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Ovidiu Stan avatar image
Ovidiu Stan asked

AC IN Current limiting bug in parallel installations


                  Hello people. A few months ago i discovered a a bug in limiting the input current to AC IN for Multis/Quattros, but ONLY IN PARALLEL SYSTEMS. If I only have 1 Multi/Quattro per phase, the limitation works perfectly, but when I have at least 2 inverters per phase (as is the case with one of my systems - 6 Quattros 15 000, three phase,  parallel, 2 Quattros per phase)  it no longer works as it should. More precise, if I set In Ve.Bus System Configurator, let's say, a limit of 35 amps for each inverter, that is 70 A per phase and after that I upload the configuration on the inverters, it works ok. If, however, I later need to increase or decrease the respective limit, let's say to 75 A per phase, the VeBus system, normally, as specified in the manual, should divide 75 A by 2 = 37.5A per inverter . But it only does this with the Master inverter, the slave still remains with the initial setting in VeConfigure, in this case, of 35 A. Because I make programming in Node-Red for these systems through which , in order to force the system to take current from the batteries, I set the limitations to AC IN dynamically, depending on the SoC: for example, up to 20%, let me accept a limit of, say, 70A per phase, and below 20%, let me increase limit to 100 A per phase, so that the batteries do not run out at night, this bug prevents me from doing this dynamic AC input limiting. I repeat, this works perfectly for simple single-phase and three-phase systems, but it does not work at all in parallel. I kept hoping that someone from Victron would discover this bug and solve it, but it didn't happen untill now, so maybe they will see this here or maybe someone here has found an workaround. I am also attaching a video/screenshot for better understanding.
Node-REDmultiplus in parallelbug report
ac-in-current-limiting-bug-in-parallel.mp4 (3.4 MiB)
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derrick thomas avatar image
derrick thomas answered ·

This is normal in parallel setups. The master is always in control of the slave so the current limit is being controlled by the master and not the slave. The current limit setting in the slave is meaningless.

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Ovidiu Stan avatar image
Ovidiu Stan answered ·

screenshot-20230817-201407-chrome.jpgNo, it's not normal. When you set the limit for 60 amps, for example, the system divides this equally to the number of inverters. If you have 2 inverters, each gets a limit of 30 amps, if you have 3 inverters, each gets a limit of 20 amps, and so on. My issue is that this works perfectly when it's configured via Ve Configure, but it doesn't work when it's configured remotely through the control panel in VRM or through Node-Red.


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nickdb avatar image nickdb ♦♦ commented ·
You are misreading this. What you set will be multiplied by the number of parallel inverters. You need to divide it by the number of systems for it to work.

If you set 60A on the master and you have 3 inverters, that equates to 180A.

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Ovidiu Stan avatar image Ovidiu Stan nickdb ♦♦ commented ·

You are right. And it also should apply the other way around. You set 180A, it should divide it by 3, and set each inverter 60A. But it doesn't do it, it just does it for the master inverter, the slaves remain to the original setting. Watch the video, you can understand better what I'm saying.

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derrick thomas avatar image derrick thomas Ovidiu Stan commented ·
You are not understanding what is happening. Even though the slaves remain at the previous setting, it is irrelevant since the master controls them all. If the slave is set at 60 and the master is set at 10, the total is still just 20 because the slave follows the master.
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Ovidiu Stan avatar image Ovidiu Stan derrick thomas commented ·
I don't think so, it doesn't make any sense. Also, in real life tests, it doesn't work. When I had the initial system, 3 Quattros, setting the limit to 60 amps worked perfect, the current drawn was almost never above that limit. Once I expanded the system with another 3 Quattros in paralllel, meaning now I have 2 inverters per phase, setting the 60 amps limit in the initial VeBus Sys. Configurator still works fine. But as soon as I modify that limit, up or down, from the control panel or Node-Red, the system goes haywire and doesn't respect the limit anymore. And I mean by a lot. I have 70 amps limit and it draws up to 100 amps, which, obviously destabilizes the whole system and stalls my backup generator.
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derrick thomas avatar image derrick thomas Ovidiu Stan commented ·

Sorry I don't have an answer for you then. In my parallel inverters when I change the input limit thru vrm, node red, or display panel only the master shows the change in the configuration but the overall limit is applied as expected. Maybe someone from Victron can look at your system remotely and offer an explanation.

Edit: one other thought...is all the wiring both ac and DC exactly identical between parallel inverters? Inverters all the same model and within a year or less of manufacturer date? Resistance in wiring and inverters is much more relevant when wiring parallel inverters. Small differences in wiring and resulting variables in resistance can have the effect you are seeing. There is no communication between parallel inverters in regards to "balancing" the loads (what I mean is that the balancing is not 'computer controlled'), this is dependant upon correct wiring and similar resistance values between units.

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Ovidiu Stan avatar image Ovidiu Stan derrick thomas commented ·
I know the recommendations about the wiring and yes, they are absolutely identical, to the millimeter.
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derrick thomas avatar image derrick thomas Ovidiu Stan commented ·

Put a clamp meter on each unit and compare the current flowing thru each parallel unit. Make sure they are identical. For example, if you have 30 amps flowing thru one unit and 40 amps thru the other paralleled unit then you have an imbalance. There may be enough difference in resistance between units to cause a big imbalance.

Edit to add: you will want to check both AC and DC side for imbalance. Even though the wiring is identical, there may be internal differences in the inverters.

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seb71 avatar image seb71 derrick thomas commented ·

From what I understood, the current limit works fine as long as he sets the value in each inverter (master and slave on all phases, so 6 inverters to set). That would exclude any wiring issue.


The problem is that he wants to frequentlly change the value.

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derrick thomas avatar image derrick thomas seb71 commented ·

Maybe more clarification is needed. There seems to be two different issues. When changing the input limit from vrm or remote display, the new limit is only being changed in the master configuration and not the slave configuration. This does not matter since the slave follows the master setting anyway. The second issue I believe the OP is explaining is that the current limit is not being observed, the inverters are drawing more than the limit. This can be caused by differences in resistance between the parallel units.

To the OP...can you clarify? If you set the limit using ve configuration on both the master and slave units will the total current limit be observed and adhered to? Or do you still have the issue of drawing more current than what the limit is set to? We need to determine if this is actually a software issue or a hardware issue. There is more going on under the hood than just making software settings.

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Ovidiu Stan avatar image Ovidiu Stan derrick thomas commented ·
So, after several days of intensive testing, I have come to the conclusion that you are right. Despite the fact that the slave doesn't show the correct settings for AC IN, it seems to follow the master. The fact that the whole VeBus system doesn't respect those limits is, most probably, due to the fact that I am using ESS (instead of PV assistant) together with a generator (i found an explanation from Victron in another thread here about this). But, if I don't interfere with the settings for longer periods, like one entire night, for example, the system eventually follows my limits overall, even though, for example, I set 25 Amps as the limit and it spikes for good amount of times up to 100 Amps, before trying to stay under 25 again. Luckily I have a big generator as a backup which can handle these spikes easily. But, by morning, the system consumes also energy from the battery as I program it, so, I guess I will accept this, for now. Whenever I used the PV assistant, however, those limits are respected more accurately, but there is another story here which I will develop into another thread.
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