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Dave van Dongen avatar image
Dave van Dongen asked

Cut off input voltage lower than 180 volt

I have a 3 phase system with 3 * 5 kVA MultiPlus, running in Ethiopia. Every evening the gird voltage of phase 1 drops to around 175 volt. So the installation switches to inverter mode, instead of pass-through. But the house can handle the 175 volt and we don't want to use the batteries, so we want the MultiPlus to accept the 175 volt. But the minimum value for the input voltage in the configuation is 180 volt. Any ideas how to set this value lower? (175 or 170 volt would be great) Or another work around?

MultiPlus Quattro Inverter Charger
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10 Answers
tilo avatar image
tilo answered ·

I don´t see a reason why a Multiplus should not be able to maintain a certain minimum voltage at AC Input (180V AC) under certain conditions. Of course that would have to be a new feature.


If it is practical or will work, or have a noticeable effect will depend on the grid impedance (resistance). If the grid is weak because of a long grid cable in the "last mile", then the voltage fluctuations will be influenced (or caused) by the consumers of this house. This can easily be tested with a water heater. If grid voltage is 190V, then you turn on a 2 kW heater and voltage drops to 180V, then each 1 kW of power flow will cause 5V voltage drop. Then the same voltage drop (or rise) will occur if the Multiplus injects power to the grid (which is in practice an extreme or unlimited form of "power assist", or simply working synchronized with the grid, as all grid inverters do). If it injects 1 kW to the grid, in this example the voltage will raise 5V.


So let´s assume we have such a weak grid. If the Multiplus is consuming 2 kW from the grid and the grid voltage is dropping to 180V, it could start to reduce AC input current and increase inverter power from the battery to "maintain" the 180V at the input, in case the voltage drops further. The "limit" of this function would be reached when the input current is reduced to 0A and there is still just 180V, then there is nothing more that can be done. Otherwise you would have to start to inject energy to the grid from the battery to maintain 180V, which is not the idea.

By the way, such an "AC Input voltage maintaining" function would also be useful at the upper voltage limit for cases with grid injection in weak grids. The problem there is high voltage, and the grid inverters shut themselves off by injecting power and thus raising voltage above the upper limit where they have to disconnect by national regulations. Instead of just keeping injecting with full power and overshooting the voltage limit and then disconnect, it could start reducing injection power to stay below the upper limit.

@Dave_van_Dongen: In case you have a long cable between the grid meter and the Multiplus with a voltage drop of 5 or 10V, you might improve the cable section to reduce the voltage drop, or move the Multiplus closer to the grid meter (and have the voltage drop after the Multiplus). Ideal would be if the electricity company could improve cabling in the "last mile" to your house, but that is unlikely as it is expensive for them. But you could ask them to raise the output voltage in the medium to low voltage transformer that supplies your house, this does not imply material cost and they might be willing to do it. Usually those transformers can be adjusted in their output voltage. To reduce the flickering of the lamps when the inverter disconnects from the grid, you might reduce the inverter voltage from 230V to 200V or less, or try with led lamps with a good driver that maintains a stable current(=light) output with different supply voltages. If always the same phase of the 3 phases is lower than the others, try moving loads to the other phases. If you are willing to invest a little, add a voltage stabilizer before the Multiplus with the low input voltage (or in all 3 phases), then you should not have those problems any more.


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max-b avatar image max-b commented ·

But this solution you propose would consume power from the battery which is what the OP do not want. In the use case of the OP, the grid line being @ 175V most of the power to the house would come from inverting. This is not what was intended. So I don't understand why this answer is the accepted one. Even if it is interesting in that context it does not propose a solution to the problem. Or did I miss it ?

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Dave van Dongen avatar image Dave van Dongen max-b commented ·

Yes, you are right, we veered of course...
But I got the impression that my problem isn't going to be solved, at least from the Victron side. (I could install a voltage regulator externally)
There seems to be no way the inverter will accept anything lower than 180 volt, although I think it would be possible and easy to just allow it, with the condition that it the inverter then only works in straight pass-through. (no charger, etc.)

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Dave van Dongen avatar image Dave van Dongen commented ·

Can we make this a feature request...!? ;-)

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markus avatar image
markus answered ·

I am sorry, but this is a hard coded setting bound. ... I tried hardly everything, to change another setting (Low Voltage shutoff) to set it below setting bounds, with absolutely no success.

A bit of a weird solution would be, to use isolation transformers, as they boost the voltage up a bit.

Regards,

Markus

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Dave van Dongen avatar image Dave van Dongen commented ·

I am wondering what is the reason this setting is hard-coded at 180 volt, because it seems quite high. In Africa I have seen mains voltages (of "230 volt") as low as 147 volt. If I choose to pass-through this voltage and not to start inverting, that would be a good option for these conditions. And as long as I am only in pass-through mode, it doesn't matter. If the charger doesn't work in these conditions, it could just be turned off. And I would say the charger can work with these voltages, because other battery chargers do work in these conditions. (not optimal, no)

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markus avatar image markus ♦♦ Dave van Dongen commented ·

Yes, that would be interesting what's behind this limit. Another weird solution (sorry for having no serious ones ready) would be to rectify the weak AC input and feed it in a PV inverter...

