Dual battery: one pattern for all three rigs
The 4Runner's dual-battery setup works well; the plan is to repeat it in the F100 and the Chevy, with the same parts where possible and the same monitoring everywhere.
The pattern
- Starter battery stays as it is: the engine always starts.
- House battery (the fridge, audio, radios, the vehicle box) charged from the alternator through a DC-DC charger, not a plain isolator: it charges the house battery's chemistry properly (lithium included), and keeps the starter battery from being dragged down.
- Solar into the house battery through its own charger, where there's a roof for it.
- A battery monitor (shunt) on the house battery; starter battery voltage measured too.
- Fusing at each battery, and a main disconnect for the house side.
To match the 4Runner exactly: its chemistry, DC-DC charger or isolator, monitor and fusing go here once noted. (To fill in.)
Monitoring (misra, per vehicle)
Facts: starter voltage, house voltage, current and state of charge, the DC-DC charger's state, solar input, engine running (RPM or ignition). Things to cross-check:
- the charger says it's charging but house current says otherwise
- the engine is running but the starter battery isn't rising (alternator, belt, wiring)
- state of charge from the shunt disagrees with resting voltage (a drifting shunt, an ageing battery)
- the house battery drains with everything off (a parasitic load)
Per vehicle
| Starter side | House side | Notes | |
|---|---|---|---|
| 4Runner | 12 V, modern alternator | (as built: to note) | the reference |
| 1974 F100 | 12 V, negative ground | restore the second battery where the old aux sat; DC-DC from the alternator | a straightforward copy |
| 1949 Chevy | 6 V generator, untouched | isolated 12 V house system charged by solar and shore power (decided) | see below |
The Chevy is the odd one out. Common DC-DC chargers expect a 12 V input, so they can't charge from a 6 V generator. Decided: an isolated 12 V house system kept up by solar and shore power, with no electrical connection to the car's 6 V side (the ignition switches it through a relay coil). The car stays original.