Dyness Batteries are going into protection mode

Had something similar crop up on my narrowboat setup last year, though single-phase rather than three-phase. Running a MultiPlus-II 48/3000 with a bank of batteries and they kept dropping into protection mode on startup — that little LED would flash on, system would refuse to play ball.

Turned out to be a pre-charge issue. The inverters were pulling enough inrush current on startup to spook the BMS into thinking something was seriously wrong. A few things that helped me get it sorted:

• Staggered the startup sequence rather than everything coming on at once
• Checked the BMS comms were actually talking to the Cerbo GX properly (DVCC settings were a bit off)
• Made sure battery temp was above the minimum threshold — narrowboat in February isn't exactly warm

For a three-phase setup with three MultiPlus-IIs, I'd imagine that inrush is significantly worse since you've effectively got three inverters all demanding current simultaneously. Are your Dyness units connected via CAN bus to the GX device? If the BMS isn't handing off state-of-charge data properly, the system can behave oddly on startup.

Also worth checking:

• VEConfigure — is ESS assistant configured identically across all three inverters?
• Firmware all matching on the MultiPlus units?

Anyone else running Dyness with Victron three-phase? Curious whether this is a known compatibility quirk or more of a config issue. Would be useful to know what firmware version the Dyness BMS is on as well.

@EdCampbell84 that rang bells for me too — spent a baffling fortnight on the cut last summer chasing exactly this.

What finally cracked it on my boat was checking the DC cable runs. I had an undersized negative return creating a voltage drop the Victron's BMS assistant was interpreting as a genuine low-cell event. The batteries were fine; the perceived voltage at the battery terminals under load looked catastrophic.

Worth doing:

• Measure voltage directly at the battery terminals under load
• Compare against what your MPPT or MultiPlus is reporting
• Check every busbar connection for resistance with a clamp meter

Also — if you're running Dyness specifically, their BMS communication timeout thresholds are quite aggressive. If the CAN/RS485 link to your inverter hiccups even briefly, they'll pull the plug as a precaution.

What cable gauge are you running between batteries and inverter?

@EdCampbell84 @RetiredNurse — classic one this. Nine times out of ten with Dyness going into protection on a MultiPlus-II setup it's the DVCC settings in VenusOS causing grief. Check your CVL, CCL and DCL limits in the DVCC screen — if Venus is receiving BMS data but the limits aren't being respected properly, the inverter can briefly demand more current than the BMS will tolerate, especially during inverter inrush on startup.

Also worth checking your BMS cable comms — I've seen dodgy RJ45 connections on the CAN bus cause the BMS to momentarily lose communication, which triggers a protective shutdown as a failsafe.

On my boat I run a Cerbo GX and had to manually cap the DCL in VRM after a firmware update quietly reset it. Five minutes in Remote Console sorted it.

@EdCampbell84 worth checking your DVCC settings in VenusOS if you've got a GX device in the loop. Had this exact headache on my boat — Dyness BMS was seeing a slightly different voltage to what the Multiplus reported, and it kept triggering high-cell protection.

Fix for me was:

• Enable DVCC and set a CVL about 0.2V below the Dyness max
• Make sure SVS (shared voltage sense) is on
• Check the BMS CAN comms are actually being read properly in the Victron console

Also double-check your battery cable lengths are balanced — uneven resistance causes one module to see higher voltage than others and trips the whole bank. Dyness are pretty sensitive to that compared to, say, Fogstar setups.