Smart shunt display

Been meaning to post about this for a while after a similar schoolboy error with my shepherd's hut setup.

Fitted a Victron SmartShunt 500A last spring and spent about three days convinced it was faulty. State of charge was all over the place, kept reading wildly optimistic numbers even after hammering the 12V loads overnight. Couldn't figure it out.

Turns out I'd wired the negative from my Fogstar Drift 100Ah straight to the busbar, bypassing the shunt entirely. So the thing was essentially measuring fresh air. Moved everything so the only negative path back to the battery runs through the shunt, and suddenly it's reading like a proper instrument.

Classic mistake but I've seen it catch a few people out — especially when you're retrofitting a shunt into a system that already had a negative busbar kicking about. You end up with parallel paths and the shunt misses half your current draw.

Few questions for those who've been through similar:

• Do you bother with the VictronConnect app display on its own, or have you added a separate GX device like a Cerbo to get a proper screen on the wall?
• Anyone using a Raspberry Pi with Venus OS as a cheaper alternative for the cabin display side of things?
• How tight do you keep your tail current settings for a LiFePO4 bank? Factory default always feels a bit off to me.

Feels like the SmartShunt is brilliant once it's set up correctly, but the initial config has more gotchas than Victron would have you believe from the marketing fluff.

What are others running for display solutions?

@Robbo three days is actually impressive restraint — I spent a fortnight convinced my SmartShunt was lying before realising I'd set the charged voltage threshold wrong and it was never hitting 100% SOC to calibrate itself 🤦

Classic trap that one — the shunt's only as smart as the muppet who configured it via the app.

@Robbo the truncated posts aren't helping but I suspect I know where this is going — synchronisation issues after the shunt loses reference voltage, typically when the van's hook-up drops out overnight.

My static has a SmartShunt 500A paired with a Fogstar Drift 200Ah, and the displayed SOC was routinely 15-20% optimistic until I tightened up the charged voltage, tail current, and charged detection time parameters in the VictronConnect app. The defaults are frankly too generous for LiFePO4.

Worth double-checking:

• Charged voltage threshold (I run 13.8V for my setup)
• Tail current set to roughly 4% of capacity
• That the shunt is genuinely the only path back to the negative busbar

@DevonNomad a fortnight suggests possibly a wiring issue rather than calibration — any parasitic loads bypassing the shunt entirely?

@Robbo @DevonNomad — similar experience on my narrowboat install. The synchronisation trigger thresholds are the thing most people overlook. By default the SmartShunt considers the battery "full" and resets SOC to 100% based on:

• Charged voltage threshold
• Tail current (as % of capacity)
• Detection time

With LiFePO4 the tail current setting in particular needs adjusting from the lead-acid defaults — Victron's out-of-box figures are too conservative and the shunt never sees a legitimate sync point, so drift compounds over every cycle.

Worth connecting via VictronConnect and cross-referencing the Charged Voltage setting against your actual BMS absorption termination voltage. On my 280Ah Fogstar cells I dropped the tail current to 1% and tightened the detection time, which resolved what looked like catastrophic SOC drift but was simply the shunt never resetting cleanly.

@Robbo yeah the sync triggers are the key thing nobody reads in the manual properly (guilty myself)

Two things that sorted mine for the garden office:

• Charged voltage threshold — needs to match what your charger actually hits, not Victron's default. My Fogstar lithium charges to 56.8V so I had to set it there specifically
• Tail current — default 4% is often too high for LiFePO4, dropped mine to 1-2% and suddenly it was syncing properly at end of charge

Also worth checking your floor voltage setting. If the shunt thinks 0% is lower than your BMS cutoff you'll never see accurate readings at the bottom end either

The VictronConnect app makes tweaking all this dead easy once you know what you're looking for. Took me an embarrassing amount of time to find it though 🙄