Normal charging voltage

[badrano]

I have a 6.2 merc, dual battery. When I start up the engine, the voltage gauge starts off pretty close to the 10v mark and then then works it's way to the 13v mark (I'm thinking the gauge is not that accurate). Took a meter to it and right at start up, the meter reads low 12v like 12.1 or so and then works its way up to 12.8, 12.9 while at idle. After adding a little throttle to get to around 1000 rpms, the meter reads about 13.1v but then back down to 12.8-12.9 at idle. I was taking the reading at the jumper terminals by the batt switch.
Is this normal? For some reason I've been thinking that the charge voltage should be a tad over 13v at idle.

 

[alldodge]

Should be closer to 14.5V
Might have a shorted cell. What is the voltage with motor off?

 

[badrano]

Should be closer to 14.5V
Might have a shorted cell. What is the voltage with motor off?

That's what I thought.
The voltage at the jumper terminals is around 12.5v engine off...that's was just the one battery ON.
I should check voltage on both. Any possibility the battery isolator is going bad....for all I know it's the original one...15 yrs old? I guess I should take a reading there as well.

 

[alldodge]

Engine and battery charger off and your at 12.5V and not bad, full charge is 12.7V

Don't see the isolator as a problem yet. With motor rev real short above 1800 should start the ALT charging at full 14.5V. If you can read 14.5 at the ALT and stay there. The isolator would drop the voltage around 0.7V so should be 13.8V at the battery.

 

[badrano]

Engine and battery charger off and your at 12.5V and not bad, full charge is 12.7V

Don't see the isolator as a problem yet. With motor rev real short above 1800 should start the ALT charging at full 14.5V. If you can read 14.5 at the ALT and stay there. The isolator would drop the voltage around 0.7V so should be 13.8V at the battery.

Batteries at 12.4 to start.
Engine at idle right after start up....12.4 at the jumper terminals...eventually works its way to 12.8-12.9. Once at 12.9, off the alternator in to the isolator around 13.5-13.6.

Rev to 800 rpms, off the alternator around 14.5 and around 13.5 at the jumper terminals/both isolator outputs. On average, seems like the voltage drop is a little more than the 0.7v

Drop back to idle, 13.5 or so off the alternator.

The voltage gauge is a little off as the needle is slightly below the 13 mark when measuring 13.5 at the jumper terminals. I've just never seen a gauge read that low before after start up and take a minute or two to get near the 13 mark.

 

[alldodge]

Boat gauges can be off, so if your using a hand held then need to have your ALT tested

 

[badrano]

Boat gauges can be off, so if your using a hand held then need to have your ALT tested

All measurements using the multi-meter.
I take it then you think the alt is acting up?

 

[alldodge]

Its either the ALT is unable to supply enough power or one of the batteries has an issue