alternator works but not charging

[OttawaAquaBoy]

Hi all,

I'm having an issue with my charging system in my 3.0L Mercruiser.

I had some squealing a couple weeks ago and determined the belt was loose. I tightened it and I was showing about 13V on the ammeter. This week I had the squeal again and noticed that the bracket holding the alt was backed out about 3.4 inch. I tightened that in, ran the boat for a bit with no issue then noticed I was no longer charging.

I put a volt meter on the alt and was getting ~26.7volts - I was also getting 26.7 volts on the yellow with red on what turns out to be the tilt trim solenoid (640-3387M identified with a stamp 8996158) now I thought this might be the issue as the other three terminals all lead to ground, with the boat running or not. I thought it might have been the recifier but I guess not. Should the two small terminals on top both be ground?

The alt is an upgrade as I am running a two battery system. It is a self-exciting alt that kicks in around 2500 rpm

Any ideas why I appear to be getting good voltage at the alternator but it appears that the system isn't charging the batteries. Under load the ammeter shows ~12V and will drop down to 11V while underway. I was able to run for a couple hours today on one battery and it appeared to be still around 12V when I got back. This is on top of starting the engine 5 or 6 times during trouble shooting yesterday.

Any idea where I should start to look?

Thanks in advance!
Paul

 

[Eric 3.7LX Alpha 1]

Re: alternator works but not charging

Are you sure you have the meter set on the right spot. Never seen an alternator with an output of 26.V on a 12v DC system.

 

[Bondo]

Re: alternator works but not charging

I put a volt meter on the alt and was getting ~26.7volts -

Ayuh,.... If the alternator is Working,...
You should be seeing 13.6V everywhere, or anywhere in the system, when Running/ Charging...

 

[OttawaAquaBoy]

Re: alternator works but not charging

I was under the assumption that the alt will put out AC and require some sort of inverter to DC?

 

[Don S]

Re: alternator works but not charging

I have no clue what or where you are testing to get 26 or 27 volts, But alternator (in the modern world) with internal regulators convert AC to DC automatically.
Second, you have a VOLT meter, not an AMP meter. You can't read VOLTS on an AMP meter. You would be reading VOLTS. So which do you have, Amp or Volt meter? Makes a big difference.
Do you have a year for what you are working on. Do you have an external regulator on this "Upgrade" you did to your charging system.

Next, Yellow/red striped wire is power from the key switch to the start solenoid, not trim.

Are you using any kind of a manual, or just doing whatever you think is right?

 

[OttawaAquaBoy]

Re: alternator works but not charging

I appreciate the input, I guess I used the wrong terms.

sorry, wrong term - voltage gauge on the dash, not ammeter). my bad, voltage is the only thing I'm talking about.

I used a volt meter and tested at the alternator, I was working with a neighbor who was manning the volt meter so I don't know what he had it set to but it was reading 26.7 at the 2 terminal alternator (26.7 divided by 2 would be around the 13.5 which is what I should see, correct?) I'm trying to find out what the volt meter was set to.

I am using a manual but could not identify the unit that seemed to not make sense ( 3 terminals showing ground, one hot). I figured that unit was a rectifier or regulator since it was also reading 26.7 and thought that perhaps that was the problem. The unit I have mentioned (which I brought back and have in my hand) is located on a bracket about 4 or 5 inches above the starter (not attached to the starter which has the solenoid attached to it, no?) identified as a tilt trim solenoid pictured here at the bottom http://www.foreandaftmarine.com/Solenoidsmercuriser.htm This is not the original engine so the wires may have been changed at some point.

As for the charging system, the mechanic who replaced the engine installed a heavy duty alternator because I installed a simple A/B switch, there have been no other "upgrades" or anything crazy.

I'm not doing anything but trouble shoot. When I discovered that solenoid with the 3 grounds one hot I figured I may have landed on the issue. Guess not.....

So for clarity and a starting point, does anyone know if the top two (small) terminals on a four terminal unit with 8996158 stamped on the back should both be to ground (left terminal 1 wire, right terminal has two wires). I was not able to trace them all without getting into unwrapping the harness.

Thanks again,

 

[Bt Doctur]

Re: alternator works but not charging

Those are slave solenoids, smalll lugs: 1 gets the small yel/red wire and the other small lug goes to ground. large lugs: 1 gets the red w/ purple stripe (main feed from breaker), the other gets yel w/ red stripe(goes to starter solenoid.

 

[OttawaAquaBoy]

Re: alternator works but not charging

thanks for the information, so if I'm showing ground on the two small terminals and one of the large terminals, is that an indication that this unit has failed or is it symptomatic of something else.

everything appears to be working normally on the boat, starter, tilt, gauges, engine runs like a top. Only symptom I see is the voltage gauge reading less than 12 volts.

I confirmed the meter was set to AC, tested a 12V DC battery with the meter set to AC and it read ~27 volts

Thanks again,
Paul

 

[Bt Doctur]

Re: alternator works but not charging

If you claim the motor starts and runs normally THEN your using /reading/hooking it the meter , all wrong.
Remove the coil wire
crank engine over a few times
attach meter to battery terminals and note reading
replace coil wire and start engine
check meter reading again , it should be more that what you read earlier
Yes: charging normally, No: not charging, needs service

 

[OttawaAquaBoy]

Re: alternator works but not charging

I'll try that next weekend, thanks for the help!