Equilibrage des cellules

Been mulling something over and curious whether others have run into this.

I've got a 48V bank on my narrowboat — four 12.8V LiFePO4 cells in series (Fogstar Drift 100Ah units). Running a Victron Multiplus 48/3000 alongside a SmartSolar MPPT 150/35 and a Cerbo GX pulling it all together.

Lately I've been getting low voltage alarms on one cell during discharge, even though the overall bank voltage looks reasonable. Classic sign of cell imbalance as far as I can tell.

A few questions I'm trying to work through methodically:

• Is this a BMS issue or a genuine capacity mismatch between cells? One cell could simply be degrading faster than the others.
• Does the SmartSolar absorption phase give enough headroom for passive balancing to do its job? I'm wondering if my absorption time is set too short.
• Has anyone used active balancers alongside a standard BMS on a series bank like this? Seen some cheap units on Amazon but not sure whether they're worth the hassle or a fire risk.

Worth noting — the bank is about 18 months old and lives in a fairly damp bilge environment, so I can't rule out a dodgy connection introducing resistance on that one cell's terminals. That's my next physical check.

Has anyone diagnosed something similar? Particularly interested if you're running Victron kit and whether tweaking the VE.Configure charge profile made any difference.

@ExFirefighter classic series-string balancing headache. A few things worth checking:

1. Passive vs active balancing — Fogstar Drift BMS does passive balancing, which is slow and only kicks in near top of charge. If your cells are drifting mid-SOC, that's a red flag for a weak cell rather than a balancing issue.

2. Let it top balance — run a slow absorption charge (57.6V, low current) and leave it sitting there for a good few hours. Passive balancers need time.

3. Check individual cell voltages with a multimeter during charge. One cell racing ahead = replace it, not balance it.

Had similar on my own LiFePO4 bank last winter — turned out one cell was just tired. No amount of balancing fixed it properly.

What's your Victron absorption setpoint set to currently?

@ExFirefighter with four Fogstars in series I'd absolutely chuck a Victron Battery Balancer across the mid-point — it's basically the cheapest peace of mind you'll ever buy for a 48V LiFePO4 string, and mine's kept my shepherd's hut bank drama-free for two winters now.

@ExFirefighter one thing nobody's mentioned yet — make sure your charge parameters are actually set correctly for LiFePO4 on the Victron side. Had mine drifting badly on the van and it turned out the absorption voltage was slightly too low, so one cell never hit full SoC and lagged behind permanently.

Check your DVCC settings too if you're running a Cerbo or similar. Wrong cell count configured there caused me a right headache for weeks before I spotted it.

Also worth logging a few charge cycles with VictronConnect before throwing hardware at it — you might find it's a settings fix rather than a balancer job.

@ExFirefighter worth checking whether your Multiplus charge profile is actually reaching a true absorption voltage long enough for the cells to balance internally. On my van setup I found the Victron default absorption time was too short — the BMS was cutting out before cells had time to equalise.

Also consider this: if one Fogstar Drift unit is consistently the outlier (always high or always low), that cell may simply have lower capacity than the others due to manufacturing tolerance. Worth doing a manual top-balance — fully charge each unit individually to 3.65V before reconnecting in series. Tedious but it properly resets the baseline and often resolves persistent drift without needing additional hardware.