Anyone else finding their B2B charger struggles to keep up when the alternator's under load?

Been running a Victron Orion-Tr Smart 12/12-30A in my Transit for about eight months now, feeding a 200Ah lithium leisure battery. Generally it's been brilliant, but I've noticed on longer motorway runs where I've got the air con blasting and maybe towing a small trailer, the Orion seems to throttle back quite a bit — sometimes dropping to around 15-18A output rather than the full 30A. Temps under the bonnet are reasonable, nothing mad, so I don't think it's purely thermal throttling.

My suspicion is that the alternator voltage is sagging enough under combined load that the Orion's input is hovering right at the edge of its threshold. The van's a 2019 Transit with the 2.0 EcoBlue and the standard 180A alternator — which sounds plenty on paper, but clearly isn't with everything pulling at once. I've got 6mm² cable running about 1.2 metres from the starter battery terminals, so I don't think cable resistance is the culprit, though I'm happy to be corrected.

Has anyone dealt with this and found a practical fix? I'm wondering whether bumping up to the 18A input threshold version makes any sense, or whether the answer is just a bigger alternator. Also curious if anyone's successfully run two Orions in parallel to get more charge current without pushing the single unit so hard.

Hey @Shaun1970, interesting one this. Worth checking whether your alternator is actually being properly protected - some of the newer Transits have a smart alternator that the Orion handles fine in isolation, but once you're running climate control, headlights, and other ancillaries simultaneously, the alternator's output voltage can dip enough that the Orion throttles back or temporarily disconnects to protect itself.

Have you looked at the Victron Connect app history to see if it's logging any input undervoltage events during those motorway runs? That'd confirm whether it's a supply issue rather than the charger itself struggling.

Also worth double-checking your cable sizing on the input side - voltage drop under sustained 30A draw can be sneaky even with what looks like adequate cable.

Same issue cropped up on my van build. Turned out my alternator was thermally throttling before the Orion even got chance to pull full amps — worth sticking a clamp meter on the alternator output on a hot day vs cold start, the difference can be surprising.

Also check your Victron Connect app for the input voltage threshold — if it's set too high it'll back off earlier than needed. I dropped mine slightly and gained a few amps sustained.

One thing @DailyProject is probably hinting at — smart alternators on newer Transits are a whole other headache. If yours has variable voltage charging, the Orion might be seeing weird input and getting confused. What year's your Transit?

@Shaun1970 the Orion-Tr Smart has input current limiting in the app settings — if you haven't dialled that down from the default, you're essentially asking your alternator to sprint a marathon whilst towing a caravan uphill.

Also worth logging the actual input voltage with VictronConnect during a run — if it's sagging below 13V the Orion will throttle itself anyway, which might explain the inconsistency you're seeing rather than anything catastrophic. My Transit setup did exactly this until I realised the factory alternator wiring to the leisure circuit was 6mm² doing the job of 10mm².

@BatteryAlan beat me to the input limiting thing but also worth knowing your Transit alternator is probably already crying into its bearings before the Orion even enters the chat — mine gave up the ghost at 60k miles and I'm pretty sure my Fogstar 200Ah was part of the murder weapon 🔪

@Shaun1970 One thing nobody's mentioned yet — have you checked your cable sizing on the input side? I had a similar situation with my Orion-Tr 30A and found voltage drop across undersized cable was causing the unit to pull harder than needed, which compounded the alternator stress. Victron recommend keeping input voltage drop to an absolute minimum. Worth sticking a multimeter on both ends of your input cable under load and seeing what you've actually got. Even a small drop can make a noticeable difference to efficiency and output. Also, if your Transit is the newer 2.0 EcoBlue, those engines run the alternator pretty hard anyway with all the stop-start and regen systems — the alternator isn't really designed with leisure charging in mind from the factory.

Interesting thread — I've got the same unit in my motorhome and had a similar head-scratch moment. One thing worth adding: have you checked what the Orion is actually seeing on the input voltage during those runs? If the alternator is struggling, the input voltage may be drooping enough that the Orion is throttling back automatically as a protective measure rather than anything being misconfigured.

You can watch it live in the VictronConnect app — hook up via Bluetooth while someone else drives and keep an eye on the input voltage graph. Mine was dropping to around 13.1V on a hot day with the aircon hammering, and output dropped noticeably. Sorted it partly by running the B2B only once the engine was properly warm and the alternator had settled.

@Shaun1970 Worth checking the alternator voltage under load with a multimeter at the B2B input terminals — not at the battery, at the unit itself. I was seeing a 0.8V drop across a poorly crimped connector on mine, which caused the Orion to throttle back significantly. The Victron app shows input voltage in real time so you can log it whilst driving. If it's dipping below 13V consistently you're fighting a losing battle regardless of cable sizing or input current limits. Sorted mine with decent Anderson connectors and proper heat-shrink crimps rather than the bullet connectors the previous owner had bodged in.

@DucatoProject good shout on measuring at the terminals rather than the battery — makes a real difference where you probe.

One thing I'd add: engine temp plays into this too. My Transit alternator voltage drops noticeably in slow traffic when everything's cooking. The Orion just backs off. Nothing wrong with the unit, it's doing its job.

If you've got the Victron app connected, check the input voltage log over a run — you'll see exactly when it's throttling and why. Saved me a lot of head-scratching on my setup.

@Shaun1970 One thing I haven't seen mentioned yet — have you checked your input voltage threshold settings in the Victron Connect app? The Orion-Tr Smart defaults to a fairly conservative start voltage, and if your alternator's struggling under load (air con, headlights, the lot), it might be repeatedly dropping out and restarting rather than charging continuously. Worth logging a longer journey via the app to see if you're getting those interruptions. Bumping the start voltage down slightly and the shutdown threshold too can make a noticeable difference to overall charge consistency on motorway runs.