2003 Mercury 115 FOURSTROKE Voltage Regulator

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GoldenDaze
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2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby GoldenDaze » Fri Jun 19, 2020 10:05 am

[This topic is moving to SMALL BOAT ELECTRICAL for further discussion.--jimh]

Hi all. I have a 2003 Mercury 115 FOURSTROKE EFI, one of the early Mercury four-stroke-power-cycle engines with a Yamaha powerhead. A few weeks ago I was surprised by the a low-voltage alarm (from a SONAR), and the console voltage gauge agreed. By the time I got back to the dock [the console voltmeter] was reading about 9-Volts. While I didn't check it with a indepedent voltmeter at the time, I assume the reading was correct since the engine would barely crank over and would not restart. I have a dual-battery system so I wasn't too worried.

The following day I took the boat to a nearby ramp to pull it, and it initially appeared like everything was fine. Now, with the boat on the trailer a fully-charged battery showed 12.6 Volts DC with a good quality multimeter. When I started the motor and brought it up to about 2,000-RPM. The battery showed 13.6 Volts DC which seems perfectly reasonable. The battery stayed at 13.6 Volts DC for about three minutes, then started to slowly decay. Over the course of another three minutes it dropped to 12.2 Volts DC, indicating that the motor was now putting a load on the battery. After shutdown the voltage returned to 12.6 Volts DC. At no point was any significant AC voltage present in the circuit. An immediate restart showed continued low voltage. I'm now thinking this was exactly what happened on the way to the ramp; good output at first then falling away.

I'm assuming this is caused by a bad voltage regulator because, well, what else could it possibly be? But it seemed like really weird behavior to me. Any thoughts?

-Bob
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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby biggiefl » Fri Jun 19, 2020 10:32 am

Does that engine have a belt driven alternator next to the flywheel?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

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Phil T
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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby Phil T » Fri Jun 19, 2020 10:42 am

Bob -

Hope you are using a barrel instead of muffs to run the engine more than 1,000 rpm while on the trailer. If not, please do.

Regards.
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1992 Outrage 17, 1992 Evinrude 115

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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby GoldenDaze » Fri Jun 19, 2020 10:45 am

biggiefl wrote:Does that engine have a belt driven alternator next to the flywheel?


No, it has a stator ring under the flywheel.
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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby jimh » Fri Jun 19, 2020 10:51 am

BOB--anytime the engine is running the battery voltage should rise from its resting voltage. The resting voltage of a lead-acid battery at near full charge should be about 12.6-Volts, or perhaps slightly higher. By "resting voltage" I mean the voltage after all charging current has been removed, and the battery has been resting with no load or no charging for several hours.

A typical regulated outboard engine charging output voltage should be about 14.5-Volts. When the engine is running above idle speeds, the engine alternator should put out this sort of voltage and provide plenty of current to charge the battery.

For an outboard engine to need to draw current from the battery while it is running at any speed above minimum idle speed would be unusual. Even at minimum idle, the engine should be generating enough electrical power to run itself and have a few Amperes left to charge the battery.

If I am following your narrative, you report that the battery terminal voltage before engine start was 12.6-Volts. That is a proper terminal voltage.

Immediately after engine start the battery terminal voltage rose to 13.6-Volts. This indicates the engine was supply charging current to the battery.

At about six minutes after engine start the battery terminal voltage was down to 12.2-Volt. This is abnormal, and a voltage lower than the resting voltage of the battery indicates the battery is under load and sending current to the engine and other electrical loads. The engine is no longer charging the battery.

After engine shut off, the battery terminal voltage rose to be 12.6-Volts again. This is close to the resting voltage measured before engine start, so the battery appears to have enough stored electrical energy to be able to operate the engine load for a few minutes without becoming deeply discharged. The battery appears to be in good condition.

Your diagnosis that the engine voltage regulator may have failed is possible, but there could be another problem. The generation of electrical power from the engine may have failed, so there is no voltage to regulate at the regulator.

I don't know the details of the 2003 Mercury branded Yamaha 90, but typically Brunswick would have put their own electrical components on the Yamaha powerhead. As Nick's inquiry infers, there may be a belt-drive automotive-type field excited alternator. Or there could be a permanent magnet alternator.

If there is a belt-driven field-excited alternator, the rectifiers and the regulator are usually mounted integrally with the alternator coil.

In a permanent magnet alternator, the rectifiers and regulator are usually mounted separately, and only a coil assembly is under the engine flywheel.

In either case, the problem seems to be lack of battery charging current. Since there was some indication of charging current immediate after engine start, my best inference is that there is an electrical component that when cold is working correctly, but as soon as there is some current flow the device begins to heat up, and after a few minutes of heating it stops working. I use the work "device" because the "device" could be an electrical connection that is intermittent and changes with temperature. Or the "device" could be an active component, like a rectifier or voltage regulator. An active component is more likely to fail after it warms to higher temperature.

