but are compounding it by trying to make things happen. Let’s go to the new switch. On the back where you attach the cables, it should say 1, COMMON (or FEED), 2. Battery No. 1 should hook to 1, battery No. 2 to 2 and the engine’s main cable to COMMON. Using your voltmeter hooked to the switch post and a ground, or even an audible boat accessory, disconnect any battery at its POS post to determine if it’s No. 1 or No. 2. Once you’ve determined which is which, remove your COMMON cable and, using the posts on the back of the switch, touch the cable to each of the battery selector posts. This will give you voltage while ignoring the switch position. You’ll probably find both batteries are good. The problem probably was originally a defective selector switch. Now, look at the back of the new switch, and the old. I know you marked the cables and installed them on the new switch in the exact same positions, but do the mounting posts read 1—COMMON—2, or 1—2—COMMON on both switches? If they’re different, and I’ll bet they are, you’ve unwittingly changed the selector positions, and nothing works right. Adding the battery charger just overrides the switch position and gives you power everywhere.

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