Mercury 60-HP Cause of Alarm about Voltage

[NorthShoreWhaler]

When the engine speed of my 2015 Mercury 60-HP outboard increases to 5,000-RPM, a voltmeter indicates 15.7-Volts, on the VesselView application code 621-24 appears, and an alarm indication is made. When the engine is in gear at idle speed the voltage is 14.4-Volts.

Q1: would the variation in voltage from 14.4-Volts at idle speed to 15.7-Volts at 5,000-RPM be a sign of a failed voltage regulator?

ASIDE: The engine is used on a Boston Whaler 150 Super Sport and has the Command Thrust gear case.

[jimh]

If the voltmeter is measuring the battery terminal voltage, then when the reading is 14.4-Volts that is the standard and normal charging voltage for a six-cell lead-acid storage battery.

There is a general trend in any sort of engine-driven alternator that with increasing engine speed there will be increasing voltage output.

That at 5,000-RPM the measured voltage becomes 15.7-Volts is somewhat abnormal, as generally the effect of the battery itself and the voltage regulation in the alternator would try to maintain the output voltage to be closer to 14.4-Volts. If the battery itself is old and its internal resistance is much higher than would be found in a new battery, the battery maybe able to have its terminal voltage pulled much higher, particularly after the battery reaches a fully-charged state.

I am not familiar with your particular engine, so to infer that the higher than normal reading must be due to a failed regulator is difficult. If the regulator were not working at all, the occurrence of exactly the right charging voltage of 14.4-Volts at idle would be a very odd coincidence.

Q2: how old is the battery?

Q3: what is the storage capacity of the battery in Ampere-hours?

Q4: what is the resting terminal voltage of the battery when no charging current is being supplied and the battery has not been charge for at least an hour?

Q5: is the engine alternator a belt-drive automotive-type field-excited alternator or a permanent magnet under-flywheel alternator directly rotated by the engine crankshaft?

[NorthShoreWhaler]

Q2: how old is the battery?

Two-years old

Q3: what is the storage capacity of the battery in Ampere-hours?

70 Ampere-hours

Q4: what is the resting terminal voltage of the battery when no charging current is being supplied and the battery has not been charge for at least an hour?

12.4 volts

Q5: is the engine alternator a belt-drive automotive-type field-excited alternator or a permanent magnet under-flywheel alternator directly rotated by the engine crankshaft?

Stator

[MarkCz]

Q6: is the battery a vented, flooded-cell, lead-acid battery with removable caps to check electrolyte levels?

[jimh]

Q5: is the engine alternator a belt-drive automotive-type field-excited alternator or a permanent magnet under-flywheel alternator directly rotated by the engine crankshaft?

Stator

In alternator nomenclature a stator is a coil assembly that does not move or rotate.

Both an automotive-type belt-driven field-excited alternator and an under-flywheel permanent-magnet alternator have a stator, so your answer does not identify the type of alternator.

[jimh]

I don't see any definitive evidence of the cause of the higher than normal voltage, but the voltage regulator is the most likely suspect (based on the age and storage capacity of the attached battery tending to exclude it as the cause).

There are many discussions on many boating-related websites about Mercury 60-HP FOURSTROKE engines having failed voltage regulators, but typically the problem is NO charging output, not excessive voltage on the charging output. But having such a preponderance of these charging problems related to failure of the voltage regulator assembly tends to direct attention to that component as the cause of the problem.

Perhaps trying to push current into that large 70-Ampere-hour storage battery was too much load for the regulator and alternator. The alternator output for this (still somewhat unknown) engine would be rated for only 17-Amperes output if it were the 60-HP FOURSTROKE model.

I will assume the alternator is a permanent-magnet type, with the stator located under the flywheel and permanent magnets embedded into the flywheel. That configuration would use an external voltage regulator, a component completely separate from the alternator itself. (The automotive-type field-excited belt-driven alternator would typically have an internal voltage regulator.) If my assumption is correct, you should give the external alternator assembly a close visual inspection--and also a sniff-test. External alternators used by Mercury are often reported to have a burnt odor when they have failed, but, again, usually those failures result in no charging.

If you happen to have another battery that you know to be in perfect condition, another test would be to substitute a different battery and see what effect that has on the alternator output at 5,000-RPM.

Older batteries tend to have their internal resistance rise, and the higher internal resistance in the battery allows a charging device to more easily raise the terminal voltage of the battery above the usual range of about 14.4 to 14.6-Volts.

Another concern with any measure of voltage is the accuracy of the voltmeter. When trying to assess a voltage in the 12 to 14-Volt range, the voltmeter accuracy should be very good, say better than three percent. Three percent error in 12-Volts is 0.36-Volts. In terms of assessment a lead-acid battery state of charge, an error of 0.36-Volt magnitude is significant error.

For this reason, please give more details about how the voltage is being measured any the voltmeter accuracy.

[NorthShoreWhaler]

Thank you for the response. I’m using voltage as measured by my Garmin sonar. When researching the alarm it appears that the Mercury high voltage alarm is triggered by 16 volts so there would be a degree of error from the measurement provided on my Garmin screen as I’ve never seen 16 volts on it.

I’ve ordered a new voltage regulator and will report back when I get it changed.

[jimh]

I’m using voltage as measured by my Garmin sonar.

That device can probably measure two source, depending on how it is configured.

1. the NMEA-2000 network data sent from the propulsion engine about its battery voltage or perhaps its alternator voltage, or
2. the input voltage to the GARMIN device from the boat's 12-Volt power distribution.

The best measurement would be to have a high-accuracy DVM voltmeter with a DC accuracy of about 1-percent measure the battery terminal voltage right at the battery terminals.

For example, a FLUKE 114 DVM has a basic DC voltage accuracy of 0.5-percent (0.005 * 12 = 0.06-Volts) and sells for about $185.

My theory on testing tools: you might as well get measurement tools that produce very accurate measurements.

[NorthShoreWhaler]

I am happy to report that a new voltage regulator solved the problem. I am able to run the boat at 5600 rpm and am seeing 14 volts at full throttle on the Mercury Vessel View Mobile app.

On a side note I figured out how to display voltage in the Mercury Vessel View Mobile phone app. Tapping the rpm number gives a menu of other parameters to monitor which includes voltage.

[jimh]

I am happy to report that a new voltage regulator solved the problem.

The ability to so rapidly find the voltage regulator assembly available seems to reflect that the rate of failure of that component might be rather high, and that is why the part is kept in stock all the time.

Thanks for the report of the ultimate remedy to the problem of excessive voltage output from the outboard engine alternator to the battery charging circuit.