What the $%^! Is Wrong With My Generator???

By Herb Knight

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The answer to the question “What’s wrong with my generator?!” is the most sought-after from our Product Support Department. It is normally asked right after the boat goes dark.

The first question I always ask is, if they can smell anything like burnt plastic or if they saw any smoke or flames from the gen-end. If the answer is yes, it is usually game-over. If the answer is no, the next question is what is the output voltage? Most responses are “none”, but none means zero. Residual voltage is somewhere between 20 – 80 volts AC and low voltage vs none is all the difference in the world. Residual voltage means the windings have not completely lost their magnetism. With residual voltage you still have a chance of making repairs on the fishing grounds.

The first item to check is the Automatic Voltage Regulator (AVR). The AVR stabilizes the voltage coming from the generator by taking the fluctuating voltage and changing it into a constant voltage. Voltage fluctuation mainly occurs due to variation in the load on the generator coming from the boat. The AVR monitors the electrical voltage with sensing leads attached to the bus bar of the generator end. As more power is demanded from the generator, the voltage will drop. In layman’s terms, the regulator sees a load has been applied to the generator and tells the diode bridge to provide more excitation DC voltage to the field circuit to increase output voltage to compensate for the new electrical requirement.

Inspect the wiring inside the box on top of the generator end. Look for loose or chafed wires. A chafed wire will cause the AVR to have an erratic reading and may give you that smoke or burnt smell we asked about earlier. At the same time, look at the connections to the AVR. As most are spade terminals, it is possible to have the female side expand and cause a loose connection. Ensure all the connections are a tight fit.

With the generator still in the off position, remove the end cover (normally plastic), and perform an inspection of the wiring, diode bridge and windings. Look for loose or missing bolts, loose or broken wires and burnt or discolored windings. Inspect the cleanliness of the windings, as oil-soaked or dirty windings are a failure waiting to happen. Keep in mind that most of the smaller generators are a single, sealed bearing design, they do not require maintenance. Depending on annual usage, the bearing should be replaced every three to five years depending on manufacturers’ recommendations. The half-life of the engine or 20,000 hours is a good rule of thumb.

One of the troubleshooting tests we do is to check what the AVR is telling the diode bridge. We do this by measuring with a volt/ohm meter set to DC voltage on the F+ and F- terminals on the AVR. This is done with the generator running, so do follow all safety precautions. The normal output, depending on which generator you have, will be between 14 – 34 volts DC. If generator output voltage changes, the Automatic Voltage Regulator (AVR) increases or decreases the flow of excitation currently directed to the generator field windings. Generator output voltage is increased or decreased by changing the current supply (number of flux lines) to the generator. Thus, if you have no output voltage to the field and you have checked everything else, then the odds are that you probably have a bad AVR.

Stay tuned for our next episode of What Is Wrong With My Generator?! when we will discuss testing diodes on the diode bridge. If you have any questions give us a call at 206-280-1094.