Re: Dual Battery Management
Prior to starting the engine, the operator would turn the battery switch to the BOTH position so that he or she had the full cranking power of the batteries. Once the engine started, the operator would leave the switch in the BOTH position while powering to the day's destination so that both batteries were charged. Once a sailboat began sailing sans engine, or a powerboat dropped the hook, the operator would (in theory) turn the battery switch to the 1 or 2 position, so that the other battery would be reserved for starting. When it was time to crank the engine again, the battery switch would be turned to BOTH, or possibly to the reserved battery, and the engine would be started. <br /><br />The problem, of course, is that this requires a lot of thought on the part of the operator, who is trying to relax in the first place. The inevitable result is that at some point, the boater accidentally leaves the battery switch in the BOTH position, resulting in two very dead batteries.<br /><br />What's the solution?<br />We strongly recommend that you select and wire your batteries differently from the way the factory wired them. Use a stout starting battery to crank your engine, based on your engine's cranking requirements. Use a larger house battery with triple the capacity of your daily DC requirements. Now this is where it gets complicated: we DON'T recommend the use of a traditional OFF-1-BOTH-2 battery switch. Instead, consider using three OFF-ON battery switches as follows: one switch to connect your starting battery to your starter circuit; one switch to connect your house battery to your boat's distribution panel; and one switch to parallel your battery systems if either battery fails. <br /><br />With this switch set-up, you simply turn your engine and house switches to the ON position whenever you are onboard, whether anchored, starting your engine, or sailing. The battery parallel switch remains OFF unless there is a complete failure of either battery bank or you have run your starting battery down trying to crank a reluctant engine. When your engine is off, the starting battery is safely isolated from the house loads. It cannot be discharged, even if you leave your stereo on all night, listening to Jimmy Buffett and blending margaritas. <br /><br />How do I charge both banks simultaneously?<br />By isolating starting and house banks, you face a challenge trying to charge them from a single source like single-output chargers or alternators. If you violate the "separation" of the two banks, you face the probability of two dead batteries due to "operator brain-fade". That's why we are great believers in the West Marine Battery Combiner and Heart Pathmaker, Balmar Dual Output Alternators, and to a lesser degree, battery isolators. These products sense the voltage of the battery banks and connect the batteries together whenever one battery's voltage is elevated. Both banks charge simultaneously and remain combined until the voltage drops, whereupon they are disconnected from one another. It's much like having a very attentive engineer flip your battery parallel switch on and off at exactly the right moment. The result is maximum charging performance for two banks, and complete isolation of the two banks to ensure that you can start your engine.
<br /><br />You don't need 3 batteries for combiners. 2 is all. They have LEDs that indicate when they are working. They are solid state (silicon), voltage sensing relays hermetically sealed in a box smaller than a pack of cigarettes. So, if they don't fail out of the package they last as long as silicon usually lasts (25 years or something)? They also have thermal and current overload protection so a bad battey or short won't kill your electrical system becuase it will automatically isolate the batteries.<br /><br />With combiners, you turn your switch on and go and never have to worry about anything at all.
