Hello, I’ve been looking for a solution for several months now…
I wanted the following configuration: two MultiPlus-II 5 kVA units per phase in a three-phase setup, making six MultiPlus units in total. In principle, it works, but I’m encountering two problems:
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I’m using a 12 kVA AVR diesel generator. Above 10 A, with the engine warm (it’s worse when cold), I get a current oscillation on the input. Even when trying to change the boost factor, it doesn’t make much difference, especially since the consumption on the AC OUT side is practically zero, so I suspect the charger section is responsible for this. Does anyone have any ideas for improving things? The generator keeps getting hit with power spikes. The oscillations are around 4–5 seconds long, varying from half to twice the power. The engine speed only varies by 2–3 Hz.
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To deal with this, I thought I would limit the input current (and accept that I wouldn’t be running the generator at 75% load for optimum efficiency), but it’s impossible to limit the input current below 12 A (6 A for one MultiPlus and 6 A for the other), with 6 A being the minimum limit. I tried disconnecting one of the inputs, but the system goes into fault mode as soon as it tries to switch to that input. I also tried an advanced configuration that I liked: two MultiPlus units per phase, configured with two inputs—one MultiPlus per phase managing one input, and another MultiPlus per phase managing the other input. The two outputs are then correctly connected in parallel. This configuration, created using VE.Bus System Configurator, works, but it isn’t recognised by the Cerbo GX. So I can’t use it.
Today I tried the “series” configuration: a first network of three MultiPlus units supplying the AC in of a second network of three MultiPlus units. The first network inverts and charges the batteries when necessary and when the generator is running; the second assists the first when the first is overloaded. I’d describe this solution as a bit of a bodge. I chose so many MultiPlus units to power my largest load, a 4 kW three-phase compressor. Naturally, the problem occurs on start-up with only three inverters in the series configuration I’ve just tested. The neon lights still go out when it starts, but I had left the UPS function enabled on the inverters receiving power from the first network, so perhaps they disconnected their input for a few seconds (I didn’t have time to check).
If anyone has any ideas, I’m completely out of options at this point. Since the installation is operational, I’m trying to avoid carrying out loads of tests, and it takes an age to reconfigure everything each time.
Have a good evening
As for solution 2 AC IN, in my opinion it’s just a configuration issue, because it’s a solution that works, including for the GX display.
When you say that it isn’t recognised, what exactly happens?
Hello,
Thank you for your reply. It’s been a while since I carried out this test. If I remember correctly, I saw an “unknown status”, sometimes interspersed with all sorts of strange readings, before returning to “unknown status”. The display kept alternating.
I seem to remember subsequently finding in some Victron documentation (I can’t remember which one) that this type of configuration wasn’t recognised by a Cerbo GX. It’s a shame, as it would be a great setup. If I’ve missed something in the configuration, I’d really appreciate it if this setup could work.
Hello,
I’m revisiting this topic because I’d like to develop my installation and move on to the second phase, namely adding photovoltaic panels. The issue I initially encountered, which I still haven’t solved, will determine how I proceed. For the time being, I’ve found a compromise that I’m not particularly happy with: I disabled PowerAssist, which allows me to go below 6 A, the lower input limit for a MultiPlus II 5000 VA. As I have two of them in parallel per phase, that meant a 12 A minimum. I would really have liked to be able to operate the MultiPlus units with two inputs and one output, but as mentioned previously, they weren’t properly recognised by the GX. However, I may have found a new lead in the GX configuration: AC input 2 is set to unavailable, and could that be the reason?
If I can’t get this principle to work, I’ll go with three Multi RS units for my solar panels and connect the generator to them. The MultiPlus units will therefore operate solely as inverters, and if I’m ever connected to ENEDIS, I’ll connect that supply to the MultiPlus units. In the attached diagram, I’ve only included the MultiPlus and GX sections. The cables are 50 mm² and 5 m long in total (+ and −). I only noticed afterwards in the documentation that 70 mm² is recommended, but according to Victron Toolkit, 50 mm² is more than sufficient, and I never run at very high power. I’ve also never noticed any DC ripple problems.
elec_stockage.pdf (84.2 KB)
You need to configure the system with two inputs and one output. In this case, MultiPlus 1 takes priority over MultiPlus 2, but if there is nothing on input 1, MultiPlus 2 will connect. In fact, this is equivalent to creating a Quattro with two MultiPluses!
Thank you for your very quick reply; the MultiPlus configuration was working perfectly. It’s on the Cerbo GX side that I’m having problems. However, I just discovered that I had this configuration set up in the GX.
I thought it was purely informational, just to have an alarm if the grid input was missing, but perhaps it does more than that? If that is the problem, I’ll try the configuration again with two inputs. It’s really powerful what you can do in terms of configuration with VE.Bus Configurator and the MultiPlus units.
It’s both: the MultiPlus units need to be configured with two inputs and one output.
And in the GX, you need to define the input type.
