Options for charging battery bank with engine alternator

[luvrbus]

Zero, thought I would pass this information a friend of ours stopped to show his new Marathon last night and I checked his battery system for you  they use 2- 140 amp alternators for the house and 1- 140 amp for the chassis and this is for only 6 4-D house batteries and 2- 4000w stacked inverters, you may need something larger for 12 -8Ds     good luck

[belfert]

You need to size for the load, not the number of batteries.  Marathon is probably assuming the two inverters could be heavily loaded thus the two alternators. 

[Kenny]

What about sizing the charging system for the rate of battery drain and battery recovery you can live with. The load is going to vary depending on what your using. To size for the worst case load, you don't need all the batteries but you would need a rather large charging system. The beauty of having many batteries is you can down size all of your battery charging systems. The batteries are now there to provide power in times when additional loading is needed for short periods. The rate of discharge and recovery is now dependant on the charging system and what you can live with.

Rather than adding an additional alternator, you may want to utilize the original bus alternator to charge both the bus and house batteries using a high amp relay. This was depicted in a recent issue of the Bus Conversion Magizine wereas the alternater with the engine running always charges the bus batteries and after the engine is started and aired up, a relay connects the house batteries to the same alternator. This senerio keeps the house and bus batteries separate while the engine is not running.

The purpose of a large battery banks is to provide reserve power in times of high current usage and to downsize the charging systems. Why put a lot of money into hugh power generation (generators, chargers) if its really only used for short periods. Let additional batteries provide that reserve power for those short periods.

Kenny 

[Zeroclearance]

Thanks guys for your latest replies.   I have a question with regards to the isolators.   If the alternator is charging the house batteries, what prevents the "bus" voltage to drop on it's battery bank.   ie driving at night with headlamps on. 

[Kenny]

An isolator or relay connects the house batteries to the alternator after the engine is running. The bus batteries are aways connected to the alternator thus always charging when the engine is running.

Kenny

[luvrbus]

Zero, his coach  had  Newmar Integrators on the battery banks not isolators to me they worked like a solenoid but were automatic or manual may be something else for you to consider. Isolators work like a check valve allowing current flow in one direction and integrators worked on the same principal but have a override      good luck

[Zeroclearance]

So per one of the recent Bus Conversion articles, a pressure switch could be put in place to trip the relay/isolator.   I'll Google the Newmar hardware>BTW, Thanks for looking at the Marathon.

[Kenny]

Zero
I'll look for the issue of the article and let you know. It was well written, listed many options and in the end provided a simple and effective solution.

Kenny