Voltage problems

[capthorace]

Port engine - Crank engine and volts go to 13.5 VDC. (In the green)
Stb Engine - Crank engine and volts go to 13.5 VDC.

Now the problem - port engine voltage falls back to 12VDC (not in the green)after the ignition switch for stb engine is turned on.

Any suggestions on why this happens?

[CClassic28]

What motors in the boat? If Cummins B's, it could be the grid heater pulling more voltage than the Alt. puts out.

Chris

[capthorace]

7.4 Volvo gas jack shaft

[backman]

check if your alternator is putting out 13.5-13.8 volts

Thats the 1st place I would look.

[outriggers]

Check voltage at the alternator terminals. If it's good there you have some other problems.

For it to drop back to 12v you would have to have a pretty big load on it which I doubt is happening. It's probably related to poor connections if you have good voltage at the alternators and it was working ok previously.

[capthorace]

There are three solonoids in line at the aft engine room. I know the bottom one is for 12 VDC. I presume the others are for the port and stb engines. But what for?

[outriggers]

If you have the owners manual the wiring diagram is in it. I have a 25' so I only have two solenoids. One is for house power and the other parallels the batteries for starting. You may have the same arrangement.

[Patriot]

There are three solonoids in line at the aft engine room. I know the bottom one is for 12 VDC. I presume the others are for the port and stb engines. But what for?

One is the MAIN (energized by the MAIN switch on the dash) That switch and associated solenoid closes the cicuit, thus providing 12V DC power to your 12V distribution panel under the console and thus the dash panel switch gangs. Only the 2 bilge pump float switches are wired to the hot side of the solenoid such that they retain 12V power even when the "Main" switch on the dash is OFF.

The other two are parallel solenoids. A quote from my manual: "The parallel solenoids are activated automatically when the ignition switch is turned to the "Start" position. The purpose of these solenoids is to momentarily parallel all batteries while the solenoid motor is engaged"

From what you describe I would check the battery and all connections to the parallel solenoid for the engine that has low voltage after start. After start is the first time in the sequence that that battery and associated connections stand alone without the benefit of parallel. If the voltage on that engine does not recover after a bit of time then I would suspect the charging system of that engine.