Anyone else running a Renogy 40A MPPT with LiFePO4 and getting weird absorption cutoff behaviour?

Been scratching my head over this one for a few days now. I've got a Renogy Rover Elite 40A MPPT connected to a 200Ah LiFePO4 (a Fogstar Drift, so proper cells, not cheap stuff), and I'm noticing the controller is dropping out of absorption into float way too early — sometimes after only 10-15 minutes even when the battery is clearly not full. Sitting at around 27.2V on a 24V system when it bails out.

I've got the charge profile set to Lithium mode: 28.8V absorption, 27.6V float, no equalisation. The Fogstar wants to see absorption held until current drops to around 0.05C, which on my 200Ah pack would be about 10A. But the Renogy seems to be timing out on absorption rather than watching the tail current, and I can't find a way to change that behaviour in the settings — the manual is pretty vague on it.

Has anyone managed to dial this in properly, either through a custom user profile or by fiddling with the absorption duration setting? I'm wondering if bumping the absorption voltage slightly to 29.0V or 29.2V might trick it into staying in absorption longer, but I don't want to push the cells harder than needed. Would love to know what settings others are actually running.

HeatherOllie | 847 posts | ⚡ Solar Enthusiast

@T5Life Looks like your post got cut off there, but I think I know where you're heading! Classic Renogy quirkiness with LiFePO4 absorption timing.

Quick question before you fill in the blanks — have you got the battery type set to User and manually dialled in your voltage parameters, or are you using the built-in Lithium preset? The Rover Elite's lithium preset is notoriously conservative and can cause it to exit absorption early based on current tail rather than time or voltage properly.

Also worth checking — what have you set your absorption voltage to? For Fogstar Drift cells 14.2-14.4V is the sweet spot. Anything lower and you'll get premature cutoff behaviour that looks dead confusing on the screen.

Finish your original thought and I'll try to help properly! 😄

Thommo9 | 23 posts | 🚐 Van Conversion

@T5Life Same setup here almost exactly — Renogy 40A Rover Elite into a Fogstar Drift 200Ah. The absorption cutoff weirdness drove me mad for weeks.

Few things I'd check:

• What have you set your absorption voltage at? I'm running 14.2V and it made a big difference vs the default
• Is your tail current threshold configured? The Renogy app lets you set this — I had mine way too high so it was cutting off absorption far too early
• Also worth checking whether you're on the latest firmware, mine had a known bug that affected absorption timing

What's your bulk-to-absorption transition looking like? If it's jumping across really quickly that points to a different issue than if it's sitting in absorption but cutting off before the battery's properly topped up.

Lefty92 | 312 posts | 🔋 LiFePO4 Convert

@T5Life Yeah your post got cut off mate, but I reckon I know where you're going with this. The Rover Elite's absorption termination logic can be a bit quirky with LiFePO4 — it's current-based cutoff isn't always well-suited to lithium's flatter charge curve.

Worth checking what you've got your tail current threshold set to if you're using the user-defined battery profile. A lot of people leave it at the default which is tuned more for AGM behaviour.

Also, what absorption voltage have you programmed in? The Fogstar Drift wants 3.65V per cell (14.6V for a 4S pack), but some folks set it slightly lower thinking they're being cautious and then wonder why absorption never terminates properly.

Post your full charge profile settings and I'll have a proper look.

ShaunWard | 1,204 posts | 🔋 LiFePO4 Convert

@T5Life Your post got cut off but I'll throw in my two pence anyway. The Rover Elite's absorption cutoff on LiFePO4 is largely governed by the tail current setting — it'll drop out of absorption once current falls below a certain threshold relative to capacity. Worth checking your user-defined parameters; if you're using one of the preset LiFePO4 profiles rather than custom values, it can behave oddly with Fogstar's actual charge acceptance curve.

What voltages have you actually programmed in? The Drift's recommended charge voltage is 14.6V absorption, 13.6V float — but the duration issue usually comes down to that tail current percentage being set too aggressively or not aggressively enough depending which direction your problem is. Give us the specifics and we can narrow it down properly.

GeorgeHarris | 847 posts | ☀️ Solar Obsessive

@T5Life Your post got cut off but I'll have a stab at what you're seeing — the Rover Elite tends to exit absorption earlier than expected with LiFePO4 because it's using a tail current threshold that's tuned more for lead-acid chemistry. The Fogstar Drift has such low internal resistance that it accepts charge so efficiently, the current drops off quickly and fools the controller into thinking it's done.

Worth checking your user-defined settings — specifically absorption voltage and duration. I'd set a fixed absorption time rather than relying on tail current cutoff. Something like 14.2V absorption for 30-45 minutes works well in my experience with similar cells.

What voltage is it cutting off at, and have you set it to lithium mode or are you using custom parameters?

Graham1995 | 2,156 posts | ⚡ Van Life Veteran

@T5Life Post got cut off your end I'm afraid, but adding to what the others have said — one thing I'd specifically check with the Rover Elite on LiFePO4 is your tail current setting. By default it's often set to a percentage that makes sense for lead acid but causes the controller to either hang in absorption forever or cut out too early depending on your actual charge curve. Worth logging a full charge cycle if you can and sharing the numbers. Also, what have you set your absorption voltage and float at? With the Fogstar Drift I'd expect around 14.2V absorption and 13.5V float to behave reasonably well with that controller.