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In this design example, a Sterling DC to DC converter is used to charge a lithium house bank with the Start battery as the "Source". So for example, if we are charging the Lithium Bank at 60Amps over 3hrs, how is this justified when a Start battery is not designed to provide high current over a long period of time?
Read the Sterling B2B instructions, it only starts charging when the voltage of the start battery / alternator is above 13.2V so it will be still charge the domestic battery when the engine battery is on float and once the alternator shuts down it will stop charging to avoid discharging the engine battery. All info is easily found.
Generally the idea is to only charge the House bank when the vehicle is running and therefore the charge current is sourced from the alternator rather than the Start battery. The DC/DC converter either automatically senses the alternator output or has a separate signal fed from the ignition of the vehicle. This becomes a bit more tricky with modern vehicles with 'smart' alternators where the alternator is disconnected at times or used for regenerative braking.
So if the Alternator has external regulation, and that is connected to the start battery, how is high amperage current obtained from the Alternator if the start battery is fully charged, and the external regulator has gone into float mode? Are we missing something here? How is this compensated so even with a full start battery, the Alternator can still provide high output current into the DC/DC converter?
I'm fairly sure the voltage drop when the DC-DC charger turns on will trigger the alternator to output if the starter battery is full.
You obviously need to make sure your alternator isn't going to get overloaded. Mine's 150A on the campervan and I have a Orion Tr Smart charger that's only gonna pull 30A.
Edit: See here for the Engine On Detection https://www.victronenergy.com/upload/documents/Engine-on-detection-set-up-Orion-Tr-Smart-DC-DC-Charger-EN.pdf
