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TOPIC: Alternator problems

Alternator problems 24 Aug 2017 17:00 #1

  • shastabro
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I have a 91 3288 with a house (accessory) battery and starting battery and I have been having some issues with the starboard alternator. My system is configured as outlined below.

The port alternator charges the starting battery (no problem there) and the starting battery is not connected to the charger or the house battery, which is how I like it.

The starboard alternator is a different story, it charges the house battery which is also connected to the shore power battery charger. Recently the starboard alternator does not seem to work properly or seems to be charging at a low voltage.

Now usually my house battery is fully charged anyway because I have it charged on shore power. I forgot to unplug shore power before starting my starboard motor and I'm wondering if this is why the alternator is not working properly. It used to work fine but now, I noticed, if I bring the motors up to high RPM (around 2500 or more) the alternator starts working again but if I am running at slower speeds (which I usually am) it only sits at around 12 volts. I am wondering if anyone else has had this problem or can provide any helpful input before I start getting in there? Of course its on the side that is almost inaccessible. Is there some kind of voltage regulator or diode that I may have fried by forgetting to unplug shore power before starting starboard motor?

Thanks in advance for any input you can provide

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Alternator problems 24 Aug 2017 17:18 #2

  • Ruffryder
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I have seen it happen especially with older chargers with no blocking diodes.
I always turn off my AC main breaker before starting.

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Alternator problems 26 Aug 2017 18:34 #3

  • makonnen
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1998 Bayliner 2655 5.7 merc BIII, dual cranking batteries, charging goes to the battery selector.

I can't help you much but wanted to mention that I am noticing the same issue. I never really pay much attention to my voltmeter guage. But I noticed this season that it sometimes dips below "13" on the guage. The odd thing is that sometimes its above "13" as well??? The battery open circuit voltage as measured by my volt meter never dips below 12.6/12.7 volts. I don't remember my alternator ever dipping below 13V when the engine is running, then again I rarely pay attention to it so I'm not sure. My batteries are 7 years old, Costco category 24 135Amp-Hour. Its the same result when I switch to either battery or both.

Here is the really odd thing, I get the same result when I plug in to shore power running off the battery charger. Sometimes it charges as 13.1-13.5V, other times, the batteries sits at 12.6-12.8V. Again I rarely pay much attention to this. I assume the battery charger on the boat is automatic and will shut itself down when the OCV is correct to avoid drying out the battery? I'm not sure.

I'm going to start diagnosis by cleaning the battery terminals and checking / tightening the connections. I may replace both batteries next season as they will be 8 years old. I already checked the water and electrolyte with a guage. I'll likely replace the alternator just because I've never done it in the 8 years I owned the boat. Tossing between a straight stock / Delco replacement or an upgrade to a Balmar alternator or something.

What steps are you taking?

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1998 Bayliner Ciera 2655, 5.7 BIII

Alternator problems 26 Aug 2017 19:17 #4

  • Pcpete
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I keep my starting and house batteries separate, as in the crossover is turned off. My starter battery is a 27 series, the same configuration as from the factory and has worked well since I installed it last fall. My house batteries are four golf carts. I replaced the original battery charger at the same time with a new solid state unit. I keep the inverter system independent from the house and staring batteries.
Sometimes my alternators need to be woken up by increasing the rpms, but not often. The one on my muscle car is the one that always needs to be bounced to get it to 13.5 but I'm told that's not uncommon.
It may be that you want to have your alternators looked at in the off season by a specialty shop to give them a tune up. I'm not sure you have a problem, more like a situation. My 2 cents.

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Alternator problems 27 Aug 2017 00:42 #5

  • captharv
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I have a 2001 2452 with the factory Pro mariner 15 amp. I have started the engine many, many times while the charger was on. No problems. The chargers have separate leads to the batteries and are isolated from each other using diodes. Putting a starter load on it merely kicks the charger into the high current mode for maybe a few seconds. Then it goes into a normal mode. The alternator has three windings. They each have a positive and negative diode, and isolate the windings from each other and the outside world. I was in my earlier years a certified automotive electrical tech and have rebuilt may alternators. One thing which will kill one fast: reverse polarize it. The battery will pump 100 amps thru the diodes and stator faster than you can say oh. s**t, and greet you with smoke. Then go out and buy a rebuilt.

