question

What size interconnects between batteries?

You you TRIPLE CHECKED that all connections are clean, properly torqued (cable terminals, fuse terminals, breaker terminals, inverter terminals, etc.), and any crimps are of high quality?

Have you enabled DVCC and turned on SVS and SCS to share your shunt voltage/current with all GX attached components? STS too if you have a temperature sensor.

Run a lighter constant load - say 50-70A. With a separate voltmeter, measure voltage at the battery terminals and at the inverter terminals. 5' of 4/0 should only drop 0.03V, but there are other resistances in the system, so a little more is expected. If you see a notable drop, start measuring voltage across all components in the circuit, and you should find the culprit.

Those are some great suggestions. I have checked all of the connections to make sure they are torqued and the crimps are high quality.

The cable size between batteries is 2 awg. I might wonder about that, but the shunt is reading their output and it doesn't drop as much as the inverter thinks, so I'm optimistic about them.

I have not enabled dvcc nor any of the other settings. I will do those and run a lighter load to test them.

Thank you

The drop to 13.0V feels excessive to me. Recommend you conduct the testing before you enable DVCC.

I run a 13500 A/C in my RV no-problem on a 24/3000/2x120. A few comments on things you've said:

"allows for 100 Amps continuous, 200 Amp surge for 30 seconds, and 1/2 second surge for loads over 200 Amp" -- if this is the spec for a single battery (which sounds about right), and you have 6x in parallel, then you can do 600A continuous, 1200A surge for 30 sec, etc. Your batteries themselves can handle the load just fine.

"The cable size between batteries is 2 awg" "5' of 4/0 between the battery output and the inverter." 2 AWG seems _way_ too small for battery interconnect (unless you mean 2/0). Yes, they're shorter, but still running a _lot_ of juice. Honestly I'd go at least 1/0 here. Look into very fine-stranded cable here too as it's incredibly flexible vs standard "welding" cable (though it has more voltage drop).

Questions:

How are your batteries connected? For an example of a 1s2p (1 series, 2 parallel, i.e. 2 batteries total) setup -- please excuse my _awful_ scratched-together paint skills -- obviously you've got 6, but are you connected like the left, or the right (with green going to the load/inverter)?

Are you using the external voltage sense on the inverter?

Hi jimduchek, thanks for the response. Yes it is 2awg not 2/0, so if 2awg for battery interrconnect is way to small then that might be the majority of my problem. I originally based those sizes because the max wire size into/from the charge controller is 2awg. Perhaps I need to increase those quite a bit, but because the 4/0 is like your green wires in your right hand drawing I am pulling from all of them in parallel.

With 6 batteries in parallel you do NOT want to daisy chain from one battery to the next. You need to use a busbar or common stud with equal length cables from each battery to the busbar/stud:

This way you divide total current equally between batteries and the interconnections can in fact be smaller. To match the 4/0 wires you are using from battery to Multi, each battery to busbar/stud needs 1/6 the area. So #2 from each battery should be sufficient.

If you wire like the top drawing, currents in each link between batteries add with each battery so the end link much more current and higher voltage drop than the first one. You may also exceed the ampacity of the jumpers. Not so in either of the lower drawings.

The current will also not be balanced between batteries so one battery may be tasked with supplying more than it's BMS permits and shut down. This would cause a cascade in which all batteries will eventually shut down.

You should also look at voltage drops across other components in the system. At these currents EVERYTHING is a resistor and there will be voltage drop across it. Check the voltage drop across fuses, switches, each cable, etc.

For high current tests in my RV I use the water heater's electrical element. It's about 1500 watts and a pure resistor of constant load. About as perfect a load as you can get. Note that some hair driers use diodes for their low power settings and inverters and other power sources don't really like that asymmetric load. You'll hear nasty noises coming from your inverter's transformer. Should be OK but best to use something else for system testing.

I would normally agree with the busbar recommendation, but given that you're current draw is barely over the 1C rating for a single battery, and if you have a bank in which all batteries are operating within limits, you just accept that some of the will last a little longer than others.

Additionally, beefy interconnects simulate bus bars with very short connections to the battery terminals.

Lastly, even with bus bar connections, I would follow Victron's recommendation to attach the main leads to the opposite ends of the bus bars per Victron Wiring Unlimited.

In other words, upgrade to 1/0 or 2/0 interconnects, and you effectively have a busbar configuration.

But before you do any of that, I would conduct the testing necessary to confirm the presence of voltage drop.

You can see there is quite a bit of imbalance in the batteries (13.04 vs 12.76). That's 0.28 volts of your drop right there. At minimum, you are taking a significant amount of current from the battery at the exit end. I'd focus there. In a heavily load situation this could trip the first battery's BMS which would then cascade to the rest of the bank. Additionally, the first battery in the string will discharge faster then the far end. The good thing in your system is your 6 batteries aren't heavily loaded. The 3000 VA Multi max current draw would be around 250 amps out of an available 600. Peaks should also not be a concern since the batteries have 30 seconds of double current. But look closely at system voltage drops. You are measuring at substantially less than the 250 and WAY less than the 500 peak currents. Peak currents are usually what causes a low voltage shutdown.

The first change I would recommend is to increase the jumper size. 4/0 is recommended but even 2/0 will help substantially. #2 is 0.5 ohms per 1000 foot, 2/0 is .15 ohms per 1000 foot (3 times better). Just replacing the jumpers wit 2/0 should take the 0.28 volt drop (first batter to last battery) down to 0.08 volts.

Next, take positive from one end of the bank and negative from the opposite end. This will come close to cutting the overall voltage drop in half.

A further enhancement would be to take power from BOTH ends of the bank. That is two positive wires and two negative wires. These can be half the size of your 4/0 monster cables -- down to 2/0 would be similar in overall voltage drop. Just keep both positives and both negatives equal length.

An infrared temperature meter helps locate hot spots. Run the system for 10-20 minutes on high load to heat everything up then scan the wiring, connections, fuses, switches, ... This should provide focus for additional improvements. The cable crimps can be a source of voltage drop if not done correctly. Check these carefully with the temperature meter or by hand.

As an illustration of various wiring topologies, I ran a couple of Circuit Lab simulations:

The first shows positive and negative taken from the same end of the battery bank. Notice the currents in the series resistors decrease drastically as you move away from the battery:

The second is if you take positive and negative from opposite ends of the bank:

While not exactly balanced in this simulation, you can see that there is far less variation in individual battery currents. Obviously, reducing any resistance will improve balance.

I haven't seen any mention of a soft-start on the AC. My big AC (15000BTU) only pulls 1700 watts. easily handlable by a 3000VA inverter. It's only ~150amps from my 12v system. however, compressor starting is a tough business. my inverter and shunt are not fast enough to see the surge load startup. with my clamp meter, I can see a peak of 571 amps drawn on compressor startup. that's 6800 watts and should trip the overload protection on a 3000VA. adding a soft-start to the AC will stop the capacitor from rapidly charging after a compressor start.

to make things worse compressors get harder to start when they are hot and after 10 minutes of use this is probably what you are seeing. it clicks on, drains the cap, and that cap asked for all it can and trips the over current protection.

with a soft-start on both my AC's I can run both the 15000 and 13000btu AC on a MultiPlus-II 2x 120V at around 2300 watts on average. can't do it long as I only have 1000AH usable storage but with my 320amp alternator, I can run them while cruising down the road which was actually my goal as before I had to run my generator while driving.

soft starts aren't cheap ($250 per ac) but they work and they make your ACs quieter, no more clunk when they turn on and off.