question

@ralexbell, do I read this correctly that you have a 35mm2 (2AWG) wire connecting your battery switch to your busbar on both the POS and NEG connections?

If so, that's the problem and must be corrected immediately; the minimum cable gauge that should be used anywhere in the circuit between a MultiPlus and its batteries is 70mm2 (2/0AWG) and in fact it's generally recommended to use (2) 2/0 wires (thus why there are two POS and two NEG connection posts inside the MultiPlus) or one 4/0 cable.

Using any length of 35mm2 cable in the circuit will create a massive -and very dangerous- voltage drop along that length, particularly when running your Multi under heavy load.

This will not necessarily be reflected in your battery voltage readings because the problem isn't at the battery - the problem is that the Multi isn't getting the voltage it needs. It's shutting down because it is experiencing under-voltage, not because your batteries are under-voltage.

Also, I just want to confirm a couple of things:

1. In your post of your wiring, you list the BMV shunt on the POS side... I want to make sure that's a typo, since the shunt goes on the NEG side.

2. I don't see a fuse at the battery on the POS side listed anywhere. Hopefully you just left that out of your list, but if you don't have a fuse on your POS line at the battery, please immediately install an appropriate fuse. Generally this is a 400A fuse - either ANL or Class T, though this fuse size is determined by the cabling you're using to connect the device since the fuse exists to protect your wiring, not particularly the device.

In sum: The MultiPlus should be immediately disconnected and the installation corrected, with the appropriate-gauge (2/0 minimum, 4/0 strongly recommended) cable installed on both the POS and NEG lines, an appropriate fuse installed at the battery on the POS line, and the BMV shunt correctly installed. When the system is connected properly, I am sure that this error will no longer be seen.

I urge that you contact a qualified and experienced DC systems installer to assist you with this. Improper installation of components will lead to component malfunction (as you can tell), premature failure, and can also pose a significant risk to personal and property damage.

For reference:

MultiPlus Manual

BMV-7xx Manual

Hi @ralexbell

I suspect your alarms registered in your first screen are 'Pre-alarms', the actual shutdown coming at a lower V. Nor would I get too excited about the V reported, could be just a 'sample time' thing.

If you look in the Inverter tab of VE,Config, what are they set to? It's all very well trying to protect your expensive Li's by handling them with kid-gloves, but you can overdo this in the real world where an odd 'spike' could shut you down.

Seems 12.5V is where your video baulks. If it's set to shutdown there, try it a little lower.

Wiring/junction health should be visible between your Multi's and BMV's readings of V. Is there actually a real difference?

** UPDATE ** All the wire is now 262 mcm Diesel Locomotive Cable (135mm2) with crimped and soldered lugs, and the switches are 600A. The low voltage warning light still flashes but we have not had a random low voltage error shutdown since -- several months :-).