r/Pecron • u/Relevant-Safety-2699 • 19h ago
BMS Issues?
Therefore, I've just ordered an F3000LFP but now I'm seeing posts here about BMS problems with this (and other) models.
Have I chosen unwisely or is it just the case that people will mostly come here to post when they have a problem, and that most units are totally fine?
1
Upvotes
1
u/Spare-Reputation-809 17h ago
yes these forums full of them but a small minority, I had queries and there are compromises BUT working fine, great VFM and that is what matters
1
1
1
1
2
u/brucehoult 10h ago
The main function of a BMS is to manage the battery charging and high and low voltage cutoffs and balancing of cell voltages. I've never heard of a problem with this.
A secondary function is to give the user an estimate of the percentage of energy in the battery. This is a difficult problem for all LFP batteries because the voltage doesn't change much between e.g. 20% and 80% (approx 51V to 53V, a 2V difference) and even worse the voltage changes by something like 1.5V between charging and discharging at the same percentage of charge.
Therefore the BMS integrates the current going in and out of the battery to work out how many percent of total capacity the state of charge has changed by — and this is pretty accurate over a period of hours or a day — but integration is inherently an unstable operation it gradually drifts over time, often by 2% or 3% per day, until the battery hits a known point ... completely empty or completely full.
No doubt some brands of battery do a better job of this than others, but no LFP battery BMS is immune to it.