Noob with MP2GX that won't turn on the inverter

Seen this exact flavour of pain with my garden office build — brand new MP2GX, fresh Pytes battery, and the inverter just sits there like a sulking teenager refusing to get out of bed.

Nine times out of ten it's one of these culprits:

• BMS comms not established — if the MP2GX hasn't shaken hands with the battery over VE.Can or the relevant interface, it'll lockout the inverter as a safety measure. Check your DVCC settings in VictronConnect and make sure the correct battery monitor is selected.
• Low SoC lockout on first boot — Pytes units sometimes report a daft state of charge on initial power-up before the BMS has calibrated. The MP2 sees 0% and panics.
• VRM showing the unit but ESS assistant not loaded — classic trap this one. VRM presence doesn't mean the assistants are configured. You need VEConfigure to actually load the ESS assistant onto the device, full stop.

On firmware v3.79 specifically, I'd also double-check the inverter "switch" setting in VictronConnect — there's been a known quirk where it defaults to Charger Only mode after a firmware flash and nobody notices because the unit looks like it's doing something.

Anyone else had the Pytes V16 take an age to settle on first boot? Mine took a good 20 minutes before the MP2 would even acknowledge it properly. Nearly convinced myself I'd bought a very expensive paperweight for the cabin.

What does your system log in VRM show — any alarms or just radio silence?

@DuctTapeDave the sulking teenager analogy is spot on 😄

Nine times out of ten with a fresh MP2GX + Pytes combo it's the DVCC settings not being configured correctly in VenusOS. The Pytes uses CANbus communication, so if DVCC isn't enabled and set to let the battery manage charge/discharge limits, the MP2 just... sits there confused.

In VenusOS go to Settings → DVCC and confirm:

• DVCC enabled ✅
• SVS (Shared Voltage Sense) enabled ✅
• SCS disabled (let the Pytes handle it)

Also double-check your BMS Assistant is loaded in the MP2 via VE.Configure — without it the unit won't respect the CANbus signals properly.

Had almost identical on my boat build last spring before I spotted the BMS Assistant was missing. Twenty minutes of head-scratching sorted by one checkbox.

@DuctTapeDave @LakelandNomad — worth checking whether the inverter is actually disabled in VictronConnect rather than a battery comms issue. Fresh out of the box, the MP2GX sometimes ships with the inverter switch set to off in the device settings. Sounds stupidly obvious but I've seen it catch people out twice on this forum alone.

Also — if you're on a narrowboat or anywhere with a long cable run, double-check your DC cable sizing. The MP2GX is surprisingly sensitive to voltage drop on startup; if the battery voltage at the unit dips below the low-voltage cutoff during inverter inrush, it'll just refuse to start and give you nothing useful on the display.

What does VRM or VictronConnect actually show as the inverter state?

@DuctTapeDave @PennineNomad makes a good point about VictronConnect — but also double-check your BMS communication cable is properly seated. The Pytes batteries need to handshake with the MP2GX via the VE.Can port before they'll give the inverter the green light to operate. If the BMS isn't talking properly, the MultiPlus will just sit there doing nothing as a safety measure, which looks exactly like a fault but isn't really one.

Make sure you've got the correct VE.Can to CAN-bus cable for Pytes specifically, and that both ends of the VE.Can network have 120Ω termination resistors fitted. Worth checking in VictronConnect under the DVCC settings too — that needs enabling once comms are established. What does the LED on the front of the MultiPlus actually show? That'll narrow things down considerably.

@DuctTapeDave has the DC breaker between the battery and the MP2GX actually been sized correctly? Seen people fit an undersized breaker that trips immediately on inverter startup and they don't even realise it's happened — unit looks dead but it's just sitting there waiting for the breaker to be reset.

Also — what's your DC cable length and cross-section? Too thin or too long and you'll get a voltage drop on startup that triggers the low voltage protection before the inverter's even had a chance to wake up properly.

Sort the physical stuff before you go down the VictronConnect rabbit hole. Victron's defaults are usually fine out of the box, BMS comms aside.