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Author Topic:   Mercury 60-HP Voltage Regulator Failure
bloller posted 04-02-2010 10:12 PM ET (US)   Profile for bloller   Send Email to bloller  
Today I noticed that the voltage shown on my Smartcraft guage was at 11.8 to 12-volts while underway [on a 2004 Mercury 60-HP outboard motor]. Before it was around 14-volts while underway. I also believe that the voltage regulator under the cowling may have overheated. I smelled a faint burning odor but saw no burnt wiring.

I previously contacted Mercury to see if this particular [motor] was part of any recall and was told no. I guess I will have to take it to a dealer since it is still under warranty being purchased new in 2008.

Does this situation force me to suspend use of my motor?

number9 posted 04-03-2010 01:13 AM ET (US)     Profile for number9  Send Email to number9     
Have you had the opportunity to check the voltage at the battery terminals with a VOM or DVOM to confirm it's not charging and your gauge is reading correctly?
jimh posted 04-03-2010 09:09 AM ET (US)     Profile for jimh  Send Email to jimh     
If the battery voltage measures only 11.8-volts when the engine is running, the most logical conclusion is there is no charging current being supplied to the battery, the battery is supplying current to the engine, and the battery is being deeply discharged by the load.

To correlate battery terminal voltage with battery state of discharge, see the chart in the REFERENCE article at

A battery terminal voltage of 11.8-volts corresponds to about 75-percent discharged.

If you continue to operate the motor without the motor supplying charging current to the battery, the battery charge will continue to be drained away. Eventually there will be no charge in the battery. A very deep discharge of the battery is considered to be harmful to the battery and will likely reduce its capacity to hold a charge.

The perception of a burning smell from an electronic component generally indicates the electronic component has reached a high temperature that is above its normal operating temperature range. Solid-state electrical components often fail if overheated. The failure mode of the component is hard to assess without more investigation. In general there are two modes of failure possible:

--the component fails into an open circuit

--the component fails into a closed circuit

If the rectifier or regulator assembly has failed into an open circuit condition, it is unlikely to cause further damage as no current flows in an open circuit. If the rectifier or regulator assembly has failed into a closed circuit condition, more damage can occur. High current will flow into a closed circuit. More components can be damaged. The current is generated by the alternator stator winding, and it may overheat and become damaged. Even if the short circuit does not damage other components from the high electrical current flow, the heat generated may cause damage.

I do not recommend continued operation until you assess the failure mode of the electronic. If the regulator-rectifier assembly is no longer hot when the engine is running, it probably has failed to an open circuit. Further operation will probably not cause more damage to the charging circuit, but your battery will continue to be discharged.

bloller posted 04-03-2010 12:29 PM ET (US)     Profile for bloller  Send Email to bloller     
I have taken the motor to a dealer and will post more information when I have it. It appears that the voltage regulator that was recalled for 2002-2003 models is indeed the one contained in my motor. Why Mercury would not recall my motor as well is beyond me.
jimh posted 04-04-2010 11:50 PM ET (US)     Profile for jimh  Send Email to jimh     
It is quite easy to speculate why the manufacturer did not recall your motor but did recall an earlier model, even though the voltage regulator component was the same in both cases (according to you). There may be other differences in the two different models of the motor that account for the difference in the recall policy. For example, in your motor there may be a circuit protection device (such as a fuse, a circuit breaker, or a fusible link) that is included which is missing from the models being recalled. Or, there may be other changes which remove the potentially dangerous situation that caused the hazard which is the reason for the recall. For example, a fuel line might have been re-routed in your model moving it away from the rectifier-regulator assembly. Again, these are just some speculations that I offer to show you that there could be a logical reason why your engine is not recalled.

It will be interesting to see if the failed voltage regulator-rectifier component is replaced with a part that has the same part number.

bloller posted 04-20-2010 09:50 PM ET (US)     Profile for bloller  Send Email to bloller     
I replaced the faulty voltage regulator on my own and problem is now solved. I got tired of waiting for the dealer service and did not like their lack of security in their yard but that is another story. I decided not to take it to another dealer as it would be much further away. By the time I drove back and forth several times burning several tanks of gas, I could have just bought the new part myself.

The part number was 893640A02 for the kit with new exhaust cover, thermostat and added fuse assembly. Cost was about $143. The voltage regulator alone is part number 893640T01. It costs about $110. I have not yet installed the new exhaust cover as I am still unsure if it is necessary.

It would have been nice though to see how Mercury would or would not have dealt with the problem. This was a very easy and relatively inexpensive fix and the motor has performed excellent otherwise with over 100 hours. I just hope it does not become a recurrin problem.

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