ellaine avatar image
ellaine asked

Can I have two Multiplus II in parallel to increase inverting capacity?

Does anyone know if I can wire two Multiplus II 12/3000/120 in parallel to get 6000w of inverter? And if so what else would it affect and that I need to change on the settings?

Here’s my set up:

800Ah 12v battery bank

1000W solar panels

60amp dc-dc charger (30amp Orion x2 parallel)

30amp shore power.

Gonna be running a couple of 1800w appliances at the same time so needing about a 4000w inverter.

Or would anyone have an alternative they may know of? Already thinking I should just get the 12v/5000w Quattro, but wanting to see if two multi pluses would work.

I would really appreciate some insights.


Multiplus-IImultiplus in parallelmultiple inverters
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5 Answers
nickdb avatar image
nickdb answered ·

The spec sheet lists parallel and 3-phase operation for that model. Just remember parallel systems are complex and you really need to know what you're doing, or disappointment may follow.

A 5kVA multi would be a lot easier and more efficient.

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iand avatar image iand commented ·

There isn't a 12V 5000W Multiplus or MP II. A Quattro 12/5000 costs EUR3908 and has 94% efficiency with 30W zero-load power, the MP II 12/3000 is EUR1524 with 93% efficiency and 13W zero load power. So two MPIIs are cheaper and a little bit lower drain with no load, and can provide more power, but are more of a pain to install.

Having said all that I hope the OP has a battery bank capable of providing 4000W since this will be getting on for 400A, many 800Ah batteries won't be very happy with this...

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jacobjned avatar image
jacobjned answered ·

It is possible to have them the two units in parallel provided their firmware is also the same. Also would suggest you go through this link as well the PDF document 'Wiring Unlimited'. When paralleling systems there also some electrical cabling in terms of thickness, length, etc. to consider. As @nickdb suggested, depending on your situation (budget as well), it would be less complicated, from an installation point of view , to install one large unit as opposed to paralleling smaller units.

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kevgermany avatar image
kevgermany answered ·

Look at the cost/practicality of going to 24 or better, 48V for the batteries. Simple rewire would achieve this. Much better for the load you have, and it's bound to increase in future.

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t1-terry avatar image
t1-terry answered ·

I have installed a few Multiplus inverters in parallel set ups and it is easier to get the interface cables that go between the laptop and the VE bus in the inverter, than trying to do it via the dip switches. First thing is to update both inverters to the latest operating version so there is no confusion between the inverters, but it is not necessary to update the version every time a new one comes available, only do it if the new version will give you some improvement you will benefit from having .... and naturally, update both inverters.

You need to set up one inverter as the master, the other as the slave. When you have them linked correctly. both inverters will be shown in the program so you can choose which you want to be the master and which one the slave.

Halve the shore power input current because now each inverter will see this amount of current as it's maximum available and charge to this limit .... to limit the input shore current to 10 amps, then set the input current to 5 amps and each inverter will only draw 5 amps from the shore power for a total of a 10 amp load on the shore power circuit.

Seriously undersize the cable conductor size for both the shore power in and the inverter output and run these cable as long as you can fit them in your system .... the idea is to force the inverters to share the load and cable resistance works well to achieve this result.

Be sure the linking RJ45 cable is not tight between the units, any strain will result in either one of the plugs making a good continuous contact, or a wire pulling out of the plug contact, from experience, this will send you running in circles trying to figure out just what is going on ....

As far as the battery cables, the first one to the mega fuse needs to be crazy big, 95mm sq seems to work well and don't forget the negative to the shunt needs to be the same crazy big. From the shunt to the inverter, as long as the run is less than a mtr (3 ft) 0 gauge (50mm sq) cable of equal lengths will work fine, the same from the mega fuse to each inverter, but just the negative cables need to be the same length as do the positive cables, not all 4 cables the same length ... hope that makes sense.

Set the warning and shut down battery voltage as low as you feel safe, on our lithium battery set ups we drop the warning voltage to 11v rather than 11.8v and the shut down to 10v rather than 11v. This is because the inverter senses the battery voltage at the input terminals, not from the BMV, so the battery voltage may read fine but the inverters start to flash and alarm or eeven shut down well before the battery voltage is really that low.

The reset voltage still needs to be high enough to avoid the load suddenly dropping the sensed voltage and shutting down again resulting in an on/off/on/off issue and damaging electrical gear and possibly the inverters themselves.

As far as the Multiplus 2 units in parallel, still a work in progress ...

T1 Terry

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larsea-dk avatar image larsea-dk commented ·

Great instruction:-)

But what do you mean by „ Multiplus 2 units in parallel, still a work in progress“? Are there issues with paralleling the multiplus II?

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kevgermany avatar image kevgermany ♦♦ larsea-dk commented ·
Work in progress means not done/complete.
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larsea-dk avatar image larsea-dk kevgermany ♦♦ commented ·
Okay, I just thought that you were not sure if it works. I have a single mp2 in ESS only connected AC-in and connected to my grid L1. I want to install an extra on L2 due to grid infeed restriction per phase and I need to feed more power to grid to have a stable system. I have 7,5kWp PV and 2pcs 250/100 chargers.

I think this is called "Dual Phase 120", but is this correct? and is this possible?

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Ryan avatar image Ryan commented ·
Hey mate, I'm looking to set up 2x MP2 12/3000 in parallel and it sounds like you have some great advice. A couple questions for you please

I'm in australia so I was going to use 2.5mm2 flex cable from the inverters to the breakers- probably 1-2m for each unit. Will this be fine and do both AC cables need to be the same length?

For the DC side, I was thinking 70mm2 cables from the batteries- Mega Fuse- Inverter. Again about a 1-2m run and I was thinking just the 1 positive and negative cable per inverter. The batteries are 12v 300Ah and I will have 2 of them in parallel. You talk about having the positive and negative cables the same length but I don't understand what cables in particular you are refering to.

Any help would be great thanks


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nickdb avatar image nickdb ♦♦ Ryan commented ·

Best read the wiring unlimited guide and the 3phase/parallel system document.

The manual has the minimum cable requirements as well.

Parallel systems are best not done without having completed the free training or fully acquainting yourself with the docs.

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jessiejim1 avatar image
jessiejim1 answered ·

Yes, you can wire two Multiplus II 12/3000/120 in parallel to get 6000w of inverter. However, you would need to make sure that the wiring is done correctly and that the settings are adjusted accordingly to prevent any issues. Another option would be to consider the 12V/5000W Quattro as you mentioned.

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