FJ Cruiser dual battery in action
On 8 January , 2018 by PaulWhen I decided to install the dual battery system I heard a lot of conflicting stories about using a voltage sensitive relay or a dc-dc charger. The apparent issue is that with a smart alternator, the battery may not charge.
What I installed was a Redarc SBI12 voltage sensitive relay with manual over-ride. I also installed a Matson Bluetooth voltmeter to see what the system is doing.
The auxiliary battery drives a number of circuits including a fridge circuit. When the voltage sensitive relay isolates the start battery, the Metson monitors the auxiliary only.
The results can be seen in the graph below:
It starts at midnight with the fridge cycling (it was super hot outside and I had my Engel set to super cold). Then at 10am we start driving with lots of stops until we settle for the day around 6pm. On this day I connected the fridge to mains power at around 10pm.
The voltage drops when the isolator is on to around 12.3V . In the morning, the start battery is fine and then both charge between 13.4V and 13.7V whilst driving.
In summary, the SBI12 redarc VSR works well even with the FJ Cruisers modern smart alternator.
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