DC Current Blocking Diode

http://uk.farnell.com/ixys-semiconductor/dsi17-12a/diode-rec-1200v-25a-stud-do4/dp/1841859

If the alternator output is rectified to DC, as it will be to charge batteries, then there is no need to worry about a connected mains battery charger as these have a bridge rectifier also towards the back end of their output circuitry.

The diodes in the alternator will be forward biased diodes to charge the battery and to provide electric power to the other electric loads of the system. The voltage regulator directly controls the alternator rotor current to then regulate the output voltage of the alternator to a suitable voltage to charge the battery. No blocking diode is needed. A blocking diode will actually defeat the charging of the battery and create many problems for several other electric loads.

Are you asking the following? You have an AC charger connected at all times and are worried if the engine alternator will cause a problem? The answer is no, you can have them both connected simultaneously, the engine alternator will adjust its output accordingly. Same as if you have two main engines charging a single battery. If there is a very heavy draw, such as a windlass, the lower rated source may drop off line.

This answer was provided by a major manufacturer of marine chargers and inverters, neither of the battery manufacturers responded.

You're still trying to get to the bottom of your ruptured cranking batteries right?

http://cr4.globalspec.com/thread/79477#comment870164

The alternator on the engine is rated at 55A it doesn't mean that it will push that all the time. The current it delivers is dependent on the demand or load presented to it.

no load=no current.

At 55A it sounds like a bog ordinary automotive alternator which is designed to charge batteries just fine. Sticking a current limiting device between it and the batteries is a bit bodgy and a total waste of time and effort. Patchwork at best.

Have you actually measured what the alternator and your auxiliary chargers are doing?

I asked you in the other thread whether the battery dude checked this and you didn't respond.

You're flying blind with bent crutches it seems.

If it worked before it will work again. Stop guessing and start investigating.