Victron MPPT + DIY LFP 12v JKBMS configuration

Been running almost exactly this setup in my motorhome for about 18 months now — Victron SmartSolar 100/30 paired with a 200Ah DIY LFP pack managed by a JK BMS, so hopefully this is useful.

The key thing that tripped me up initially was the charge profile. Victron's default lithium preset is fine but not ideal for DIY cells. I ended up setting:

• Absorption voltage: 14.2V
• Float: 13.5V
• Absorption time: 20 minutes (fixed, not adaptive)

The JK BMS handles the real protection layer, so I don't need the MPPT pushing hard at top-of-charge for ages. Keeps the cells happier long-term.

One gotcha worth mentioning — if you're using the BMS load disconnect to cut the Victron's battery connection under fault conditions, make sure your MPPT is configured to handle that gracefully. Mine threw a fault the first time the BMS tripped and I hadn't set the battery safe mode correctly in VictronConnect.

Also, tail current on the MPPT. Set it to around 2-4% of your battery capacity in amps. Stops it sitting in absorption forever on a partially cloudy day.

Has anyone else connected their JK BMS to the Victron via the RS485 adaptor for proper DVCC communication? I've been tempted but not sure it's worth the faff for a 12V system. Curious what others have found.

Really useful thread @DorsetDweller, thanks for starting it. One thing worth mentioning that catches people out — make sure your Victron is set to the Lithium preset rather than leaving it on a lead-acid profile. Sounds obvious but I've seen it missed more times than I'd like to admit! 😄

Also, with the JK BMS, I'd strongly recommend enabling the cell voltage balancing display in the JK app and just keeping an eye on drift across your cells, especially in the first few months. My own pack showed one cell lagging slightly during early cycles that I'd have completely missed otherwise.

Are you using the Victron VE.Direct cable to log your data? Makes spotting any charging irregularities so much easier over time.

Good points being raised here. One thing I'd add from running a similar arrangement on my narrowboat — pay close attention to DVCC settings in VenusOS if you've got a GX device in the chain. Getting the JK BMS to communicate charge current limits properly via the Victron ecosystem took me longer than I'd like to admit.

Specifically, watch the SVS (Shared Voltage Sense) and SCS (Shared Current Sense) toggles. Enabling both when your BMS is already reporting via CANbus can cause the MPPT to get contradictory instructions and behave erratically — absorption times going haywire, that sort of thing.

Also worth checking your JK firmware version. Anything below around 10.x had some known quirks with the Victron protocol implementation. @DorsetDweller — what firmware are you running on your JK? Might be relevant if others are seeing odd charge curve behaviour.

Running this exact combo in my shepherd's hut — Victron SmartSolar 75/15 with a 100Ah Fogstar DIY LFP pack and JK BMS.

One thing nobody's mentioned yet: absorption time. The Victron default absorption duration is way too long for LFP. I've mine set to around 20 minutes max. Leaving it at the default means you're sitting at 14.2v for ages doing essentially nothing useful, and some BMS units will start getting twitchy.

Also worth checking whether your JK BMS has the balance-on-charge-only setting enabled. Mine was balancing at rest which was causing minor confusion with the Victron's tail current detection.

@DorsetDweller — did you end up using the VE.Direct cable to monitor from the app? Curious whether you're seeing accurate SOC or whether you're still relying on the BMS figures for that.

Really helpful thread — I'm planning something similar for a garden office setup and potentially some light EV charging capability down the line.

Quick question for @DorsetDweller or @ValleyTony: when you programmed the Victron absorption and float voltages for LFP, did you go with the commonly cited 14.2V / 13.5V, or did you tweak those based on what the JK BMS was reporting?

Also wondering whether the JK BMS UART connection to the Victron via a Raspberry Pi (using Venus OS) is worth the effort for monitoring, or if just relying on the Victron app is sufficient for a simpler static install like a garden office rather than a mobile setup?

My loads will be fairly predictable — office equipment during the day — so I'm not sure if the added complexity of full integration is justified.