Multiplus II 48/8000 - Random "OVERLOAD WARNING" messages

[Anarchy2007]

EDIT
I have since managed to succesfuly replicate the overload event warnings by running a weed-eater (800W) on “AC LOADS” and “GRID LOADS” (this is not the only device that causes the issue). This causes an overload event warning within a minute or two. This seems to confirm my original assumption that the high impedance of the supply cable coupled with a voltage drop may be the root cause (maybe even some type of resonance). Disabling LOM and lower grid voltage under Country Code to 180VAC did not help either. The question:
Why an overload event warning & how to stop the warnings?

Hi everyone,
I’ve been struggling with this installation since it was first installed about a year back. It was a replacement of a 5KW Microcare system that ran perfectly for around 10 years. The main reason for replacement was the ESS feature.

EDIT 2025-02-07T22:00:00Z
I decided to edit the block diagram for clarity

• AC LOADS = Grid loads but measured by Carlo Gavazzi meter (Also suplemented with PV power)
• Critical Loads = AC Out 1 & AC Out 2 (AC Out 2 is programmed in assitans to supply upto battery 40% or turn on/off depending on input of temp connector)
• Heavy Loads = supply upstream / utility / grid
• Cable - Battery to busbar 50mm2 (3M max)
• Cable - Busbar to inverter 50mm2 (1M max)
• Cable - MPPT to Busbar 25mm2 (1M max)
• Cable - PV 6mm2 (20M max)
• The grid supply cable is very long 200M (4 core 25MM2 doubled up)

Device: VE.Bus System
WARNING: Overload

This is a more extreme example, but generally when a high load is drawn upstream from the inverter it generates this error.

This only happens when ESS is enabled. The assumption is that an input voltage drop at the Multiplus is what is responsible (although not everytime, this was monitored by GRAFANA for 6 months). It is at the best it can be with the long supply cable. The question is what can I do to stop the overload warnings? Somtimes it wil generate a warning with a critical load of 500W and an upstream load of 1KW with a small 1V drop.

I HAVE ATTEMPTED THE FOLLOWING:

• Disabled LOM (Loss Of Mains)
• Decreased inverter voltage to 220VAC (this seemed to lessen the warnings)
• Limited inverter output
• Had the whole PCB replaced by our supplier (THIS SORTED OUT THE REDICILOUSLY LOUD HUMMING NOISES)
• Replaced the Pylontech battery bank with BSL
• Replaced battery DC wiring with 50mm
• Disabled ESS (This is the only solution that works but defeats the purpose)

[DuivertNL (Marc)]

Its not really clear how its wired… are the heavy loads on ac out 2 or are they on grid and multiplus input side?

Is your DC wiring the right size? 2x50mm2 positive and 2x50mm2 negative (short lenght, longer needs 2x 2x70mm2)

[Anarchy2007]

"Its not really clear how its wired… are the heavy loads on ac out 2 or are they on grid and multiplus input side? "

• Sorry, I thought diagram was clear enough. Grid side, between Carlo Gavazzi meter and Multiplus input

“Is your DC wiring the right size? 2x50mm2 positive and 2x50mm2 negative (short lenght, longer needs 2x 2x70mm2)”

• 3M at absolute max 10KW / 200A (incl. inrush currents) I’m confident 50mm will suffice (see I didn’t mention that in original post)

Note: This only happens with ESS enabled. The warnings do not appear at all when grid is disconnected (ie inverter mode). Drawing high loads up to 6KW from batteries only does not generate the overload warning

[DuivertNL (Marc)]

1x 50mm2 is half of minimum recommended size… so clearly not big enough

[Anarchy2007]

2x50mm2 for this system is complete overkill and way over spec

Assuming a constant load at the actual maximum constant power output of the 8KVA MPII @ 25° = 6.4KW / 125.5A (±) the cable (50mm2) sizes are well within the recommended field for the MPII 8KVA.

Considering that good design practice will include a 25% (±) overhead. ie designed for a constant maximum load of no more than 4.8KW / 94.1A (±) it is clear that 35mm2 would’ve sufficed.

It has already been established, and mentioned twice, the overload error does not occur in Inverter mode or without grid present, regardless of the load. If you actually look at the above graphs you will note that the error above was generated at an AC-Out-1 (Battery / PV) load of 688W (51V @ 13.50A) and a GRID load of 4KW (±)

According to Victron this is known issue that occurs rarely when using a long (high impedance) supply cable. According to Victron this may be rectified by disabling LOM in ESS. (it does not work for me)

[nickdb (Nick)]

If you’re talking about DC cabling, at nominal 52V the draw is > 150A, that doesn’t even account for it’s peak power which is why Victron’s required spec as per the manual is 2 x 50mm, and why 8kVA and above have dual + and - battery terminals.

As for LOM, yes, if you have a poor grid connection it can cause issues and overload warnings, but they should be infrequent on current generation code. If it is constantly happening, the issue is likely broader.

Having infrequent overloads myself due to an iffy grid connection, disabling LOM as a test made no difference.