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wkirby avatar image
wkirby answered ·

I am from Africa, so I can well believe that it is possible to have an extremely low Voltage like that delivered to a customer. Usually because the grid's safety mechanisms are malfunctioning or they have been bypassed.
However, 147V is very very low for a 230V system, even 180V is well below allowable limits (216V) in countries where the grid rules are still enforced.
I know you said "in passthrough" but what is the inverter expected to do in a grid failure? It would suddenly start making 230V. In that case how do you define a grid failure? 100V maybe?
In the case of the charger, is it still expected to charge at 2KW with half of its supply voltage missing?
You see what I mean, there has to be a line somewhere at which point a "grid failure" is declared. It's nice that we have a choice in VE.Configure, but it can't be just any Voltage we want.

When designing an electronic product, there have to be limits to the design. Of course, it would be possible to design a product that automatically works from 50V to 300V, but to design for such a wide input Voltage range would be very expensive.
In the same way, customers have choose between 230V versions and 120V versions when selecting a MultiPlus - for example.
In fact, 147V is actually closer to 120V than it is to 230V!

So I think a 180V lower limit (<20%) is quite acceptable for the given design.

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Dave van Dongen avatar image
Dave van Dongen answered ·

As I don't see any damage done by allowing a threshold of 175-170 volt, in this case, on the input, I would be happy to have that option.
I choose Victron because it can deal with rough grid conditions, otherwise there would be other solutions. (Actually in this case the Victron installation is replacing a SolaX 3 phase 10 kW hybrid inverter that couldn't deal with the grid conditions and rejected the grid the whole time. But the Victron solution is twice as expensive as that inverter, mainly for this to work...)
Like I mentioned, I wouldn't mind that the charger doesn't work or delivers less power.

@mvader (Victron Energy Staff) What do you think?

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ commented ·

Hi; I think what Warwick said; the 180V is not arbitrary; its a hardware limit. And behind that a design choice.

In most cases with such low grid the setup is to ignore the grid (which is does) and power from the battery.


We do have wide input battery chargers; which you could add (yes this means increasing cost)

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Dave van Dongen avatar image
Dave van Dongen answered ·

In this situation, where the voltage dips below 180 volt on 1 phase every evening and not being able to set this threshold a bit lower at 175 or 170 volt in VE.Configure, now leads to 2 issues:

1: Every evening the inverters switch to inverting mode. (all 3 of them! See https://community.victronenergy.com/questions/3307/not-use-switch-as-a-group-in-an-ess-configuration.html?childToView=3345#answer-3345) This means that the battery is being used every evening without it being necessary. The customer wants to keep the lifetime of the batteris as long as possible, so this daily cycle is not very helpful with that. Normally the batteries are being used a few times every week, only when there is a grid blackout.

2: The voltage fluctuates, so during a few hours it sometimes dips below 180 volt, but sometimes it rises to above 183 volt (the value at which I programmed the reconnect). So in the house it is like a disco now: the light are dim when the voltage is 181 volt. Then the voltage drops more and the inverters kick in, so we have 230 volt, so we have bright lights. Then the voltage rises above 183 volt and the inverters go in pass-through and the lights dim again. Etc, etc.

Notice how both issues are counter acting. (I could put the reconnect voltage value higher to prevent the flickering lights, but that means the battery is used even more and vice versa.) But if I could set the cut-off voltage to 170 volt, both issues would be solved.

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max-b avatar image
max-b answered ·

@GreenTecSense

What I have done in my place where the main is from a small hydro with home made ballast switching regulator is to be true "online" inverting from 24V, while a charger is feeding the 24V from main. The batteries are kept high, unless the current demand is higher than the main limit. The Multiplus is inverter only. I know this is asking for two devices rather than one…

Then the keypoint is for the charger to handle the low voltage. And I must says that I have experienced that the Skylla charger is not working well with low input. I did not check it precisely but the threshold must be around 200V.

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markus avatar image markus ♦♦ commented ·

Hi, search for Multiplus + PowerAssist.

Regards,

Markus

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max-b avatar image max-b markus ♦♦ commented ·

I have used PowerAssist for years before changing my setup. PowerAssist is great but it's not true online and all variations on main AC pass-through to the domestic lines.

Current setup is much safer for all appliance on the inverter AC out.

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markus avatar image markus ♦♦ max-b commented ·

I had to do some serious setup on my Multi to get it, to accept the AC variations coming from my genset. With standard settings, it was very sensitive to AC variations.

