Strange behavior Victron BP220 disconnects the legacy load approx 10A when Multiplus

[CaptainRivet]

Hi all,
Helping a friend installing Electrodacus BMS with all Victron equipment in his boat and getting a strange problem:
A Multiplus 3000/12/120 is directly connected to the battery bank and controlled via Aux 1 and 2. the boats old legacy main load (chartplotter, bilge pumps, fridge,lights…) max 50A is connected via a BAttery protect to the battery too. The battery protect is on Lithium mode, connected to Electrodacus via Same 817 optocopler then the Multiplus inverter as 2nd load, controlled by the same load cut off output on Electrodacus BMS. So you can see from 817 optocopler red lamp on that BP and inverter is shut on by Electrodacus.
Tested the system today and all is fine, Electrodacus shuts on/off the BP and Multiplus inverter (load cut off) and charge cut off Multiplus charge, the OrionDc2dc and the MPPTs.
That all works fine, even the Multiplus inverter drawing 230A for 45min straight. But if we max the inverter out to 280A draw the battery protect shuts suddenly off the old legacy load while the inverter stays on drawing 280A. It’s not the Electridacus that shuts it off, both red optocopler are on but BP shuts off. The cell voltages are around 3,0-3,2V under this load, undervoltage is 2,8V with a 3sec delay means it must be 3sek under 2,8V so BMS shuts off, which it didn‘t as otherwise the MP would be switched off too but was running all time fine.
As soon as we reduce the load to 230A the BP shuts on the old legacy load again.
What’s the problem here???
On LI mode the BP undervoltage Levels are disabled with LI mode and 12,3V on the BP is not undervoltage cut off condition either.
560AH Bank is at 70%SOC and 13,3V With 10A load on the legacy load with the BP and shut on and drawing 230A for 30min straight via inverter it gets down to 12,6V all is fine and work as should but at 280A it is 12,3V shown in bt-App and Electrodacus, the BP shuts off the old legacy house with 10A load on it.
Why? Based on what? It’s in Li mode and the BMS is not shutting it off….but who does shut down BP then in LI mode?
Anybody an idea what’s the problem here???

[lmxr]

Interesting problem and strange behavior indeed.

A suggestion for testing: to rule out the BMS, enable the BatteryProtect using a cable directly to the battery instead of to the BMS?

[CaptainRivet]

We found the issue: the remote cable inputs on the BP220 where twisted H on L and L on H.
It’s actually a triggering circuit that just gets interrupted=open=shutdown by the BMS so you think that polarity doesn’t matter. Well it did. We could reproduce the issue and the fix, connect them correct on H to + and L to - and it works.
Again very bad design Victron.
How can a seperate remote trigger loop can cause such behavior?