[DuivertNL (Marc)]

Read the supplied manual of the multiplus, minimum wiring size is in there for a reason…

ESS has a grid setpoint, so it will supply your heavy load on ac in to that setpoint, if your heavy loads starts, grid voltage will drop because of your bad grid connection, the multi will adjust its voltage to grid (cant make more voltage than whats supplied)

When voltage drops, current will rise so the inverter has to power more,
thats whats causing the overload warning

You say it also happens with low loads (1kw) but what kind of load is it? If its a load with a high start current or bad powerfactor that could be the isseu too ( in combination with bad grid)

What also could help is to have a wider voltage range in the multi where it accepts lower and higher voltage (probaply you need the grid settings password for that), because you cant upgrade your grid cable

[Anarchy2007]

“Read the supplied manual of the multiplus, minimum wiring size is in there for a reason…
Your list is not a DC but AC list, thats totally different”

• The above DC BATTERY CABLE specs were taken from Victron’s website. https://www.victronenergy.com/upload/documents/BatteryCables.pdf

“You say it also happens with low loads (1kw) but what kind of load is it? If its a load with a high start current or bad powerfactor that could be the isseu too ( in combination with bad grid)”

- Constant load (AC-OUT-1) is usually 500w to 1KW. General household low current devices, fridge, TV, etc. no high inrush currents. (AC-OUT-2 has an oven connected to it but this is hardly ever used). This home was designed rather power efficient
- Devices with high inrush current: 1x 1.5KW submersible pump (connected upstream at grid side). There is also an electrical lawnmower that is used but again it is connected upstream. These are used once weekly Overload warnings may also, but not always, occur while any of these are running (why I mentioned before that i’m pretty confident it has to do with a MPII input voltage drop)

!!!THIS IS A VERY IMPORTANT PART!!!
"When voltage drops, current will rise so the inverter has to power more,
thats whats causing the overload warning"

True, but my conern is why the MPII gives an overload warning event for loads upstream (yes they are suplemented (and measured by the Carlo Gavazzi meter) but surely the inverter should supply what it can only and get the rest from grid without an obverload warning.

“Wha*t also could help is to have a wider voltage range in the multi where it accepts lower and higher voltage (probably you need the grid settings password for that), because you cant upgrade your grid cable”

- Lowest input voltage was set to 180VAC before the PCB was replaced. it did not help either. Grid code was also set to non compliant,

This system was closely monitored with a dedicated server running Grafana for about 6 months. the log intervals were around 25ms and although slight GRID SIDE voltage drops were observed during the overload warning events it was mostly insignificant. Some times as low as 215VAC (during these events) but mostly about 5 - 7VAC variance from the measured 225VAC input. At no point was AC-OUT-1 even close to being overloaded. (except for during trouble shooting, in these cases it did not generate an overload warning)

I’m 100% sure that it is not an actual overload event. I do realise I can simply ignore the events, BUT unfortunately my compulsiveness won’t allow that.

[Anarchy2007]

52V x 150A = 7.8KW (excl losses) The inverter cannot constantly supply that load. It can however supply maximum 6.4KW constantly (on paper). 6400/51 = 125.49A (my bat is nom. 51VDC)

But all this is irrelevant as the overload does not come from or occur during high battery drain.

Yes it is infrequent, but it drives me crazy. I would love to find the actual root but after a year I would gladly settle for getting rid of the notification.

[nickdb (Nick)]

@Anarchy2007

But all this is irrelevant as the overload does not come from or occur during high battery drain.

It doesn’t have to. Low frequency inverters lean on the battery more than a HF one. Batteries can absolutely cause overloads and not at full loads. Often seen on packs that have been marginally sized. Wiring can play a part in that. Nonetheless, the victron spec was quoted and more is more. When you follow all the recommendations, it is rare to run into an issue.
These systems are used when connected to some seriously poor grids - my whole region is like that. And yet, overloads don’t just happen.
Not trying to convince you, if you don’t want to follow best practice that is your call, but the advice you receive from experienced members isn’t going to change. Use it or not.

[Anarchy2007]

It has nothing to do with trusting or not trusting your advice. I appreciate your input but in this case it is not the problem. The battery and battery wiring was the very first thing that was looked at. The battery bank and wiring was replaced (see my original post).

I am not thumb sucking an issue here, I have been trouble shooting this system for over a year, even had the head Victron guys at our suppliers look at the system.They couldn’t find the issue either and reffered the issue to Victron (as you are obviously aware. As an installer I cannot contact Victron directly). Victron advised they replace the PCB. This was done last week, the event in the first post was the first warning event since the PCB was replaced.

[Anarchy2007]

I have managed to replicate the issue with a weed-eater running on “GRID LOADS” and “AC LOADS”. The same weed-eater running on “CRITICAL LOADS” does not create the OVERLOAD WARNINGS. I can say with 100% confidence that the issue does not lie with the battery cables as suggested. The issue has been escalated again to Victron’s technical department (level 3) by our suppliers.