Alternator and Charging Issues

[RangerJim]

2006 Mercury ProXs 225 hp
SN: 1B263101

Fishing yesterday and half way through the day starting get a beep when hitting the trim and a low battery indication on the smartcraft gauges which was showing about 11.9 volts and the console graph about 11.6 volts.

Troubleshooting today and here are the results with DVOM unless otherwise noted. (Fully charged 31 series X2 AGM that is only about a month old)

Voltage at the battery (Engine Off): 12.85 volts
Voltage at the battery (Engine Idle): 12.56 volts DVOM - 12.4 Smartcraft
Voltage at Red Output Terminal (Engine Idle): 0.995 volts

Voltages at small connector
Red wire, Engine off/Key On: 12.84 Volts
Purple wire, Engine off/Key On: 12.68 Volts

Red wire, Engine Off, Key Off: 12.83 Volts
Purple wire, Engine Off, Key Off: 0 Volts

Also cleaned both ends of the alternator ground wire/strap.

Researching old threads on here, the voltage reading at the red output terminal is really low? I checked it at least a dozen times and approx the same reading every time (approx 1.00 volt, give or take).

My suspicions is a bad alternator?

[JOE54]

mine too

[EuropeanAM]

Double check that voltage at the large red output terminal- should have at LEAST battery voltage (unless fusable link lead is damaged).

[RangerJim]

Double check that voltage at the large red output terminal- should have at LEAST battery voltage (unless fusable link lead is damaged).

I checked it a number of times since it was so low and kept getting the same. But I'll go out and recheck it now.

[EuropeanAM]

Also make sure your battery switch is turned ON when testing.

If indeed you have no voltage at the large red output terminal, you likely have a failed alternator AND a failed fusible link lead.

[RangerJim]

There are two battery switches/breakers in the bilge area. One for the trolling motor and the other is for all the electrical on the boat (i.e. pumps, lights, etc). The motor and trim isnt on a battery switch.

Anyway, rechecked everything and basically the same numbers.

Voltage at the battery (Engine Off): 12.88 volts
Voltage at the battery (Engine Idle): 12.52 volts DVOM
Voltage at Red Output Terminal (Engine Idle): 0.991 volts

Voltages at small connector
Red wire, Engine off/Key On: 12.82 Volts
Purple wire, Engine off/Key On: 12.67 Volts

Red wire, Engine Off, Key Off: 12.84 Volts
Purple wire, Engine Off, Key Off: 0 Volts

I did check for continuity on the fusible link, I am assuming I did it correctly. Put the DVOM in the continuity mode and put the red lead on the alternator output and put the black lead on the solenoid post at the other end. Per the Klein DVOM, a reading of "OL" means open circuit.

[RangerJim]

Pulled fusible link lead off the engine this morning and tested for continuity on bench. Open circuit reading. So that is definitely an issue. I do recall when I swapped in the new X2 a few weeks ago that I accidentally got a wrench across the positive and negative batt terminals for a split second. Though I have been fishing a couple of times since then for 3 to 4 hour trips.

So would something as simple as a blown fusible link cause the alternator to not charge properly? Finger crossed that replacing it will solve the problem and alternator was good after all.

[JOE54]

yes sir sure will

[RangerJim]

Just replaced the fusible link and least I am now getting 12.52 volts at the alternator output which is better than the approx 1.00 volts I was getting. However looking at some old posts on here, 12.52 looks lower than normal. (Should be in the 13 to 14 volt range at idle, correct?)

The new readings are below.

Voltage at the battery (Engine Off): 12.83 volts
Voltage at the battery (Engine Idling about 5 minutes): 12.52 volts DVOM and 12.4 on Smartcraft
Voltage at Red Output Terminal (Engine Idling): 12.45 volts
Didnt bother with the voltages at small two wire connector.

Maybe I hit the daily double and had a bad fusible link and bad alternator at the same time?!

[smoken86]

Sounds like the alternator took a crap, it probably took the fuse out when it went.

[Savage]

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Sounds like the alternator took a crap, it probably took the fuse out when it went.

Well this is what took out the fusible link.......Alternator will be fine

I do recall when I swapped in the new X2 a few weeks ago that I accidentally got a wrench across the positive and negative batt terminals for a split second

[RangerJim]

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Well this is what took out the fusible link.......Alternator will be fine

Now I am confused....lol

I did replace the fusible link today. So are you saying that the alternator is working fine with 12.52 Volts at the battery and 12.45 volts at Red Output Terminal (Engine Idle)? I dont want to pull the alternator off if it isnt necessary. Previous posts on here indicate that should see 13 to 14 volts at the alternator output at engine idle.

[massbays]

don't test alternator @ idle speed. bump it up to about 1200 rpm.
I would expect to see 13/14v @ 1200.
blown fuse 1200 I would expect to see very hi voltage 18/20v.
testing @ alternator output post.

[lpugh]

If battery is the proper one and fully charged and in good condition it should exceed 14 volts within 5 minutes at idle.

[RangerJim]

If battery is the proper one and fully charged and in good condition it should exceed 14 volts within 5 minutes at idle.

X2 battery that is a few weeks old and fully charged. Never saw it get above 12.52 and was pretty close to 5 minutes and did bring it to around 1000 rpm but only for a few seconds.

[SilverFox579]

If battery is the proper one and fully charged and in good condition it should exceed 14 volts within 5 minutes at idle.

Correct, I've never seen less than 13.8vdc at idle even upon initial startup.

[JOE54]

+1 ^^^^ yep

[smoken86]

You already did all the appropriate tests and from the beginning your tests showed the alternator was bad. You only had .99 at the output terminal. If it was supplying proper voltage (even with the blown fuse) you would have seen it at the terminal. You are only seeing battery voltage from the connection at the starter solenoid.

[RangerJim]

+1 ^^^^ yep

Just dropped it off at alternator shop for a rebuild! hopefully that takes care of it.

(PS: Going back in my feeble memory, what actually happened is the alternator went out on me over the weekend and then when I was troubleshooting the issue on Monday, I remember arcing the output post on the alternator to ground when I was trying to remove the rubber boot. Believe that is when the fusible link got blown.

So public service announcement: always disconnect the positive lead on the battery before doing anything involving electricity.... )

[Savage]

Going back in my feeble memory, what actually happened is the alternator went out on me over the weekend and then when I was troubleshooting the issue on Monday, I remember arcing the output post on the alternator to ground when I was trying to remove the rubber boot. Believe that is when the fusible link got blown

Well that makes more sense. It wasn't likely that the "daily double" happened at the exact same time the fuse link stopped holding, due to the wrench incident.