POWERBOATER’S GUIDE TO ELECTRICAL SYSTEMS
Figs. 5-15a, b. The Blue Sea System battery combiner.
no battery isolator. Figure 5-13 shows a similar arrangement with the isolator. Figure 5-14 shows a twin-engine installation with dual battery switches and an isolator.
Battery Combiners Relative newcomers to battery interconnectivity are devices known as battery combiners. These devices, available from all major marine equipment vendors, offer significant advantages over diode-type battery isolators. Unlike conventional isolators, combiners don’t suffer from the inherent voltage drop caused by diodes, which results in more precise battery charging control. These new combiners incorporate voltage-sensing circuitry that automatically connects or disconnects multiple batteries (combined) based on whether they are charging or discharging. You can think of these combiners as electronic devices with some built-in intelligence. Diode isolators do not have such intelligence, which requires you to make some compromises, especially when you are combining different kinds of batteries, such as a cranking battery and a deep-cycle battery. Cranking batteries recharge much more quickly than deep-cycle batteries. In the old days, this meant that when combining batteries, cranking batteries were typically overcharged while deep-cycle batteries continued to charge. The Blue Sea unit shown in figure 5-15a over82
comes that problem by just turning off the charge to the cranking battery in the circuit once the battery reaches a prescribed voltage level. Additionally, the new combiners allow temporary isolation of house loads from the engine circuit during engine cranking to protect sensitive electronics. So there is no more “blinking out” of electronic gear during engine starting, when the whole system used to experience so much voltage drop that many electronic devices couldn’t function normally.
Testing Your Batteries Even with proper maintenance, all batteries wear out eventually. The trick is to know when replacement is really required. In my 35 years of experience dealing with storage batteries, I’d say that they are the most frequently misdiagnosed component in any electrical system. People assume that because their engine is turning over more slowly than usual, the battery is at fault and it needs replacement. More often than not, the battery is not the culprit, but rather a loose or poor connection, or perhaps a fault with the charging system. Before you can make any real determination of the condition of your battery or begin any other serious testing, you must first test your battery. You need to recharge your battery first, then check the battery’s load-handling capability.
