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Roman Štembera avatar image
Roman Štembera asked

Is Multiplus II 3000/48V 35 capable of transferring 45Amps?

Hi, can anyone explain max current the Multi is capable to transfer. The manual says:
multiplus-ii-3000-48v-45a-ttransfer.png

I have opened the Multiplus case and I see only 32 Amps relays there:

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20210309-220346.jpg

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From the photos above you can see there are only 32Amps relays. I think the relays will blow up in the case the Multi will add its 13 Amps to the 32Amps on AC-In.

Is the manual stating wrong numbers? I have searched the specs of the relays and it seems they are not able to handle 45 A even for short period of time.


Can someone explain why the 32 relay is used when Victron declares that it should handle max 45 Ams? How to size the circuit breaker here? I think 32A circuit breaker should be enough in the case 32 Amps relays are used internally by Multi.

Multiplus-IIMultiPlus Quattro Inverter Charger
multiplus-ii-3000-48v-45a-ttransfer.png (60.9 KiB)
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20210309-220402.jpg (724.0 KiB)
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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

The transfer relay is rated for 32A the additional 13A from the Multi are behind the transfer relay.

mp-ii-transfer.png

The breaker at the AC input should be rated for 32A.


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Roman Štembera avatar image Roman Štembera commented ·

Yes. But the AC OUT2 is behind 32 Amp relay so I think it can be overloaded in full load situation when there is no consumption on AC out 1. What CB to put on AC OUT2? Isnt it design problem to have only 32Amp relay on AC out 2 while transferring 45 Amps here?

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Roman Štembera avatar image
Roman Štembera answered ·

The design of Multiplus II 3000 is wrong. AC-OUT-2 relay can burn out in the case the 45 Amps is transferred only to the AC-OUT-2. I think there should be 45 Amps relay on AC-OUT-2. I have asked Victron representative and he has redirected me to the forum considering previous answer from @Matthias Lange - DE as correct. @Matthias Lange - DE - please review your answer.

Until resolved, I need to put 32 Amps CB to the AC-OUT-2 to protect the relay. Please beware of attaching the 45 CB to the AC-OUT-2. This can lead to the situation where the AC-OUT-2 relay is overloaded with 45 Amps as it is designed only for 32 Amps. See the picture below - the purple current flow is dangerous.19352-mp-ii-transfer.png


19352-mp-ii-transfer.png (87.7 KiB)
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

I never wrote something about AC OUT 2 and also the manual never says that you can use 32A+13A at AC OUT 2, that only applies to AC OUT 1.

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Roman Štembera avatar image Roman Štembera Matthias Lange - DE ♦ commented ·

Manual does not say anything about circuit breaker on AC-OUT-2. From the statement regarding AC-OUT-1 mentioned above, I would add the 45 CB to the AC-OUT-2 as well, unless I have opened the Multiplus and found the relays sizing. From the block diagram you can see the same power can be delivered to AC-OUT-2 as well. The manual does not say the CB on AC-OUT-2 should be smaller.

Ok, not sure the statement in manual is good or not, I think this should be mentioned. I will ad 32 A CB on AC-OUT-2 and 45 A CB on AC-OUT-1. In the case this is wrong approach, please comment. I appreciate any opinion here. Takeover is also to check the internals of the device prior to design. This is not usual.

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ Roman Štembera commented ·

What kind of system do you planing that it can happen to pull 32A (or more) on AC OUT 1 and 2? Sounds very uncommon to me.

BTW a 32A circuit breaker will not trip immediately if you pull 33A. You can easily pull 45A for a couple of minutes before it will trip.

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Roman Štembera avatar image Roman Štembera Matthias Lange - DE ♦ commented ·

3x230V system (not three phase system) with solar panels.

L1 is for non-breaking loads and the L1+L2 phases are for breakable loads. During normal situation (grid available), the L1 and L2 +L3 are shorted forming 3x230V inside of the multi. During overload, the shortenng of phases is canceled (external TeSys D conactors) and normal 3x400V system is used. During grid outage, the L1 is powered only.

This is why so much power is transferred via multi.

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Roman Štembera avatar image Roman Štembera commented ·

I have just bought the additional Multiplus II 3000/48. It comes with HW revision 18 (the problem was detected on HW rev 15). Inside of HW Revision 18, there is 32Amps relay on the AC-OUT2 replaced by Panasonic 40A relay with doubled contacts(see the picture attached).

1622724143799.png

(I guess internal wiring is to have the AC-OUT2 relay using the two contacts in parallel to achieve 80A). It seems that from HW revision 18 the problem is fixed.

I have question: Is it possible to put these two HW revision (HW15 + HW18)in parallel?

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1622724143799.png (1.4 MiB)
ejrossouw avatar image ejrossouw Roman Štembera commented ·

Please be VERY mindful of working with electricity if you are unable to read correctly. Firstly, the Panasonic on your image is rated 35A and not 40A from what I can see? Also, in your post, it states the powerassist is on AC1. Hope this helps. PS - These devices are certified by many professional bodies in many countries for safety and use on the public grid, so ...

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Roman Štembera avatar image Roman Štembera ejrossouw commented ·

Perhaps I do not read correctly your statements and do not understand the message. The relay is rated for 40A max current (look at the specs). It has additional NO contact carrying max 1A (my mistake, this was overlooked as I briefly checked the spec sheet, did not noticed the second contact is for 1Amp only). I am electrical engineer so I understand electricity :-)

The powerasist is on AC-OUT1 but also on AC-OUT2 - from the block schema you can see they are connected. The AC-OUT2 disconnects when grid not available or on special request from assistant or external control. So the new relay is capable of 40A transfer to AC-OUT2.


Can anyone respond to the following questions please?

ASSUME:

  • Grid available
  • Mains connected
  • PowerAssist enabled
  • Battery full
  • No load on AC-OUT-1.
  • AC-OUT-2 is connected.
  • 45 Amps resistive load on AC-Out-2.

Questions:

  1. How big the transfer current can be from AC-IN to AC-OUT-2? (I asume 32 Amps)
  2. How big current the multi can add to AC-OUT-2 from inverter? (I assume 13 Amps)
  3. Is the total current 45 Amps on AC-OUT-2 during the assumed situation? (I assume YES)
  4. Will the relay on AC-OUT-2 overload under these conditions (I assume yes).
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ Roman Štembera commented ·

The relay is rated for 35A. It is printed on it and in all spec-sheets I can find.

20352-20210603-130205.jpg


If you have concerns about to overload the relay you have two options:

1. use a 5kVA MultiPlus with 50A relays

2. design you system that you never can pull more than 32A (or 35A) on AC OUT 2

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