Battery wiring (1 Viewer)

[Betteron2wheels]

I have a question for the electrically-smart folks. My 450 has a dual battery system with an ACR between. I'm going to run power to the back and need to decide on wire size. I was going to go with 4g, but since I'm living in it part time I am using an optima to supplement my in-hood deep cycle to power a fridge, I would like to tie the optima into the house battery. I'll have a high amp switch between the two and a 50-60A fuse coming off the battery. If I close the circuit with one of the batteries at full charge and the other at low charge, how much demand will the low one make for amperage? If I connect the two with high differential in charge will the low battery pull enough amps to overload the wire/fuse?

Thanks!

 

[Jakes40]

calling Mr. Edd

@emorth

 

[Stumpalama]

Ed just drew up a diagram for me for something similar.

 

[emorth]

Good project. I'll put together a schematic for you. Most likely tomorrow.

 

[emorth]

If I close the circuit with one of the batteries at full charge and the other at low charge, how much demand will the low one make for amperage? If I connect the two with high differential in charge will the low battery pull enough amps to overload the wire/fuse?

The batteries should not be discharged below 10.5 volts. Below that damage starts to occur and the batts will start to lose capacity. I don't think the fridge will work below 11V ??? So, if one batt is discharged to 10.5 and the other is charged and at 12.5 the difference is 2V. Not at lot of current is going to flow. A 100A alternator feeding a batt at 10.5 will flow a lot more current.

First cut at a schematic.
Rule #1: The fuses are to protect the wire, not the device at the end. The 4 gauge wire needs a fuse at both ends since it can be powered by the party batt and the fridge batt with the switch closed.
Option #1: Diode, no switch. The diode "D" is a "check valve" that lets current flow in one direction. With the diode in the circuit, current will only flow in to the fridge batt and fridge when the engine is running. The fridge is the only load on the fridge batt.
Option #2: Switch, no diode. With the switch "SW" open the fridge batt and fridge are isolated. With the switch closed, the fridge batt is connected to the party batt and the party fuse panel. Fridge batt and party batt are now supplying current to party fuse panel. Switch will need to be closed when engine is running to charge fridge batt and open when engine is off to prevent the fridge batt from "back feeding" into the party fuse panel and discharging the fridge batt. If the party battery discharges, the switch can be closed to provide current to the party fuse panel but the party battery will also put a load on the fridge batt.
Option #3: Both diode and switch. With switch open, option #1 works. Fridge batt is charged via diode. With switch closed, Option #2 works. Fidge batt is connected to party fuse panel and party batt.

What are the Ah (Amp hours) of the party and fridge batteries?