Wednesday, Nov 12, 2008 at 21:04
John,
I have a dual battery setup in my Jack, controlled by a Piranha DB150S Controller.
On top of this I also have a 75Ah Thumper and a 39 amp in-car charging unit.
The way it works is this:-
The DB150S prioritises the starting battery to receive whatever charge that is necessary from the alternator, then once it has reached a specific voltage, will swap over to allow anything connected to the auxiliary circuit to be charged.
This generally happens within a minute or so because the starting battery is in good condition and not normally subjected to much current draw.
Once the auxiliary circuit is connected through the controller, the auxiliary battery in the engine bay receives whatever charge that is required.
The In-car charging unit for the Thumper is also connected to the auxiliary battery, so charging current also flows through the circuit to the Thumper in the back and connected whilst travelling.
The fridge is connected to the auxiliary battery when travelling, then when setting up
camp, I remove the thumper and fridge and locate in the annex of the camper trailer. I also connect an 80 watt solar panel to the thumper to help maintain a charge for an indefinite period.
The auxiliary car battery is a backup should I need it, but that is unlikely.
In your situation, you don't need the dual battery controller, simply the in-car charging unit for at least the 75 Ah unit. This would be connected to your primary battery.
For the 120 Ah battery in the trailer, I would be inclined to have a separate circuit via an Anderson connector to and Arrid Twin Charge controller in the trailer and then to the trailer battery.
This setup will limit the need for heavy duty cable, but increase the voltage at the remote (trailer) end to enable correct charging of the trailer battery through the vehicle alternator.
The Arrid Twin Charge Controller setup is very common for correct charging of remote batteries by the vehicle alternator. It boosts the voltage level if necessary to remove voltage drop, the most common cause of inadequate voltage supply to a trailer battery.
Although the Arrid Twin Charge may also be possible of charging the Thumper in the back of your vehicle, I would prefer to have two separate circuits, one for each battery system.
I am sure you will receive expert advise from the guys at Home of 12 Volt.
Just be aware there are several ways of achieving a good result.
Bill
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