Charging Start Battery via Solar

Q&A and troubleshooting
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1

Got a slightly complicated electrickery ⚡️ question… Motorhome with solar on roof to 2 LiPo house batteries parallel at 12V via Victron MTTP 100/20 48V → Orion Smart 24/12 20A Isolated DC-DC step down charger which also takes in 24V alternator power when the engine is on. 500A/50mV shunt to show battery flow and health. Very nice system.

In case of getting stuck somewhere with flat start batteries (e.g. left lights on) I would like to add a charger from solar to the start batteries without creating a loop (solar → start batteries → house batteries → start batteries → house batteries ad infinitum). I am thinking of a Victron 12/24V DC-DC charger but is there is there anything that would stop the loop short of a manual dual pole switch?

2

That should work using an Orion TR 2/24-15 (360 W) and by programming the charge voltage for that one to 26V, battery protect cutoff on the 12V side at 13V and the existing Orion to start charging the house battery only once the starter battery is above 27V. Thus, the required source voltage for either Orion is higher than the charge voltage of it’s opponent and the loop can’t happen.

3

Thank you for that - a nice solution. I am new to Victron so the learning curve is a little steep :grinning_face: