kmorgan avatar image
kmorgan asked

Multiplus 2 in parallel Again!

My question is are they right about the HW rev? reading all the posts on here they were wrong to advise it does not matter.....???

details below.. i'm not looking for setup answers just the HW question..

So i have a happy MP2 GX 48/5000 everything is working great. But we want more power!

So i emailed Victron tech support with all my inverter details, HW ref 02 etc etc and asked the specific question about hardware rev: and got the answer below

Recommended solution would be to add a second Multiplus II connected in parallel using a RG45 cable
Both Units must be running the same version of firmware, hardware revision does not matter
Cable lengths and thickness coming out of the inverters must be identical
The two units should be programmed before being connected using VE quick config and configured as master and slave
Total inverting power would be 10kw
Charging ability doubles

But as soon as i set them up in Parallel the system goes haywire.

1.Does not get anywhere near grid set point either to high or too low

2. will not charge the batteries at full current, pull from the grid instead of battery

3. etc etc.

multiplus in parallel
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Alexandra avatar image Alexandra ♦ commented ·


Parallel systems are notoriously difficult to get right. not unusual to see up to 25% difference between them. Always better to go up to a bigger unit in terms of simplicity.

Have all the wiring sizes recommendations been followed in the manual? Resistance is the key to getting the system well balanced, both in DC and AC wiring.

Have you worked through the manual and the training linked there? There are a few good tips in there, some contrary to what you might be doing. Such as AC cable length and sizing.

How have they been programmed? ESS?

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1 Answer
t1-terry avatar image
t1-terry answered ·

The first thing to check is both inverters are running the later version firmware to determine if they are compatible .... there is stuff in here to help understand the differences

The next step is to update the firmware version so they are both the same. Leave the AC out disconnected on both inverters so if there is a wave pattern conflict the smoke doesn't come out or the buzzing and red light flashing if you are lucky.

Next thing to make sure you get right, the linking communication cable cable between the two inverters must be wired in parallel and 8 wire RJ45 plugs, not 6 wire and RJ12 plugs, even though they do fit, and some things will actually work, problems are just waiting for a chance to happen.

I use 1.5mmsq 2 core plus earth ribbon cable for both the power in and power out, there is some resistance but it really does help with balancing the load between each inverter.

I only use a single Mega fuse, 95mm sq cable from the battery to the fuse and equal length ) gauge (50mm sq) cable from there to the inverters. same deal between the battery and the shunt and shunt to inverters.

Make the 1.5mm sq output cables as long as practical before linking them together in the power board into a single circuit breaker. The reason for the single fuse and single circuit breaker, you don't want one inverter dropping out and leaving it all to the other inverter to carry the load ..... it should just shut down when it looses its partner, but should and will are worlds apart.

Drop the low battery warning down lower than you would for a single inverter or you will get false low battery voltage alarms, the same for the low battery shut down, but set the reset voltage a bit higher to cover for the load when the system comes back on so it doesn't drop the battery voltage below the shut down voltage point.

That long undersized cabling is the important part, one you do that they seem to work together ok, even under high load where the power assist kicks in

T1 Terry

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