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[pkmarine]

I am looking for some help troubleshooting a charging issue.  Its a twin 350hp 3126 engine application.  Both engines are displaying the same symptom of apparent non-charging. 

There are two banks of two group 27 AGM batteries that test within spec, and the alternators have been removed and bench tested and found to be OK.

Prior to starting the engines, the system voltage is at 12.8 volts.  When the ignitions are turned on the voltage drops to 12.3 volts.  When the engines are cranked the voltage drops to 10.5.  After starting, the voltage rises to 12.3 volts, where it settles.  As the engines are running; if the port engine rpm is increased, there is no change in the voltage.  If the starboard engine rpm is increased, the voltage rises to 12.5 volts. 

While the engines are running, I have checked the voltage at the alternators, and at the batteries, and the voltage is the same.

What am I missing here?  I would expect the voltage to rise to 13+ volts.  The batteries are ok, the alternators are ok, the are obviously all connected, so why are the alternators not putting out?

[dave10010]

The air intake heater draws a huge amount of current (100+ amps). Heater is on until the coolant temperature reaches 130 degrees. As a test, disconnect the intake heater relay and then measure battery voltage.

[cabo35]

Did you ever figure out what your problem was?  I have two 3126b engines in my boat and I am having the exact same issue.

I just put in five new group 31 AGM batteries and tested the alt.  They are all fine but I can't get more the 12.8 to 13.0 volts out after running at 2100 RPM's for almost an hour.  Seems low.