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Dave van Dongen avatar image Dave van Dongen markus ♦♦ commented ·

I don't think PowerAssist is going to help me because of 2 reasons:
1: I run ESS and PowerAssist cannot be enabled when you run ESS.
2: PowerAssist will supplement Amps from the inverter/battery when the Amps from the shore connection is not enough. As far as I know PowerAssist will not bump the voltage. If it would, I would definitely by using it, that would be a brilliant solution! :-)

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markus avatar image markus ♦♦ Dave van Dongen commented ·

Yes, Power Assist is not the solution in this case unfortunately. I only mentioned it because Max_B wrote, a Multi is an inverter only.

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max-b avatar image max-b markus ♦♦ commented ·

Ah, ok. I meant "The Multiplus is used as inverter only", in this new setup. I do know that Multiplus is able to charge and power-assist. I suppose everybody buying such a device do know it.

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max-b avatar image
max-b answered ·

@WKirby and staff

This is not exactly related to OP question, but I suggest Victron should have a true online inverter device line with all Multiplus protocol features. Moreover with the option of (dis)allowing pass-through of input AC to output AC. If the charger section is tolerant enough this would solve such use cases.

Such a device is more expansive since it needs more components. But for sensitive equipments in a poor AC input conditions, it is a true security.

Currently the Victron product range features inverter only and charger only devices, but they have less CCGX interfacing capabilities and control option than the Multiplus. That's why I bought a new 3kW Multiplus to replace my 12y old 2kW which was not CCGX able, rather than a simple inverter, even if it is currently used as inverter only. More remote control (and also a backup charger if the Skylla fails)

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boekel avatar image
boekel answered ·

Do you need a 'true' 3 phase system? or could you do with 3x 1 phase? (so no 3 phase users in the system)

If you could work with 3 seperate phases you could have every phase work as a stand alone system, and when one phase get's to low it will be supported by the other two phases through the inverters.

the use of an isolation transformer (as these put out a slightly higher voltage on the output) on the single phase that gets to low is an interesting idea - but only if under other circumstances the voltage doesn't get to high.

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Dave van Dongen avatar image
Dave van Dongen answered ·

@Boekel Thanks 4 your reply. I don't have 3 phase users, so I do not nee a true 3 phase system. But you can make a true 3 phase system where the inverters switch independently, like you mention.
I can just switch off "Switch as a Group", but this doesn't work with ESS program, so I have to fall back to Hub1 Policy 2, in my case.
I am planning to do that in the next couple of days.
I created a topic for that as well: https://community.victronenergy.com/questions/3307/not-use-switch-as-a-group-in-an-ess-configuration.html
The voltage never gets above 215 olt, but an isolation transformer is costly.

PS. I post this a separate answer, because when I insert the same text (less than 600 characters) as a comment, I can't "Submit" it, with no error message given... :-(

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Dave van Dongen avatar image
Dave van Dongen answered ·

Actually I would think this could be a great feature: "Voltage Assist". We now have "Power Assist". With a weak shore connection (Example: limited to 6A, so 1380 VA) you can still bump the power output, because the inverter can take the extra needed power from the battery. (So in the example, the inverter can deliver 2380 VA, because it will take 1380 VA from the shore connection and then it will take the other 1000 VA out of the battery.)
I would say (I am not sure about the technical details, but correct me if I am wrong) this could be possible with voltage in the same way. But the mechanism is now not controlled by the current limit of the shore connection, but by the voltage supplied by the shore connection/grid.
So if the shore connection or grid only delivers 170 volt, as in my case and you have specified the output voltage of the inverter needs to be 180 volt minimum, then the inverter simply adds enough extra power from the battery until the voltage on the output side meets the desired voltage.
On the technical side: As fas as I know, with the same power demand, adding power on the supply side, will result in an increase of voltage. So if a control loop similar to the "Power Assist" control loop is implemented that is controlled by the difference in voltage on the input side and the desired voltage on the output side, this could work.
I think this could be a great feature.
(Even here in my house in The Netherlands the voltage is usually closer to 210 volt (and sometimes below!) than it is to 230 volt, so even here it would be useful.)

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wkirby avatar image wkirby ♦♦ commented ·

OK, so as you know it does this by disconnectiog from the grid, then it can supply the 230V. The input Voltage cannot be different from the ouput Voltage unless they are disconnected from each other.
Are you suggesting that it remains connected to the grid and then push the grid Voltage up? Someone will need to inject a lot of power into the grid to get the grid Voltage up above 180V? A few MW, or maybe more should be enough to do this. It is not possible for a tiny little baby MultiPlus to do this, it doesn't do it which is why it disconnects when the Voltage gets too low.

Separate Charger and Inverter boxes will provide this disconnection between input and output. You suggested having a machine with a charger and an inverter as separate units inside. It's probably more efficient to just get two MultiPlus', one for charging and one for inverting.

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Dave van Dongen avatar image Dave van Dongen wkirby ♦♦ commented ·

Ok, I see what you mean and why voltage assist would not be possible.
Just for my understanding: I am wondering how this works with Power Assist, because then also the inverter remains in pass-through and the power from the battery ends up on the output side. How is it being prevented that this added power does not flow to the grid/shore connection? Just wondering...

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