12-VOLT BOAT 'LECTRICS problem might be. Battery Status — Age-related chemical changes and low battery charge will increase the internal resistance of your batteries, resulting in less output efficiency. A battery might read 12.7 volts, but not be able to deliver high current long enough for engine starting. This is like trying to water a big garden quickly with a small diameter hose. It doesn’t work very well; the pressure is there, but not the needed flow rate. It’s the same with batteries. Adequate current-carrying capacity is as important as the voltage. So, battery voltage cannot be relied on as the sole measure of true charge. However, a multimeter or an accurate built-in panel voltmeter may be used to get a 'rough approximation' of battery capability. With the engine off and the battery charger or other charging systems off, look for: • Battery voltages that drop rapidly and significantly (1 volt or more) when under load, say with a few lights on. Significant differences in voltage between batteries (0.5 volts). • Batteries that do not achieve and maintain a higher voltage after a charge, especially after a 'rest period' of 4 or 5 hours (assuming the battery is not used). • Wet cell batteries may be accurately tested with a hydrometer, but the newer AGM and Gel batteries are not easily directly tested by the user. Electrical Distribution Problems — It’s essential to strive for low-resistance electrical distribution wiring. Especially critical is to have low cable resistance
Also, your multimeter can check for proper on/off switch operation, voltage levels, proper low resistance wiring paths through connectors, and for continuity of wiring leading through unknown paths to lights and other devices. Consulting the references listed and others is highly recommended. Starter Motors — If your engine starter motor doesn’t work, be sure that the heavy black battery cables are tight and free of corrosion where they connect to the engine block. This is a notorious problem point. To be sure, remove and clean the cables with a stainless brush or sandpaper. Caution: Many engines are wired to deliver 12 volts to the large positive starter terminal at all times, regardless of how the main battery switches are set. Whenever the large red (positive) battery cable is removed for inspection or cleaning at the starter motor end, be sure to disconnect the other end at the battery post (positive) first. Check for 12 volts between the heavy, black battery ground cable (negative) connected to the engine block and the heavy, red battery cable (positive) on the
It’s essential to strive for low-resistance electrical distribution wiring. from the positive battery terminals leading to the main battery switches, to the power distribution panel, and the negative cables (black) leading to the engine block, and back to the negative terminal of the battery. Excessive resistance at these points can waste battery energy resulting in low operating voltage at all the various circuits connected to the main power distribution panel. The multimeter may be used to check voltages at critical points like the heavy positive (red) terminal at the starter motor, at the main distribution panel, and at other places like the power strips and connectors for mast lights. Page 146 •
Latitude 38
• January, 2006
starter motor. For those with more experience and confidence with a multimeter, you can check for 12 volts on the smaller starter solenoid terminal when the starter switch or button is on. If no voltage is present, look for a blown fuse or a defective start switch in the wiring behind the engine control panel or in the engine room. Be sure to refer to your engine manual for the precise location of this terminal. Caution: A misstep here may result in dangerous sparks, and the engine may inadvertently turn over if a wrong connection is made in the starter wiring. Assure that 12 volts are present at
Doing your own repairs and installations can be safisfying. But you can really screw things up if you don't know what you're doing.
the start key switch and separate start button, if so equipped. Questionable Alternator Output — Look at the battery voltage right after starting your engine. A working alternator is shown by a steady increase in voltage across any battery that is switched in. Charging systems vary, but look for voltages at least in the 13-volt range after 5 to 10 minutes. Most alternators can put out a maximum of around 14.3 volts for wet cell batteries. AGM and Gel batteries require different alternator output voltages. Check your documentation for your specific setup. It’s normal for engines with simple, basic (non-step regulated) alternators to produce the highest charging current (Amperes) when battery charging first begins. Typically, the charging current will drop to a much lower value after 15 or 20 minutes. This is a major disadvantage for those needing a faster battery charge and is why newer-style charging systems use alternators set up with step-charging regulators to charge batteries more quickly and efficiently. VHF Radio Antenna Problems — Most masthead VHF antenna units have a “loading coil” that, electrically, is a low resistance (less than 1 ohm). To test for a complete antenna cable connection (continuity) from your radio all the way to the masthead, first unplug the male VHF connector to your radio. Use your multimeter to measure resistance between the