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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby jimh » Fri Jun 19, 2020 10:57 am

OK--saw your reply that the alternator coils are under the flywheel, and the alternator is most likely a permanent magnet alternator. The rectifier and regulator are separate components and remote from the coil assembly. It is also possible that the coil assembly (often called the stator because it is stationary and does not rotate) could have failed. When I owned two 1987 Yamaha engines with permanent magnet alternators, I had to replace the stator coil assembly in both of them.

DId you observe any abnormal readings on the engine tachometer when this problem is occuring?

By any chance do you have an auxiliary engine that also has a battery charging output? If so, have you operated both the main engine and auxiliary engine simultaneously while both were connected to the same battery and both trying to charge the battery?

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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby GoldenDaze » Fri Jun 19, 2020 11:30 am

jimh wrote:DId you observe any abnormal readings on the engine tachometer when this problem is occuring?


The tachometer has been reading normally. I'm guessing that means the stator coils are good. As the regulator replacement is a lot easier than the stator, I'll start with that and move on to the stator if necessary.

It's perfectly believable that something on this 17-year-old engine is broken, but the fact that it works correctly upon a cold start but then degrades seems very odd to me.
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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby biggiefl » Fri Jun 19, 2020 11:41 am

Not sure about Mercury engines but OMC engines the tach would be erratic or not working and voltage would spike when the rectifier went bad. With spiking I mean around 17volts which is dangerous. I am assuming that when it gets warm/hot it is failing. I would try a mercury engine forum which would probably get you a quick diagnosis. I found this from 2008. Guy had the same problem as you stated.

someGuySomeWhere wrote:Re: 2001 115hp fourstroke charging problem-Update:Problem Solved

Voltage Regulator/Rectifier was at fault.
Ordered a new one from BAM Marine part #881346T
Installed and getting 14v.@ idle Haven't tested on the water, but seems OK on the trailer. We'll see if it lasts. You'll be hearing back from me if it doesn't last.

BTW: Found parts on ********** under Engine Model #1115F23YY or #1115F13ZD
for a little less that what I had paid.
Hope this may help someone in the future.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby jimh » Fri Jun 19, 2020 12:21 pm

Here is an aftermarket part for $28 on Amazon:

https://www.amazon.com/REGULATOR-RECTIF ... B06XXKSGHB

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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby jimh » Fri Jun 19, 2020 12:54 pm

GoldenDaze wrote:...that [the charging system] works correctly upon a cold start but then degrades seems very odd to me.


Heat causes many electronic components to breakdown and fail. Heat-caused failure is not unusual.

A voltage regulator can take many forms. If a very simple circuit is used as a voltage regulator, all excess voltage produced by the voltage generating source is discarded in the form of heat. If the regulator is housed in a metal enclosure with a large air-cooled finned heat sink, there is a good chance its design uses very simple methods of regulation, and just throws out any extra voltage to produce heat in the heat sink.

Inside the regulator there are certain to be electrolytic capacitors. The worst environment for an electrolytic capacitor is a hot environment. Electrolytic capacitors have liquid dielectric fluids, and their service life is in inversely proportional to the operating temperature, that is, the warmer the ambient environment the shorter the service life. Ten or 15 years of service in a hot environment is probably about the most to be expected from them, unless the capacitors are very special components and certified for high ambient temperatures and extreme long service life. You can expect that type of component on the Voyager space probe, but not expect that sort of component in an outboard engine.

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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby jimh » Fri Jun 19, 2020 12:59 pm

I don't think you can rule out the stator coils yet. They could be a cause. I hope not. Although the coil assembly probably is not too expensive, typically the flywheel must be removed to access the stator coil. Flywheel removal and reinstallation usually requires some special tools, and often the engine ignition timing needs to be checked after any change in the flywheel.

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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby GoldenDaze » Fri Jun 19, 2020 3:05 pm

I have a new voltage regulator on order. If that doesn't fix the charging problem, then the stator coils will be next. I'm not particularly concerned about removing the flywheel, and it would be a good opportunity to replace the timing belt--which still looks perfect, but if I'm going in there, why not.
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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby GoldenDaze » Tue Jun 30, 2020 9:09 pm

Tonight I replaced the voltage regulator.

I did purchase the same [jimh] pointed out on Amazon. It was significantly less expensive than other options, which normally would make me a little nervous about the quality. The regulator is no longer available as an OEM part, and I imagine that all available parts from whichever source probably come from the same factory in China. Which is more than likely the same place where the original OEM part came from anyway.

This was an incredibly easy replacement; remove the intake air baffle and there in the clear on the front of the block is the regulator assembly. It was a 10-minute job.

After replacement, initial unloaded battery voltage was 12.4 VDC, which rose to 13.7 VDC when the engine started, running at a fast idle of about 1200-RPM. As the battery charge topped off, the voltage floated up to 13.9-14.0 VDC and remained there for 15 minutes or more. Looks like we are good to go! Thanks again for all the comments, folks. Happy boating!

-Bob
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Re: 2003 Mercury 115 FOURSTROKE Voltage Regulator

Postby jimh » Wed Jul 01, 2020 12:48 pm

Hi Bob--glad to hear about the good outcome. Getting a follow-up when the problem is solved is always a nice ending to a thread.