Originally Posted by talk2cfs
I have a 3000w/6000w inverter and am ready to put my system together, but could use some help. I'm adding another large bus battery just for the inverter and would like to use a breaker box, shore cable in addition to a charger to keep that battery charged while running. Does anyone have a simple diagram of how I should hook this all up and in what order? Thinking I might need a switch to go from shore to camp mode. Thanks
There is no easy answer; there are too many variables based on the inverter and the other components in the system. I can give you some general ideas though and you can go from there.
Do you realize what size DC wire you'll need for that inverter at 3000 watts!?! You're pulling 250-amps out of your battery at full continuous load (at 3000 watts, not the 6000 watt surge). The smallest wire you should consider is 4/0 and that's if the distance from the battery to the inverter is in the 3 to 4 foot range (6 to 8 foot round trip). The voltage drop on the DC side escalates quickly so if you go longer distances you'll be looking at some very large and very expensive wire). It also means you'll take something like an 8D battery (about 245 amp-hours) to it's 50% level in about 10 minutes if you're at 3000 watts and dead in about 20 minutes. You probably don't intend to use 3,000 watts but you must size the wiring for the maximum that the main panel will allow you to draw (a 30-amp main breaker will allow up to 3300 watts or so) or the max the inverter will allow. So if you have a 50-amp main breaker (and the inverter feeds it) you need to size the wire for 5500 watts since the inverter will allow up to 6000 watts on a surge.
In general you want a battery system (in amp-hours) that's equivalent to 20% of the inverter's rating (in watts). So a 3,000 watt inverter should be supported by 600 amp-hours of battery capacity (about 6 Group 31 batteries or 3 4Ds). Then you want your charging source to be no smaller than about one fourth (in amps) of the capacity of the battery system (in amp-hours). So, a 600 amp-hour system should have a 150-amp charging source at the minimum.
Another thing you must consider for the safety of all concerned is the system ground. Code requires that the AC system be grounded to the chassis of the vehicle when NOT on shorepower and DISCONNECTED from the chassis ground when on shorepower. That is, there can be only ONE point of ground at any one time and it has to follow the source of power. If you don't have an automatically switching inverter then you're probably best served by using a transfer switch designed for the purpose. The automatic ones are nice since when you connect and disconnect from shorepower they automatically switch the source and the ground.
I've run out of time but this should get you started. Take a look at some of the solar and boat web sites dedicated to battery systems and you'll start to get a good feel for how it's typically done.
I can answer more questions later if you have some.