Thanks guys. I just thought that a converter would serve another purpose other than being a charger. I guess the manufacturers marketers think can get more money for a converter than for a charger. I also understand the purpose also, it will help prevent someone from using a cheap charger and burn the rig down.
Typically on cruising boats, we have 3 battery banks in addition to a generator, so when we buy a charger, it has to be a 3 bank charger. The banks are as follows: One bank is for the port engine, one bank for the starboard engine and one bank for the house batteries. The port and starboard engines just have one starting battery for each engine and are charged as separate banks. The House bank typically has 2 or more batteries in parallel to run everything except for engines. That accounts for the 3 banks
The generator has a separate starting battery and is not normally included or counted as a bank because the generator is self charging it's own battery.
In addition, we have an Inverter that is getting it's power from the House battery bank only. On boats my size (36') the Inverter is usually only about 1000 to 1500 Watts. Our Inverter is only wired to energize the switches on the AC Panel for the fridge and the starboard side AC outlets which includes the TV, fluorescent lights, small ice maker and fans.
When we are running, the alternators are charging the batteries as we go.
This eliminated the need to run the generator. When anchored out somewhere, our 2 house batteries will hold up for about 12 hours before going down to 10.5 V which is our Inverter shut off point. By using the separate banks, we dont have to worry about running down the starting batteries.
In addition, we have a Battery Isolator. It is a unit that is basically large diodes. The DC inputs are the engine alternators and the DC outputs are the battery banks. The Isolator isolates each battery bank from inadvertantly stealing 12V DC from eachother. Without the isolator, sometimes one bank can steal electricity through the alternator from anothe bank.