Schema_prevu.pdf (81.0 KB)
Good evening,
I finally had the opportunity to repeat this test. It finally works, with proper communication with the GX. Thank you! The inverter status on the GX alternated between “conversion” and “unknown”; the same applied to the generator and the other information. What I did was shut down the inverters (not just restart the VE.Bus), then restarted the GX so that it would no longer see the VE.Bus system and would therefore remove it. I then restarted the inverters; they were detected by the GX, but not completely (I can no longer remember what was wrong). After a second restart of the GX, everything was displayed correctly.
I had not gone as far as deleting the devices, so I think the GX was switching between the old and the new configuration.
However, this raises a few other points. My configuration is therefore as follows:
- 6 Pylontech US50000 batteries connected to one another, with the first one connected to the Cerbo GX via CAN.
- A three-phase generator with AVR regulation (FG Willson 13.6) connected to AC In 1, configured as a generator. I do not currently have an EDF grid connection. AC In 2 is therefore not connected, but is configured as grid on the GX.
- 6 MultiPlus units in three-phase configuration, with 2 MultiPlus units per phase. The AC inputs are now properly separated, so I can limit the current to 6 A (with PowerAssist enabled), whereas previously, with the two AC inputs in parallel, I had a minimum of 12 A, as stated in the documentation.
Before this new configuration, I had therefore disabled PowerAssist, even though I wanted to use this function for high current demands. This allowed me to go below that limit, but the regulation is not very stable initially at around 6 A; the lights (neon lighting) flicker slightly. Initially, I wanted to run the generator at 9 kW, compared with its maximum of 12 kW and 13.6 kW peak, but I experienced even worse input-current oscillations. I therefore limited it to 12 A, or approximately 7 kW. It feels as though the inverter and generator regulation sometimes enter into resonance, but I am not really sure which parameter to adjust (I cannot do anything on the generator side). I noticed that it was worse when cold, which is understandable. To limit this phenomenon and avoid wasting too much diesel on preheating, I let it run unloaded for 8 minutes (the preheating time), then use a ramp with noedread to increase the current limit from 6 to 12 A. I get this behaviour with or without PowerAssist. Would my only adjustment variable therefore be the boost factor when PowerAssist is enabled? For now, I have left the factory setting, 2.
I also wanted the MultiPlus units to take over in the event of a current surge, but this does not seem to work. PowerAssist is enabled, yet I experience a fairly significant voltage drop at the output when I start a 4 kW three-phase compressor. Here are the tests I carried out, and perhaps these are the circumstances in which it does not work. In all cases, there was approximately 300 W of consumption on the most heavily loaded phase:
- 3 MultiPlus units only (1 per phase) in inverter-only mode: the neon lights switch off and then come back on after start-up, and the PC UPS detects a power failure.
- 6 MultiPlus units (2 per phase) in inverter-only mode: the neon lights dim very slightly. PC UPSs are fine.
- 6 MultiPlus units (2 per phase) with AC In 1 (generator) operating and charging the batteries at approximately 12 A on AC In, i.e. the current-limit value: the neon lights switch off and then come back on after start-up, and the PC UPS detects a power failure. The AC In connection disconnects from the generator and then tries to reconnect (with the compressor still running). The first attempt fails, but the second succeeds. One of the phases did remain assisted by the inverter because it was slightly more heavily loaded; the others were balanced.
I therefore have the impression that, apart from an incorrect PowerAssist coefficient setting, only 3 inverters assist with starting the compressor; on the other 3 connected to AC In 2 (the unconnected grid), this function is not enabled. Should I perhaps have enabled it? In this configuration, I am having difficulty understanding how the assistance works, and I have not found any documentation on the subject. Do you have any ideas?
If this is not possible or is unreliable, I am considering expanding my PV array, which is currently being tested with 3 500 W panels in series and an MPPT 150/35. I would therefore use 3 Multi RS units, 1 per phase, and 6 strings of 6 500 W panels (approximately 250 V per string). The MultiPlus units would then only be used as inverters. I have attached the proposed architecture; what do you think?
Thank you
What output power do you have? To blow neon lights with 10 kVA, they must be drawing a fair bit.
With 10 kVA, i.e. two MultiPlus units per phase, it works, but only in inverter mode. When I’m connected to the generator, it cuts out, just as it does with a single unit, i.e. 5 kVA per phase. When I tested starting the 4 kW three-phase compressor, I should have had no more than about 200 W on the most heavily loaded phase. Given the motor’s starting current, I’m not surprised that with only 5 kVA I get a voltage drop that causes the lights to go out. That’s why I was aiming for 10 kVA, thinking it could also provide backup power by reprogramming the remaining MultiPlus units. But it seems that PowerAssist only works on the three units the generator is connected to and doesn’t provide assistance using all six. I haven’t tested configuring all the MultiPlus units on a single input, because with PowerAssist you can’t go below 12 A.