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Alternator problems 27 Aug 2017 03:00 #6

  • Warba Warrior
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makonnen wrote: 1998 Bayliner 2655 5.7 merc BIII, dual cranking batteries, charging goes to the battery selector.

I can't help you much but wanted to mention that I am noticing the same issue. I never really pay much attention to my voltmeter guage. But I noticed this season that it sometimes dips below "13" on the guage. The odd thing is that sometimes its above "13" as well??? The battery open circuit voltage as measured by my volt meter never dips below 12.6/12.7 volts. I don't remember my alternator ever dipping below 13V when the engine is running, then again I rarely pay attention to it so I'm not sure. My batteries are 7 years old, Costco category 24 135Amp-Hour. Its the same result when I switch to either battery or both.

Here is the really odd thing, I get the same result when I plug in to shore power running off the battery charger. Sometimes it charges as 13.1-13.5V, other times, the batteries sits at 12.6-12.8V. Again I rarely pay much attention to this. I assume the battery charger on the boat is automatic and will shut itself down when the OCV is correct to avoid drying out the battery? I'm not sure.

I'm going to start diagnosis by cleaning the battery terminals and checking / tightening the connections. I may replace both batteries next season as they will be 8 years old. I already checked the water and electrolyte with a guage. I'll likely replace the alternator just because I've never done it in the 8 years I owned the boat. Tossing between a straight stock / Delco replacement or an upgrade to a Balmar alternator or something.

What steps are you taking?


I would guess you need new batteries. I've lived in Northern Minnesota/Northern Wisconsin my whole life. If you can get 5 years out of a vehicle battery here you are doing well I am thinking 8 years out of a battery anywhere is pretty good. .
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Alternator problems 27 Aug 2017 15:56 #7

  • makonnen
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Warba Warrior wrote:

makonnen wrote: 1998 Bayliner 2655 5.7 merc BIII, dual cranking batteries, charging goes to the battery selector.

I can't help you much but wanted to mention that I am noticing the same issue. I never really pay much attention to my voltmeter guage. But I noticed this season that it sometimes dips below "13" on the guage. The odd thing is that sometimes its above "13" as well??? The battery open circuit voltage as measured by my volt meter never dips below 12.6/12.7 volts. I don't remember my alternator ever dipping below 13V when the engine is running, then again I rarely pay attention to it so I'm not sure. My batteries are 7 years old, Costco category 24 135Amp-Hour. Its the same result when I switch to either battery or both.

Here is the really odd thing, I get the same result when I plug in to shore power running off the battery charger. Sometimes it charges as 13.1-13.5V, other times, the batteries sits at 12.6-12.8V. Again I rarely pay much attention to this. I assume the battery charger on the boat is automatic and will shut itself down when the OCV is correct to avoid drying out the battery? I'm not sure.

I'm going to start diagnosis by cleaning the battery terminals and checking / tightening the connections. I may replace both batteries next season as they will be 8 years old. I already checked the water and electrolyte with a guage. I'll likely replace the alternator just because I've never done it in the 8 years I owned the boat. Tossing between a straight stock / Delco replacement or an upgrade to a Balmar alternator or something.

What steps are you taking?


I would guess you need new batteries. I've lived in Northern Minnesota/Northern Wisconsin my whole life. If you can get 5 years out of a vehicle battery here you are doing well I am thinking 8 years out of a battery anywhere is pretty good. .


I live in Vancouver BC, we get mild winters here. But I would agree, 5-6 years is about the life of a battery out here for cars and trucks. But I cannot fault these two boat batteries. The electroyte tests fine, nice and clear. I have a home made load tester that pulls 300A, they load test fine. But you're right I think next year its time to replace them no matter what. Going to replace the alternator too. Why not...

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1998 Bayliner Ciera 2655, 5.7 BIII
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