First let me thank you all for your help on so many different issues. This form has been invaluable to me. I have a 2000 280ss with twin Mercruiser 5.7. I've been having charging problems and noticed the other day that when my port motor is on the voltage goes to 14 volts, but when only my starboard motor is on there is no voltage reading at all on the voltmeter. I am assuming this is a blown alternator on the starboard motor. My question is this, do both alternator charge both batteries? Does each battery get assigned to one motor? The boat has two, Dual Purpose batteries. I appreciate any insight on how these are wired. The wiring is all hidden so it's very difficult for me to analyze. In any case I will replace the alternator that is not reading any voltage, but I'm curious if the remaining motor is now charging both batteries and if that is sufficient until I get time to change it. Thanks so much.
Alternator voltage question.
- Thread starter luriesd
- Start date
SabrToothSqrl
Well-known member
Do you have two voltmeter gauges? My boat only has one.
My boat is winterized and my wrist is broken so I can't tell you which side it is off the top of my head.
I am about 80% sure that everything I have is on my port engine.
I do think it was kind of shitty of them to only install one voltage gauge.
Each engine starts from and charges only one battery. (assuming your boat is set up like most dual engine dual battery boats). This is the way the engine factory recommends it.
Each uses their respective battery.
You should have a switch that allows you to bridge them temporarily for the sole purpose of starting both engines if one of the batteries is dead.
On my formula and I assume similar ones a single battery is used for auxiliary systems.
So all of your lights radios pumps etc. all run off of the same battery and engine.
Systems that are specific to one side run off that sides engine. ex: drive trim motor.
This way even if you blast the radio all day and completely kill the port battery you can start the engine that has a good battery (strb) then bridge the two to start the remaining engine and then turn off the bridge.
At least that's how I do it, I should probably Google to make sure that is correct.
If your alternator was dead, the battery would be dead after running it because it would be using the battery to run the computer and the spark plugs and all of the electrical systems that support your engine. In a modern car you might get 20 or 30 miles before this happens. I have no idea how far a boat would go without an alternator.
They are easy enough to replace but I would not unless you can identify it is an issue.
Generally speaking you want to put a handheld multimeter to check DC voltage on the battery with the engine off. Then start the engine let it warm up for a little bit, and check the voltage on the battery again. Assuming it's around 12 V without the engine running it should be close to 14 with the engine running just over idle.
I replaced my port alternator last year because the engine would not shut off when I turn the key off because some internal diode had broken and you cannot replace that part individually.
More recently my starboard aftermarket alternator started a horrible belt squeal and radio interference so that was replaced with an OEM one.
If it does need replacing I recommend OEM only.
I got to know these specific engines very well last winter when I replaced both of them in my boat.
If you Google factory service manual PDF and the type of engine you should find it fairly easily. It's about 600 pages and tells you all about this stuff.
My boat is winterized and my wrist is broken so I can't tell you which side it is off the top of my head.
I am about 80% sure that everything I have is on my port engine.
I do think it was kind of shitty of them to only install one voltage gauge.
Each engine starts from and charges only one battery. (assuming your boat is set up like most dual engine dual battery boats). This is the way the engine factory recommends it.
Each uses their respective battery.
You should have a switch that allows you to bridge them temporarily for the sole purpose of starting both engines if one of the batteries is dead.
On my formula and I assume similar ones a single battery is used for auxiliary systems.
So all of your lights radios pumps etc. all run off of the same battery and engine.
Systems that are specific to one side run off that sides engine. ex: drive trim motor.
This way even if you blast the radio all day and completely kill the port battery you can start the engine that has a good battery (strb) then bridge the two to start the remaining engine and then turn off the bridge.
At least that's how I do it, I should probably Google to make sure that is correct.
If your alternator was dead, the battery would be dead after running it because it would be using the battery to run the computer and the spark plugs and all of the electrical systems that support your engine. In a modern car you might get 20 or 30 miles before this happens. I have no idea how far a boat would go without an alternator.
They are easy enough to replace but I would not unless you can identify it is an issue.
Generally speaking you want to put a handheld multimeter to check DC voltage on the battery with the engine off. Then start the engine let it warm up for a little bit, and check the voltage on the battery again. Assuming it's around 12 V without the engine running it should be close to 14 with the engine running just over idle.
I replaced my port alternator last year because the engine would not shut off when I turn the key off because some internal diode had broken and you cannot replace that part individually.
More recently my starboard aftermarket alternator started a horrible belt squeal and radio interference so that was replaced with an OEM one.
If it does need replacing I recommend OEM only.
I got to know these specific engines very well last winter when I replaced both of them in my boat.
If you Google factory service manual PDF and the type of engine you should find it fairly easily. It's about 600 pages and tells you all about this stuff.
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Very interesting thank you so much. So if I am hearing you correctly, it might be totally normal to see Zero voltage when I am running just one engine and that alternator might actually be working perfectly? Is there a way to test it just the alternator before I replace one that works perfectly? I will have to trace the wires and see if I can tell which battery goes with which motor I guess. Thanks so much for the information this forum is saved me thousands of dollars and many hours of work! Have a great 2021.
SabrToothSqrl
Well-known member
assuming you only have 1 gauge, its only hooked to 1 of your engines.
so, yes, no reading if that engine is off, is normal.
again, cheap and stupid of Formula to give us 1 gauge vs. 2.
if i cared enough I guess I could wire in a 2nd one.
but i'm saving my pennies for a bigger toy.
yes, just check voltage at the battery w/engine running.
so, yes, no reading if that engine is off, is normal.
again, cheap and stupid of Formula to give us 1 gauge vs. 2.
if i cared enough I guess I could wire in a 2nd one.
but i'm saving my pennies for a bigger toy.
yes, just check voltage at the battery w/engine running.
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Will40
Member
Maybe this link to manual for sun sports can help you. A common battery config, same as my PC, is one battery for port engine and aux (house) and the other battery is starboard engine start only with the temporary tie switch in between both. The best recommendation was made to put a DC multimeter on the starboard battery, check battery voltage, then start starboard engine and watch the voltage change from a 12V to 13-14VDC and you know your alternator is working. If not or how good it is working is to have a 12VDC load to clip on the battery while the engine is running. For about $30-$40 you can get a low end 12VDC battery digital load tester to clip on battery to test alternator and battery health. Good little tool to keep in your tool box.
https://formulaboats.azurewebsites.net/wp-content/uploads/2015/05/123437_SunSport_OM.pdf
Hope this helps you along. Good luck
https://formulaboats.azurewebsites.net/wp-content/uploads/2015/05/123437_SunSport_OM.pdf
Hope this helps you along. Good luck
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