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Alternator output?

BF 20 D outboards didn't come equipped with "alternators" as we generally know them. They have a single charge coil that produces ac volts that is then rectified through a full phase bridge rectifier/regulator assembly.

If your outboard has a manual choke your charge coil is rated at 6 amps.

Auto choke models (electric start) came equipped with 12 amp coils.

It is my understanding that the rated amps should be available for battery charging throughout the rpm range of the engine although, I haven't done any empirical testing of available amps at various speeds.

I don't see any other specific tests or information about the system in the shop manual.

Good luck.
 
jgmo said:
BF 20 D outboards didn't come equipped with "alternators" as we generally know them. They have a single charge coil that produces ac volts that is then rectified through a full phase bridge rectifier/regulator assembly.

If your outboard has a manual choke your charge coil is rated at 6 amps.

Auto choke models (electric start) came equipped with 12 amp coils.

It is my understanding that the rated amps should be available for battery charging throughout the rpm range of the engine although, I haven't done any empirical testing of available amps at various speeds.

I don't see any other specific tests or information about the system in the shop manual.

Good luck.
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I C thanks but here is the situation. I have a 26ft aluminum sedan with a 10 ft. Been. It has a 1996 5.7 mercruser and a brovo 3 . The kicker is a 2006 Honda 20 hp. The boat has a Garmen TR 1 Gold for. It the electronics is a Raymarine. C90 wide a 1159 hummingbird and a Raymarine A 70 and two Scotty riggers. If I don’t run the C90 everything works but the hummingbird s picture sucks. At 3000 rpm the Honda puts out 12.3 v is there a way to get it up to 13.5 output so that I don’t have to run the Mercedes at idle all day.? Thank s jgmo
 
That's a bunch of loads for the charging system. It was really only intended to replenish the battery if it's a 6amp and if it's a 20amp it should replenish the battery while powering the running lights.

At any rate, I'm not convinced it's even charging from what you're saying. A fully charged 12v storage battery theoretically has 12.6 volts potential at rest.

The charging voltage SHOULD be about 1.5 to 2 volts above battery voltage depending on the regulator set point.

To accurately assess the charging system you need to start with a fully charged battery that is in good condition and then measure the volts at the positive and negative terminals with no loads turned on.

This gives you a base point to work with. Then, as you add loads the voltage will drop. When the loads pull the volts down below 12.5 volts, the charging system is overloaded and the battery is being slowly discharged in order to run the loads.

Have you checked the 20 amp charge fuse?

If the fuse is good, then next I would test the system as I've described. If the charging doesn't rise to at least 13.6 volts I would clean all connections, starting at the battery cables and also at the starter motor solenoid if electric start.

Remember, grounds are just as important as positive in an electrical circuit and clean, shiny connections prevent voltage drops in the system. The marine environment is hard on electrical connections and they need to be cleaned more often than in most cars.

At 2300 rpm that little charge coil should be putting out over 50 volts ac before going through the rectifier. But that little system can only do so much.
 
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