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Kaspars asked

TWO multiplus-II 5k parallel problem. DUAL standalone options?


I am having difficulty running two multiplus-ii 5000 in parallel. Located in Europe i have a 3-phase incoming connection, but for parallel connection using 1-phase off-course.

They do function alright in parallel and system is stable if i do run them from DC (solar mppts and batteries) but as soon i apply incoming AC there is some issues and so far i have 2 different scenarios:

Both multis are connected on the same phase AC-in with common ground and earth.

AC-out-1 and ac-out-2 are also paralleled between multis with common ground and earth.

Both multis connected to the same battery bank.

All DC and even AC-in and ac-out cables are same dimensions and lengths.

Scenario #1. Both multis connected (and set up) in parallel without any assistants installed:

When AC-in is switched on (after a 60s delay) they start to hum quite loud in wave pattern - louder-quieter. Meanwhile the loads on AC-out are being supplied.

I cant accept that as normal, therefore i do not connect them to AC-in at the moment.

Scenario #2. Same connection but now with ESS assistants installed on both multis:

When AC-in is switched on (after a 60s delay) a very rapid LOUDER than without ESS humming takes place that is VERY short and results in disconnect with the slave unit displaying the overload red led for a sec. Loads eventually being dropped as well.

This happens WITH or WITHOUT connected loads on AC-out.

That is a scary event so i am not repeating it.

Meanwhile CERBO does not give any other error except "grid lost" so no clues there.

I did test both units standalone, with ac-in and ess installed. works as expected.

I did test and replace data cables between multis and cerbo. also tried to place them in different routes. no change.

I suspect one of the multis is defective as it is different from the other - it is louder in normal operation and it has "more noises" inside of it. Also it does not follow the AC-2 out relay assistant setting and start switching on-off the relay at 90% SOC while it is set to turn on only when SOC is 95% higher and turn off below 92%. same setting on both multis. and the internal battery monitor is not enabled.

i see there has been a very similar issue:

unfortunately data cable replacement and relocation did not change a thing.

I understand there is a possibility to connect them multis in parallel-standalone connection when one of them is connected to cerbo through MK3. but that is not a solution to solve the current issue as i expect to be able to use all advertised applications.

please help me to solve this mysterious issue.

I have spoken to my local distributor but their knowledge/experience is not sufficient to solve this.

Multiplus-IImultiplus in parallelconnection issue
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1 Answer
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Kaspars answered ·

As to add a separate thread of this same question i write it in a comment.

To look at other option of using both multis in my system i consider standalone-parallel connection.

I do not see it documented anywhere only on few community threads. if there is a documentations please guide me on that.

Unclear questions in this scenario i have so far are:

1. Can i connect separate AC-in phases for each multi.

2. Can the NEUTRAL of AC-out of both multis be shorted in a distribution box.

3. If i understand that correct only one of the multis can be used to charge batteries from the grid. So is there any difference which one that will be. And to do that simply disabling charger on the other multi is enough?

4. As they are standalone and i have a 3-phase connection from grid, if i connect a 3-phase load between the current transformer of each multi on the AC-IN phase and the third phase to the line coming from the grid, can the 2 phases be supplied from multis to feed the 3-phase load?

4.A i think it should be ok as if i feed back to grid the phase is being modified to be same as incoming current, right? so should be no difference if i connect my load 0,5 meter from the multiplus ac-in or my neighbor connects his 3-phase load few hundred meters away on the line. Just want to confirm my idea with you experienced people.

@Matthias Lange - DE i see you have commented on this solution earier, could you please expand a little more?

1 comment
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dennis-hejselbak avatar image dennis-hejselbak commented ·

Hello Kaspars - Did you get this resolved or does it still not work ?

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