Alternator or Battery Bank?

Hampton

Hampton

Air Defense Dept
TECHNICAL Contributor
Nov 26, 2006
7,628
Panama City, Fl
Boat Info
2008 44 Sedan Bridge
Engines
Cummins QSC-500's
Straight Drives
My house batteries ran a little low, unexpectedly a couple of months ago. I have noticed that my DC gauge on the engine instruments is reading at about 12.3V on the port side (house) and 13.8 on the starboard side. Would a faulty battery cause this? They are group 31 AGM batteries from Sears.

Or, do I need to pull the alternator and have it tested? It would be easier for me to swap out the house batteries with the bow thruster batteries. They are all the same.
 
I just went through the exact same thing. My 0000 ground cable from the port battery was not making a good connection. You should have three big ground cables on your block. Make sure they are rock solid, especially the one coming from the battery.
 
I will. I just re-secured the battery cable connections at the batteries, but I did not consider the other end. Thank you. What are the signs of a bad alternator? We run 100 hours a year, but are on shore power or generator 99% of the time, so, does it really matter? I'm sure it does, just curious. Also, I just re-secured the connections on the alternator. Must check grounds. It's always the ground in these things, isn't it?
 
My stbd alternator gauge acted the same way the weekend at the beginning of a long day of running, mostly at 1500 RPMs. Towards the end of the day it was back up around 13v. I blame it on the fridge.
 
I am chasing the same demons so I replaced all the batteries just because they are all 4 years old. Port side is still fluctuating 12v - 14v with increased RPMs so I felt there is still a connection issue. I traced all the cables to the batteries and alternators, no issues. Didn't think to check the grounds....could be the fridge...could be the alternator breaking down.
 
CAMELLA said:
I had the same issue with my starboard engine, I replaced the alternator and all is good.
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My fear is that I replace the alternator and all is not good. It may come to trying that though. I could swap them. Sounds like a lot of work.
 
If you do need an alternator, I got mine from Seaboard Marine, great service and price. Tony Athens is who I dealt with.
 
CAMELLA said:
If you do need an alternator, I got mine from Seaboard Marine, great service and price. Tony Athens is who I dealt with.
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Thanks! I'll keep them in mind.
 
Hampton said:
My fear is that I replace the alternator and all is not good. It may come to trying that though. I could swap them. Sounds like a lot of work.
Click to expand...

I thought about doing all those same swaps but decided that was too much work. So I disconnected the starter cable from the alternator and tested its output with the engine running (but since I had no ground connection I didn't get a reading on my dvm). My next step was going to be to pull the alternator and have it bench tested.
 
I had what I thought was a bad port starter. Found out after charging and testing my Optima 31AMG's 2 were bad. I just got 3 new ones. I guess they only last 3 years.
 
I wrote this once before but, oh well, I'll write it again. I have never understood the AGM craze. I use good old Interstate SRM-27 (group 27) deep cycle wet cell on both this boat and my 300DA. Went 5 years plus, strong. Hardly ever had to add water. Never ran down when on the hook (although I do like to use the generator). Less than $100 each. Plus my 175 Sport still has the factory Group 24 Interstate in it from 2009.
 
ZZ13 said:
I wrote this once before but, oh well, I'll write it again. I have never understood the AGM craze. I use good old Interstate SRM-27 (group 27) deep cycle wet cell on both this boat and my 300DA. Went 5 years plus, strong. Hardly ever had to add water. Never ran down when on the hook (although I do like to use the generator). Less than $100 each. Plus my 175 Sport still has the factory Group 24 Interstate in it from 2009.
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Bill....just curious about using deep cycle vs starting?
 
Hampton said:
My house batteries ran a little low, unexpectedly a couple of months ago. I have noticed that my DC gauge on the engine instruments is reading at about 12.3V on the port side (house) and 13.8 on the starboard side. Would a faulty battery cause this? They are group 31 AGM batteries from Sears.

Or, do I need to pull the alternator and have it tested? It would be easier for me to swap out the house batteries with the bow thruster batteries. They are all the same.
Click to expand...

John,

I assume when you refer to instruments gauge it's when the engines are fired up.

There should be no need to take the alts off for testing. You should be able to test them on the boat and it's best do it at different RPMs, just to make sure if they're shut or just starting to go bad.

Based on the info you've provided and assuming that 12.3V reading is at any RPMs, I'd say that your alt is going bad (assuming that all connections are fine). If that's the case, there's no need to buy new ones, you can have your alt rebuilt for 1/2 the price.
 
Alex F said:
John,

I assume when you refer to instruments gauge it's when the engines are fired up.

There should be no need to take the alts off for testing. You should be able to test them on the boat and it's best do it at different RPMs, just to make sure if they're shut or just starting to go bad.

Based on the info you've provided and assuming that 12.3V reading is at any RPMs, I'd say that your alt is going bad (assuming that all connections are fine). If that's the case, there's no need to buy new ones, you can have your alt rebuilt for 1/2 the price.
Click to expand...

Alex, where would I find such an alternator rebuild shop?

So my miracle fix of cleaning the ground must have just been a fluke because my port engine is back in the same situation as John's. So I'll ride along with him on this thread.
 
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ZZ13 said:
Alex, where would I find such an alternator rebuild shop?

So my miracle fix of cleaning the ground must have just been a fluke because my port engine is back in the same situation as John's. So I'll ride along with him on this thread.
Click to expand...

Bill,

I've used my local shop that rebuilds all starters, alts, etc. I guess looking onlone or yellow pages should give you some in your area. Also, you might want to consider on bumping the alt from 130AMP to 160AMP. I did it for mine.
 
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Thanks Alex. Any tricks to getting the port side belt cover off on the Cummins 6CTA? Looks like there are three mounting points with an angle bracket at each point. Do I remove the single bolt that holds each bracket to the block? Rather than try to get at the two that hold each bracket to the cover. They are kinda hidden by the cover. Also looks like the lower inward bracket shares the bolt that holds the engine to the mount. That looks scary. Maybe I am not looking at that right.
 
Belt cover has 4 thumb screws. Very easy. I had a windlass motor rebuilt for $75. Will definitely go for the rebuild, after checking the ground as discussed.
 
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