Woody avatar image
Woody asked

How much is too much?

I just recently finished building a system in my RV that consists of a solar array (not a part of my problem) 6 100AH 12v Battle Born batteries wired as 300AH 24v, mated to 2 24v 3000w Multiplus inverter/chargers wired in parallel.

My question is how much wattage should I be able to pull from this system when the batteries are fully charged? Currently I'm running into issues where the entire system will overload and spontaniously shut down or just give me an overload warning when I have one A/C unit running (consuming 1400w with 300w to other loads) and I try to use something like an electric kettle, hair dryer or toaster all in the 1400 to 1800w range. This seems very low even if a parallel system doesn't give me a combined 6000w it should be more than 3200-3500 shouldn't it?

Have I wired something wrong? I don't have a colorGX so I only use the Victron Connect app and it doesn't show me that they are running in parallel but they do only show wattage and usage numbers on one unit after I switched to parallel (the switch did not improve my ability to use electricity btw) I've attached a schematic of how I wired my system if it helps. Once the two inverters output their power it's combined at a breaker and then each leg powers one side of my breaker box. I've tried placing the load on breakers on both sides and the issue exists no matter if the load is on the same leg as the A/C or the opposite.

MultiPlus Quattro Inverter Chargermultiplus in parallel
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5 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Are the Multis configured to run in parallel?

You will need a MK3 Interface and a PC to do that.

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Woody avatar image Woody commented ·

Yes they are configured to run in parallel. I initially had issues with that but was able to fix it by replacing the UTP cable.

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Meine_Energiewende avatar image
Meine_Energiewende answered ·

and DC wire lenght should be taken really seriously.

There are training videos in at victron professional to understand and analyse overload problems.


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Woody avatar image Woody commented ·

Yes I made sure the DC and AC cables are all the same length. I'm not a Victron Professional so how would I get to see those videos?

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JohnC avatar image JohnC ♦ Woody commented ·

Shh, don't tell everybody. Log in here as an 'installer', (which you are), and click on Videos.


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Woody avatar image Woody JohnC ♦ commented ·

Oh awesome. I'll do that.

So I thought hard about the cable lengths and now I'm second guessing myself and wondering if when I was actually making connections if I might have clipped an AC cable coming or going to the inverters to "tidy up" what would be the best way to see if a cable is a different length or do I need to just pull the cables and measure them? I only have one meter so I cant run readings from two lines at the same time.

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marekp avatar image marekp Woody commented ·

Set the constant load and measure AC current flowing through each multi using clamp meter.

Currents should be the same.

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mrseas avatar image
mrseas answered ·

Can you add some screen shots of how you have the Multi's configured in VE.Connect ?

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ejrossouw avatar image
ejrossouw answered ·

Hi @woody. Small point, the systems are 2400w each and not 3000W leaving you with a little less headroom, although it should be adequate.

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Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@Woody there are some great other suggestions here, but I will add a few things:

1. As shown in your diagram, you have your parallel wiring incorrect - right now (as shown) all of the charge and discharge current of your system is passing through the bottom two batteries in your diagram, which doesn't evenly distribute the load or charge current and will inevitably cause damage to all of your batteries. Please see Victron's free book Wiring Unlimited for the 4 (and only 4) acceptable ways to parallel-wire a battery bank. This alone may well be the cause of your issues, since those first two batteries (effectively, the first 24v battery) is bearing the brunt of your entire system load.

2. Your battery bank is rather undersized for what you're trying to do... as specified in the user manual, the 24v/3kVA MultiPlus requires a minimum of 200-700Ah to perform to spec; obviously when you have 2 Multis, you'll need to double those numbers, meaning that at bare minimum you should have 400Ah at 24v for both Multis to perform to specification. That's not to say that they won't work with less, obviously, it's just that they will, indeed, shut down under lower load than you would see if you had the proper Ah capacity under them.

3. Another thing to check is, simply, all your crimps and other connections. A single poor crimp or loose bolt will overheat under load and cause problems, including the Multis shutting down and/or one or more of the BBs BMSs to shut down.

4. Please also ensure that, as specified in the Battle Born user manual, you individually and fully charged each 12v battery independently prior to connecting them in series/parallel. The importance of this cannot be over-emphasized. If you did not do that, then please disconnect all batteries from the system, fully charge them individually (at 14.4v) as the manual instructs, and then reconnect them correctly - depending on your exact installation constraints, I'd wager the "Diagonal" method described in Wiring Unlimited will be easiest for you to accomplish.

I would definitely start by properly re-wiring your battery bank (unless you didn't individually charge the batteries, in which case start there) so that those bottom two BBs aren't trying to handle the entire load of your system, but then certainly go through and double-check your cable sizing and lengths, all of your crimps and connections, and everything else to be sure things are correct.

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