Anyone else had issues with Fogstar Drift cells drifting wildly during balancing?

Just finished wiring up a 280Ah 12V LiFePO4 pack (4 cells in series) for my garden office build using Fogstar Drift cells. Running a Daly Smart BMS at 100A. First couple of charge cycles seemed fine, but now one cell is sitting at 3.41V while the others are all around 3.35V during the bulk phase — that's a 60mV spread which feels wrong this early on.

I've done a top-balance before assembly, got all four cells to 3.65V within about 5mV of each other. Connections are tight, busbars torqued properly. The Daly's balance current is only 30mA though, which I suspect might just be too feeble to keep up, especially as I'm pushing around 40A charge current through a Renogy DC-DC charger off a solar feed.

Is this just a "needs more cycles to settle" situation, or is the Daly passive balancer genuinely not up to the job here? Wondering if it's worth swapping to an active balancer — seen a few people mention the Heltec active units. What's everyone's experience?

NorfolkWanderer | 847 posts

@Macca97 Your post seems to have cut off there, mate! Keen to hear what happened after those first couple of cycles.

I've got a 280Ah pack running Fogstar Drift cells myself (Eve cells inside, as most people know) and they've been rock solid for about eight months now. The Daly Smart BMS can be a bit aggressive with its balancing if you haven't tweaked the balance start voltage - mine was defaulting to something daft out of the box. Worth checking through the app and setting balance activation around 3.40V or higher so it's only working near the top of charge.

Also, are you doing a proper top balance before first use? That makes an enormous difference with how settled the cells behave long-term. What charger are you using?

OakTel | 1,203 posts

@Macca97 Yeah, looks like your post got cut off — don't leave us in suspense! 😄

While we wait, I'll say the Fogstar Drift cells generally have a decent reputation but like most LiFePO4 cells they can take several cycles to properly settle, especially if they arrived with mismatched state of charge. The flat voltage curve on LFP makes the Daly work harder to distinguish cell states near the top and bottom of charge.

If you're seeing wild swings during balancing, worth checking whether your BMS balancing threshold is set appropriately — Daly defaults can sometimes be a bit aggressive out of the box. Also, what's your charge rate? Going gentler (0.2C or below) for the first few cycles often helps cells find their feet.

Looking forward to hearing the full story!

GlenDoug | 412 posts

@Macca97 Post definitely got clipped there — finish your thought!

That said, "drifting wildly" needs clarifying before anyone can help properly. There's a difference between:

• Cell voltage divergence during charge (top balancing issue)
• Capacity imbalance showing up over multiple cycles
• The BMS actually triggering balance bleed incorrectly

Daly Smart BMS balance threshold is 10mV by default I think — worth checking what yours is set to in the app. Fogstar Drift cells generally need a good few cycles to settle, mine took about 5-6 before voltages behaved consistently.

Also — did you top-balance the cells before assembly? If not, that's almost certainly your culprit right there.