Volt meter shows 10-11 volts when running full throttle...odd, right?

[Sea_Ray_Seattle]

I've been having this issue ever since buying the boat 2 months ago... boat is plugged into shore power when it's not in use, but when I turn on the motor the volt meter reads 11-11.5 volts and stays like that until I get up to full throttle where it then jumps up to 12.5 volts... but nothing in between.

Yesterday, I realized that I forgot to plug in the shore power when I got to the boat, but it had only been two days since last driving it and I forgot that I left the water pressure button on. We spent a good portion of the day with stereo on (which has a small amp too) and fridge running - driving for a bit then floating for 45 minutes at a time. All day long the volt meter (even at full throttle) showed 10-11 volts.

The volt meter on the boat should show the alternator volts, not the aggregate battery power at that time, right?

Anyway, all that seems really concerning, right?? Is there such a thing as the alternator kind-of-working where it only puts out 10v and slowly wears down the battery? (seems like motor wouldn't run long if that were the case... and it was purring just fine).

I plugged in my Garmin 4200 chartplotter and I set a volt alarm to 9.0v and the alarm would flicker on for about 1/2 a second and then immediately turn off. It made me even more confused.

Any thoughts as to what is going on?

(I have a 1996 Sea Ray 270, 2 large dry cell batteries and 1 small car/boat battery. Alternator is after market, installed 5-7 years ago.)

 

[terminaldegree]

Well, you can double check with a multimeter to see if the voltage matches the gauge. Most marinas and auto parts stores can load test batteries and alternators, so you can locate the fault.

Be careful with your electronics-- I've read here about people screwing them up by running them at the wrong voltage. On a boat with failing batteries, I once froze the chartplotter at engine startup, but it seemed okay after rebooting it.

 

[chrissrv195]

It could be the alternator or a battery. Doesn't sound like a short though, unless you keep having breakers or fuses pop.

A typical alternator needs to be outputting at least 13-14.5 volts to fully recharge a 12 volt battery. If it (the alternator) isn't putting that out the battery will never never able to achieve a full charge of 12 to 12.5 volts.

You can either use a multimeter to test output directly off the alternators hot & ground wires, or use a battery load tester on the battery while the engine is running. Load test the battery with the tester when the engine is off. This would also tell you if your gauge is incorrect.

If the battery's good then I'd bet the output has diminished from the alternator(this is common) which would need replacing or rebuilt. Mostly easier to replace these days.

It might be putting out 10-12 volts, which would be enough to power most of the system & start the boat, but not for long.

Just my opinion though, I deal with this kind of stuff at the shop often though. :thumbsup:

 

[The Bill Collector]

Load test your batteries and you'll have a much better idea of whats going.....

 

[Nehalennia]

Load test your batteries and you'll have a much better idea of whats going.....

I agree. How old are the batteries?
It's easy to pull the alternator for testing too, but start with the batteries.

 

[OldSkool]

If the batteries are bad they will require much more voltage. To the point of killing the alt. The alt is most likely bad as you need to achieve WOT to get it to 12-12.5 volts. Usually and internal regulater has burnt out because of the over charging. If you find that you also need to replace the batteries, replace both if they are old. An old battery along side a new one will kill the new battery.

The guy's are square on this on, heed their counsel.

 

[boatmailster]

I also think that voltage regulator on alternator is a problem. He is saying that batteries hold charge when plugged to shore power or he wouldn't be able to crank the engine.

 

[northern]

I had similar problem Port engine metesr reading weres 9 to 11 volts at upper and lower helm. Multi meter read 9 to 11 volts. at the same gauges. The main volt meter in the cabin in the electric panel read 13+ Batteries with multi meter 13. Engine started and ran well. After 2 years of looking form time to time there was a loose wire on the ignition key switch in the main electric panel. After tighening I got 13+ volts on both pper and lower gauges.

 

[Sea_Ray_Seattle]

How do you go about testing the voltage regulator to see if that's the cause? (and which one is it?)