Had a bit of a frustrating weekend with my setup and wondered if others have hit the same wall. I've got a Victron Orion-Tr Smart 12/12-30A isolated running off a 2019 Ford Transit's alternator, feeding a 200Ah lithium (Battle Born) in the back. On a cold start it pulls beautifully — seeing 28-29A no problem. But after an hour or so of motorway driving, especially on a warm day, the output seems to creep down to around 18-20A. The Orion itself isn't throwing any thermal warnings in the app, so I don't think it's the B2B overheating.
My suspicion is the alternator itself is voltage-dropping under sustained load once it's warm, which then confuses the Orion's input threshold settings. I've got the input lockout set to 13.0V, and I wonder if the alternator is just barely staying above that on a hot run. The cable run from the starter battery to the Orion is about 1.8 metres of 10mm² so I don't think voltage drop there is the culprit, but I'm not ruling it out.
Has anyone actually measured alternator output voltage at the terminal when warm versus cold? I haven't got a clamp meter with me on the road so I've been relying on what the Victron app reports at the Orion's input, which might not be the full picture. Wondering whether fitting a dedicated alternator sense wire would make any difference, or if this is just a known limitation of Transit alternators under load.