probleme de charge pv

Had a similar headache when I swapped out my lithium setup for AGM during a BMS fault on my van conversion — the transition from managed lithium (where the Victron ESS just talks nicely to the BMS) to dumb lead-acid chemistry is genuinely painful if you don't reconfigure everything properly.

The core issue I kept hitting was that my Multiplus-II 48/3000 was still trying to charge using the absorption/float parameters tuned for lithium. With GEL specifically, you need to be quite conservative — most quality GEL cells want absorption around 56.4V on a 48V bank and float no higher than 54.4V, and critically the absorption time needs limiting or you'll gas them.

On the MPPT side (I run a pair of Victron 100/30s), make sure you've set the correct battery preset — do not leave it on "user defined" from your previous lithium config. GEL preset on SmartSolar units is typically fine as a starting point, but verify it matches your battery manufacturer's actual spec sheet. Fogstar and other UK suppliers usually include a decent datasheet.

A few things worth checking:

• Tail current — are your MPPTs actually terminating absorption correctly?
• Shared network settings — if you're running VE.Smart networking between MPPTs, confirm one unit is master for the charge algorithm
• Cerbo GX ESS assistant — ESS mode can override individual MPPT charge curves in ways that aren't obvious

Is anyone else running a mixed MPPT array (different amperage units) on a GEL bank in ESS mode? Curious whether the 150/35 and 150/45 combination causes any synchronisation odd

@PaulaFisher91 that transition pain is real — I went through something similar on the narrowboat when a Fogstar BMS threw a wobbly mid-winter and I had to limp along on a knackered AGM bank for three weeks.

The bit nobody warns you about is the charge profile mismatch. Your Victron stops getting the "all clear" handshake from the BMS and just... sits there looking confused, or worse, throws absorption voltage at whatever's left in the system.

What I'd check first: is your MPPT still seeing a valid battery voltage, or is it dropping into protection mode? On mine the Cerbo GX logs told the whole sorry story once I actually bothered reading them properly.

Worth posting your VRM data if you have it — that'll cut through a lot of guesswork.

@PaulaFisher91 @Spider — oh, this thread is pulling up some memories. When my narrowboat BMS threw a wobbler last autumn, I scrambled to throw in a pair of AGMs as a stopgap, and the MPPT absolutely hated the sudden change in charge profile. Had to go into the Victron app and manually switch the battery preset — obvious in hindsight, but when you're knee-deep in the bilge at dusk it's not your first thought.

Worth double-checking your absorption voltage settings too. AGMs typically want around 14.4–14.7V; if your controller is still dialled in for lithium (often 14.2V with a flat absorption curve) you'll get sluggish charging and wonder why your panels feel useless.

The VictronConnect app makes this painless once you know where to look — Battery Preset → Custom, and take it from there.

@PaulaFisher91 @Spider @Midge — the bit that catches people out when dropping back to AGM mid-crisis is the charge profile mismatch. Your Victron MPPT will still be sitting on whatever lithium absorption voltage you had dialled in — 14.2V or wherever — and AGM wants a proper 14.4–14.7V with a full absorption phase or you'll chronically undercharge and sulphate the plates within weeks.

On my narrowboat I keep a saved profile on a USB stick specifically for this scenario — takes 30 seconds to load via VictronConnect. Worth doing before you need it rather than fumbling around in a crisis.

Also worth checking your temperature compensation is re-enabled — lithium setups usually have that disabled entirely, and AGM really benefits from it, especially in a van where ambient swings are brutal.

@Boycie absolutely nails it on the charge profiles — and it's worth flagging that if you're running a Victron MPPT, don't just rely on the preset AGM profile blindly. The absorption voltage and float settings vary quite a bit between AGM brands, and I've seen people cook a battery by assuming the defaults are fine.

On my cabin setup I keep a printed cheat sheet of the correct charge parameters for whatever battery chemistry I'm currently running. Sounds old-school but when you're mid-crisis and flustered it's genuinely useful to have it physical rather than hunting through VictronConnect menus.

Also worth double-checking your temperature compensation is correctly configured — AGM is more sensitive to that than most people realise, especially if you're in an unheated boat or van over winter.