Low Voltage

[HandsFree]

I have a 1997 3100 open with 454's. Here in the great lakes we troll at very low speeds (i.e. 1.8 to 2.8 mph). In order to do that I run one engine at a time. When I use the port engine my volts stay between 12 and 13 but when I use the starboard engine the volts slowly drop, the last time it was down to a little less then 11. When I raise the RPMS to over 1000 it begins to slowly rise. I am thinking it is the alternator, is there an easy way to check it? Could it be some sort of regulator that is not working properly. Any suggestions? 

[NYMarine1]

I have a 1997 3100 open with 454's. Here in the great lakes we troll at very low speeds (i.e. 1.8 to 2.8 mph). In order to do that I run one engine at a time. When I use the port engine my volts stay between 12 and 13 but when I use the starboard engine the volts slowly drop, the last time it was down to a little less then 11. When I raise the RPMS to over 1000 it begins to slowly rise. I am thinking it is the alternator, is there an easy way to check it? Could it be some sort of regulator that is not working properly. Any suggestions? 

I don't know about the 454's but the 8.1Ls on my 35 have voltage regulators that don't open/activate until around 1000 RPMs.  I think that is the way they are designed.  My port engine alternator charges the engine batts and my starboard engine alternator charges the house batts.  Until I hit 1K, the voltage does drop.  When im in the 5 mph zone I usually drop the starboard engine to 500 RPMs and bump up the port engine to 1K RPMs; probably don't need to though.

[Silver Rush]

I have a 1997 3100 open with 454's. Here in the great lakes we troll at very low speeds (i.e. 1.8 to 2.8 mph). In order to do that I run one engine at a time. When I use the port engine my volts stay between 12 and 13 but when I use the starboard engine the volts slowly drop, the last time it was down to a little less then 11. When I raise the RPMS to over 1000 it begins to slowly rise. I am thinking it is the alternator, is there an easy way to check it? Could it be some sort of regulator that is not working properly. Any suggestions? 

The 31 open has Balmar alternators with separate Balmar voltage regulators,designed for 4 stage charging in a cruising environment. I have a 96 open with the 454s and had bad regulators when i bout it an one bad alternator. I could have had everything rebuilt but I too troll lake Michigan. I opted to replace both alternators with new Balmar alternators with smaller pulleys and internal regulators. Now i get great charge for all my systems while trolling.

[HandsFree]

I have a 1997 3100 open with 454's. Here in the great lakes we troll at very low speeds (i.e. 1.8 to 2.8 mph). In order to do that I run one engine at a time. When I use the port engine my volts stay between 12 and 13 but when I use the starboard engine the volts slowly drop, the last time it was down to a little less then 11. When I raise the RPMS to over 1000 it begins to slowly rise. I am thinking it is the alternator, is there an easy way to check it? Could it be some sort of regulator that is not working properly. Any suggestions? 

The 31 open has Balmar alternators with separate Balmar voltage regulators,designed for 4 stage charging in a cruising environment. I have a 96 open with the 454s and had bad regulators when i bout it an one bad alternator. I could have had everything rebuilt but I too troll lake Michigan. I opted to replace both alternators with new Balmar alternators with smaller pulleys and internal regulators. Now i get great charge for all my systems while trolling.

Thanks for your response. Could you be more specific as to which alternator you chose and the size of the pulleys. Seeing as I am unable to do the work myself (Hands Free) I would like to get my son to do it while he is still stationed in Ludington.

Thanks
Dennis

[Silver Rush]

I am not exactly sure on the specifics, if you are in Ludington call Todd Johnson at Johnson's Supreme Marine. He does all the work on my 31 and does a great job.

[HandsFree]

I am not exactly sure on the specifics, if you are in Ludington call Todd Johnson at Johnson's Supreme Marine. He does all the work on my 31 and does a great job.

Thanks, I know Todd, I will call him.

[Dakota773]

As an FYI, the Port engine loads the house panel, so a little drag or drop might be related to running the refrig at sea. At least that what I discovered on my 98 31 open.

Discovered this when I tripped the house battery breaker and went out.  At idle, the house panel dropped the load so much the electronics switched off.  Only the port engine at a higher rev. (like 1100 vs 800) upped the load enough to compensate.  

[NYMarine1]

Just as a follow-up, although I have not really thought much about it, even at low idle (below 1K RPMS) when my helm batt gauges read low, the DC panel readings for the engine/house banks are reading well above 12.

Just food for thought.

[Chris Burkard]

As mentioned above, one alternator on one engine charges the house bank and the other engine alternator charges the engine bank. Running one engine only for a long period of time is going to allow one bank to discharge. You should have a 3rd battery switch that says "Emergency Interconnect". If you engage this switch while you are only running one engine, that one alternator will charge both engine and house battery banks.

Keep in mind that if your electrical draw exceeds the alternator output , you are still going to see a discharge. The boat was never designed to operate on one engine for long periods. The alternators output were chosen based on them charging their perspective banks at a moderate load at a moderate rpm. You are asking 1/2 of the system output to charge 100% of the system at the lowest possible rpm no less.

Also keep in mind that by engaging the "Emergency Interconnect", you no longer will have an emergency supply of power should the entire system allowed to be discharged.

You could solve this issue by allowing both engines to run while only one engine in gear, or upgrading to higher output alternators where one can handle the entire vessel load while at idle.

Good Luck!