What does the voltmeter tell me?

Prosideus

Prosideus

Active Member
Jun 5, 2012
635
Franklin, TN - Old Hickory Lake
Boat Info
1995 220 BR Signature
Prior Boat:
400 Sedan Bridge 1996 Cats 3116
Engines
Mercruiser 5.7
Ok electrically savvy folks, need your wisdom. I took the pano pic of my gauges recently. You can see the starboard voltmeter is lower that port. Exactly what is this telling me? Is my alternator going bad?

4d50c757d63c177e33a805b543c43d2c.jpg



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Your starboard meter is right where mine was when I found my alternator had completely quit.
 
The gauge is telling you its not reading the same as the other. First thing you need to do is, get a diagnostic digital volt meter and start testing. It can be anything from a bad gauge, faulty connection or terminal end, to a failed or failing alternator. Start at the battery and then work toward the alternator if the reading is low or go to the helm and work back if the voltage at the battery is good.
 
I bought a new (not rebuilt) 160amp from Seaboard Marine (sbmar.com), so it was kinda pricey. I was given a price of $150 for a rebuilt from a local shop.
 
David,

I have just had to replace both alternators. We found the OEM supplier for Caterpillar and discovered t hat they no longer make an exact replacement. The physical size and fit is the same; the only difference is these are 90A output and OEM was about 56A. If you are interested in wading into the details, you should be able to match what you have. I can send you either the manufacturer's website, or hand you off to the parts guy at our dealership. They will make a margin, but something like this can probably be dropped shipped with a credit card.


Leece-Neville is the OEM manufacturer and to get you started, here is their website:

http://www.prestolite.com/pgs_products/alt_search.php

This is the alternator that crossed to my 1996 Caterpillar 3116's:

http://www.prestolite.com/pgs_produ...tail_id=897&item=8MR2070TA&product=Alternator


Now, I have no way of knowing whether or not this alternator will fit your engines of if the wiring is compatible with the wiring on your boat.......but they were a direct replacement for those on my 1996 450DA.


If you want to involve a great parts guy, call:

John Mass
Treasure Island Marina
3650 Thomas Drive
Panama City Beach FL 32408

850-234-6533
ext. 23

Only talk to John. Marsha may answer the phone, but she does primarily Mercruiser and outboard parts, so she won't be of much help. Tell John I asked you to call him and just ask for his help. The marina is going to make a mark up, but John knows I send him knowledgable folks who don't need hand holding and he'll treat as fair as he can within their system.
 
Check the battery lead from the alternator - I had the ring terminal break which resulted in a no-charge (low) voltage reading. I was getting ready to pull the alternator to have it rebuilt when I noticed the broken lead. I got a new terminal from the electrical supply house (that was twice as thick as the original lug), crimped it on and reconnected the lead.

I thought that the resulting disconnecting of the battery lead may have damaged the alternator but it was fine.
 
Update, and further assistance needed....

So I tested the batteries and each bank were providing the proper resting voltage. I also was able to see the voltmeter test corresponded with the voltage display on the main breaker panel for each bank of batteries. We went out on a cruise, and the helm gauges showed that the starboard gauge continued to drop voltage as we continued our ride. It dropped to only 10 volts output. When we returned to the dock, the main breaker panel showed the port batteries properly holding a charge at 13.0, and the starboard had depleted to around 12.0.

Today I pulled the alternator and took it to have it bench tested at the local auto part supply store. The tech did not have the correct pigtail to do the test, but by turning the alternator by hand could feel and hear the bearings. He indicated in is most likely bad and/or going bad. He stated that it was probably reading correctly starting out, and as it heated up, the voltage reading just continued to drop. Not knowing much about this and without me telling him what I was trying to accomplish, his explanation was spot on with what I experienced. So here is where I need some help. I have a basic understanding of alternators and electricity, but I am totally nervous about screwing something up when I replace this thing. Please see the picture. The left pic is what I pulled, the middle pic is the replacement Leece-Neville unit I will be purchasing, along with the wiring diagram from the prestolite website.

My questions and descriptions are as follows (since they are not showing well in the pic):
The pic on the left, top left arrow points to a wire that was bolted to another wire.
The bottom left is where the main battery cable connected.
The bottom right is where another small wire connected.

The middle pic, the question is should I disconnect the red wire as connected here and bolt it to the same wire as in the first pic?

Thanks in advance - David.

NewWiring.jpg
 
Last edited:
Still Struggling - need more guidance please.

BT, thanks for the post. I have installed a new alternator, perhaps only to find I may have misdiagnosed my problem. So new alternator (and belt). Here are the facts.

Voltage on main panel for both port and starboard banks read ~13.
After replacing Alternator on Stbd, fire up engine and helm voltmeter reads under 12.
Fire up Port engine and voltmeter at helm reads 14.
Both alternators at the alternators read 14.
Back at the main panel, stbd bank of batteries now down to 12.
Up to helm and rev stbd engine, helm voltmeter creeps up to 12.
Turn off port engine and STBD ENGINE DIES with port engine.

Frustrated at this point - could it be a bad battery? The charger is charging both banks I believe based on readings at main panel. Could the battery be strong enough to just start the engine and then begin draining on a bad cell in one of the batteries in the stbd bank? What could be creating such a drain on the batteries?

Is it possible to test this by changing by battery selector switches (I have two). Change the A on one to B and the B on the other to A? Would that be the same as physically swapping the banks of batteries to see if the behavior changes to the other engine? Not sure where to go from here. Any help appreciated.

David
 
Keep in mind that the Leece-Neville alternators need a few rpm's to start producuing voltage. Mine need 850 rpms before the dash panel shows more then 13v, once the alternator is producing, the voltage doesn't drop below 13.6V.
 
Turn off port engine and STBD ENGINE DIES with port engine.

Something is wrong there, somehow both engine electrical systems are combined
Guessing its twins so remove the pos cable from 1 battery and see what works and what dosent. With one cable removed you should only access one engines gauges, charging system and starter.
Then connect that cable and remove the other pos battery cable and see what works and what dosent.
Report the results, check your messages
 
The way the 400DB is wired from the factory is with the stbd and port battery banks completely separate circuits. You should be able to turn off one side with the battery switch and operate the opposite engine normally.

With both engines running, you should be able to completely remove one battery from each bank without an engine dying. Once the 3116 is running, the only electrical requirement is a fuel supply solenoid with works down to about 10.5V and draws very, very little amperage. If I were taking a wild guess here, I think you may have an emergency start solenoid sticking closed since that is the only place on the boat where the 2 battery banks are connected to each other......unless someone has changed some wiring and has accidently fed one bank to the other in a circuit somewhere.
 
That year 400DB also has a battery isolator with both battery banks and both alternators connecting to it. Maybe something is up with that isolator.
 
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