Victron MPPT + DIY LFP 12v JKBMS configuration

Been running this exact combo on my narrowboat for about eighteen months now, so thought I'd chip in.

My setup is a 280Ah DIY LFP pack with a JK BMS wired up to a Victron SmartSolar 100/30. The key thing that took me a while to nail down was getting the charge profile right — LFP is unforgiving if you're sloppy with the absorption voltage.

I've got mine set at:

• Absorption: 14.2V
• Float: 13.5V
• Absorption time: 1 hour (fixed, not adaptive)

The JK BMS handles cell-level protection, but I still let the Victron do the heavy lifting on charge termination. What I don't do is rely on the BMS to disconnect as a normal part of the charge cycle — that's emergency-only territory in my book.

One thing worth mentioning for anyone on a boat or van — the VE.Direct cable running into VictronConnect is brilliant for keeping an eye on things remotely when you're away from the boat. Caught a dodgy connection on my positive busbar early because the yield figures looked off.

The bit I'm still fiddling with is whether to enable the tail current setting to end absorption early. Anyone here using that with JK BMS and found a sweet spot? I'm wondering if 2% of capacity is too aggressive for a 280Ah bank or whether I should push it closer to 4%.

Would love to hear how others have configured theirs, especially if you're running multiple panels in different orientations — that's my next headache.

@StormySocket nice one, keen to hear the rest of that sentence 😄 looks like your post got cut off mate!

Running a similar-ish setup in my shepherd's hut - Victron SmartSolar 75/15 with a Fogstar Drift 100Ah. One thing I'd add for anyone lurking: get the absorption and float voltages dialled in properly for LFP - Victron defaults are set for AGM/GEL out the box and will stress your cells if you don't change them.

Typical LFP targets:

• Absorption: 14.2V
• Float: 13.5V
• Absorption time: minimal (5-10 mins)

The JK BMS will protect you when things go sideways, but better to not rely on it constantly. Let the MPPT do the heavy lifting correctly first.

Great thread, interested to see where both @StormySocket and @George1975 were going with their posts before they got cut off! Forum gremlins clearly having a field day today 😄

I'll add what I can in the meantime. With this combo the thing that caught me out initially was getting the charge absorption voltage right for LFP. Victron defaults aren't really optimised for lithium out of the box, so worth setting absorption to around 14.2V and float at 13.5V rather than leaving it at lead-acid defaults.

Also make sure your JK BMS high voltage disconnect is set slightly above your Victron charge ceiling so the BMS is genuinely a last resort rather than cycling constantly. Lots of folk get this backwards and wonder why their BMS keeps tripping.

Happy to share my exact settings if that's useful once the full posts come through!

Looks like half this thread has gone missing 😄

While we wait for @StormySocket and @George1975 to reappear — I'm looking at a very similar setup for my motorhome build and have a specific question about the JKBMS to Victron communication side of things.

Is anyone using the BMS's RS485/UART port to feed data into a Cerbo GX, or are you all just relying on the BMS to handle cell-level protection independently while the Victron works off its own absorption/float settings?

Reason I ask — I've seen conflicting advice about whether it's worth bothering with proper BMS-to-Victron comms on a 12v leisure setup, or whether just setting conservative charge parameters on the SmartSolar is sufficient protection in practice.

While @Squib waits — the Victron/JK combo is solid but there are a few non-obvious configuration points worth covering properly.

On the SmartSolar side, disable the built-in BMS assistant if you're relying on the JK for cell-level protection — they can conflict. Set absorption to 3.45V/cell (so 13.8V for 4S) and float at 13.5V. Some people push absorption higher but on a narrowboat you're cycling daily, so longevity beats capacity.

For the JK specifically:

• Set overvoltage protection at 3.65V/cell
• Balance trigger around 3.40V
• Enable "charge current limit" via the BMS output rather than relying purely on the Victron current limiting

The DVCC feature in VictronConnect is worth enabling if you've got a GX device in the loop — lets the BMS talk directly to the MPPT.

What's your cell brand, @StormySocket? EVE or CATL changes the voltage curve recommendations slightly.