POWERBOATER’S GUIDE TO ELECTRICAL SYSTEMS the black probe to the negative post, and set it to the AC volt scale. Run the engine up to a fast idle, switch the meter to the alternating-current volt scale, and check the reading. You should have no more than 0.250 volt AC at the battery. If the reading you get is greater than that, the diodes in your alternator are defective and the alternator must be serviced.
Draw Test
Fig. 6-10. AC ripple-voltage test. Your black meter lead should be connected to a known good ground and the red lead to the B+ (output) lead on the back of your alternator. Remember to make sure that your meter is set to the AC volt scale.
If you have one of the LED testers shown in figure 6-9, alternator testing is a one-step procedure. The tester has red and black leads and probes just like your multimeter. Attach the red probe to the B+ terminal at the back of the alternator and the black probe to a nearby ground (one of the alternator mounting bolts will do), and start the engine. Observe the LEDs on the meter. Any lights flashing or constantly lit indicate a problem with either the alternator or the voltage regulator (assuming the alternator is getting excitation voltage as described earlier). Follow the instructions printed on the tester to determine what course of action is required. Figure 6-9 shows the LED tester connected and ready to check a charging system. If you’re not sure which terminal is B+ on your alternator, refer to figure 6-1. If you don’t have the tester, you can do an alternating-current ripple test using your multimeter, as shown in figure 6-10. Connect your meter leads to the battery with the red probe to the positive post and 94
The last test I will mention is the draw test. Particularly in the marine environment, it’s possible to get electrical crossovers from a hot wire to a nearby ground, causing a voltage leak that can drain your battery. Testing for crossover current is fairly simple, but a few precautions need to be mentioned. You’re looking for a constant electrical draw on your battery. Make sure all the electrical accessories on your boat are turned off and the engine is not running. Make sure you have disconnected everything including any radios and stereos with memories and clocks that bypass the switches. Next, disconnect the positive terminal at the battery. Set your multimeter to read amps and connect it in series with the terminal end of the battery cable and the positive post on the battery. A reading of any significant amperage (over 0.01 amp) indicates something on board is draining your battery. Now you must locate which circuit is the culprit. If your boat has fuses, isolate each circuit by removing the circuit fuses one at a time and checking to see if the amperage reading is eliminated or reduced. If you have circuit breakers, carefully turn off the breaker switches one at a time until the amperage reading disappears or decreases to practically nothing. Once you have located the circuit that’s causing the battery to be discharged, you should be able to troubleshoot the circuit just as I described above.
Outboard-Engine Charging Systems Outboard-engine charging systems come in two varieties: with or without voltage regulators. The unregulated systems have an alternator built into the top of the engine that puts out constant amperage of 5 or 6 amps (or more on newer, bigger engines) any time the engine is running. Regulated systems use a volt-
