Yixiang diy 16ah battery jk bms setting troubles...

Had exactly this faff with my JK BMS last summer — the default cell overvoltage protection kicks in way too aggressively for LiFePO4 and you end up wondering why your Victron keeps throwing a strop at 95% charge.

Few things worth checking on the JK app:

• Cell overvoltage protection — set around 3.65V, recovery at 3.55V
• Balance start voltage — drop it to 3.40V so it's actually doing something useful during the bulk phase
• Charge overcurrent — depends on your cells but Yixiang 16Ah pouches aren't going to thank you for anything too aggressive

The sneaky one that caught me out was the "Cell count" setting — if it's even one cell off, the whole pack voltage calculation goes sideways and the BMS starts protecting against voltages that don't actually exist. Worth double-checking that first before diving into the finer settings.

Also, are you connecting via Bluetooth or the USB cable? The Bluetooth on my JK was showing slightly stale data and I spent an embarrassing amount of time chasing a ghost fault.

What's the actual symptom you're seeing — is it cutting out on charge, discharge, or just sitting there looking confused like the rest of us?

@BenJackson yeah the JK defaults are clearly written with NMC chemistry in mind — totally wrong territory for LiFePO4.

For a 16Ah pack I'd be setting:

• Cell OVP: 3.65V
• Cell OVP release: 3.60V
• Cell UVP: 2.90V (some go 3.00V to be safe)
• Balance start voltage: 3.40V

The bit that catches people out is the OVP release threshold — if it's too close to your OVP trigger, the BMS cycles in and out of protection constantly, which looks to your Victron like a comms fault rather than a voltage issue. Maddening to diagnose.

What's your charge voltage set to on the Victron side? If you're pushing 14.6V absorption into a 4S pack that's 3.65V per cell at the top — absolutely no headroom before OVP triggers.

@BenJackson @ForestBoater — spot on about the chemistry mismatch. For LiFePO4 I'd set cell OVP no higher than 3.65V with a recovery around 3.55V. The JK's default 4.2V trigger is NMC territory and will absolutely confuse a Victron MPPT that's already trying to do its own absorption logic — they end up arguing like two sat-navs giving contradictory instructions.

Worth checking your cell undervoltage whilst you're in there too — default is often set dangerously low for LiFePO4. I run mine at 2.8V trigger, 3.0V recovery on my 280Ah Yixiang cells (garden office build).

One gotcha: after changing JK parameters, do a full power cycle rather than just saving settings — I've seen values not properly commit otherwise. Caught me out twice before I twigged what was happening.

@TracyAllen is on the right track. I'd actually go slightly more conservative — 3.60V cell OVP for daily cycling, saves the top of your cells long-term. Recovery threshold around 3.55V so it doesn't chatter.

The other one that catches people out on JK firmware is the cell UVP — defaults are often set dangerously low. Bump that up to 2.90V minimum, 2.80V recovery.

Also check your balance start voltage — should be around 3.40V for LiFePO4, not the default which is usually set higher and means balancing barely triggers during a normal charge cycle.

Had all these same headaches setting up my Fogstar cells last year. Once you sort the chemistry-appropriate values it all plays nicely with Victron. Just take your time, change one parameter at a time and monitor it.

@Wez1961 @TracyAllen both making solid points — worth adding that the release voltage matters just as much as the trigger point. Had my shepherd's hut setup throwing fits until I realised the OVP release was set only 0.02V below trigger, so the BMS was chattering on and off like a nervous wreck. Bumped the hysteresis to around 0.1V (so trigger 3.60V, release 3.50V) and it settled right down. The JK app isn't always obvious about which field does what — the Chinese labelling in some firmware versions doesn't help. Worth cross-referencing with the JK BMS manual PDF floating around on the Fogstar Discord; someone's done a proper annotated LiFePO4 settings walkthrough that saved me a lot of head-scratching.